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Martin + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: A Population Study of the Prairie Vole (Microtus ochrogaster) in Northeastern Kansas + +Author: Edwin P. Martin + +Release Date: April 7, 2012 [EBook #39396] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK POPULATION STUDY OF PRAIRIE VOLE *** + + + + +Produced by Chris Curnow, Paula Franzini, Joseph Cooper +and the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + +</pre> + + + + +<hr class="fulldoubleweightblack" /> +<hr class="fullunderblack" /> +<p class="h3"> +<span class="smcap">University of Kansas Publications</span></p> +<p class="h4"><span class="smcap">Museum of Natural History</span></p> +<hr class="shortthinblack" /> +<p class="h3flat">Volume 8, No. 6, pp. 361-416, 19 figures in text</p> +<p class="h3flat">April 2, 1956</p> +<hr class="fullunderblack" /> +<p class="spacer"> </p> + +<h1 id="booktitle">A Population Study +of the Prairie Vole (Microtus ochrogaster) +in Northeastern Kansas</h1> + +<p class="h4">BY</p> + +<p class="h4">EDWIN P. MARTIN</p> +<p class="spacer"> </p> +<p class="h4"><span class="smcap">University of Kansas<br /> +Lawrence</span><br /> +1956 +</p> +<p class="spacer"> </p> + + +<hr class="chap" /> +<p class="h4"> +<span class="smcap">University of Kansas Publications, Museum of Natural History</span><br /> + +Editors: E. Raymond Hall, Chairman, A. Byron Leonard, Robert W. Wilson<br /><br /> +</p> + +<p class="h4">Volume 8, No. 6, pp. 361-416, 19 figures in text<br /> +Published April 2, 1956<br /> </p> +<p class="spacer"> </p> +<p class="h4"><span class="smcap">University of Kansas</span><br /> +Lawrence, Kansas<br /></p> +<p class="spacer"> </p> +<p class="h5">PRINTED BY<br /> +FERD VOILAND, JR., STATE PRINTER<br /> +TOPEKA, KANSAS<br /> +1956<br /> +<br /> +25-9225<br /> +</p> + + + +<hr class="chap" /> + + +<h2><a name="Contents" id="Contents">Contents</a></h2> +<div class="center"> + <table summary="contents" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td align="left"> </td> + <td align="left"> </td> + <td align="right"><small>PAGE</small></td></tr> + <tr> + <td colspan="2" align="left">INTRODUCTION</td> + <td align="right"><a href="#introduction">363</a></td></tr> + <tr> + <td colspan="2" align="left">GENERAL METHODS</td> + <td align="right"><a href="#general_methods">364</a></td></tr> + <tr> + <td colspan="2" align="left">HABITAT</td> + <td align="right"><a href="#habitat">366</a></td></tr> + <tr> + <td colspan="2" align="left">POPULATION STRUCTURE</td> + <td align="right"><a href="#population_structure">373</a></td></tr> + <tr> + <td colspan="2" align="left">POPULATION DENSITY</td> + <td align="right"><a href="#population_density">376</a></td></tr> + <tr> + <td colspan="2" align="left">HOME RANGE</td> + <td align="right"><a href="#home_range">380</a></td></tr> + <tr> + <td colspan="2" align="left">LIFE HISTORY</td> + <td align="right"><a href="#life_history">383</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Reproduction</td> + <td align="right"><a href="#reproduction">383</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Litter Size and Weight</td> + <td align="right"><a href="#litter_size">386</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Size, Growth Rates and Life Spans</td> + <td align="right"><a href="#size_growth">388</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Food Habits</td> + <td align="right"><a href="#food_habits">397</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Runways and Nests</td> + <td align="right"><a href="#runways">398</a></td></tr> + <tr> + <td align="left"> </td> + <td align="left">Activity</td> + <td align="right"><a href="#activity">400</a></td></tr> + <tr> + <td colspan="2" align="left">PREDATION</td> + <td align="right"><a href="#predation">401</a></td></tr> + <tr> + <td colspan="2" align="left">MAMMALIAN ASSOCIATES</td> + <td align="right"><a href="#mammalian_associates">403</a></td></tr> + <tr> + <td colspan="2" align="left">SUMMARY AND CONCLUSIONS</td> + <td align="right"><a href="#summary">408</a></td></tr> + <tr> + <td colspan="2" align="left">LITERATURE CITED</td> + <td align="right"><a href="#literature">411</a></td></tr> + </tbody> + </table> +</div> + + +<hr class="chap" /> + +<p><span class="pagenum"><a name="Page_363" id="Page_363">[363]</a></span></p> + +<h2> +A POPULATION STUDY<br /> +OF THE PRAIRIE VOLE (MICROTUS OCHROGASTER)<br /> +IN NORTHEASTERN KANSAS<br /> +</h2> + +<h4>By<br /> + +Edwin P. Martin</h4> + + + + +<h2><a name="introduction" id="introduction">INTRODUCTION</a></h2> + + +<p>Perhaps the most important species of mammal in the grasslands of +Kansas and neighboring states is the prairie vole, <i>Microtus +ochrogaster</i> (Wagner). Because of its abundance this vole exerts a +profound influence on the quantity and composition of the vegetation +by feeding, trampling and burrowing; also it is important in food +chains which sustain many other mammals, reptiles and birds. Although +the closely related meadow vole, <i>M. pennsylvanicus</i>, of the eastern +United States, has been studied both extensively and intensively, +relatively little information concerning <i>M. ochrogaster</i> has been +accumulated heretofore.</p> + +<p>I acknowledge my indebtedness to Dr. Henry S. Fitch, resident +investigator on the University of Kansas Natural History Reservation. +In addition to supplying guidance and encouragement in both the +planning and execution of the investigation, Dr. Fitch made available +for study the data from his extensive field work. Interest in and +understanding of ecology were stimulated by his teaching and his +example. Special debts are also acknowledged to Mr. John Poole for the +use of his field notes and to Professor E. Raymond Hall, Chairman of +the Department of Zoology, for several courtesies. Dr. R. L. McGregor +of the Department of Botany at the University of Kansas assisted with +the identification of some of the plants. Drawings of skulls were made +by Victor Hogg.</p> + +<p>Of the numerous publications concerning <i>Microtus pennsylvanicus</i>, +those of Bailey (1924), Blair (1940; 1948) and Hamilton (1937a; 1937c; +1940; 1941) were especially useful in supplying background and +suggesting methods for the present study. Publications not concerned +primarily with voles, that were especially valuable to me in providing +methods and interpretations applicable to my study, were those of +Blair (1941), Hayne (1949a; 1949b), Mohr (1943; 1947), Stickel (1946; +1948) and Summerhayes (1941). Faunal and ecological reports dealing +with <i>M. ochrogaster</i> and containing useful information on habits and +habitat included those of Black (1937:200-202), Brumwell +(1951:193-200; 213), Dice (1922:46) and Johnson (1926). Lantz (1907) +discussed the economic relationships of <i>M. ochrogaster</i>; the section +of his report concerning the effects of voles on vegetation was +especially useful to me.</p> + +<p>Fisher (1945) studied the voles of central Missouri and obtained +information concerning food habits and nesting behavior. Jameson +(1947) studied <i>M. ochrogaster</i> on and near the campus of the +University of Kansas. His report is especially valuable in its +treatment of the ectoparasites of voles. In my investigation I have +concentrated on those aspects of the ecology of voles not treated at +<span class="pagenum"><a name="Page_364" id="Page_364">[364]</a></span>all by Fisher and Jameson, or mentioned but not adequately explored by +them. Also I have attempted to obtain larger samples.</p> + +<p>The University of Kansas Natural History Reservation, where almost all +of the field work was done, is an area of 590 acres, comprising the +northeastern-most part of Douglas County, Kansas. Situated in the broad +ecotone between the deciduous forest and grassland, the reservation +provides a variety of habitat types (Fitch, 1952). Before 1948, much +of the area had been severely overgrazed and the original grassland +vegetation had been largely replaced by weeds. Since 1948 there has +been no grazing or cultivation. The grasses have partially recovered +and, in the summer of 1952, some grasses of the prairie climax were +present even on the parts of the Reservation which had been most +heavily overgrazed. Illustrative of the changes on the Reservation +were those observed in House Field by Henry S. Fitch (1953: <i>in +litt.</i>). He recalled that in July, 1948, the field supported a closely +grazed, grassy vegetation providing insufficient cover for <i>Microtus</i>, +with such coarse weeds as <i>Vernonia</i>, <i>Verbena</i> and <i>Solanum</i> +constituting a large part of the plant cover. By 1950, the same area +supported a lush stand of grass, principally <i>Bromus inermis</i>, and +supported many woody plants. Similar changes occurred in the other +study areas on the Reservation. Although insufficient time has elapsed +to permit analyses of successional changes, it seems that trees and +shrubs are gradually encroaching on the grassland throughout the +Reservation.</p> + +<p>The vole population has changed radically since the Reservation was +established. In September and October of 1948, when Fitch began his +field work, he maintained lines of traps totaling more than 1000 trap +nights near the future vole study plots without capturing a single +vole. In November and December, 1948, he caught several voles near a +small pond on the Reservation and found abundant sign in the same +area. Late in 1949 he began to capture voles over the rest of the +Reservation, but not until 1950 were voles present in sufficient +numbers for convenient study.</p> + +<p>I first visited the Reservation and searched there for sign of voles +in the summer of 1949. I found hardly any sign. In the area around the +pond mentioned above, however, several systems of runways were +discovered. This area had been protected from grazing for several +years prior to the reservation of the larger area. In House Field, +where my main study plot was to be established, there was no sign of +voles. Slightly more than a year later, in October, 1950, I began +trapping and found <i>Microtus</i> to be abundant on House Field and +present in smaller numbers throughout grassland areas of the +Reservation.</p> + + + +<hr class="chap" /> +<h2><a name="general_methods" id="general_methods">GENERAL METHODS</a></h2> + + +<p>The present study was based chiefly on live-trapping as a means of +sampling a population of voles and tracing individual histories +without eliminating the animals. Live-trapping disturbs the biota less +than snap-trapping and gives a more reliable picture of the mammalian +community (Blair, 1948:396; Cockrum, 1947; Stickel, 1946:158; +1948:161). The live-traps used were modeled after the trap described +by Fitch (1950). Other types of traps were tested from time to time +but this model proved superior in being easy to set, in not springing +without a catch, in protecting the captured animal and in permitting +easy removal of the animal from the trap. A wooden box was placed +inside the metal shelter attached to each trap and, in winter, cotton +batting or woolen scraps were placed inside the boxes for nesting +material. With this insulation against the cold, voles could survive +<span class="pagenum"><a name="Page_365" id="Page_365">[365]</a></span>the night unharmed and could even deliver their litters successfully. +In summer the nesting material was removed but the wooden box was +retained as insulation against heat.</p> + +<p>Bait used in live-traps was a mixture of cracked corn, milo and wheat, +purchased at a local feed store. The importance of proper baiting, +especially in winter, has been emphasized by Howard (1951) and +Llewellyn (1950) who found an adequate supply of energy-laden food, +such as corn, necessary in winter to enable small rodents to maintain +body temperature during the hours of captivity. The rare instances of +death of voles in traps in winter were associated with wet nesting +material, as these animals can survive much lower temperatures when +they are dry. Their susceptibility to wet and cold was especially +evident in rainy weather in February and March.</p> + +<p>Preventing mortality in traps was more difficult in summer than in +winter. The traps were set in any available shade of tall grass or +weeds; or when such shade was inadequate, vegetation was pulled and +piled over the nest boxes. The traps usually were faced north so that +the attached number-ten cans, which served as shelters, cast shadows +over the hardware cloth runways during midday. Even these measures +were inadequate when the temperature reached 90°F. or above. Such high +temperatures rarely occurred early in the day, however, so that +removal of the animals from traps between eight and ten a. m. almost +eliminated mortality. Those individuals captured in the night were not +yet harmed, but it was already hot enough to reduce the activity of +the voles and prevent further captures until late afternoon. When it +was necessary to run trap lines earlier, the traps were closed in the +morning and reset in late afternoon.</p> + +<p>Reactions of small mammals to live-traps and the effects of prebaiting +were described by Chitty and Kempson (1949). In general, the results +of my trapping program fit their conclusions. Each of my trapping +periods, consisting of seven to ten consecutive days, showed a gradual +increase in the number of captures per day for the first three days, +with a tendency for the number of captures to level off during the +remainder of the period. Leaving the traps baited and locked open for +a day or two before a trapping period tended to increase the catch +during the first few days of the period without any corresponding +increase during the latter part of the period. Initial reluctance of +the voles to enter the traps decreased as the traps became familiar +parts of their environment.</p> + +<p>At the beginning of the study the traps were set in a grid with +intervals of 20 feet. The interval was increased to 30 feet after +three months because a larger area could thus be covered and no loss +in trapping efficiency was apparent. The traps were set within a three +foot radius of the numbered stations, and were locked and left in +position between trapping periods.</p> + +<p>Each individual that was captured was weighed and sexed. The resulting +data were recorded in a field notebook together with the location of +the capture and other pertinent information. Newly captured voles were +marked by toe-clipping as described by Fitch (1952:32). Information +was transferred from the field notebook to a file which contained a +separate card for each individual trapped.</p> + +<p>In the course of the program of live-trapping, many marked voles were +recaptured one or more times. Most frequently captured among the +females were number 8 (33 captures in seven months) and number 73 (30 +<span class="pagenum"><a name="Page_366" id="Page_366">[366]</a></span>captures in eight months). Among the males, number 37 (21 captures in +six months) and number 62 (21 captures in eight months) were most +frequently taken. The mean number of captures per individual was 3.6. +For females, the mean number of captures per individual was 3.8 and +for males it was 3.4. Females seemingly acquired the habit of entering +traps more readily than did males. No correlation between any +seasonally variable factor and the number of captures per individual +was apparent. To a large degree, the formation of trap habits by voles +was an individual peculiarity.</p> + +<p>In order to study the extent of utilization of various habitats by +<i>Microtus</i>, a number of areas were sampled with Museum Special +snap-traps. These traps were set in linear series approximately 25 +feet apart. The number of traps used varied with the size of the area +sampled and ranged from 20 to 75. The lines were maintained for three +nights. The catch was assumed to indicate the relative abundance of +<i>Microtus</i> and certain other small mammals but no attempt to estimate +actual population densities from snap-trapping data was made. In +August, 1952, when the live-trapping program was concluded, the study +areas were trapped out. The efficiency of the live-trapping procedure +was emphasized by the absence of unmarked individuals among the 45 +voles caught at that time.</p> + +<p>Further details of the methods and procedures used are described in +the appropriate sections which follow.</p> + + +<hr class="chap" /> + +<h2><a name="habitat" id="habitat">HABITAT</a></h2> + + +<p>Although other species of the genus <i>Microtus</i>, especially <i>M. +pennsylvanicus</i>, have been studied intensively in regard to habitat +preference (Blair, 1940:149; 1948:404-405; Bole, 1939:69; Eadie, 1953; +Gunderson, 1950:32-37; Hamilton, 1940:425-426; Hatt, 1930:521-526; +Townsend, 1935:96-101) little has been reported concerning the habitat +preferences of <i>M. ochrogaster</i>. Black (1937:200) reported that, in +Kansas, <i>Microtus</i> (mostly <i>M. ochrogaster</i>) preferred damp +situations. <i>M. ochrogaster</i> was studied in western Kansas by Brown +(1946:453) and Wooster (1935:352; 1936:396) and found to be almost +restricted to the little-bluestem association of the mixed prairie +(Albertson, 1937:522). Brumwell (1951:213), in a survey of the Fort +Leavenworth Military Reservation, found that <i>M. ochrogaster</i> +preferred sedge and bluegrass meadows but occurred also in a +sedge-willow association. Dice (1922:46) concluded that the presence +of green herbage, roots or tubers for use as a water source throughout +the year was a necessity for <i>M. ochrogaster</i>. Goodpastor and +Hoffmeister (1952:370) found <i>M. ochrogaster</i> to be abundant in a damp +meadow of a lake margin in Tennessee. In a study made on and near the +campus of the University of Kansas, within a few miles of the area +concerned in the present report, Jameson (1947:132) found that voles +used grassy areas in spring and summer, but that in the autumn, when +the grass began to dry, they moved to clumps of Japanese honeysuckle +(<i>Lonicera japonica</i>) and stayed among the shrubbery throughout the +winter. Johnson (1926:267, 270) found <i>M. ochrogaster</i> only in +uncultivated areas where long grass furnished adequate cover. He +stated that the entire biotic association, rather than any single +factor, was the key to the distribution of the voles. None of these +reports described an intensive study of the habitat of voles, but the +data presented indicate that voles are characteristic of grassland and +that <i>M. ochrogaster</i> can occupy drier areas than those used by <i>M. +pennsylvanicus</i>. +<span class="pagenum"><a name="Page_367" id="Page_367">[367]</a></span> Otherwise, the preferred habitats of the two species +seem to be much the same.</p> + +<p>In the investigation described here I attempted to evaluate various +types of habitats on the basis of their carrying capacity at different +stages of the annual cycle and in different years. The habitats were +studied and described in terms of yield, cover and species +composition. The areas upon which live-trapping was done were studied +most intensively.</p> + +<p>These two areas, herein designated as House Field and Quarry Field, +were both occupied by voles throughout the period of study. Population +density varied considerably, however (<a href="#img005">Fig. 5</a>). Both of these areas +were dominated by <i>Bromus inermis</i>, and, in clipped samples taken in +June, 1951, this grass constituted 67 per cent of the vegetation on +House Field and 54 per cent of the vegetation on Quarry Field. +Estimates made at other times in 1950, 1951 and 1952 always confirmed +the dominance of smooth brome and approximated the above percentages. +Parts of House Field had nearly pure stands of this grass. Those traps +set in spots where there was little vegetation other than the dominant +grass caught fewer voles than traps set in spots with a more varied +cover. <i>Poa pratensis</i> formed an understory over most of the area +studied, especially on House Field, and attained local dominance in +shaded spots on both fields. The higher basal cover provided by the +<i>Poa</i> understory seemed to support a vole population larger than those +that occurred in areas lacking the bluegrass. Disturbed situations, +such as roadsides, were characterized by the dominance of <i>Bromus +japonicus</i>. This grass occurred also in low densities over much of the +study area among <i>B. inermis</i>. Other grasses present included <i>Triodia +flava</i>, common in House Field, but with only spotty distribution in +Quarry Field; <i>Elymus canadensis</i>, distributed over both areas in +spotty fashion and almost always showing evidence of use by voles and +other small mammals; <i>Aristida oligantha</i> and <i>Bouteloua +curtipendula</i>, both more common on the higher and drier Quarry Field; +<i>Panicum virgatum</i>, <i>Setaria</i> spp., especially on disturbed areas; and +three bluestems, <i>Andropogon gerardi</i>, <i>A. virginicus</i> and <i>A. +scoparius</i>. The bluestems increased noticeably during the study period +(even though grasses in general were being replaced by woody plants) +and they furnished a preferred habitat for voles because of their high +yield of edible foliage and relatively heavy debris which provided +shelter.