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diff --git a/37450-h/37450-h.htm b/37450-h/37450-h.htm new file mode 100644 index 0000000..0c9b8f1 --- /dev/null +++ b/37450-h/37450-h.htm @@ -0,0 +1,2874 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> + <html xmlns="http://www.w3.org/1999/xhtml"> + <head> + <meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" /> + <meta http-equiv="Content-Style-Type" content="text/css" /> + <title> + The Project Gutenberg eBook of Aspects Of Reproduction And Development + in the Prairie Vole (Microtus ochrogaster), by Henry S. 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Fitch + +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: Aspects of Reproduction and Development in the Prairie Vole (Microtus ochrogaster) + +Author: Henry S. Fitch + +Release Date: September 17, 2011 [EBook #37450] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK ASPECTS OF REPRODUCTION AND *** + + + + +Produced by Chris Curnow, Tom Cosmas, Joseph Cooper and +the Online Distributed Proofreading Team at +http://www.pgdp.net + + + + + + +</pre> + + + +<div class="book"><!-- Begin Article --> +<a name="cover" id="cover"></a> +<div class="fig_center" style="width: 237px;"> +<img src="images/cover.jpg" width="237" height="395" alt="" title="" /> +</div> +<br /> +<br /> + +<p><span class="pagenum"><a name="Page_129" id="Page_129">[Pg 129]</a></span></p> +<div class="center"> +<br /> +<br /> +<img src="images/bar_double.png" width="100%" height="15" alt="double bar" /> +<div class="caption2 smcap">University of Kansas Publications</div> +<br /> +<div class="caption2 smcap">Museum of Natural History</div> +<br /> +<img src="images/bar_single.png" width="125" height="15" title="bar" alt="bar" /> +<br /> +<div class="caption2">Volume 10, No. 4, pp. 129-161, 8 figs. in text, +<ins title='Correction: was "4 tables"'>6 tables</ins></div> +<br /> +<img src="images/bar_single.png" width="250" height="15" title="bar" alt="bar" /> + <span class="caption2">December 19, 1957</span> +<img src="images/bar_single.png" width="250" height="15" title="bar" alt="bar" /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<div class="caption1"> +Aspects of Reproduction and Development<br /> +in the Prairie Vole (Microtus ochrogaster)<br /> +</div> +<br /> +<br /> +<br /> +<br /> +<div class="caption3">BY</div> +<br /> +<br /> +<div class="caption2">HENRY S. FITCH</div> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<div class="caption2"> +<span class="smcap">University of Kansas</span><br /> +<span class="smcap">Lawrence</span><br /> +1957<br /> +</div> +<br /> +<br /> +<br /> +</div> + +<p><span class="pagenum"><a name="Page_130" id="Page_130">[Pg 130]</a></span></p> +<div class="center"> +<div class="caption3"> +<span class="smcap">University of Kansas Publications, Museum of Natural History</span><br /> +<br /> +Editors: E. Raymond Hall, Chairman, Henry S. Fitch,<br /> +Harrison B. Tordoff<br /> +<br /> +<br /> +<br /> +<br /> +Volume 10, No. 4, pp. 129-161, 8 figs. in text, +<ins title='Correction: was "4 tables"'>6 tables</ins><br /> +<br /> +Published December 19, 1957<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<br /> +<span class="smcap">University of Kansas</span><br /> +Lawrence, Kansas<br /> +<br /> +</div> +<br /> +<br /> +<br /> +<br /> +<div class="caption4"> +PRINTED IN<br /> +THE STATE PRINTING PLANT<br /> +TOPEKA, KANSAS<br /> +1957<br /> +<img src="images/union_label.png" width="71" height="26" alt="Look for the Union Label" title="Look for the Union Label" /><br /> +29-5936<br /> +</div> +</div> +<br /> +<br /> +<br /> +<br /> + +<p><span class="pagenum"><a name="Page_131" id="Page_131">[Pg 131]</a></span></p> + +<div class="caption2"><a name="Aspects_of_Reproduction_and_Development" id="Aspects_of_Reproduction_and_Development"></a> +Aspects of Reproduction and Development +in the Prairie Vole (Microtus ochrogaster)</div> +<br /> +<div class="caption3">BY</div> +<br /> +<div class="caption2">HENRY S. FITCH</div> +<br /> +<br /> + +<div class="caption2"><a name="INTRODUCTION" id="INTRODUCTION"></a> +INTRODUCTION</div> + +<p>The prairie vole is by far the most abundant mammal on the +University of Kansas Natural History Reservation and on grassland +areas throughout northeastern Kansas. This vole therefore affects +the vegetation, perhaps more than any other native vertebrate, and +it is an important food source for most of the vertebrate predators. +Since the Reservation was established, in 1948, more data have been +accumulated concerning this vole than for any other species of +animal there. From February, 1950, to February, 1954, a grid of +live-traps at 50-foot intervals was set for several days each month +in a three-acre field inhabited by voles, and the population of +marked individuals was studied throughout the four-year period. From +November, 1953, to June, 1956, a half-acre trap grid with 20-foot +interval was used on an area adjoining the three-acre field. Other +trap lines in somewhat different habitats were maintained for +shorter periods as a basis for comparison. By June, 1956, a total of +some 3550 voles had been caught and recorded 14,750 times in all. +The present report is a preliminary attempt to analyze, in part, +these extensive data, and is concerned with certain phases of the +species' reproduction and growth that have bearing on the observed +population changes from month to month and from year to year on the +Reservation.