</p> + +<p>On House Field the most common forbs were <i>Vernonia baldwini</i>, +<i>Verbena stricta</i> and <i>Solanum carolinense</i>. On Quarry Field, +<i>Solidago</i> spp. and <i>Asclepias</i> spp. were also abundant. All of them +seemed to be used by the voles for food during the early stages of +growth, when they were tender and succulent. The fruits of the horse +nettle (<i>Solanum carolinense</i>) were also eaten. The forbs themselves +did not provide cover dense enough to constitute good vole habitat. +Mixed in a grass dominated association they nevertheless raised the +carrying capacity above that of a pure stand of grass. Other forbs +noted often enough to be considered common on both House Field and +Quarry Field included <i>Carex gravida</i>, observed frequently in House +Field and less often in Quarry Field; <i>Amorpha canescens</i>, more common +in Quarry Field; <i>Tradescantia bracteata</i>, <i>Capsella bursapastoris</i>, +<i>Oxalis violacea</i>, <i>Euphorbia marginata</i>, <i>Convolvulus arvensis</i>, +<i>Lithospermum arvense</i>, <i>Teucrium canadense</i>, <i>Physalis longifolia</i>, +<i>Phytolacca americana</i>, <i>Plantago major</i>, <i>Ambrosia trifida</i>, <i>A. +artemisiifolia</i>, <i>Helianthus annuus</i>, <i>Cirsium altissimum</i> and +<i>Taraxacum erythrospermum</i>. Both areas were being invaded from one +side by forest-edge vegetation; the woody plants noted included +<span class="pagenum"><a name="Page_368" id="Page_368">[368]</a></span> +<i>Prunus americana</i>, <i>Rubus argutus</i>, <i>Rosa setigera</i>, <i>Cornus +drummondi</i>, <i>Symphoricarpus orbiculatus</i>, <i>Populus deltoides</i> and +<i>Gleditsia triacanthos</i>.</p> + +<p>In House Field the herbaceous vegetation was much more lush than in +Quarry Field and woody plants and weeds were more abundant. A graveled +and heavily used road along one edge of House Field, leading to the +Reservation Headquarters, was a barrier which voles rarely crossed. A +little-used dirt road crossing the trapping plot in Quarry Field +constituted a less effective barrier. The disturbed areas bordering +the roads were likewise little used and tended to reinforce the +effects of the roads as barriers. There were almost pure stands of +<i>Bromus japonicus</i> along both roads. No mammal of any kind was taken +in traps set where this grass was dominant.</p> + +<p>Because seasonal changes in vole density followed the curve for rate +of growth of the complex of grasses on the Reservation, and because +years in which there was a sparse growth of plants due to dry weather +showed a decrease in the density of voles, the relationships between +productivity of plants and vole population levels on the two study +areas were investigated. In both fields the composition of the plant +cover was similar, and the differences were chiefly quantitative. In +June, 1951, ten square-meter quadrats were clipped on each of the +areas to be studied. The clippings from each were dried in the sun and +weighed. From Quarry Field the mean yield amounted to 1513 ± 302 lbs. +per acre; while from House Field the yield was 2351 ± 190 lbs. per +acre (<a href="#tab001">Table 1</a>). Using experience gained in making these samples, I +periodically estimated the relative productivity of the two areas. +House Field was from 1.5 to 3 times as productive as Quarry Field +during the growing seasons of 1951 and 1952. Although House Field, +being more productive, usually supported a larger population of voles +than Quarry Field the reverse was true at the time of the clipping +(<a href="#img005">Fig. 5</a>). +</p> +<p> +<br /> +</p> + +<p class="center"><span class="smcap"><a name="tab001" id="tab001"></a>Table 1. Relationship Between Yield and Various Population Data</span></p> +<div class="center"> + <table summary="Yield and population data" class="maintables" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td class="tdtopleft"> </td> + <td class="tdtopright"> House Field</td> + <td class="tdtopright"> Quarry Field </td> + </tr> + <tr> + <td class="tdmainleft"> Yield in June, 1951, lbs./acre</td> + <td class="tdmainright">2351 ± 190</td> + <td class="tdmainright"> 1513 ± 302</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Microtus</i>, June, 1951, gms./acre</td> + <td class="tdmainright">3867</td> + <td class="tdmainright"> 5275</td> + </tr> + <tr> + <td class="tdmainleft"> Per cent immature <i>Microtus</i>, June, 1951</td> + <td class="tdmainright">29.85</td> + <td class="tdmainright">38.02</td> + </tr> + <tr> + <td class="tdmainleft"> Ratio <i>Microtus</i>, June/March</td> + <td class="tdmainright">0.73</td> + <td class="tdmainright">2.63</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Sigmodon</i>, June, 1951, gms./acre</td> + <td class="tdmainright">1376</td> + <td class="tdmainright">746</td> + </tr> + <tr> + <td class="tdmainleft"> Per cent immature <i>Sigmodon</i>, June, 1951</td> + <td class="tdmainright">35.72</td> + <td class="tdmainright">44.44</td> + </tr> + <tr> + <td class="tdmainleft"> Ratio <i>Sigmodon</i>, June/March</td> + <td class="tdmainright">1.40</td> + <td class="tdmainright">2.25</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Microtus-Sigmodon</i>, June, 1951, gms./acre</td> + <td class="tdmainright">5243</td> + <td class="tdmainright">6021</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Microtus</i> mean, gms./acre/month</td> + <td class="tdmainright">2922</td> + <td class="tdmainright">1831</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Sigmodon</i> mean, gms./acre/month</td> + <td class="tdmainright">802</td> + <td class="tdmainright">335</td> + </tr> + <tr> + <td class="tdmainleft"> <i>Sigmodon-Microtus</i>, gms./acre/month</td> + <td class="tdmainright">3728</td> + <td class="tdmainright">2166</td> + </tr> + + </tbody> + </table> +<br /> +</div> + +<p>Although no explanation was discovered which accounted fully for the +seeming aberration, two sets of observations were made that may bear +on the problem. In June, 1951, the population of voles and cotton rats +on Quarry Field was increasing rapidly whereas in House Field that +trend was reversed. The trends were reflected by the percentages of +immature individuals in the two populations and by the ratios of the +June, 1951, densities to the March, 1951, densities (<a href="#tab001">Table 1</a>). Perhaps +the density curve was determined in part by factors inherent in the +population and, to that extent, was fluctuating independently of the +environment (Errington, 1946:153).</p> + +<p>The flood in 1951 reduced the population of voles and obscured the +normal seasonal trends. Although House Field produced a heavier crop +of vegetation, Quarry Field produced a larger crop of rodents, chiefly +<i>Microtus</i> and <i>Sigmodon</i>. In House Field, however, the ratio of +<i>Sigmodon</i> to <i>Microtus</i> was notably higher. Presumably the cotton +rats competed with the voles and exerted a depressing effect on their +numbers. The intensity of the effect seemed to depend on the abundance +of both species. That this depressing effect involved more than direct +competition for plant food was suggested by the fact that in House +Field, with a heavy crop of vegetation and a seemingly high carrying +capacity for both herbivorous rodents, the biomass of voles, and of +all rodents combined, were lower than in Quarry Field which had less +vegetation and fewer cotton rats. The relationships between voles and +cotton rats are discussed further later in this report.</p> + +<p>When the centers of activity (Hayne, 1949b) of individual voles were +<span class="pagenum"><a name="Page_369" id="Page_369">[369]</a></span> +plotted it was seen that there was a shift in the places of high +density of voles on the trapping areas. This shift seemed to be +related to the advance of the forest edge with such woody plants as +<i>Rhus</i> and <i>Symphoricarpos</i> and young trees invading the area. These +shifts were clearly shown when the distribution of activity centers on +both areas in June, 1951, was compared with the distribution in June, +1952 (<a href="#img001">Fig. 1</a>). The shift was gradual and the more or less steady +progress could be observed by comparing the monthly trapping records. +It was perhaps significant that during the summers the centers of +activity were less concentrated than during the winter. The shift of +voles away from the woods was more nearly evident in winter when the +voles were driven into areas of denser ground cover, which provided +better shelter. +</p> + +<div class="figcenter"> +<a name="img001" id="img001"></a> +<img src="images/fig01.png" width="316" height="600" alt="Progressive encroachment of woody vegetation" /> +<p class="caption" ><span class="smcap">Fig. 1.</span> Progressive encroachment of woody vegetation +onto study areas, and the accompanying shift of the centers of +populations of voles. Activity centers of individuals were calculated +as described by Hayne (1949b) and are indicated by dots. The +cross-hatched areas show places where the vegetation was influenced by +the shade of woody plants.</p> +<p class="link"><a href="images/fig01lg.png">View larger image</a></p> +<br /> +</div> + +<p>From 1948 to 1950 and again in 1952 and 1953 I trapped in various +habitat types in a mixed prairie near Hays, Kansas. Before the great +drought of the thirties, <i>Microtus ochrogaster</i> was the most common +species of small mammal in that area. Since 1948, at least, it has +been taken only rarely and from a few habitats. No voles have been +taken from grazed sites. In a relict area, voles were trapped in a +lowland association dominated by big bluestem. Since 1948 only one +vole has been trapped in the more extensive hillside association +characterized by a mixture of big bluestem, little bluestem and +side-oats grama. None was taken in the upland parts of the relict area +where buffalo grass and blue grama dominated the association.</p> + +<p>In the pastured areas there are nine livestock exclosures established +by the Department of Botany of Ft. Hays Kansas State College. These +exclosures included many types of habitat found in the mixed prairie. +All of these exclosures were trapped and voles were taken in only two +of them. An exclosure situated near a pond, on low ground producing a +luxuriant growth of big bluestem and western wheat grass, has +supported voles in 1948, 1949, 1952 and 1953. An upland exclosure +containing only short grasses also supported a few voles in 1953.</p> + +<p>An examination of the nature of the various plant associations of +the mixed prairie indicates that yield of grasses, amount of debris +and basal cover may be critical factors in the distribution of voles. +The association to which the voles seemed to belong was the lowland +association. Hopkins <i>et al</i> (1952:401; 409) reported the yield of +grasses from the lowland to be approximately twice as great as from +the hillside and upland in most years. Probably equally important to +the voles was the fact that debris accumulation in the lowland was +<span class="pagenum"><a name="Page_371" id="Page_371">[371]</a></span>approximately five times as great as in the upland and approximately +2.5 times as great as on the hillside (Hopkins, unpublished data). The +unexpected presence of voles in the short grass exclosure was probably +due to two factors. In ungrazed short grass, basal cover may reach 90 +per cent (Albertson, 1937:545), thus providing excellent cover for +voles. Also, the ungrazed exclosure had greater yield and a thicker +mat of debris than the grazed short grass surrounding it and was thus +a relatively good habitat, although it did not compare favorably with +the lowland type.</p> + +<p>Samples of the populations of various areas, obtained by +snap-trapping, gave further information regarding the types of +vegetation preferred by voles. Voles were taken in all ungrazed and +unmown grasslands trapped in eastern Kansas, although some of the +areas were not used at all seasons of the year nor in years having a +low population of <i>Microtus</i>. Reithro Field, similar to Quarry Field +in its general aspect, had a heavy population of voles in the spring +and summer of 1951, a time when voles were generally abundant. On the +same area the population of small mammals was sampled in the summer of +1949 and, though occasional sign of voles was seen, not one vole was +trapped. Later trapping, in the spring and summer of 1952, also failed +to catch any voles and Fitch (1953, <i>in litt.</i>) caught none in several +trapping attempts in 1953. These later times were characterized by a +general scarcity of voles. Reithro Field was drier, with less dense +vegetation, than the two main study areas and had larger percentages +of little bluestem (<i>Andropogon scoparius</i>) and side-oats grama +(<i>Bouteloua curtipendula</i>) and smaller percentages of <i>Vernonia</i>, +<i>Verbena</i>, <i>Solanum</i> and <i>Solidago</i>.</p> + +<p>Various species of foxtail (<i>Setaria</i>) dominated most roadsides in the +vicinity of the Reservation. Voles almost always used these strips of +grass but never were abundant in them. Voles were taken near the +margin of a weedy field, fallow since 1948, but there was none in the +middle of the field. Most individuals were confined to the grassy +areas around the field and made only occasional forays away from the +edge. The dam of a small pond on the Reservation and low ground near +the water were used by <i>Microtus</i> at all times. In the summer of 1949 +no voles were taken anywhere on the Reservation but their runways were +more abundant around the pond than in the other places examined. Of +all the areas studied in the summer of 1949, only the pond area had +been protected from grazing in previous years. <i>Polygonum coccineum</i> +was the most prominent plant in the pond edge association. A few voles +were trapped in large openings in the woods, where a prairie +vegetation remained and where voles seemingly lived in nearly isolated +groups.</p> + +<p>Voles were rarely taken in grazed or mown grassland or in fields of +alfalfa, stubble or row crops. The critical factor in these cases +seemed to be the absence of debris or other ground cover under which +runways and nests could be concealed satisfactorily. Woods, rocky +outcroppings and bare ground were not used regularly by voles. Fitch +(1953, <i>in litt.</i>) has taken several <i>Microtus</i> in reptile traps set +along a rocky ledge in woods but most of these voles were subadult +males and seemed to be transients. Fields in the early stages of +succession also failed to support a population of voles. Such areas on +the Reservation were characterized by giant ragweed, horse weed, +thistles and other coarse weeds. Basal cover was low and debris +scanty. Not until an understory of grasses was established did a +population of voles appear on such areas. The coarse weeds seemed to +<span class="pagenum"><a name="Page_372" id="Page_372">[372]</a></span> +provide neither food nor cover adequate for the needs of the voles.</p> + +<p>An analysis of trapping success at each station in House Field further +clarified habitat preferences. The tendency of voles to avoid woody +vegetation was again demonstrated. Not only was the population +concentrated on that part of the study plot farthest from the forest +edge but, as a general rule, voles tended to avoid single trees or +clumps of shrubby plants wherever these occurred on the area. As an +example, trap number 18 never caught more than one per cent of the +monthly catch and in many trapping periods caught nothing. This trap +was under a wild plum tree. Adjacent traps often were entered; the +general area was the most heavily populated part of the study plot. +Only under the plum tree was there a relatively unused portion.</p> + +<p>Traps number 29 and 30, in the shade of a large honey locust tree, +also caught but few voles. Trap number 30 was only six feet from the +base of the tree and caught but one vole throughout the study period. +These two traps caught more <i>Peromyscus leucopus</i> than any other pair, +however, and both of them also caught pine voles (<i>M. pinetorum</i>). The +area shaded by this tree permitted an extension of parts of the forest +edge fauna into the grassland.</p> + +<p>In spite of the marked general tendency to avoid woody plants, some +voles made their runways around the roots of blackberry bushes, sumac +and wild plum trees. Some nests were found under larger roots, as if +placed there for protection. More vegetation was found under the woody +plants which the voles chose to use for shelter than under those which +they avoided. It seemed probable that the actual condition avoided by +voles was the bareness of the ground (a result of the shade cast by +the woody plants) rather than the woody plants themselves.</p> + +<p>Running diagonally across the eastern half of the trapping plot in +House Field there was a terracelike ridge of soil. On each side of +this ridge there was a slight depression. Observations of the study +plot in the growing season showed this strip to produce the most +luxuriant vegetation of any part of the plot. Clip-quadrat studies +confirmed this observation and showed the bluegrass understory to be +especially heavy. This strip included the areas trapped by traps +numbered 4, 5, 17, 18, 22, 23 and 37. With the exception of trap +number 18, discussed above, these traps consistently made more +captures than traps set in other parts of the plot. In winter, these +traps also caught more harvest mice (<i>Reithrodontomys megalotis</i>) than +any other comparable group of traps.</p> + +<p>Although the amount of growing tissue of plants probably is at least +as important to voles as the total amount of vegetation, some +correlation seemed to exist between the density of grassy vegetation +and the density of populations of voles. A mixed stand of grasses, +with an obvious weedy component, can support a larger population of +voles than can either a nearly pure stand of grass or the typical +early seral stages dominated by weeds. Probably the more or less +continual supply of young plants provided preferred food easily +available to voles. A more <a name="homogeneous" id="homogeneous"></a><ins title="Original has homogenous">homogeneous</ins> vegetation would tend to pass +through the young and tender stage as a unit, thus causing a feast to +be followed by a relative famine.</p> + +<hr class="chap" /> +<h2> +<a name="population_structure" id="population_structure">POPULATION STRUCTURE</a></h2> + + +<p><span class="pagenum"><a name="Page_373" id="Page_373">[373]</a></span> +During the period of study the percentage of males in most of my +samples was less than 50 per cent (<a href="#img002">Fig. 2</a>). Only once, in June, 1952, +did the mean percentage of males in samples from three areas (House +Field, Quarry Field, Fitch traps) exceed that level and then it was +only 50.1 per cent. On several occasions, however, the percentage of +males in a sample from a single area was slightly above 50 per cent. +The highest percentage of males recorded was 56.69 per cent, in a +sample taken from the Quarry Field population in June, 1952. In the +samples taken in April, 1952, the mean percentage of males was 39.67 +per cent, the lowest mean recorded. The low point for one sample was +28.02 per cent in August, 1952, from Quarry Field. The mean percentage +of males in all samples taken was 45.02 ± 2.72 per cent. Percentages +observed would occur in random samples taken from a population with 50 +per cent males less than one per cent of the time. Exactly 50 per cent +of the young in the 65 litters examined were classified as males but +the sample was small and the sexing of newborn individuals was +difficult.</p> + + +<div class="figcenter"> +<a name="img002" id="img002"></a> +<img src="images/fig02.png" width="428" height="600" alt="Graphs of population structure" /> +<p class="caption" ><span class="smcap">Fig. 2.</span> Graphs of population structure showing the +monthly changes in the mean percentages of juveniles, subadults, +adults and males in samples from the three study areas.</p> +<p class="link"><a href="images/fig02lg.png">View larger image</a></p> +<br /> +</div> + +<p>The extent to which sex ratios in samples were affected by trapping +procedure was not determined. A possibility considered was that the +greater wandering tendency of males (Blair, 1940:154; Hamilton, +1937c:261; Townsend, 1935:98) impaired the formation of trap habits +(Chitty and Kempson, 1949:536) on their part and thus unbalanced the +sex ratios of the samples. If this were the explanation, the apparent +sex ratio on larger areas would more nearly approximate the true +ratio, and the frequency of capture of females would exceed that of +males. The evidence is somewhat equivocal. In the populations +described here the mean number of captures per individual per month +was 2.31 for females, which was significantly greater (at the one per +cent level) than the 2.20 captures per individual per month which was +the mean number for males. This difference supports the idea that +differences in habits between the sexes result in distorted sex ratios +in samples obtained by live-trapping. Mean percentages of males did +not, however, differ significantly between the House Field-Quarry +Field samples and the samples from the Fitch trapping area, nearly +five times as large.</p> + +<p>Three age classes, juvenal, subadult and adult, were separated on the +basis of condition of pelage. The percentage of adults in populations +varied seasonally (<a href="#img002">Fig. 2</a>). January, February and March were the +months when the adult fraction of the population was highest and +October and November were low points, with May and June showing +percentages almost as low. The only marked variation in this seasonal +pattern occurred in July and August, 1952, when the percentage of +adults rose sharply. This was due to a depression in the reproductive +rate during the dry summer of 1952, which is discussed later in this +report. Juveniles made up only a small fraction of the population from +December through March and a relatively large fraction in the +October-November and May-June periods (<a href="#img002">Fig. 2</a>). Again, July and August +of 1952 were exceptions to the pattern as the percentages of juveniles +in these months fell to midwinter levels. As expected, the curve of +the percentages of subadults in the population followed that of the +juveniles and preceded that of the adults. The mean percentages for +the thirty month period for which data were available were: adults, +77.72 ± 4.48 per cent; subadults, 14.06 ± 3.14 per cent; and +juveniles, 8.22 ± 2.62 per cent. Seasonal and yearly changes in the +population structure occurred, with notable variation in the ratio of +<span class="pagenum"><a name="Page_374" id="Page_374">[374]</a></span> +breeding females to the entire population, as discussed in this report +under the heading of reproduction.</p> + +<p>Since some of the juveniles did not move enough to be readily +trapped, the real percentage of juveniles in the population was +probably far greater than that shown by trapping data. I tried, +<span class="pagenum"><a name="Page_375" id="Page_375">[375]</a></span> +therefore, to estimate the number of juveniles on the study plot each +month by multiplying the number of lactating females by the mean +litter size. As expected, the results were consistently higher than +the estimate based on trapping data. The discrepancy was largest in +April, May, June and October. During the winter there was no important +difference between the two estimates. Even when the discrepancy was +greatest, the estimated weight of the juveniles missed by trapping was +not large enough to modify the picture of habitat utilization in any +important way. I chose, therefore, to count only those juveniles +actually trapped. Although probably consistently too low, such a +figure seemed more reliable than an estimate made on any other basis.</p> + +<div class="figcenter" > +<a name="img003" id="img003"></a> +<img src="images/fig03.png" width="514" height="600" alt="Percentages of individuals surviving" /> +<p class="caption" ><span class="smcap">Fig. 3.</span> Percentages of individuals captured each month +surviving in subsequent months. The graph shows differential survival +according to time of birth. Individuals born in autumn seem to have a +longer life expectancy. The numbers on the lines refer to months of +first capture.</p> +<br /> +</div> + +<p>A study of the age groups in each month's population revealed a +<span class="pagenum"><a name="Page_376" id="Page_376">[376]</a></span> +differential survival based on the season of birth. Blair (1948:405) +found that chances of survival in <i>Microtus pennsylvanicus</i> were +approximately equal throughout the year. In the present populations of +<i>M. ochrogaster</i>, however, voles born in October, November, December +and January tended to live longer than those born in other months +(<a href="#img003">Fig. 3</a>). Presumably these animals, born in autumn and early winter, +were more vigorous than their older competitors and were therefore +better able to survive the shrinking habitat of winter. Their +continued survival after large numbers of younger voles had been added +to the population probably was permitted by the expanding habitat of +spring and summer. The percentage of the population surviving the +winter of 1951-1952 was approximately double the percentage surviving +the winter of 1950-1951. This difference seemed to be due to the +smaller population entering the winter of 1951-1952 rather than any +major difference in the environmental resistance.</p> + +<p>As a consequence of the differential survival, most of the breeding +population in the spring was made up of animals born the previous +October and November. <a href="#img004">Fig. 4</a> shows that in February, when the +percentage of breeding females ordinarily began to rise, 51.6 per cent +of the population was born in the previous October and November. Voles +born in these two months continued to form a large part of the +population through March (45.1 per cent), April (38.5 per cent), May +(23.9 per cent), June (18.7 per cent) and July (16.2 per cent) (<a href="#img004">Fig. 4</a>). +These percentages suggest that the habitat conditions in October +and November were probably important in determining the population +level for at least the first half of the next year.</p> + + +<div class="figcenter"> +<a name="img004" id="img004"></a> +<img src="images/fig04.png" width="424" height="600" alt="Differential survival of voles" /> +<p class="caption" ><span class="smcap">Fig. 4.</span> Differential survival of voles according to +month when first caught. Each column represents the percentage of the +monthly sample first caught in each of the preceding months. Those +voles caught first in October and November survived longer than those +first caught in other months. Relatively few individuals remained in +the population as long as one year.</p> +<br /> +</div> + + +<hr class="chap" /> + +<h2><a name="population_density" id="population_density">POPULATION DENSITY</a></h2> + + +<p>Population densities were ascertained on the study areas by means of +the live-trapping program. Blair (1948:396) stated that almost all +small mammals old enough to leave the nest (except shrews and moles) +are captured by live-trapping. My experience, and that of other +workers on the Reservation, requires modification of such a statement. +The distance between traps is an important factor in determining the +efficiency of live-trapping. As mentioned earlier, when House Field +and Quarry Field were trapped out at the conclusion of the +live-trapping program no unmarked voles were taken. This showed that +the 30 foot interval between traps was short enough to cover the area +as far as <i>Microtus</i> was concerned. The fact that unmarked adults were +caught almost entirely in marginal traps is additional evidence. On +the other hand, the Fitch traps were 50 feet apart and voles seemed to +have lived within the grid for several months before being captured. +Fitch (1954:39) has shown that some kinds of small mammals are missed +in a live-trapping program because of variation in bait acceptance, +both seasonal and specific.</p> + +<p>A few individuals, missed in a trapping period, were captured again +in subsequent months. These voles were assumed to have been present +during the month in which they were not caught. The area actually +trapped each month was estimated by a modification of the method +proposed by Stickel (1946:153). The average maximum move was +calculated each month and a strip one half the average maximum move in +width was added to each side of the study area actually covered by +traps. The study plots were bounded in part by gravel roads and forest +edge acting as barriers, and for these parts no marginal strip was +<span class="pagenum"><a name="Page_377" id="Page_377">[377]</a></span> +added. Trap lines on the opposite sides of these roads rarely caught +marked voles that had crossed in either direction. It is perhaps +advisable to say here that the size of House Field and Quarry Field +<span class="pagenum"><a name="Page_378" id="Page_378">[378]</a></span>study plots (0.56 acres) was too small for best results in estimating +population levels (Blair, 1941:149). In the computations of population +levels the data for males and females were combined, because no +significant difference between the average maximum move of the sexes +was apparent.</p> + +<p>Fluctuations of the populations were graphed in terms of individuals +per acre (<a href="#img005">Fig. 5</a>). The variation was great in the 30 month period for +which data were available, and was both chronological and +topographical. The lowest density recorded was 25.2 individuals per +acre and the highest density was 145.8 individuals per acre. The +weight varied from a low of 847 grams per acre to a high of 5275 grams +per acre.</p> + + +<div class="figcenter"> +<a name="img005" id="img005"></a> +<img src="images/fig05.png" width="417" height="600" alt="Variations in density of voles" /> +<p class="caption" ><span class="smcap">Fig. 5.</span> Variations in density of voles from three +populations, as shown by live-trapping, and the mean density of these +populations. Juveniles are not represented in their true numbers since +many voles were caught first as subadults. The samples from the Fitch +trap line were incomplete due to the wide spacing of the traps.</p> +<br /> +</div> + +<p>There are few records of density of <i>M. ochrogaster</i> in the +literature. Brumwell (1951:213) found nine individuals per acre in a +prairie on the Fort Leavenworth Military Reservation and Wooster +(1939:515) reported 38.5 individuals per acre for <i>M. o. haydeni</i> in a +mixed prairie in west-central Kansas. High densities for <i>M. +pennsylvanicus</i> reported in the literature include 29.8 individuals +per acre (Blair, 1948:404), 118 individuals per acre (Bole, 1939:69), +160-230 individuals per acre (Hamilton, 1937b:781) and 67 individuals +per acre (Townsend, 1935:97).</p> + +<p>Because the study period included one period of unusually high +rainfall and one year of unusually low rainfall, the normal pattern of +seasonal variation of population density was obscured. An examination +of the data suggested, however, that the greatest densities were +reached in October and November with a second high point in the +April-May-June period. These high points generally followed the +periods of high levels of breeding activity (<a href="#img008">Fig. 8</a>). The autumn rise +in population may have been due, in part, to the addition of spring +and early summer litters to the breeding population, but the rise +occurred too late in the year to be explained by that alone. Another +factor may have been the spurt in growth of grasses occurring in +Kansas in early autumn, in September and October. There was a seeming +correlation between high rainfall with rapid growth of grasses and +reproductive activity, and, secondarily with high population densities +of voles. These relationships are discussed in connection with +reproduction. Lowest annual densities were found to occur in January +when there is but little breeding activity and when rainfall is low +and plant growth has ceased.</p> + +<p>Marked deviation from the usual seasonal trends accompanied flood and +drought. In the flood of July, 1951, although the study areas were not +inundated, the ground was saturated to the extent that every footprint +at once became a puddle. Immediately after the floods, on all three +areas studied, populations were found to have been drastically +reduced. The effect was most severe on the population of House Field, +the lowest area studied, and the recovery of the population there was +much slower than that of those on the other study areas (<a href="#img005">Fig. 5</a>). +Newborn voles were killed by the saturated condition of the ground in +which they lay. The more precocious young of <i>Sigmodon hispidus</i> +survived wetting better. They thus acquired an advantage in the +competitive relationship between cotton rats and voles. These +relationships are discussed more fully in the section on mammalian +associates of <i>Microtus</i>.</p> + +<p>Adverse effects of heavy rainfall on populations of small mammals +have been reported by Blair (1939) and others. Goodpastor and +Hoffmeister (1952:370) reported that inundation sharply reduced +<span class="pagenum"><a name="Page_380" id="Page_380">[380]</a></span> +populations of <i>M. ochrogaster</i> for a year after flooding but that the +area was then reoccupied by a large population of voles. Such a +reoccupation may have begun on the areas of this study in the spring +of 1952 when the upward trend of the population was abruptly reversed +by drought. While cotton rats were abundant their competition may have +been an important factor in depressing population levels of voles. The +population of voles began to rise only after the population of cotton +rats had decreased (<a href="#img019">Fig. 19</a>).</p> + +<p>In the unusually dry summer of 1952, there was a marked decline of +population levels beginning in June and continuing to August when my +field work was terminated. Dr. Fitch (1953, <i>in litt.</i>) informed me +that the decline continued through the winter of 1952-53 and into the +summer of 1953, until daily catches of <i>Microtus</i> on the Reservation +were reduced to 2-10 per cent of the number caught on the same trap +lines in the summer of 1951. The drought seemed to affect population +levels by inhibiting reproduction, as described elsewhere in this +report. A similar sensitivity to drought was reported by Wooster +(1935:352) who found <i>M. o. haydeni</i> decreased more than any other +species of small mammal after the great drought of the thirties.</p> + +<p>No evidence of cycles in <i>M. ochrogaster</i> was observed in this +investigation. All of the fluctuations noted were adequately explained +as resulting from the direct effects of weather or from its indirect +effect in determining the kinds and amounts of vegetation available as +food and shelter.</p> + +<p>The differences in densities supported by the various habitats were +discussed earlier in connection with the analysis of habitats.</p> + + + +<hr class="chap" /> +<h2><a name="home_range" id="home_range">HOME RANGE</a></h2> + + +<p>Home ranges were calculated for individual voles according to the +method described by Blair (1940:149-150). The term, home range, is +used as defined by Burt (1943:350-351). Only those voles captured at +least four times were used for the home range studies. Individuals +which included the edge of the trap grid in their range were excluded +unless a barrier existed (see description of habitat) confining the +seeming range to the study area.</p> + +<p>The validity of home range calculations has been challenged (Hayne, +1950:39) and special methods of determining home range have been +advocated by a number of authors. The ranges calculated in this study +are assumed to approximate the actual areas used by individuals and +are considered useful for comparison with other ranges calculated by +similar methods, but no claim to exactness is intended. It is obvious, +for instance, that many plotted ranges contain so-called blank areas +which, at times, are not actually used by any vole (Elton, 1949:8; +Mohr, 1943:553). Studies of the movements of mammals on a more +detailed scale, perhaps by live-traps set at shorter intervals and +moved frequently, are needed to increase our understanding of home +range.</p> + +<p>In order to test the reliability of the range calculated, an +examination of the relationship between the size of the seeming range +and the number of captures was made. For the first three months, +trapping on House Field was done with a 20 foot grid and throughout +the remainder of the study a 30 foot grid was used. The effect of +these different spacings on the size of the seeming home range was +also investigated. Hayne (1950:38) found that an increase in the +distance between traps caused an increase in the size of the seeming +<span class="pagenum"><a name="Page_381" id="Page_381">[381]</a></span>home range, but in my study the increased interval between traps was +not accompanied by any change in the sizes of the calculated ranges.</p> + +<p>The number of captures, above the minimum of four, did not seem to be +a factor in determining the size of the calculated monthly range. A +seeming relationship was observed between the number of times an +individual was trapped and the total area used during the entire time +the vole was trapped. Closer examination revealed that the most +important factor was the length of time over which the vole's captures +extended. <a href="#tab002">Table 2</a> shows the progressive increase in sizes of the mean +range of animals taken over periods of time from one month to ten +months.</p> + +<p><br /></p> + +<p class="center"><span class="smcap"><a name="tab002" id="tab002"></a>Table 2. Relationship Between Home Range Size and Length of Time on +the Study Area</span></p> +<div class="center"> + + + <table summary="Relationship Between Home Range Size ..." class="maintables" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td class="tdtop2left"> No. months on area </td> + <td class="tdtop2right"> 1</td> + <td class="tdtop2right"> 2 </td> + <td class="tdtop2right"> 3</td> + <td class="tdtop2right"> 4 </td> + <td class="tdtop2right"> 5</td> + <td class="tdtop2right"> 6 </td> + <td class="tdtop2right"> 7</td> + <td class="tdtop2right"> 8 </td> + <td class="tdtop2right"> 9</td> + <td class="tdtop2right"> 10 </td> + </tr> + <tr> + <td class="tdmainleft"> Mean range in acres </td> + <td class="tdmainright"> .09</td> + <td class="tdmainright"> .09 </td> + <td class="tdmainright"> .10</td> + <td class="tdmainright"> .14 </td> + <td class="tdmainright"> .13</td> + <td class="tdmainright"> .17 </td> + <td class="tdmainright"> .22</td> + <td class="tdmainright"> .22 </td> + <td class="tdmainright"> .26</td> + <td class="tdmainright"> .24 </td> + </tr> + + </tbody> + </table> +<br /> +</div> + + +<p>Nothing concerning the home range of <i>Microtus ochrogaster</i> was found +in the literature. Several workers, including Blair (1940) and +Hamilton (1937c), have studied the home range of <i>M. pennsylvanicus</i>. +Blair (1940:153) reported a larger range for males than for females in +all habitats and in all seasons represented in his sample. In <i>M. +ochrogaster</i>, however, I found that the mean monthly range for both +sexes was 0.09 of an acre. Blair (<i>loc. cit.</i>) reported no individuals +with a range so small as that mean, but Hamilton (<i>op. cit.</i>:261) +mentioned two voles with ranges of less than 1200 square feet. The +mean total range used by an individual during the entire time it was +being trapped showed a slight difference between the sexes. Males used +an average of 0.14 of an acre whereas females used an average of but +0.12 of an acre. This suggested that, as in <i>M. pennsylvanicus</i> +(Hamilton, <i>loc. cit.</i>), males tended to wander more than females and +to shift their home range more often.</p> + +<p>The largest monthly range recorded was 0.28 of an acre used by a +female in March, 1951, and calculated on the basis of four captures. +The largest monthly range of a male was 0.25 of an acre for a vole +caught eight times in November, 1950. The smallest monthly range was +0.02 of an acre; several individuals of both sexes were restricted to +areas of this size. Juveniles, not included in the home range study, +were usually restricted to 0.01 or, at most, 0.02 of an acre. Seasonal +differences in the sizes of home ranges were not significant. However, +the voles caught in the winter often enough to be used for home range +studies were too few for a thorough study of seasonal variation in the +size of home ranges.</p> + +<p>One female was captured 22 times in the seven-month period of +October, 1950, to April, 1951. She used an area of 0.83 of an acre, +but this actually comprised two separate ranges. From October, 1950, +through December, 1950, she was taken 17 times within an area of 0.12 +of an acre; and from January, 1951, to April, 1951, she was taken five +times within an area of 0.15 of an acre. The largest area assumed to +represent one range of a female was 0.38 of an acre, recorded on the +basis of six captures in three months. The largest area encompassed by +the record of an individual male was 0.41 of an acre. He, too, shifted +his range, being taken five times on an area of 0.07 of an acre and +twice, two months later, on an area of 0.09 of an acre. Presumably, +<span class="pagenum"><a name="Page_382" id="Page_382">[382]</a></span>the remainder of his calculated total range was used but little, or +not at all. The largest single range of a male was 0.36 of an acre, +calculated on the basis of 18 captures in seven months. The smallest +total range for both sexes was 0.02 of an acre.</p> + +<p>Many voles shifted their home range and a few did so abruptly. The +large range of a female vole, described above and plotted in <a href="#img006">Fig. 6</a>, +indicated an abrupt shift from one home range to another. More common +is a gradual shift as indicated by the range of the male shown in <a href="#img007">Fig. 7</a>. +Large parts of each monthly range of this vole overlapped the area +used in other months but his center of activity shifted from month to +month.</p> + +<div class="figcenter" > +<a name="img006" id="img006"></a> +<img src="images/fig06.png" width="550" height="235" alt="Map with cross-hatched areas showing the range +of vole #20" /> +<p class="caption" ><span class="smcap">Fig. 6.</span> Map with cross-hatched areas showing the range +of vole #20 (female). Dots show actual points of capture at permanent +trap stations 30 feet apart. Vertical lines mark area in which vole +was taken 17 times in October and November, 1950. Horizontal lines +mark area in which vole was taken five times in March and April, 1951. +This vole was not captured in December and January.</p> +</div> + +<div class="figcenter" > +<a name="img007" id="img007"></a> +<img src="images/fig07.png" width="550" height="245" alt="Map showing range of vole #52" /> +<p class="caption" ><span class="smcap">Fig. 7.</span> Map showing range of vole #52 (male) with +seeming shifts in its center of activity. Dots show actual points of +capture at permanent trap stations 30 feet apart. Solid line encloses +points of six captures in October and November, 1950. Broken line +encloses points of five captures in February and March, 1951. Dotted +line encloses points of nine captures in April, May and June, 1951.</p> +<br /> +</div> + + +<p>That home ranges overlapped was demonstrated by frequent capture of +two or more individuals together in the same trap. No territoriality +has been reported in any species of <i>Microtus</i>, to my knowledge, and +my voles showed no objection to sharing their range. Voles taken from +the field into the laboratory lived together in pairs or larger groups +without much friction.</p> + +<p><span class="pagenum"><a name="Page_383" id="Page_383">[383]</a></span></p><p>Definable systems of runways and home ranges were not coextensive. +Runway systems tended to merge, as described later in this report, and +relationships between them and home range were not apparent. Home +ranges had no characteristic shape.</p> + + + +<hr class="chap" /> +<h2><a name="life_history" id="life_history">LIFE HISTORY</a></h2> + + +<h3><a name="reproduction" id="reproduction">Reproduction</a></h3> + +<p>Reproductive activity might have been measured in a number of ways. +Three indicators were tested: the percentage of females gravid or +lactating, the percentage of juveniles in the month following the +sampling period, and the percentage of females with a vaginal orifice +in the sampling period. The condition of vagina proved to be most +useful. Whether or not there is a vaginal cycle in <i>Microtus</i> is +uncertain. Bodenheimer and Sulman (1946:255-256) found no evidence of +such a cycle, nor did I in my work with laboratory animals at +Lawrence. How much the artificial environment of the laboratory +affected these findings is unknown. The presence of an orifice seemed +to indicate sexual activity (Hamilton, 1941:9). The percentage of +gravid females in the population could not be determined accurately by +a live-trapping study and was not useful in this investigation. The +percentage of juveniles trapped in the month following the sampling +period tended to follow the curve of the percentage of adult females +with a vaginal orifice. The ratio of trapped juveniles to adults +trapped was a poor indicator of reproductive activity. Juveniles were +caught in relatively small numbers because of their restricted +movements, and no way to determine prenatal and juvenal mortality was +available.</p> + +<p>Reproductive activity continues throughout the year. Within the +thirty-month period for which data were obtained, December and January +showed the lowest percentages of females with vaginal orifices (<a href="#img008">Fig. 8</a>). +The other months all showed higher levels of reproductive activity +with a slight peak in the August-September-October period in both 1950 +and 1951. In the species of <i>Microtus</i> that are found in the United +States, such summer peaks of breeding seem to be the rule (Blair, +1940:151; Gunderson, 1950:17; Hamilton, 1937b:785). Jameson +(1947:147) worked in the same county where my field study was made and +found that the high point of reproduction was in March, although his +samples were too small to be reliable. The peak of reproductive +activity slightly preceded the highest level of population density in +each year (<a href="#img008">Fig. 8</a>).</p> + +<div class="figcenter" > +<a name="img008" id="img008"></a> +<img src="images/fig08.png" width="550" height="490" alt="Variations in density and reproductive rate of +voles" /> +<p class="caption" ><span class="smcap">Fig. 8.</span> Variations in density and reproductive rate of +voles, with variation in monthly precipitation. Abnormally low +rainfall in 1952 caused a decrease in breeding activity and eventually +in the numbers of voles. The solid line indicates the number of voles +per acre, the broken line the percentage of females with a vaginal +orifice and the dotted line the inches of rainfall.</p> +<br /> +</div> + + +<p>A marked reduction in the percentage of females having vaginal +orifices was observed in the unusually dry summer of 1952. The rate of +reproduction was found to be positively correlated with rainfall (<a href="#img009">Fig. 9</a>). +Correlation coefficients were higher in each case when the amount +of rainfall in the month preceding each sampling period was used +instead of that in the month of the sample. This suggested that the +rainfall exerted its influence indirectly through its effect on plant +growth. Bailey (1924:530) reported that a reduction in either the +quantity or quality of food had a depressing effect on reproduction. +Drought, such as occurred in 1952, would certainly have a depressing +effect on both. The critical factor seems to be the supply of new, +actively growing shoots available to the voles for food rather than +the total amount of vegetation. As far as could be determined from the +small sample of males examined, their fecundity was not affected by +rainfall. Some decrease in the percentage of males that were fecund +<span class="pagenum"><a name="Page_384" id="Page_384">[384]</a></span> +was noted in the winter and was reported also by Jameson (1947:145) +but most of the males in any sample were fecund. Thus any depression +in the reproductive rate was due to loss of fecundity by females. This +was in agreement with reports in the literature on the subject (Baker +and Ransom, 1932a:320; 1932b:43).</p> + +<p>The correlation coefficient between rainfall and the percentage of +adult females with a vaginal orifice was 0.53. This was considered to +be surprisingly high in view of the expected effects on the breeding +rate of temperature, seasonal diet variations and whatever rhythms +were inherent in the voles. When only the summer months were +considered the correlation coefficient between rainfall and the +percentage of adult females with a vaginal orifice was 0.84. This +indicated that, during the season when breeding was at its height, +rainfall was a factor in determining the rate of reproduction and when +rainfall was scarce, as in the summer of 1952, it seemed to be a +limiting factor (<a href="#img009">Fig. 9</a>).</p> + +<div class="figcenter"> +<a name="img009" id="img009"></a> +<img src="images/fig09.png" width="550" height="396" alt=" Comparison between monthly rainfall and +reproductive rate of voles in summer" /> +<p class="caption" ><span class="smcap">Fig. 9.</span> Comparison between monthly rainfall and +reproductive rate of voles in summer. The dry summer of 1952 caused a +notable decrease in reproductive activity. The correlation coefficient +between rainfall and the percentage of females with a vaginal orifice +was 0.84.</p> +<br /> +</div> + + +<p>Of the total captures 20.6 per cent involved more than one +individual. When the distribution of these multiple captures was +<span class="pagenum"><a name="Page_385" id="Page_385">[385]</a></span> +graphed for the period of study, a high correlation between the +percentage of captures that were multiple and the percentage of +females with a vaginal orifice (r = 0.70) was found. An even higher +correlation (r = 0.76) was observed between the percentage of captures +that were multiple and the population density. The higher percentage +of multiple captures may have been largely a result of fewer available +traps per individual on the area and thus only indirectly related to +the rate of reproduction.</p> + +<p>Of the multiple captures, 66 per cent involved both sexes. The +correlation coefficient between the percentage of captures involving +both sexes and the level of reproductive activity was 0.58. Among +those pairs of individuals caught together more than once, 61 per cent +were composed of both sexes. Among those pairs taken together three or +more times 76 per cent were male and female and among those pairs +taken together four or more times 80 per cent were male and female. +When adult voles stayed together any length of time their relationship +usually appeared to be connected with sex. Family groups were also +noted, as pairs were often trapped which seemed to be mother and +offspring. A lactating female would sometimes enter a trap even after +it had been sprung by a juvenile, presumably her offspring, or a +juvenal vole would enter a trap after its mother had been captured. +Such family groups persisted only until the young voles had been +weaned.</p> +<p><span class="pagenum"><a name="Page_386" id="Page_386">[386]</a></span></p> +<p>The youngest female known to be gravid was 26 days old and weighed 28 +grams. During summer most of the females were gravid before they were +six weeks old, although females born in October and after were often +more than 15 weeks old before they became gravid. The youngest male +known to be fecund was approximately six weeks old. Male fecundity was +determined as described by Jameson (1950). Difference in the age of +attainment of sexual maturity serves to reduce the mating of litter +mates (Hamilton, 1941:7) and has been noticed in various species of +the genus <i>Microtus</i> by several authors (Bailey, 1924:529; Hatfield, +1935:264; Hamilton, <i>loc. cit.</i>; Leslie and Ransom, 1940:32).</p> + +<p>For 35 females, each of which was caught at least once each month for +ten consecutive months or longer, the mean number of litters per year +was 4.07. Certain of the more productive members of the group produced +11 litters in 16 months. <i>M. ochrogaster</i> seems to be less prolific +than <i>M. pennsylvanicus</i>. Bailey (1924:528) reported that one female +meadow vole delivered 17 litters in 12 months. Hamilton (1941:14) +considered 17 litters per year to be the maximum and stated that in +years when the vole population was low the females produced an average +of five to six litters per year. In "mouse years" the average rose to +eight to ten litters per year. During this study several females +delivered two or more litters in rapid succession. This was noted more +frequently in spring and early summer than in other parts of the year. +Those females which produced two or three litters in rapid succession +in spring and early summer often did not litter again until fall. +Post-parous copulation has been observed in <i>M. pennsylvanicus</i> by +Bailey (1924:528) and Hamilton (1940:429; 1949:259) and probably +occurs also in <i>M. ochrogaster</i>.</p> + +<p>The gestation period was approximately 21 days, the same as reported +for <i>M. pennsylvanicus</i> (Bailey, <i>loc. cit.</i>; Hamilton, 1941:13) and +<i>M. californicus</i> (Hatfield, 1935:264). A more precise study of the +breeding habits of <i>M. ochrogaster</i> failed to materialize when the +voles refused to breed in captivity. Fisher (1945:437) also reported +that <i>M. ochrogaster</i> failed to breed in captivity although <i>M. +pennsylvanicus</i> (Bailey, 1924) and <i>M. californicus</i> (Hatfield, 1935) +reproduced readily in the laboratory.</p> + + +<h3><a name="litter_size" id="litter_size">Litter Size and Weight</a></h3> + +<p>In the course of this study 65 litters were observed. The mean number +of young per litter was 3.18 ± 0.24 and the median was three (<a href="#img010">Fig. 10</a>). +Three litters contained but one individual and the largest litter +contained six individuals. Other investigators have reported the +number of young per litter in <i>M. ochrogaster</i> as three or four +(Lantz, 1907:18) and 3.4 (1-7) (Jameson, 1947:146). <i>M. +pennsylvanicus</i> seems to have larger litters. Although Poiley +(1949:317) found the mean size of 416 litters to be only 3.72 ± 0.18, +both Bailey (1924:528) and Hamilton (1941:15) found five to be the +commonest number of young per litter in that species. Leslie and +Ransom (1940:29) reported the average number of live births per litter +to be 3.61 in the British vole, <i>M. agrestis</i>. Selle (1928:96) +reported the average size of five litters of <i>M. californicus</i> to be +4.8. Hatfield (1935:265), working with the same species, found that +litter size varied directly with the age of the female producing the +litter. He reported litters of young females as two to four young per +litter and of older females as five to seven young per litter. In the +<span class="pagenum"><a name="Page_387" id="Page_387">[387]</a></span>litters of <i>M. ochrogaster</i> that I examined, young females did not +have more than three young and usually had but two. However, older +females had litters of one, two and three often enough so that no +relationship, as described above, was indicated clearly.</p> + +<div class="figcenter" > +<a name="img010" id="img010"></a> +<img src="images/fig10.png" width="500" height="416" alt=" Distribution of litter size among 65 litters +of voles" /> +<p class="caption" ><span class="smcap">Fig. 10.</span> Distribution of litter size among 65 litters +of voles.</p> +<br /> +</div> + + +<p>No seasonal variation in litter size was noted. The mean size of the +litters in 1950, 2.68 ± 0.30, was significantly lower than that found +in 1951 (3.76 ± 0.20) but neither differed significantly from the mean +size of litters in 1952 (3.35 ± 0.66). The lower mean size of litters +was in part coincidental with a high population level and the higher +mean of the two later years was in part coincidental with a low +population level. Since a sharp break in the curve for population +density occurred after the flood in July, 1951, the litters were +arranged in pre-flood and post-flood categories for study. Pre-flood +litters averaged 3.07 ± 0.28 young per litter whereas post-flood +litters averaged 3.34 ± 0.48. This difference was not significant. +Increase in litter size, if it had actually occurred, might have been +a response to the increasing food supply and lower population density +after the flood.</p> + +<p>A difference in the mean number of young per litter was noted for +those litters delivered in traps as compared with those delivered in +captivity and the numbers of embryos examined in the uterus. The mean +number of embryos per female was higher than the mean number of young +per litter delivered in captivity and the mean number of young per +litter delivered in traps was lower than in those delivered in +captivity. The differences were not statistically significant. In some +instances females that delivered young voles in traps may have +delivered others prior to entering the trap or the mother or her +trapmates may have eaten some of the newborn voles before they were +discovered.</p> +<p><span class="pagenum"><a name="Page_388" id="Page_388">[388]</a></span></p> +<p>The mean weight of 16 newborn (less than one day old) individuals was +2.8 ± 0.36 grams. No other data on the weight of newborn <i>M. +ochrogaster</i> were found in the literature but this mean was close to +the 3.0 grams (Bailey, 1924:530) and 2.07 grams (Hamilton, 1937a:504; +1941:10) reported for <i>M. pennsylvanicus</i> and to the 2.7 grams (Selle, +1928:97) and 2.8 grams (Hatfield, 1935:268) reported for <i>M. +californicus</i>. No correlation between the weight of the individual +newborn vole and the number of voles per litter was observed.</p> + +<p>Although the ratio of the average weight of newborn voles to the +average weight of an adult female was approximately equal for <i>M. +pennsylvanicus</i> and <i>M. ochrogaster</i>, the ratio of the weight of a +litter to the average weight of an adult female was larger in the +eastern meadow vole because the mean litter size was larger. Perhaps +this is related to the more productive habitat in which the eastern +meadow vole is ordinarily found.</p> + + +<h3><a name="size_growth" id="size_growth">Size, Growth Rates and Life Spans</a></h3> + +<p>The mean weight of adult voles during the period of study was 43.78 +grams. The females averaged slightly heavier than the males but the +overlapping of weights was so extensive that sexual difference in +weight could not be affirmed. The difference observed was less in +December and January when gravid females were rare, suggesting that +the difference was due, at least in part, to pregnancy. Jameson +(1947:128) found, for a sample of 50 voles, a mean weight of 44 grams +and a range of 38 to 58 grams. The range in the adult voles I studied +was much greater, from 25 to 73 grams. In part, this increase in the +range of adult weights was due to a much larger sample.</p> + +<div class="figcenter" > +<a name="img011" id="img011"></a> +<img src="images/fig11.png" width="550" height="310" alt=" Relationship between rainfall and the mean +weight" /> +<p class="caption" ><span class="smcap">Fig. 11.</span> Relationship between rainfall and the +<a name="weighterror" id="weighterror"></a> +<ins title="the bottommost y-axis label in the scale of gms. is probably an error: 45 should be 35">mean weight of adult males</ins> +in summer. The abnormally low rainfall in the +summer of 1952 was accompanied by a decrease in mean weight. The solid +line represents mean weight and the broken line rainfall. The +correlation coefficient between the two was 0.68.</p> +<br /> +</div> + + +<p>During the unusually dry summer of 1952, a notable reduction in the +mean weight of adults was recorded (<a href="#img011">Fig. 11</a>). The correlation +coefficient between the mean weight of adults and the amount of +rainfall for the summer months was 0.68. It seems reasonable to +<span class="pagenum"><a name="Page_389" id="Page_389">[389]</a></span>attribute the drop in mean weight to an alteration of plant growth due +to decreased rainfall. Some of the reduction in mean weight was due to +the loss of weight in older individuals but most of it was due to the +failure of voles born in the spring to continue growing.</p> + +<p>No data on the growth rate of <i>M. ochrogaster</i> were found in the +literature. According to the somewhat scanty data from my study, +secured from observations of individuals born in the laboratory, young +voles gained approximately 0.6 of a gram per day for the first ten +days, approximately one gram per day up to an age of one month, and +approximately 0.5 of a gram per day from an age of one month until +growth ceases. This growth rate was especially variable after the +voles reached an age of thirty days. The growth rate approximates +those described for <i>M. pennsylvanicus</i> (Hamilton, 1941:12) and for +<i>M. californicus</i> (Hatfield, 1935:269; Selle, 1928:97). Although the +data were inadequate for a definite statement, I gained the impression +that there was no difference between the sexes in growth rate. In +general, young voles grow most rapidly in the April-May-June period +and least rapidly in mid-winter. Several voles, born in late autumn, +stopped growing while still far short of adult size and lived through +the winter without gaining weight, then gained as much as 30 per cent +after spring arrived (<a href="#img012">Fig. 12</a>).</p> + +<div class="figcenter" > +<a name="img012" id="img012"></a> +<img src="images/fig12.png" width="550" height="385" alt="Growth rates of two voles" /> +<p class="caption" ><span class="smcap">Fig. 12.</span> Growth rates of two voles selected to show +typical growth pattern of voles born late in the year. Growth nearly +stops in winter and is resumed in spring.</p> +<br /> +</div> + + + +<p>The recorded life spans of most voles studied were less than one +year. No accurate mean life span could be determined. Leslie and +Ransom (1940:46), Hamilton (1937a:506) and Fisher (1945:436) also +found that most voles lived less than one year. Leslie and Ransom +(<i>op. cit.</i>: 47) reported a mean life span of 237.59 ± 10.884 days in +voles of a laboratory population. In the present study one female was +trapped 624 days after first being captured; another female was +trapped 617 days after first being captured; and a male was trapped +611 days after first being captured. The two females were subadults +<span class="pagenum"><a name="Page_390" id="Page_390">[390]</a></span>when first captured. The male was already an adult when first +captured; consequently its life span must have exceeded 650 days. No +evidence of any decrease in vigor or fertility was observed to +accompany old age.</p> + +<p>Of the 45 marked voles snap-trapped in August of 1952, 21 had been +captured first as juveniles. The ages of these voles could be +estimated within a few days, and the series presented a unique +opportunity for studying individual and age variation. Only +individuals weighing less than 18 grams when first captured were used, +and their ages were estimated according to the growth rate described +above. Howell (1924) reported an analysis of individual and age +variation in a series of specimens of <i>Microtus montanus</i>, and Hall +(1926) studied the changes due to growth in skulls of <i>Otospermophilus +grammarus beecheyi</i>. The series of specimens described here differs +from those of Hall and Howell, and from any other collection known to +me, in the fact that the specimens are of approximately known age and +drawn from a wild population.</p> + +<p>Unfortunately, this sample was small, and the distribution of the +specimens among age groups left much to be desired. No specimens less +than one and one-half months old were taken and only a few individuals +older than four and one-half months. <a href="#tab003">Table 3</a> shows the age +distribution. The small size of the sample and the absence of +juveniles were due, partly, to the unusually dry weather in the summer +of 1952. The reduction in the rate of reproduction, caused by drought +(as described elsewhere in this paper), reduced the populations and +the percentage of juveniles to low levels.</p> + +<p><br /></p> +<p class="center"><span class="smcap"><a name="tab003" id="tab003"></a>Table 3. Distribution Among Age Groups of 21 Voles Used in the Study +of Variation Due to Age</span></p> +<div class="center"> + + <table summary="Distribution Among Age Groups of 21 Voles" class="maintables" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td class="tdtopleft"> Age in months</td> + <td class="tdtop"> 1<small><sup>1</sup>⁄<sub>2</sub></small></td> + <td class="tdtop"> 2 </td> + <td class="tdtop"> 2<small><sup>1</sup>⁄<sub>2</sub></small></td> + <td class="tdtop"> 3 </td> + <td class="tdtop"> 3<small><sup>1</sup>⁄<sub>2</sub></small> </td> + <td class="tdtop"> 4 </td> + <td class="tdtop"> 4<small><sup>1</sup>⁄<sub>2</sub></small> </td> + <td class="tdtop"> 6 </td> + <td class="tdtop"> 12</td> + </tr> + <tr> + <td class="tdmainleft"> No. of individuals </td> + <td class="tdmain"> 1</td> + <td class="tdmain"> 4 </td> + <td class="tdmain"> 5</td> + <td class="tdmain"> 1 </td> + <td class="tdmain"> 3</td> + <td class="tdmain"> 2 </td> + <td class="tdmain"> 3</td> + <td class="tdmain"> 1 </td> + <td class="tdmain"> 1</td> + </tr> + + </tbody> + </table> +<br /> +</div> + + +<p>In the series of voles studied, ten individuals were in the process of +molting from subadult to adult pelage. Jameson (1947:131) reported the +molt to occur between eight and 12 weeks of age and selected 38 grams +as the lower limit of weight of adults. I also found all voles molting +to be between eight and 12 weeks old but found none so large as 38 +grams without full adult pelage. This may have been, in part, due to +the dry weather delaying or inhibiting growth. Because of the small +size of the sample and the influence of the unusual weather +conditions, no conclusions concerning normal molting were drawn from +the data described below. They are presented only as a description of +a small sample drawn from a single population at one time. <a href="#tab004">Table 4</a> +summarizes these data.</p> + +<p><br /></p> +<p class="center"><span class="smcap"><a name="tab004" id="tab004"></a>Table 4. Mean Sizes and Ages of Voles Molting from Subadult to Adult +Pelage</span></p> +<div class="center"> + <table summary="Mean Sizes and Ages of Voles Molting" class="maintables" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td class="tdtopleft"> </td> + <td class="tdtopleft"> Weight</td> + <td class="tdtopleft"> Body length minus tail </td> + <td class="tdtopleft"> Condylo-basilar length</td> + <td class="tdtopleft"> Age </td> + </tr> + <tr> + <td class="tdmainleft"> Six males </td> + <td class="tdmainleft"> 32.67 gms.</td> + <td class="tdmainleft"> 106.16 mm.</td> + <td class="tdmainleft"> 23.78 mm.</td> + <td class="tdmainleft">9.67 wks.</td> + </tr> + <tr> + <td class="tdmainleft"> </td> + <td class="tdmainleft"> (30-36)</td> + <td class="tdmainleft"> (96-116)</td> + <td class="tdmainleft"> (23.2-24.4)</td> + <td class="tdmainleft">(8-12)</td> + </tr> + <tr> + <td class="tdmainleft"> Four females </td> + <td class="tdmainleft"> 29.0 gms.</td> + <td class="tdmainleft"> 100.25 mm.</td> + <td class="tdmainleft"> 23.45 mm. </td> + <td class="tdmainleft"> 10.5 wks.</td> + </tr> + <tr> + <td class="tdmainleft"> </td> + <td class="tdmainleft"> (28-30)</td> + <td class="tdmainleft"> (98-102) </td> + <td class="tdmainleft"> (23.5-23.8)</td> + <td class="tdmainleft">(8-12)</td> + </tr> + <tr> + <td class="tdmainleft"> Ten voles</td> + <td class="tdmainleft"> 31.2 gms.</td> + <td class="tdmainleft"> 103.8 mm.</td> + <td class="tdmainleft"> 23.73 mm.</td> + <td class="tdmainleft"> 10.0 wks.</td> + </tr> + <tr> + <td class="tdmainleft"> </td> + <td class="tdmainleft"> (28-36)</td> + <td class="tdmainleft"> (96-116) </td> + <td class="tdmainleft"> (23.2-24.4)</td> + <td class="tdmainleft">(8-12)</td> + </tr> + </tbody> + </table> +<br /> +</div> + + +<p>The mean age of the ten voles molting was ten weeks (8-12). Six males +<span class="pagenum"><a name="Page_396" id="Page_396">[396]</a></span> +averaged 9.67 weeks, almost a week younger than four females, who +averaged 10.5 weeks. The difference in age at time of molting between +the sexes was not significant. Differences between the sexes in other +characteristics to be described also lacked significance. Mean weights +at the time of molting were: males, 32.67 gms. (30-36); females, 29.0 +gms. (28-30); and all individuals, 31.2 gms. (28-36). Because a piece +of the tail of each vole had been removed in marking, the total length +of the voles could not be determined. Body length, excluding tail, was +used. Howell (1924:986) found this measurement subject to less +individual variation than total length and thought body length was +probably a better indicator of age. Mean body length at the time of +molting was 103.8 mm. (96-116). Males averaged longer than females and +were also more variable. The mean body length of males was 106.16 mm. +(96-116) and that of females was 100.25 mm. (98-102).</p> + +<p>Of the subadults showing no signs of molting, none was above the mean +age of molting. Twenty-five per cent of them were longer and heavier +than the mean length and weight of those that were molting. Of the 20 +adults in the series, one was below the mean weight of molting and one +was shorter than the mean length of molting.</p> + +<p>When Howell (<i>op. cit.</i>:1014) studied skulls of <i>Microtus montanus</i> he +found that the condylobasilar length was the most satisfactory means +for arranging his series of specimens according to their age. When the +skulls of my series were arranged according to their age (as +determined from trapping records) the graph of the condylobasilar +lengths showed a clear, though not perfect, relationship to age (<a href="#img013">Fig. 13</a>). No separation of sexes was made because the sample did not permit +it. In <a href="#img013">Fig. 13</a> graphs of weight, as determined in the field, and of +length (excluding tail) also were included because they are the most +easily measured characters of live voles. The graphs indicate +individual variation in these characters which limits their usefulness +in determining age.</p> + +<div class="figcenter"> +<a name="img013" id="img013"></a> +<img src="images/fig13.png" width="446" height="600" alt=" Graphs of the condylobasilar lengths..." /> +<p class="caption" ><span class="smcap">Fig. 13.</span> Graphs of the condylobasilar lengths, body +lengths and weights of a series of voles of known age. Within each age +group, the youngest vole is on the left in the graphs.</p> +<br /> +</div> + + +<p>When other cranial measurements, and ratios of pairs of measurements, +were plotted in the same order, individual variation obscured some of +the variation due to age and the curves resembled those of weight and +length of body rather than that of condylobasilar length. When the +cranial measurements were averaged for the age groups the curves +showed a relationship to age but the relationship of mean measurements +is of little use in determining the age of individual specimens. The +data described above indicated that a study of the relationship of the +condylobasilar length and age in a large sample might provide useful +information.</p> + +<p>Anyone who has examined mammalian skulls knows of many other +characters which vary with age but which are difficult to measure and +describe with precision. <a href="#img014">Figs 14</a> and <a href="#img015">15</a> are drawings of skulls of +voles of known age. The most obvious change, related to aging, evident +in the dorsal view of the skulls (<a href="#img014">Fig. 14</a>) is the increasing +prominence and closer approximation of the temporal ridges in older +specimens. The lambdoidal ridge is also more prominent in older voles, +and their skulls have a generally rougher and more angular appearance. +The individual variation evident in these ridges is probably due to +variations in the development of the muscles operating the jaws +(Howell, 1924:1003). There is an increased flattening of the roof of +the skull of older voles.</p> + + +<div class="figcenter"> +<a name="img014" id="img014"></a> +<img src="images/fig14.png" width="600" height="494" alt="Dorsal views of skulls of voles of known age" /> +<p class="caption" ><span class="smcap">Fig. 14.</span> Dorsal views of skulls of voles of known age. +(Ages 1<small><sup>1</sup>⁄<sub>2</sub></small>, 2<small><sup>1</sup>⁄<sub>2</sub></small>, 3, 3<small><sup>1</sup>⁄<sub>2</sub></small>, 4, 4<small><sup>1</sup>⁄<sub>2</sub></small>, 6 and 12 months). All × 3. </p> +<p class="link"><a href="images/fig14lg.png">View larger image</a></p> +</div> + +<div class="figcenter"> +<a name="img015" id="img015"></a> +<img src="images/fig15.png" width="600" height="492" alt="Palatal views of skulls of voles of known age" /> +<p class="caption" ><span class="smcap">Fig. 15.</span> Palatal views of skulls of voles of known age. +(Ages 1<small><sup>1</sup>⁄<sub>2</sub></small>, 2<small><sup>1</sup>⁄<sub>2</sub></small>, 3, 3<small><sup>1</sup>⁄<sub>2</sub></small>, 4, 4<small><sup>1</sup>⁄<sub>2</sub></small>, 6 and 12 months). All × 3. </p> +<p class="link"><a href="images/fig15lg.png">View larger image</a></p> +<br /> +</div> + + + +<p>From a palatal view (<a href="#img015">Fig. 15</a>) the skulls of voles also showed age +<span class="pagenum"><a name="Page_397" id="Page_397">[397]</a></span> +variation which was apparent but not easily correlated with precise +age. The median ridge on the basioccipital bone increases in +prominence in older voles. The shape of the posterior margin of the +palatine bones changes from a V-shape to a U-shape. On the skull of +the oldest (12 months) vole the pterygoid processes are firmly fused +to the bullae, a condition not found in any of the other specimens. +The anterior spine of the palatine approaches the posterior projection +of the premaxillae more closely as age increases and, in the oldest +vole is firmly attached and forms a complete partition separating the +incisive foramina.</p> + +<p>Tooth wear during the life of a vole causes a considerable variation +in the enamel patterns, especially of the third upper molar. Howell +(1924:1012) considered such variation to be independent of age, but +Hinton (1926:103) related the changes to age and interpreted them as a +recapitulation of the evolution of microtine molars. In my series, an +indentation on the medial margin of the posterior loop of the third +upper molar seemed to be related to age. This indentation was absent +in the youngest vole (one and one-half months), absent or indefinite +in those voles less than 3<small><sup>1</sup>⁄<sub>2</sub></small> months of age, and progressively more +marked in the older voles.</p> + + +<h3><a name="food_habits" id="food_habits">Food Habits</a></h3> + +<p>The prairie vole, like other members of the genus <i>Microtus</i>, feeds +mostly on growing grass in spring and summer. Piles of cuttings in the +runways are characteristic sign of the presence of voles. The voles +cut successive sections from the bases of grasses until the young and +tender growing tips are within reach. The quantity of grass destroyed +is greater than that actually eaten, a fact which will have to be +considered in any attempt to evaluate the effects of voles upon a +range.</p> + +<p>In all piles of cut plants that were examined, <i>Bromus inermis</i> was +the most common grass, and <i>Poa pratensis</i> was the grass second in +abundance. These were, by far, the most common grasses present on the +areas studied; in most places, <i>B. inermis</i> was dominant. Other +grasses present on the areas were occasionally found in the piles of +cuttings. Jameson (1947:133-136) found no utilization of <i>B. inermis</i> +by voles but that grass was present in a relative abundance of only +one per cent in the areas studied by him. The voles that he studied +ate alfalfa in large amounts and alfalfa was, perhaps, the most common +plant on the particular areas where his voles were caught. Seemingly, +the diet of voles is determined mostly by the species composition of +the habitat.</p> + +<p>Other summer foods included pokeberries, blackberries and a few forbs +and insects. Forbs most commonly found in the piles of cuttings were +the leaves of the giant ragweed (younger plants only) and dandelion. +Insect remains were found in the stomachs of voles killed in summer +and occurred most frequently in those killed in August and September. +At no time did insects seem to be a major part of the diet but they +were present in most vole stomachs examined in late summer. Laboratory +experiments with summer foods gave inconclusive results but suggested +that the voles chose grasses on the basis of their growth stage rather +than according to their species. Young and tender grasses were chosen, +regardless of species, when various combinations of <i>Triodia flava</i>, +<i>Bromus inermis</i> and <i>Poa pratensis</i> were offered to the voles. At +<span class="pagenum"><a name="Page_398" id="Page_398">[398]</a></span> +times the voles showed a marked preference for dandelion greens, +perhaps because of their high moisture content; the voles' water needs +were satisfied mostly by eating such succulent vegetation.</p> + +<p>Winter foods consisted of stored hay and fruits and of underground +plant parts. <i>Bromus inermis</i> made up nearly all of the hay and was +stored in lengths of up to ten inches in underground chambers +specially constructed for storage. Underground parts of plants were +reached by tunnelling and were an especially important part of the +voles' diet in January and February. The fruit of <i>Solanum +carolinense</i> was eaten throughout the winter and one underground +chamber, opened in February, 1952, was packed full of these seemingly +unsavory fruits. Fisher (1945:436), in Missouri, found this fruit to +be an important part of the winter diet of voles. An occasional pod of +the honey locust tree was found partly eaten in a runway. Fitch (1953, +<i>in litt.</i>) often observed girdling of honey locust and crab apple +(<i>Pyrus ioensis</i>) root crowns on the Reservation but I saw no evidence +of bark eating, perhaps because my study plots were mostly grassland. +On two occasions when two voles were in the same trap one of them was +eaten. In both traps, all of the bait had been eaten and the captured +voles probably were approaching starvation. Because the trapping +procedure offered abundant opportunity for cannibalism, the low +frequency of its occurrence suggested that it was not an important +factor in satisfying food requirements under normal conditions.</p> + + +<h3><a name="runways" id="runways">Runways and Nests</a></h3> + +<p>Perhaps the most characteristic sign of the presence of <i>Microtus +ochrogaster</i> were their surface runways and underground tunnels. Only +rarely was a vole observed to expose itself to full view. When a +trapped vole was released it immediately dove out of sight into a +runway. Once in a runway, the vole showed no further evidence of alarm +and was usually in no hurry to get away. The runways seemed to provide +a sense of security and the voles were familiar with their range only +through runway travel. The urge to seek a runway immediately when +exposed has obvious survival value.</p> + +<p>Surface runways were usually under a mat of debris. In areas where +debris was scanty or lacking, runways were usually absent. Jameson +(1947:136) reported that in alfalfa and clover fields the voles did +not make runways as they did in grassland, even in fields where +trapping records showed voles to be abundant. Typical surface runways +are approximately 50 mm. wide, only slightly cut into the ground and +bare of vegetation while in use. Usually they could be distinguished +from the runways of the pine vole, which were cut more deeply into the +ground, and those of the cotton rat which were wider and not so well +cleared of vegetation. Some runways ended in surface chambers and some +of these were lined with grass. Their size varied from a diameter of +90 mm. to 250 mm. and they seemed to be used primarily for resting +places.</p> + +<p>A runway system usually consisted of a long, crooked runway and +several branches. Two typical systems are illustrated in <a href="#img016">Fig. 16</a>. The +runway systems often were not clearly limited; they merged with other +systems more or less completely. One map showed a runway system +extending across 140 square meters and including 12 underground +burrows. All of these runways seemed to be part of a single runway +system but the system probably was used by more than one vole or +family group of voles. Sixteen of the 22 maps that were made extended +<span class="pagenum"><a name="Page_399" id="Page_399">[399]</a></span>across areas between 50 and 90 square meters. One map, mentioned +above, was larger and the remaining five smaller. The smallest +extended across only 20 square meters. Of course, the area encompassed +by a set of runways changed almost daily, as the voles extended some +runways, added some and abandoned others in the course of their daily +travels.</p> + + +<div class="figcenter" > +<a name="img016" id="img016"></a> +<img src="images/fig16.png" width="444" height="600" alt="Maps of runway systems" /> +<p class="caption" ><span class="smcap">Fig. 16.</span> Maps of runway systems of the prairie vole. +The runways follow an irregular course and are frequently changed. The +solid lines represent surface runways and the dotted lines underground +passages.</p> +<br /> +</div> + +<p><span class="pagenum"><a name="Page_400" id="Page_400">[400]</a></span></p><p>Each runway system contained underground nests. These were in chambers +from 70 mm. to 200 mm. below the surface and were up to 200 mm. in +diameter. Most systems that were mapped had from two to six of these +burrows. Most of these were lined with dried grass and seemed to be +used for delivering and nursing litters. Each burrow was connected to +a surface runway by a tunnel. Often the tunnel was short and the hole +opened almost directly into the burrow from the surface runway. Others +had tunnels several meters long. Jameson (1947:137) reported every +burrow to have two connections with the surface. In the present study, +however, I found three arrangements in approximately equal frequency +of occurrence: (1) one hole to one tunnel leading to a burrow; (2) two +holes to two short tunnels which joined a long tunnel leading to a +burrow; and (3) two separate tunnels from the surface to a burrow. The +size, depth and number of underground burrows in the systems that I +studied varied and so did those reported in the literature. Jameson +(<i>loc. cit.</i>) found burrows in eastern Kansas as deep as 18 inches, +far deeper than any found in my study. Fisher (1945:435) reported none +deeper than five inches in central Missouri. The soil data in my +study, as well as in the two reports cited immediately above, were not +adequate to permit conclusions, but the type and condition of the soil +probably determine the extent of burrowing by the voles of any given +locality.</p> + +<p>The number of voles using a runway system at one time was difficult to +ascertain. In one system, however, four adult individuals were trapped +in a ten day period. In August, 1952, at the conclusion of the +live-trapping program, a runway system was mapped which had included +two trapping stations. In the preceding ten days, four adult voles +(three males and one female) had been taken in both traps. During that +time, therefore, the runway system was shared by at least four voles. +The voles used an area that was considerably larger than that +encompassed by any one runway system, a fact obvious when the sizes of +home ranges as computed from trapping data were compared with the +sizes of the runway systems mapped. A runway system seemed not to be a +complete unit, but was only a part of the network of runways used by a +single individual.</p> + + +<h3><a name="activity" id="activity">Activity</a></h3> + +<p>Although no special investigation of activity was made, some +conclusions concerning it were apparent in the data gathered. There +have been a few laboratory studies of the activity pattern of +<i>Microtus</i> by various methods. Calhoun (1945:256) reported <i>M. +ochrogaster</i> to be mainly nocturnal with activity reaching a peak +between dark and midnight and again just before dawn. Davis +(1933:235), working with <i>M. agrestis</i>, and Hatfield (1935:263), +working with <i>M. californicus</i>, both found voles to be more nocturnal +than diurnal. In a field study of <i>M. pennsylvanicus</i>, Hatt (1930:534) +found the species to be chiefly nocturnal, although some activity was +reported throughout the day. Hamilton (1937c:256-259), however, +reported the same species to be more active in the daytime. Agreement +on the activity patterns of these species of <i>Microtus</i> has not yet +been attained.</p> + +<p>From occasional changes in the time of tending a trap line, and from +running lines of traps at night a few times in the summer of 1951, I +gained the impression that these voles were primarily diurnal. +Relatively few of them were caught in the hours of darkness. In +summer, however, their activity +<span class="pagenum"><a name="Page_401" id="Page_401">[401]</a></span> +was mostly limited to the periods +between dawn and approximately eight o'clock and between sunset and +dark. In colder weather, there was increased activity on sunny days.</p> + + + +<hr class="chap" /> +<h2><a name="predation" id="predation">PREDATION</a></h2> + + +<p>Although voles were a common item of prey for many species of +predators on the Reservation, no marked effect on the density of the +population of this vole could be attributed to predation pressure. +Only when densities reached a point that caused many voles to expose +themselves abnormally could they be heavily preyed upon. Their +normally secretive habits, keeping them more or less out of sight, +suggest that they are an especially obvious illustration of the +concept that predation is an expression of population vulnerability, +rising to high levels only when a population is ecologically insecure, +rather than a major factor regulating population levels (Errington, +1935; 1936; 1943; Errington <i>et al</i>, 1940).</p> + +<p>Scats from predatory mammals and reptiles and pellets from raptorial +birds were examined. Most of these materials were collected by Dr. +Henry S. Fitch, who kindly granted permission to use them. The results +of the study of the scats and pellets are summarized in <a href="#tab005">Table 5</a>. +Remains of voles were identified in 28 per cent of the scats of the +copperhead snake (<i>Ancistrodon contortix</i>) examined. Copperheads were +moderately common on the Reservation (Fitch, 1952:24) and were +probably important as predators on voles in some habitats. Uhler <i>et +al</i> (1939:611), in Virginia, reported voles to be the most important +prey item for copperheads. A vole was taken from the stomach of a +rattlesnake (<i>Crotalus horridus</i>) found dead on a county road +adjoining the Reservation. Rattlesnakes were present in small numbers +on the Reservation but were usually found along rocky ledges rather +than in areas where voles were common (Fitch, <i>loc. cit.</i>). The +rattlesnakes probably were less important as predators on voles than +on other small mammals more common in the usual habitat of these +snakes. The blue racer (<i>Coluber constrictor</i>) was common in grassland +situations on the Reservation (Fitch, 1952:24) and twice was observed +in the role of a predator on voles; one small blue racer entered a +live-trap in pursuit of a vole and another blue racer was observed +holding a captured vole in its mouth. The blue racer seems well +adapted to hunt voles and probably preys on them extensively. The +pilot black snake (<i>Elaphe obsoleta</i>) has been reported as a predator +on <i>M. ochrogaster</i> in the neighboring state of Missouri (Korschgen, +1952:60) and was moderately common on the Reservation (Fitch, <i>loc. +cit.</i>). <i>M. pennsylvanicus</i>, with habits similar to those of <i>M. +ochrogaster</i>, has been reported as a prey for all of the above snakes +(Uhler, <i>et al</i>, 1939).</p> +<p><br /></p> +<p class="center"><span class="smcap"><a name="tab005" id="tab005"></a>Table 5. Frequency of Remains of Voles in Scats and Pellets +</span></p> +<div class="center"> + <table summary="Frequency of Remains of Voles in Scats and Pellets" class="maintables" cellpadding="3" cellspacing="0" > + <tbody> + <tr> + <td class="tdtopleft"> Predator </td> + <td class="tdtop"> No. of scats or pellets examined </td> + <td class="tdtop"> No. containing remains of voles </td> + <td class="tdtop"> Percentage</td> + </tr> + <tr> + <td class="tdmainleft"> Copperhead </td> + <td class="tdmain"> 25</td> + <td class="tdmain"> 7 </td> + <td class="tdmain"> 28 </td> + </tr> + <tr> + <td class="tdmainleft"> Red-tailed hawk </td> + <td class="tdmain"> 25</td> + <td class="tdmain"> 3 </td> + <td class="tdmain"> 12 </td> + </tr> + <tr> + <td class="tdmainleft"> Long-eared owl </td> + <td class="tdmain"> 25</td> + <td class="tdmain"> 18 </td> + <td class="tdmain"> 72 </td> + </tr> + <tr> + <td class="tdmainleft"> Great horned owl </td> + <td class="tdmain"> 32</td> + <td class="tdmain"> 6 </td> + <td class="tdmain"> 19 </td> + </tr> + <tr> + <td class="tdmainleft"> Crow </td> + <td class="tdmain"> 25</td> + <td class="tdmain"> 4 </td> + <td class="tdmain"> 16 </td> + </tr> + <tr> + <td class="tdmainleft"> Coyote </td> + <td class="tdmain"> 25</td> + <td class="tdmain"> 3 </td> + <td class="tdmain"> 12 </td> + </tr> + </tbody> + </table> +<br /> +</div> + +<p>The red-tailed hawk (<i>Buteo jamaicensis</i>), the long-eared owl (<i>Asio +otus</i>), <span class="pagenum"><a name="Page_402" id="Page_402">[402]</a></span> +the great horned owl (<i>Bubo virginianus</i>) and the crow +(<i>Corvus brachyrhynchos</i>) fed on <i>Microtus</i>. All four birds were +fairly common permanent residents on the Reservation (Fitch, 1952:25). +The low density and the strict territoriality of the red-tailed hawk +(Fitch, <i>et al</i>, 1946:207) prevented it from exerting any important +influence on the population of voles, even though individual +red-tailed hawks ate many voles. Predation by the long-eared owl was +especially heavy; remains of voles were identified in 72 per cent of +its pellets examined. Korschgen (1952:39) found remains of voles in 70 +per cent of 704 pellets of the long-eared owl. The reason for the +heavy diet of <i>Microtus</i> seems to be that both the owl and the vole +are especially active at dusk. A group of long-eared owls, living near +the edge of Quarry Field, probably exerted an influence on the density +of the local population of voles because of the high ratio of predator +to prey animals. The crows ate some, and perhaps most, of their voles +after the animals had died from other causes. Other birds, mostly +raptors, occurring in northeastern Kansas and reported to prey on +voles include the sharp-shinned hawk (<i>Accipiter striatus</i>), Cooper's +hawk (<i>A. cooperi</i>), red-shouldered hawk (<i>Buteo lineatus</i>), +broad-winged hawk (<i>B. platypterus</i>), American rough-legged hawk (<i>B. +lagopus</i>), ferruginous rough-legged hawk (<i>B. regalis</i>), marsh hawk +(<i>Circus cyaneus</i>), barn owl (<i>Tyto alba</i>), screech owl (<i>Otus asio</i>), +barred owl (<i>Strix varia</i>) and shrike (<i>Lanius excubitor</i>) (Korschgen, +1952:26; 28; 34; 35; 37; McAtee, 1935:9-27; Wooster, 1936:396).</p> + +<p>Coyotes, house cats and raccoons were identified as predators on voles +in the study areas. Remains of voles were present in 12 per cent of +the scats of the coyote (<i>Canis latrans</i>) examined. In Missouri, +Korschgen (1952:40-43) reported remains of voles in slightly more than +20 per cent of the coyote stomachs that he examined. Fitch (1948:74), +Hatt (1930:559) and others have reported other species of <i>Microtus</i> +as eaten by the coyote. Although coyotes were rarely seen on the +Reservation, coyote sign was abundant (Fitch, 1952:29) and coyotes +probably ate large numbers of voles. House cats (<i>Felis domesticus</i>), +seemingly feral, were observed to tour the trap lines on several +occasions and were noted by Fitch (<i>loc. cit.</i>) as important predators +on small vertebrates. Four cats were killed in the course of the study +and remains of voles were found in the stomachs of all of them. On +several occasions, raccoon tracks were noted following the trap line +when the traps had been overturned and broken open, suggesting that +raccoons are not averse to eating voles although no further evidence +of predation on voles by raccoons was obtained. Fitch (<i>loc. cit.</i>) +reported raccoons (<i>Procyon lotor</i>) to be moderately common on the +Reservation. Reports of predation by raccoons on voles are numerous +(Hatt, 1930:554; Lantz, 1907:41). The opossum (<i>Didelphis +marsupialis</i>), common on the Reservation, occasionally eats voles +(Sandidge, 1953:99-101). Other mammals which are probably important +predators on voles on the Reservation, though no specific information +is available, are the striped skunk (<i>Mephitis mephitis</i>), spotted +skunk (<i>Spilogale putorius</i>), weasel (<i>Mustela frenata</i>) and the red +fox (<i>Vulpes fulva</i>). Eadie (1944; 1948; 1952), Shapiro (1950:360) and +others have reported that the short-tailed shrew (<i>Blarina +brevicauda</i>) was an important predator on <i>Microtus</i>. Shrews were +present on the Reservation but were not trapped often enough to permit +study.</p> + +<p>The variety of vertebrates preying on voles suggests that they occupy +a position of importance in many food chains. Errington (1935:199) and +McAtee (1935:4) refer to voles as staple items of prey for all classes +<span class="pagenum"><a name="Page_403" id="Page_403">[403]</a></span>of predatory vertebrates. An attempt to evaluate prey species was made +by Wooster (1939). He proposed a formula which involved multiplying +the density of a species, its mean individual weight, the fraction of +the day it was active and the fraction of the year it was active to +give a numerical index of prey value. Although his methods of +determining population densities would now be considered questionable, +the purpose of his investigation merits further consideration. He +reported <i>M. ochrogaster</i> to be second only to the jack-rabbit (<i>Lepus +californicus</i>) as a prey species in west-central Kansas.</p> + + + +<hr class="chap" /> +<h2><a name="mammalian_associates" id="mammalian_associates">MAMMALIAN ASSOCIATES</a></h2> + + +<p>In the course of live-trapping operations several species of small +mammals other than <i>Microtus ochrogaster</i> were taken in the traps. +Also, from time to time, direct observations of certain mammals were +made and various types of sign of larger mammals were noted. These +records gave a picture of the mammalian community of which the voles +were a part. The three associated species which were most commonly +trapped were <i>Sigmodon hispidus</i>, <i>Reithrodontomys megalotis</i> and +<i>Peromyscus leucopus</i>. These three species have been commonly found +associated with <i>Microtus</i> in this part of the country (Fisher, +1945:435; Jameson, 1947:137).</p> + +<p>The Texas cotton rat, <i>Sigmodon hispidus</i>, was the most commonly +trapped associate of the voles between November, 1950, and February, +1952. Although a greater number of individuals of the harvest mouse +were taken in a few months, the cotton rat had a greater ecological +importance because of its larger size (<a href="#img017">Figs 17</a>, <a href="#img018">18</a>, <a href="#img019">19</a>). The cotton +rat was an especially noteworthy member of the community for two +reasons. It has arrived in northern Kansas only recently and its +progressive range extension northward and westward has attracted the +attention of many mammalogists (Bailey, 1902:107; Cockrum, 1948; +1952:183-187; Rinker, 1942b). Secondly, <i>Sigmodon</i> has long been +considered to be almost the ecological equivalent of <i>Microtus</i> and to +replace the vole in the southern United States (Calhoun, 1945:251; +Svihla, 1929:353). Since the two species are now found together over +large parts of Kansas their relationships in the state need careful +study.</p> + +<div class="figcenter" > +<a name="img017" id="img017"></a> +<img src="images/fig17.png" width="525" height="615" alt=" Variations in density and mass of three common +rodents on House Field" /> +<p class="caption" ><span class="smcap">Fig. 17.</span> Variations in density and mass of three common +rodents on House Field. The upper graph shows the sum of the biomass +of the three rodents. In the two lower graphs the solid line +represents <i>Microtus</i>, the broken line <i>Sigmodon</i>, and the dotted line +<i>Reithrodontomys</i>.</p> +</div> + +<div class="figcenter" > +<a name="img018" id="img018"></a> +<img src="images/fig18.png" width="550" height="635" alt=" Variations in density and biomass of three common +rodents on House Field" /> +<p class="caption" ><span class="smcap">Fig. 18.</span> Variations in density and biomass of three +common rodents on Quarry Field. For key, see legend of <a href="#img017">Fig. 17</a>.</p> +</div> + +<div class="figcenter" > +<a name="img019" id="img019"></a> +<img src="images/fig19.png" width="418" height="600" alt=" Variations in density and biomass of three common +rodents on House Field" /> +<p class="caption" ><span class="smcap">Fig. 19.</span> Changing biomass ratios of three common +rodents on House Field and Quarry Field. In late 1951 and early 1952 +the cotton rats attained relatively high levels and seemingly caused +compensatory decreases in the numbers of voles. The solid line +represents <i>Microtus</i>, the broken line <i>Sigmodon</i>, and the dotted line +<i>Reithrodontomys</i>.</p> +<br /> +</div> + + + +<p>Both this study and the literature (Black, 1937:197; Calhoun, <i>loc. +cit.</i>; Meyer and Meyer, 1944:108; Phillips, 1936:678; Rinker, +1942a:377; Strecker, 1929:216-218; Svihla, 1929:352-353) showed that, +in general, the habitat needs of <i>Microtus</i> and <i>Sigmodon</i> were +similar. Studies on the Natural History Reservation, both in +connection with my problem and otherwise, suggested, however, that +<i>Sigmodon</i> occurred in only the more productive habitat types used by +voles, where the vegetation was relatively high and rank. On the +Reservation the cotton rat was found mostly in the lower meadows; they +were more moist and had a more luxuriant vegetation than the higher +fields. Although a few cotton rats were taken in Quarry Field and +still fewer in Reithro Field, the population of those hilltop areas +did not approach, at any time, the levels reached on House Field, +which produced a more luxuriant cover. Only when the levels of +population were exceptionally high did the cotton rats spread into +less productive habitats. At all times, there were areas on the +Reservation used by <i>Microtus</i> which could not support a population of +<i>Sigmodon</i>.</p> + +<p>The cotton rats reacted differently to the floods of July, 1951, +than did the voles. Although the population of the cotton rat +decreased slightly immediately after the wet period, this decrease was +<span class="pagenum"><a name="Page_404" id="Page_404">[404]</a></span> +insignificant when compared with the drop in population level of other +species of small mammals on the same area. During the autumn of 1951 +and until March, 1952, the cotton rat became the most important mammal +on the House Field study area in terms of grams per acre (<a href="#img017">Fig. 17</a>), +although the number of cotton rats per acre never matched the density +of the voles. A similar, though less pronounced, trend was observed on +the Quarry Field study area (<a href="#img018">Fig. 18</a>). One factor in the success of +the cotton rat at this time seemed to be the greater resistance to +wetting shown by very young individuals. Few adults (of any species) +marked before the heavy rains of July, 1951, were trapped in +September, 1951, when trapping was resumed after a lapse of one month. +Several subadults and some juvenal cotton rats did survive, however, +<span class="pagenum"><a name="Page_405" id="Page_405">[405]</a></span> +and provided a breeding population from which the area was +repopulated. Cotton rats are born fully furred and able to move well, +and are often weaned at ten days (Meyer and Meyer, 1944:123-124). +Voles, on the other hand, are born naked and helpless and are often +not weaned for three weeks. It seems, therefore, that extremely wet +soil would harm the voles more than it would the cotton rats.</p> + +<p>Several instances of cotton rats eating voles, caught in the same +live-trap, were noted. There is reason to believe that young voles, +unable to leave the nest, are subject to predation by cotton rats. +This would accentuate any competitive advantage gained otherwise by +the cotton rats.</p> + +<p>The population of <i>Sigmodon</i> retained its high level, relative to +<i>Microtus</i>, until February, 1952. In March only one individual was +captured and after that none was trapped until August, 1952, when a +single subadult male was captured. Early in March, 1952, before the +<span class="pagenum"><a name="Page_407" id="Page_407">[407]</a></span>trapping period for the month had begun, the area suffered three +successive days of unusually low temperature, with snow, which lay +more than six inches deep in places. As suggested by Cockrum +(1952:185), such conditions proved detrimental to the cotton rats and, +at least to the end of the study period in August, 1952, the +population of cotton rats had failed to recover. Perhaps the extremely +dry weather which followed the heavy winter mortality delayed the +recovery of the population.</p> + +<p>These limited data seem to indicate competition between <i>Sigmodon</i> and +<i>Microtus</i> in Kansas. Extremely wet conditions seem to give <i>Sigmodon</i> +a competitive advantage whereas <i>Microtus</i> is better able to survive +dry summers and severe winters. However, these relationships need +further clarification by an intensive study of the life history of +<i>Sigmodon</i> in Kansas (especially the more arid western part), +including its coactions with the communities it has invaded +successfully recently.</p> + +<p>The harvest mouse (<i>Reithrodontomys megalotis</i>) also was a common +inhabitant of the study plots, but this small rodent seemed not to be +a serious competitor of the voles, as its food consists almost +entirely of seeds (Cockrum, <i>op. cit.</i>:165) not usually used by voles. +In this study, at least, no conflict over space was apparent. Harvest +mice frequently were taken in the runways of voles and even in the +same trap with voles. Reithro Field, the part of the Reservation +having the heaviest population of the harvest mouse, differed from the +habitats that were better for voles in being higher, drier and less +densely covered with vegetation. However, during the summer of 1951 +when the voles were most abundant, Reithro Field supported a large +population of voles. Estimates of population of the harvest mouse were +of doubtful validity in summer because it was readily trapped only in +winter and early spring. Many individuals marked in late spring were +not trapped again until late autumn although presumably they remained +on the area. This seasonal variation in trapping success seemed to be +a matter of acceptance and refusal of bait (Fitch, 1954:45).</p> + +<p>The presence of the wood mouse (<i>Peromyscus leucopus</i>) on the study +plots indicated an overlapping of habitats. Both House and Quarry +Fields were on the ecotone between forest and meadow and a mixture of +mammals from both types of habitat occurred. No sign of the homes of +the wood mouse was found on the study plots, and on the larger trap +line, operated by Fitch, wood mice were captured only near the edge of +the woods.</p> + +<p>Only six deer mice (<i>Peromyscus maniculatus</i>) were taken on the study +plots. This small number probably provided an inaccurate index of the +association of the deer mouse and the prairie vole, because samples +from snap-traps and the data of other workers on the Reservation +showed a more common occurrence of the two species together. The deer +mice seemed to prefer a sparser vegetation and did not approach so +closely to the forest edge as did the voles. It may have been, in +part, the presence of <i>P. leucopus</i> in the ecotonal region which made +it unsuitable for <i>P. maniculatus</i>.</p> + +<p>Other mammals noted on the study areas were the following: <i>Didelphis +marsupialis</i>, <i>Blarina brevicauda</i>, <i>Scalopus aquaticus</i>, <i>Canis +familiaris</i>, <i>Canis latrans</i>, <i>Procyon lotor</i>, <i>Felis domesticus</i>, +<i>Sylvilagus floridanus</i>, <i>Microtus pinetorum</i>, <i>Mus musculus</i> and +<i>Zapus hudsonius</i>.</p> + + + +<hr class="chap" /> +<p><span class="pagenum"><a name="Page_408" id="Page_408">[408]</a></span></p> +<h2> +<a name="summary" id="summary">SUMMARY AND CONCLUSIONS</a></h2> + + +<p>In the 23-month period from October, 1950, to August, 1952, the +ecology of the prairie vole, <i>Microtus ochrogaster</i>, was investigated +on the Natural History Reservation of the University of Kansas. In +all, 817 voles were captured 2941 times in 13,880 "live-trap days." +For some aspects of this study, Dr. Henry S. Fitch, resident +investigator on the Reservation, permitted the use of his trapping +records. He had captured 1416 voles 5098 times. The total number of +live voles used in the study was thus 2233, and they were captured +8039 times. In addition to the voles, I caught 96 cotton rats, 108 +harvest mice, 29 wood mice, 2 pine voles and 6 deer mice in live +traps. When Fitch's records were used, the live-trapping data covered +a thirty-month period and general field data were available from July, +1949, to August, 1952.</p> + +<p>Hall and Cockrum (1953:406) stated that probably all microtine rodents +fluctuate markedly in numbers. Certainly the populations I studied did +so, but the fluctuations were not regularly recurring for <i>M. +ochrogaster</i> as they seem to be for some species of the genus in more +northern life zones. The changes in the density of populations +described in this paper can be explained without recourse to cycles of +long time-span and literature dealing specifically with <i>M. +ochrogaster</i> makes no references to such cycles. There is, however, an +annual cycle of abundance: greatest density of population occurs in +autumn, and the least density in January.</p> + +<p>This annual pattern is often, perhaps usually, obscured because of the +extreme sensitivity of voles to a variety of changes in their +environment. These changes are reflected as variations in reproductive +success. In this study, some of these changes were accentuated by the +great range in annual precipitation. Annual rainfall was approximately +average in 1950 (36.32 inches, 0.92 inches above normal), notably high +in 1951 (50.68 inches, 15.28 inches above normal) and notably low in +1952 (23.80 inches, 11.60 inches below normal).</p> + +<p>Among the types of environmental modification to which the +populations of voles reacted were plant succession, an increase in +competition with <i>Sigmodon</i>, abnormal rainfall and concentration of +predators. In the overgrazed disclimax existing in 1948 when the study +areas were reserved, no voles were found because cover was +insufficient. After the area was protected a succession of good +growing years hastened the recovery of the grasses and the populations +of voles reached high levels. In areas where the vegetation approached +<span class="pagenum"><a name="Page_409" id="Page_409">[409]</a></span>the climax community, the densities of voles decreased from the levels +supported by the immediately preceding seral stages. The higher +carrying capacity of these earlier seral stages was probably due to +the greater variety of herbaceous vegetation which tended to maintain +a more constant supply of young and growing parts of plants which were +the preferred food of voles. Later in the period of study the +succession from grasses to woody plants on parts of the study areas +also affected the population of voles. Not only did the voles withdraw +from the advancing edge of the forest, but their density decreased in +the meadows as the number of shrubs and other woody plants increased. +These influences of the succession of plants on the population density +of voles were exerted through changes in cover and in the quality, as +well as the quantity, of the food supply.</p> + +<p>Whenever voles were in competition with cotton rats, there was a +depression in the population levels of voles. Primarily, the +competition between the two species is the result of an extensive +coincidence of food habits, but competition for space, cover and +nesting material is also present. There was one direct coaction +between these two species observed. Cotton rats, at least +occasionally, ate voles, especially young individuals. In extremely +wet weather, as in the summer of 1951, the high survival rate of +newborn cotton rats resulted in an increase in their detrimental +effect on the population of voles. However, cotton rats proved to be +less well adapted to severe cold or drought than were voles.</p> + +<p>Heavy rainfall reduced the densities of populations of voles by +killing a large percentage of juveniles. During the summer of 1951 the +competition of cotton rats further depressed the population level of +the voles, but the relative importance of competition with cotton rats +and superabundant moisture in effecting the observed reduction in +population density is difficult to judge. Perhaps most of the decrease +in population which followed the heavy rains was due to competition +rather than to weather. Subnormal rainfall, as in 1952, reduced the +population of voles by inhibiting reproduction. Presumably because of +an altered food supply, reproduction almost ceased during the drought. +Utilization of the habitat was further reduced in the summer of 1952 +because the voles did not grow so large as they otherwise did.</p> + +<p>Predation, as a general rule, does not significantly affect densities +of populations, but large numbers of predators concentrating on small +areas may rapidly reduce the numbers of prey animals. In the course of +<span class="pagenum"><a name="Page_410" id="Page_410">[410]</a></span>my study, such a situation occurred but once, when a group of +long-eared owls roosted in the woods adjacent to Quarry Field. The +population of voles in that area was probably reduced somewhat as a +result of predation by owls.</p> + +<p>Population trends in either direction may be reversed suddenly by +changes in the factors discussed above. In the fall of 1951, a +downward trend in the density of the voles was evident. At this time, +populations of cotton rats were increasing rapidly and competition +between cotton rats and voles was intensified. In February, 1952, the +population of cotton rats was decimated suddenly by a short period of +unusually cold weather. The voles were suddenly freed from the stress +of competition and the population immediately began to rise. The +upward trend began prior to the annual spring increase and was +subsequently reinforced by it. In the last part of May, 1952, the +upward trend of the population was reversed, as the drought became +severe, and the density of the population decreased rapidly. This drop +was too sudden and too extreme to be only the normal summer slump. The +relatively rapid response of voles to a heavy rain after a dry period, +first by increased breeding and later by increases in density, is one +more example of abrupt changes in population trends caused by altered +environmental conditions.</p> + +<p>In the population changes that I observed, no evident "die-off" of +adults accompanied even the most drastic reductions in population +density. The causative factor directly influences the population +either by inhibiting reproduction or by increasing infant and prenatal +mortality. The net reduction is due to an inadequate replacement of +those voles lost by normal attrition.</p> + +<p>Most voles, under natural conditions, live less than one year. Those +individuals born in the autumn live longer, as a group, than those +born at any other time. Since the heaviest mortality is in young +voles, adults which become established in an area may live more than +18 months and, if they are females, may produce more than a dozen +litters. No decrease in vigor and fertility was found to accompany +aging. A relationship between the condylobasilar length of the skull +and the age of a vole was discovered and, with further study, may +yield a method of aging voles more accurately than has been possible +heretofore. Other characteristics, varying with age, were described. +The most reliable indicator of age seemed to be the prominence of the +temporal ridges.</p> + +<p>Runway systems and burrows are used by groups of voles rather than by +individuals. Most of the activity of voles is confined to these +<span class="pagenum"><a name="Page_411" id="Page_411">[411]</a></span>runways and an exposed individual is seldom seen. A home range may +include several runway systems, and the ranges of individuals overlap +extensively. Both home ranges and patterns of runway systems change +constantly. Runways seem to be primarily feeding trails, and are +extended or abandoned as the voles change their feeding habits. Groups +of adult voles using a system of runways seem to have no special +relationship. Juveniles tend to stay near their mothers, but as they +mature, they shift their ranges and are replaced by other individuals. +Males wander more than females, and shift their ranges more often. No +intolerance of other voles exists and, in laboratory cages, groups of +voles lived together peaceably from the time they are placed together. +Crowding does not seem to be harmful directly, therefore, and high +densities will develop if food and cover resources permit.</p> + +<p>As a prey item, the prairie vole proved to be an important part of the +biota of the Reservation. It was eaten frequently by almost all of the +larger vertebrate predators on the Reservation and was, seemingly, the +most important food item of the long-eared owl. The ability of the +prairie vole to maintain high levels of population over relatively +broad areas enhances its value as a prey species.</p> + + + +<hr class="chap" /> +<h2><a name="literature" id="literature">LITERATURE CITED</a></h2> + + +<p><span class="smcap">Albertson, F. W.</span></p> + +<p class="indnt">1937. Ecology of a mixed prairie in west-central Kansas. Ecol. +Monog., 7:481-547.</p> + +<p><span class="smcap">Bailey, V.</span></p> + +<p class="indnt">1902. Synopsis of the North American species of <i>Sigmodon</i>. +Proc. Biol. Soc. Washington, 15:101-116.</p> + +<p class="indnt">1924. Breeding, feeding and other life habits of meadow mice. +Jour. Agric. Res., 27:523-536.</p> + +<p><span class="smcap">Baker, J. R.</span>, and <span class="smcap">R. M. Ransom</span>.</p> + +<p class="indnt">1932a. Factors affecting the breeding of the field mouse +(<i>Microtus agrestis</i>). Part I. Light. Proc. Roy. Soc. London, +Series B, 110:313-322.</p> + +<p class="indnt">1932b. Factors affecting the breeding of the field mouse +(<i>Microtus agrestis</i>). Part II. Temperature. Proc. Roy. Soc. +London, Series B, 112:39-46.</p> + +<p><span class="smcap">Black, T. D.</span></p> + +<p class="indnt">1937. Mammals of Kansas. Kansas State Board Agric., 13th +Biennial Rep., 1935-36:116-217.</p> + +<p><span class="smcap">Blair, W. F.</span></p> + +<p class="indnt">1939. Some observed effects of stream valley flooding on small +mammal populations in eastern Oklahoma. Jour. Mamm., +20:304-306.</p> + +<p class="indnt">1940. Home ranges and populations of the meadow vole in +southern Michigan. Jour. Wildlife Mgmt., 4:149-161.</p> +<p><span class="pagenum"><a name="Page_412" id="Page_412">[412]</a></span></p> +<p class="indnt">1941. Techniques for the study of small mammal populations. +Jour. Mamm., 22:148-157.</p> + +<p class="indnt">1948. Population density, life span and mortality rates of +small mammals in the bluegrass meadow and bluegrass field +associations of southern Michigan. Amer. Midland Nat., +40:395-419.</p> + +<p><span class="smcap">Bodenheimer, F. S.</span>, and <span class="smcap">F. Sulman</span>.</p> + +<p class="indnt">1946. The estrous cycle of <i>Microtus guentheri</i> D. and A. and +its ecological implications. Ecol., 27:255-256.</p> + +<p><span class="smcap">Bole, B. P., Jr.</span></p> + +<p class="indnt">1939. The quadrat method of studying small mammal populations. +Cleveland Mus. Nat. Hist. Sci. Publ., 5:1-77.</p> + +<p><span class="smcap">Brown, H. L.</span></p> + +<p class="indnt">1946. Rodent activity in a mixed prairie near Hays, Kansas. +Trans. Kansas Acad. Sci., 48:448-458.</p> + +<p><span class="smcap">Brumwell, M.</span></p> + +<p class="indnt">1951. An ecological survey of the Fort Leavenworth Military +Reservation. Amer. Midland Nat., 45:187-231.</p> + +<p><span class="smcap">Burt, W. H.</span></p> + +<p class="indnt">1943. Territoriality and home range concepts as applied to +mammals. Jour. Mamm., 24:346-352.</p> + +<p><span class="smcap">Calhoun, J. B.</span></p> + +<p class="indnt">1945. Diel activity rhythms of the rodents <i>Microtus +ochrogaster</i> and <i>Sigmodon hispidus hispidus</i>. Ecol., +26:251-273.</p> + +<p><span class="smcap">Chitty, D.</span>, and <span class="smcap">D. A. Kempson</span>.</p> + +<p class="indnt">1949. Prebaiting of small mammals and a new design of a live +trap. Ecol., 30:536-542.</p> + +<p><span class="smcap">Cockrum, E. L.</span></p> + +<p class="indnt">1947. Effectiveness of live traps vs. snap traps. Jour. Mamm., +28:186.</p> + +<p class="indnt">1948. Distribution of the hispid cotton rat in Kansas. Trans. +Kansas Acad. Sci., 51:306-312.</p> + +<p class="indnt">1952. Mammals of Kansas. Univ. Kansas Mus. Nat. Hist. Publ., +7:1-303.</p> + +<p><span class="smcap">Davis, D. H. S.</span></p> + +<p class="indnt">1933. Rhythmic activity in the short-tailed vole, <i>Microtus</i>. +Jour. Animal Ecol., 2:232-238.</p> + +<p><span class="smcap">Dice, L. R.</span></p> + +<p class="indnt">1922. Some factors affecting the distribution of the prairie +vole, forest deer mouse and prairie deer mouse. Ecol., +3:29-47.</p> + +<p><span class="smcap">Eadie, W. R.</span></p> + +<p class="indnt">1944. The short-tailed shrew and field mouse predation. Jour. +Mamm., 25:359-362.</p> + +<p class="indnt">1948. Shrew-mouse predation during low mouse abundance. Jour. +Mamm., 29:35-37.</p> + +<p class="indnt">1952. Shrew predation and vole populations on a limited area. +Jour. Mamm., 33:185-189.</p> + +<p class="indnt">1953. Response of <i>Microtus</i> to vegetative cover. Jour. Mamm., +34:262-264.</p> + +<p><span class="smcap">Elton, C.</span></p> + +<p class="indnt">1949. Population interspersion. An essay in animal community +patterns. Jour. Ecol., 37:1-23.</p> +<p><span class="pagenum"><a name="Page_413" id="Page_413">[413]</a></span></p> +<p><span class="smcap">Errington, P. R.</span></p> + +<p class="indnt">1935. Food habits of midwestern foxes. Jour. Mamm., +16:192-200.</p> + +<p class="indnt">1936. What is the meaning of predation? Smithsonian Inst. +Rep., 1936:243-252.</p> + +<p class="indnt">1943. An analysis of mink predation upon muskrat in north +central United States. Agric. Exp. Sta., Iowa State Coll. +Agric. Mech. Arts, Res. Bull., 320:799-924.</p> + +<p class="indnt">1946. Predation and vertebrate populations. Quart. Rev. Biol., +21:144-177.</p> + +<p><span class="smcap">Errington, P. L.</span>, <span class="smcap">F. Hamerstrom</span>, and <span class="smcap">F. N. Hamerstrom, Jr.</span></p> + +<p class="indnt">1940. The great horned owl and its prey in north central +United States. Agric. Exp. Sta., Iowa State Coll. Agric. Mech. +Arts, Res. Bull., 277:759-831.</p> + +<p><span class="smcap">Fisher, H. J.</span></p> + +<p class="indnt">1945. Notes on the voles in central Missouri. Jour. Mamm., +26:435-437.</p> + +<p><span class="smcap">Fitch, H. S.</span></p> + +<p class="indnt">1948. A study of coyote relationships on cattle range. Jour. +Wildlife Mgmt., 12:73-78.</p> + +<p class="indnt">1950. A new style live trap for small mammals. Jour. Mamm., +31:364-365.</p> + +<p class="indnt">1952. The University of Kansas Natural History Reservation. +Univ. Kansas, Mus. Nat. Hist. Misc. Publ., 4:1-38.</p> + +<p class="indnt">1954. Seasonal acceptance of bait by small mammals. Jour. +Mamm., 35:39-47.</p> + +<p><span class="smcap">Fitch, H. S.</span>, <span class="smcap">F. Swenson</span>, and <span class="smcap">D. F. Tillotson</span>.</p> + +<p class="indnt">1946. Behavior and food habits of the red-tailed hawk. Condor, +48:205-237.</p> + +<p><span class="smcap">Goodpastor, W. W.</span>, and <span class="smcap">D. F. Hoffmeister</span>.</p> + +<p class="indnt">1952. Notes on the mammals of eastern Tennessee. Jour. Mamm., +33:362-371.</p> + +<p><span class="smcap">Gunderson, H. L.</span></p> + +<p class="indnt">1950. A study of some small mammal populations at Cedar Creek +Forest, Asoka County, Minnesota. Univ. Minnesota Mus. Nat. +Hist., 4:1-49.</p> + +<p><span class="smcap">Hall, E. R.</span></p> + +<p class="indnt">1926. Changes during growth in the skull of the rodent +<i>Otospermophilus grammarus beecheyi</i>. Univ. California Publ. +Zool., 21:355-404.</p> + +<p><span class="smcap">Hall, E. R.</span>, and <span class="smcap">E. L. Cockrum</span>.</p> + +<p class="indnt">1953. A synopsis of North American microtine rodents. Univ. +Kansas, Mus. Nat. Hist. Publ., 5:373-498.</p> + +<p><span class="smcap">Hamilton, W. J., Jr.</span></p> + +<p class="indnt">1937a. Growth and life span of the field mouse. Amer. Nat., +71:500-507.</p> + +<p class="indnt">1937b. The biology of microtine cycles. Jour. Agric. Res., +54:779-790.</p> + +<p class="indnt">1937c. Activity and home range of the field mouse. Ecol., +18:255-263.</p> + +<p class="indnt">1940. Life and habits of the field mouse. Sci. Monthly, +50:425-434.</p> + +<p class="indnt">1941. The reproduction of the field mouse, <i>Microtus +pennsylvanicus</i>. Cornell Univ. Agric. Exp. Sta. Mem., +237:1-23.</p> + +<p class="indnt">1949. The reproductive rates of some small mammals. Jour. +Mamm., 30:257-260.</p> + +<p><span class="smcap">Hatfield, D. M.</span></p> + +<p class="indnt">1935. A natural history of <i>Microtus californicus</i>. Jour. +Mamm., 16:261-271.</p> +<p><span class="pagenum"><a name="Page_414" id="Page_414">[414]</a></span></p> +<p><span class="smcap">Hatt, R. T.</span></p> + +<p class="indnt">1930. The biology of the voles of New York. Roosevelt Wildlife +Bull., 5:513-623.</p> + +<p><span class="smcap">Hayne, D. M.</span></p> + +<p class="indnt">1949a. Two methods of estimating populations from trapping +records. Jour. Mamm., 30:399-411.</p> + +<p class="indnt">1949b. Calculation of the size of home range. Jour. Mamm., +30:1-18.</p> + +<p class="indnt">1950. Apparent home range of <i>Microtus</i> in relation to +distance between traps. Jour. Mamm., 31:26-39.</p> + +<p><span class="smcap">Hinton, M. A. C.</span></p> + +<p class="indnt">1926. Monograph of the voles and lemmings (Microtinae) living +and extinct. British Museum of Nat. Hist., London, xvi + 488 +pp. 15 pls.</p> + +<p><span class="smcap">Hopkins, H. H.</span>, <span class="smcap">F. W. Albertson</span>, and <span class="smcap">D. A. Riegel</span>.</p> + +<p class="indnt">1952. Ecology of grassland utilization in a mixed prairie. +Trans. Kansas Acad. Sci., 55:395-418.</p> + +<p><span class="smcap">Howard, W. E.</span></p> + +<p class="indnt">1951. Relation between low temperature and available food to +survival of small rodents. Jour. Mamm., 32:300-312.</p> + +<p><span class="smcap">Howell, A. B.</span></p> + +<p class="indnt">1924. Individual and age variation in <i>Microtus montanus +yosemite</i>. Jour. Agric. Res., 28:977-1015.</p> + +<p><span class="smcap">Jameson, E. W.</span></p> + +<p class="indnt">1947. Natural history of the prairie vole. Univ. Kansas, Mus. +Nat. Hist. Publ., 1:125-151.</p> + +<p class="indnt">1950. Determining fecundity in male small mammals. Jour. +Mamm., 31:433-436.</p> + +<p><span class="smcap">Johnson, M. S.</span></p> + +<p class="indnt">1926. Activity and distribution of certain wild mice in +relation to the biotic community. Jour. Mamm., 7:245-277.</p> + +<p><span class="smcap">Korschgen, L. J.</span></p> + +<p class="indnt">1952. A general summary of the food of Missouri predatory and +game animals. Conserv. Comm., Div. Fish and Game, State of +Missouri. July, 1952. 61 pp.</p> + +<p><span class="smcap">Lantz, D. E.</span></p> + +<p class="indnt">1907. An economic survey of the field mice (genus <i>Microtus</i>). +USDA Biol. Surv. Bull, 31:1-64.</p> + +<p><span class="smcap">Leslie, P. H.</span>, and <span class="smcap">R. M. Ransom</span>.</p> + +<p class="indnt">1940. The mortality, fertility and rate of natural increase of +the vole (<i>Microtus agrestis</i>) as observed in the laboratory. +Jour. Animal Ecol., 9:27-52.</p> + +<p><span class="smcap">Llewellyn, L. M.</span></p> + +<p class="indnt">1950. Reduction of mortality in live-trapping mice. Jour. +Wildlife Mgmt., 14:84-85.</p> + +<p><span class="smcap">McAtee, W. L.</span></p> + +<p class="indnt">1935. Food habits of common hawks. USDA Circ., 370:1-36.</p> + +<p><span class="smcap">Meyer, B. J.</span>, and <span class="smcap">R. K. Meyer</span>.</p> + +<p class="indnt">1944. Growth and reproduction of the cotton rat, <i>Sigmodon +hispidus hispidus</i>, under laboratory conditions. Jour. Mamm., +25:107-129.</p> +<p><span class="pagenum"><a name="Page_415" id="Page_415">[415]</a></span></p> +<p><span class="smcap">Mohr, C. O.</span></p> + +<p class="indnt">1943. A comparison of North American small mammal censuses. +Amer. Midland Nat., 29:545-587.</p> + +<p class="indnt">1947. Table of equivalent populations of North American small +mammals. Amer. Midland Nat., 37:223-249.</p> + +<p><span class="smcap">Phillips, P.</span></p> + +<p class="indnt">1936. The distribution of rodents in overgrazed and normal +grassland in central Oklahoma. Ecol., 17:673-679.</p> + +<p><span class="smcap">Poiley, S. M.</span></p> + +<p class="indnt">1949. Raising captive meadow voles (<i>Microtus p. +pennsylvanicus</i>). Jour. Mamm., 30:317.</p> + +<p><span class="smcap">Rinker, G. C.</span></p> + +<p class="indnt">1942a. Litter records of some mammals of Meade County, Kansas. +Trans. Kansas Acad. Sci., 45:376-378.</p> + +<p class="indnt">1942b. An extension of the range of the Texas cotton rat in +Kansas. Jour. Mamm., 23:439.</p> + +<p><span class="smcap">Sandidge, L. L.</span></p> + +<p class="indnt">1953. <a name="fooddens" id="fooddens"></a><ins title="Original has Foods, and dens">Food and dens</ins> of the opossum (<i>Didelphis virginiana</i>) +in northeastern Kansas. Trans. Kansas Acad. Sci., 56:97-106.</p> + +<p><span class="smcap">Selle, R. M.</span></p> + +<p class="indnt">1928. <i>Microtus californicus</i> in captivity. Jour. Mamm., +9:93-98.</p> + +<p><span class="smcap">Shapiro, J.</span></p> + +<p class="indnt">1950. Notes on the population dynamics of <i>Microtus</i> and +<i>Blarina</i> with a record of albinism in <i>Blarina</i>. Jour. +Wildlife Mgmt, 14:359-360.</p> + +<p><span class="smcap">Stickel, L. F.</span></p> + +<p class="indnt">1946. Experimental analysis of methods of measuring small +mammal populations. Jour. Wildlife Mgmt., 10:150-159.</p> + +<p class="indnt">1948. The trap line as a measure of small mammal populations. +Jour. Wildlife Mgmt., 12:153-161.</p> + +<p><span class="smcap">Strecker, J. K.</span></p> + +<p class="indnt">1929. Notes on the Texas cotton and Atwater wood rats. Jour. +Mamm., 10:216-220.</p> + +<p><span class="smcap">Summerhayes, V. S.</span></p> + +<p class="indnt">1941. The effects of voles (<i>Microtus agrestis</i>) on +vegetation. Jour. Ecol., 29:14-48.</p> + +<p><span class="smcap">Svihla, A.</span></p> + +<p class="indnt">1929. Life history notes on <i>Sigmodon hispidus hispidus</i>. +Jour. Mamm., 10:352-353.</p> + +<p><span class="smcap">Townsend, M. T.</span></p> + +<p class="indnt">1935. Studies on some small mammals of central New York. +Roosevelt Wildlife Annals, 4:1-120.</p> + +<p><span class="smcap">Uhler, F. M.</span>, <span class="smcap">C. Cottam</span>, and <span class="smcap">T. E. Clarke</span>.</p> + +<p class="indnt">1939. Food of the snakes of George Washington National Forest, +Virginia. Trans. 4th N. A. Wildlife Conf., 605-622.</p> + +<p><span class="smcap">Wooster, L. D.</span></p> + +<p class="indnt">1935. Notes on the effects of drought on animal populations +in western Kansas. Trans. Kansas Acad. Sci., 38:351-352.</p> +<p><span class="pagenum"><a name="Page_416" id="Page_416">[416]</a></span></p> +<p class="indnt">1936. The contents of owl pellets as indicators of habitat +preferences of small mammals. Trans. Kansas Acad. Sci., +39:395-397.</p> + +<p class="indnt">1939. An ecological evaluation of predatees on a mixed prairie +area in western Kansas. Trans. Kansas Acad. Sci., 42:515-517.</p> + + +<p><i>Transmitted May 19, 1955.</i></p> + + + +<hr class="chap" /> +<h2><a name="UNIVERSITY_OF_KANSAS_PUBLICATIONS_MUSEUM_OF_NATURAL_HISTORY" id="UNIVERSITY_OF_KANSAS_PUBLICATIONS_MUSEUM_OF_NATURAL_HISTORY">UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY</a></h2> + + +<p>Institutional libraries interested in publications exchange may obtain +this series by addressing the Exchange Librarian, University of Kansas +Library, Lawrence, Kansas. Copies for individuals, persons working in +a particular field of study, may be obtained by addressing instead the +Museum of Natural History, University of Kansas, Lawrence, Kansas. +There is no provision for sale of this series by the University +Library which meets institutional requests, or by the Museum of +Natural History which meets the requests of individuals. However, when +individuals request copies from the Museum, 25 cents should be +included, for each separate number that is 100 pages or more in +length, for the purpose of defraying the costs of wrapping and +mailing.</p> + +<p>* An asterisk designates those numbers of which the Museum's supply +(not the Library's supply) is exhausted. Numbers published to date, in +this series, are as follows:</p> + +<p>Vol. 1.</p> + +<p class="indnt">Nos. 1-26 and index. Pp. 1-638, 1946-1950.</p> + +<p class="indnt">Index. Pp. 605-638.</p> + +<p>*Vol. 2.</p> + +<p class="indnt">(Complete) Mammals of Washington. By Walter W. Dalquest. Pp. +1-444, 140 figures in text. April 9, 1948.</p> + +<p>Vol. 3.</p> + +<p class="indnt">*1. The avifauna of Micronesia, its origin, evolution, and +distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in +text. June 12, 1951.</p> + +<p class="indnt">*2. A quantitative study of the nocturnal migration of birds. +By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June +29, 1951.</p> + +<p class="indnt">3. Phylogeny of the waxwings and allied birds. By M. Dale +Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10, +1951.</p> + +<p class="indnt">4. Birds from the state of Veracruz, Mexico. By George H. +Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7 figures in +text, 2 tables. October 10, 1951.</p> + +<p class="indnt">Index. Pp. 651-681.</p> + +<p>*Vol. 4.</p> + +<p class="indnt">(Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41 +plates, 31 figures in text. December 27, 1951.</p> + +<p>Vol. 5.</p> + +<p class="indnt">1. Preliminary survey of a Paleocene faunule from the Angels +Peak area, New Mexico. By Robert W. Wilson. Pp. 1-11, 1 figure +in text. February 24, 1951.</p> + +<p class="indnt">2. Two new moles (Genus Scalopus) from Mexico and Texas. By +Rollin H. Baker. Pp. 17-24. February 28, 1951.</p> + +<p class="indnt">3. Two new pocket gophers from Wyoming and Colorado. By E. +Raymond Hall and H. Gordon Montague. Pp. 25-32. February 28, +1951.</p> + +<p class="indnt">4. Mammals obtained by Dr. Curt von Wedel from the barrier +beach of Tamaulipas, Mexico. By E. Raymond Hall. Pp. 33-47, 1 +figure in text. October 1, 1951.</p> + +<p class="indnt">5. Comments on the taxonomy and geographic distribution of +some North American rabbits. By E. Raymond Hall and Keith R. +Kelson. Pp. 49-58. October 1, 1951.</p> + +<p class="indnt">6. Two new subspecies of Thomomys bottae from New Mexico and +Colorado. By Keith R. Kelson. Pp. 59-71, 1 figure in text. +October 1, 1951.</p> + +<p class="indnt">7. A new subspecies of Microtus montanus from Montana and +comments on Microtus canicaudus Miller. By E. Raymond Hall and +Keith R. Kelson. Pp. 73-79. October 1, 1951.</p> + +<p class="indnt">8. A new pocket gopher (Genus Thomomys) from eastern Colorado. +By E. Raymond Hall. Pp. 81-85. October 1, 1951.</p> + +<p class="indnt">9. Mammals taken along the Alaskan Highway. By Rollin H. +Baker. Pp. 87-117, 1 figure in text. November 28, 1951.</p> + +<p class="indnt">*10. A synopsis of the North American Lagomorpha. By E. +Raymond Hall. Pp. 119-202, 68 figures in text. December 15, +1951.</p> + +<p class="indnt">11. A new pocket mouse (Genus Perognathus) from Kansas. By E. +Lendell Cockrum. Pp. 203-206. December 15, 1951.</p> + +<p class="indnt">12. Mammals from Tamaulipas, Mexico. By Rollin H. Baker. Pp. +207-218. December 15, 1951.</p> + +<p class="indnt">13. A new pocket gopher (Genus Thomomys) from Wyoming and +Colorado. By E. Raymond Hall. Pp. 219-222. December 15, 1951.</p> + +<p class="indnt">14. A new name for the Mexican red bat. By E. Raymond Hall. +Pp. 223-226. December 15, 1951.</p> + +<p class="indnt">15. Taxonomic notes on Mexican bats of the Genus Rhogeëssa. By +E. Raymond Hall. Pp. 227-232. April 10, 1952.</p> + +<p class="indnt">16. Comments on the taxonomy and geographic distribution of +some North American woodrats (Genus Neotoma). By Keith R. +Kelson. Pp. 233-242. April 10, 1952.</p> + +<p class="indnt">17. The subspecies of the Mexican red-bellied squirrel, +Sciurus aureogaster. By Keith R. Kelson. Pp. 243-250, 1 figure +in text. April 10, 1952.</p> + +<p class="indnt">18. Geographic range of Peromyscus melanophrys, with +description of new subspecies. By Rollin H. Baker. Pp. +251-258, 1 figure in text. May 10, 1952.</p> + +<p class="indnt">19. A new chipmunk (Genus Eutamias) from the Black Hills. By +John A. White. Pp. 259-262. April 10, 1952.</p> + +<p class="indnt">20. A new piñon mouse (Peromyscus truei) from Durango, Mexico. +By Robert B. Finley, Jr. Pp. 263-267. May 23, 1952.</p> + +<p class="indnt">21. An annotated checklist of Nebraskan bats. By Olin L. Webb +and J. Knox Jones, Jr. Pp. 269-279. May 31, 1952.</p> + +<p class="indnt">22. Geographic variation in red-backed mice (Genus +Clethrionomys) of the southern Rocky Mountain region. By E. +Lendell Cockrum and Kenneth L. Fitch. Pp. 281-292, 1 figure in +text. November 15, 1952.</p> + +<p class="indnt">23. Comments on the taxonomy and geographic distribution of +North American microtines. By E. Raymond Hall and E. Lendell +Cockrum. Pp. 293-312. November 17, 1952.</p> + +<p class="indnt">24. The subspecific status of two Central American sloths. By +E. Raymond Hall and Keith R. Kelson. Pp. 313-317. November 21, +1952.</p> + +<p class="indnt">25. Comments on the taxonomy and geographic distribution of +some North American marsupials, insectivores, and carnivores. +By E. Raymond Hall and Keith R. Kelson. Pp. 319-341. December +5, 1952.</p> + +<p class="indnt">26. Comments on the taxonomy and geographic distribution of +some North American rodents. By E. Raymond Hall and Keith R. +Kelson. Pp. 343-371. December 15, 1952.</p> + +<p class="indnt">27. A synopsis of the North American microtine rodents. By E. +Raymond Hall and E. Lendell Cockrum. Pp. 373-498, 149 figures +in text. January 15, 1953.</p> + +<p class="indnt">28. The pocket gophers (Genus Thomomys) of Coahuila, Mexico. +By Rollin H. Baker. Pp. 499-514, 1 figure in text. June 1, +1953.</p> + +<p class="indnt">29. Geographic distribution of the pocket mouse, Perognathus +fasciatus. By J. Knox Jones, Jr. Pp. 515-526, 7 figures in +text. August 1, 1953.</p> + +<p class="indnt">30. A new subspecies of wood rat (Neotoma mexicana) from +Colorado. By Robert B. Finley, Jr. Pp. 527-534, 2 figures in +text. August 15, 1953.</p> + +<p class="indnt">31. Four new pocket gophers of the genus Cratogeomys from +Jalisco, Mexico. By Robert J. Russell. Pp. 535-542. October +15, 1953.</p> + +<p class="indnt">32. Genera and subgenera of chipmunks. By John A. White. Pp. +543-561, 12 figures in text. December 1, 1953.</p> + +<p class="indnt">33. Taxonomy of the chipmunks, Eutamias quadrivittatus and +Eutamias umbrinus. By John A. White. Pp. 563-582, 6 figures in +text. December 1, 1953.</p> + +<p class="indnt">34. Geographic distribution and taxonomy of the chipmunks of +Wyoming. By John A. White. Pp. 584-610, 3 figures in text. +December 1, 1953.</p> + +<p class="indnt">35. The baculum of the chipmunks of western North America. By +John A. White. Pp. 611-631, 19 figures in text. December 1, +1953.</p> + +<p class="indnt">36. Pleistocene Soricidae from San Josecito Cave, Nuevo Leon, +Mexico. By James S. Findley. Pp. 633-639. December 1, 1953.</p> + +<p class="indnt">37. Seventeen species of bats recorded from Barro Colorado +Island, Panama Canal Zone. By E. Raymond Hall and William B. +Jackson. Pp. 641-646. December 1, 1953.</p> + +<p class="indnt">Index. Pp. 647-676.</p> + +<p>*Vol. 6.</p> + +<p class="indnt">(Complete) Mammals of Utah, <i>taxonomy and distribution</i>. By +Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables. +August 10, 1952.</p> + +<p>Vol. 7.</p> + +<p class="indnt">*1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73 +figures in text, 37 tables. August 25, 1952.</p> + +<p class="indnt">2. Ecology of the opossum on a natural area in northeastern +Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp. 305-338, +5 figures in text. August 24, 1953.</p> + +<p class="indnt">3. The silky pocket mice (Perognathus flavus) of Mexico. By +Rollin H. Baker. Pp. 339-347, 1 figure in text. February 15, +1954.</p> + +<p class="indnt">4. North American jumping mice (Genus Zapus). By Philip H. +Krutzsch. Pp. 349-472, 47 figures in text, 4 tables. April 21, +1954.</p> + +<p class="indnt">5. Mammals from Southeastern Alaska. By Rollin H. Baker and +James S. Findley. Pp. 473-477. April 21, 1954.</p> + +<p class="indnt">6. Distribution of some Nebraskan Mammals. By J. Knox Jones, +Jr. Pp. 479-487. April 21, 1954.</p> + +<p class="indnt">7. Subspeciation in the montane meadow mouse, Microtus +montanus, in Wyoming and Colorado. By Sydney Anderson. Pp. +489-506, 2 figures in text. July 23, 1954.</p> + +<p class="indnt">8. A new subspecies of bat (Myotis velifer) from southeastern +California and Arizona. By Terry A. Vaughn. Pp. 507-512. July +23, 1954.</p> + +<p class="indnt">9. Mammals of the San Gabriel mountains of California. By +Terry A. Vaughn. Pp. 513-582, 1 figure in text, 12 tables. +November 15, 1954.</p> + +<p class="indnt">10. A new bat (Genus Pipistrellus) from northeastern Mexico. +By Rollin H. Baker. Pp. 583-586. November 15, 1954.</p> + +<p class="indnt">11. A new subspecies of pocket mouse from Kansas. By E. +Raymond Hall. Pp. 587-590. November 15, 1954.</p> + +<p class="indnt">12. Geographic variation in the pocket gopher, Cratogeomys +castanops, in Coahuila, Mexico. By Robert J. Russell and +Rollin H. Baker. Pp. 591-608. March 15, 1955.</p> + +<p class="indnt">13. A new cottontail (Sylvilagus floridanus) from northeastern +Mexico. By Rollin H. Baker. Pp. 609-612. April 8, 1955.</p> + +<p class="indnt">14. Taxonomy and distribution of some American shrews. By +James S. Findley. Pp. 613-618. June 10, 1955.</p> + +<p class="indnt">15. Distribution and systematic position of the pigmy woodrat, +Neotoma goldmani. By Dennis G. Rainey and Rollin H. Baker. Pp. +619-624, 2 figs. in text. June 10, 1955.</p> + +<p class="indnt">Index. Pp. 625-651.</p> + +<p>Vol. 8.</p> + +<p class="indnt">1. Life history and ecology of the five-lined skink, Eumeces +fasciatus. By Henry S. Fitch. Pp. 1-156, 2 pls., 26 figs. in +text, 17 tables. September 1, 1954.</p> + +<p class="indnt">2. Myology and serology of the Avian Family Fringillidae, a +taxonomic study. By William B. Stallcup. Pp. 157-211, 23 +figures in text, 4 tables. November 15, 1954.</p> + +<p class="indnt">3. An ecological study of the collared lizard (Crotaphytus +collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in text. +February 10, 1956.</p> + +<p class="indnt">4. A field study of the Kansas ant-eating frog, Gastrophryne +olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in text. +February 10, 1956.</p> + +<p class="indnt">5. Check-list of the birds of Kansas. By Harrison B. Tordoff. +Pp. 307-359, 1 figure in text. March 10, 1956.</p> + +<p class="indnt">6. A population study of the prairie vole (Microtus +ochrogaster) in Northeastern Kansas. By Edwin P. Martin. Pp. +361-416, 19 figures in text. April 2, 1956.</p> + +<p class="indnt">More numbers will appear in volume 8.</p> + +<p>Vol. 9.</p> + +<p class="indnt">1. Speciation of the wandering shrew. By James S. Findley. Pp. +1-68, 18 figures in text. December 10, 1955.</p> + +<p class="indnt">2. Additional records and extensions of ranges of mammals from +Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M. +Hansen. Pp. 69-80. December 10, 1955.</p> + +<p class="indnt">3. A new long-eared myotis (Myotis evotis) from northeastern +Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84. +December 10, 1955.</p> + +<p class="indnt">More numbers will appear in volume 9.</p> + + +<hr class="chap" /> +<div class='tnote'> +<h2><a name="Transcribers_note" id="Transcribers_note">Transcriber's note:</a></h2> + +<p>A Table of Contents has been added to this ebook for the reader's +convenience.</p> + +<p>Some words in this text are found in both hyphenated and +non-hyphenated form (for instance: Condylo-basilar/condylobasilar, +mid-winter/midwinter). These variations match the text of the original +document. A few obvious punctuation errors have been repaired. +Spelling has been retained as it appears in the original publication, +except as follows:</p> + +<p>p. 372, in "A more homogeneous vegetation would tend to pass" +homogenous has been changed to <a href="#homogeneous">homogeneous</a>.</p> + +<p>p. 415, "1953. Foods, and dens of the opossum ..." has been changed to +"1953. <a href="#fooddens">Food and dens</a> of the opossum ..."</p> + +<p>In <a href="#img011"><span class="smcap">Fig. 11</span></a> the bottommost +y-axis label in the scale of gms. is probably an <a href="#weighterror">error</a>: 45 should be 35. +</p> + +<p>Some illustrations have been moved from their original locations to +paragraph breaks, so as to be nearer to their corresponding text, and +for ease of document navigation. Missing page numbers correspond to +moved full-page illustrations. + References to scale in illustration +captions are those of the original publication, and therefore do not +correspond to the scale of the images in the HTML version of this ebook.</p> + +<p>The list of University of Kansas Publications from the front of the +original document has been joined to its mate at the end of this text.</p> + +<p>Because the cover of the original document contained text exactly +duplicated on the title page, this cover information has been omitted.</p> +</div> + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of A Population Study of the Prairie Vole +(Microtus ochrogaster) in Northeastern Kansas, by Edwin P. 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