</p> + +<p>Through the studies of Jameson (1947) and Martin (1956), both made +in the same general area as my own, and several earlier studies, the +life history and ecology of the prairie vole are already well known. +The present report, with much larger amounts of data, further +clarifies certain phases of the ecology; and by using types of data +not available to Jameson and Martin I have dealt with some topics +not included in their reports.</p> + +<p>Previous studies of growth in <i>Microtus</i> have been based almost +entirely on weights. However, the weight of an individual vole may +fluctuate widely over a short period, depending on pregnancy and +parturition, length of time in a trap without food, availability of +moisture, and other factors. In the course of my study, in 1954 +<span class="pagenum"><a name="Page_132" id="Page_132">[Pg 132]</a></span> +and 1955, and parts of 1953 and 1956, measurements of total length, in +addition to weights, were recorded for most of the voles +live-trapped.</p> + +<p>To test the accuracy of measurements, successive readings were +compared in individual voles that were already of large adult size +and that presumably either had stopped growing or were growing so +slowly that the gain was scarcely detectable in the relatively short +periods involved. For 200 such readings 33 per cent were just the +same as previous records for the same animals, 24 per cent deviated +by 1 mm., 22 per cent deviated by 2 mm., 15 per cent by 3 mm., 4.5 +per cent by 4 mm., .5 per cent by 5 mm., 1 per cent by 6 mm., and .5 +per cent by 7 mm. On the average, successive measurements varied by +1.43 mm., somewhat less than one per cent of the adult vole's total +length. Occasional errors of two to four per cent were easily +eliminated because for the voles used for growth records, series of +measurements were available, with clearly defined trends. The +occasional readings that deviated from the general trend for the +individual were discarded.</p> + +<p>Measurements were recorded along with other data in the field at the +point of capture. Obtaining a reasonably accurate measurement on a +live and struggling vole required patience and practice. With the +thumb and forefinger of the left hand, I grasped the vole by loose +skin of the nape, and simultaneously grasped the tail at a point +approximately three-fourths of the distance to the tip. Then, with +gentle but steady pressure, I stretched the vole out to its full +length, meanwhile manipulating a millimeter ruler with the free +fingers, so that the vole was pressed against it, with the nose pad +at the end of the ruler.</p> + +<p>The total length measurement is considered the best index to +over-all size. The relative tail-length varies slightly between +individuals, averaging approximately 22 per cent of the total +length. Individuals having broken tails, or having the distal parts +of their tails missing, were not included. The total length can be +measured with greater accuracy than can either the head-and-body +length or the tail-length separately.</p> +<br /> + +<div class="caption2"><a name="GENERAL_SOCIAL_BEHAVIOR" id="GENERAL_SOCIAL_BEHAVIOR"></a> +GENERAL SOCIAL BEHAVIOR</div> + +<p>As compared with other mammals, voles are tolerant and somewhat +social. That individuals are not mutually exclusive (territorially) +in areas occupied was demonstrated on many occasions when more than +one individual was caught simultaneously in the same live-trap. +Injury of a vole by a trap-mate was a rare occurrence.</p> + +<p><span class="pagenum"><a name="Page_133" id="Page_133">[Pg 133]</a></span> +Multiple captures often involved a female in oestrus and one or more males, +or a female and her young, but other instances involved various +combinations of sex and age groups. As many as five adults have been +caught in a trap simultaneously at times when the population density +was high. At such times, the meadow habitat is crossed by a maze of +interconnecting surface runways and one runway may be traced +continuously for 100 yards or more. Because each individual vole +normally confines its activity to a small area, only a fraction of +an acre, it is evident that individuals living at different places +overlap in their home ranges, and also in the trailways followed in +foraging. A high degree of tolerance is indicated. Where population +is so sparse that the systems of surface runways comprise separate +and isolated units, trapping experience has shown that one such +system may harbor several or many individuals.</p> + +<p>As direct observations on voles under natural conditions are rarely +feasible, because of the animals' timidity, their utilization of +concealing cover, and tendency to crepuscular habits, best evidence +of social habits and underground life is based upon behavior of +captive individuals. Many voles were kept in confinement for varying +lengths of times, either singly or in association with others. Under +such conditions there was sometimes sporadic fighting, but it was +mainly defensive and serious injuries were rare. Two or more voles +caught at a given spot regardless of whether they were found in the +same trap simultaneously, or trapped separately within a short time, +usually were completely tolerant of each other. When at rest in +their container, such voles would huddle together in a corner or in +a nest, if materials were provided, so that collectively they +presented the minimum exposed surface. The intimacy and lack of +antagonism displayed on such occasions, suggested that the voles +were accustomed to living together amicably in the same nest +chamber. In live-trapping, "double" captures in a single trap often +involved the same two individuals. Such trap-mates were often male +and female, and in many instances the female was not in breeding +condition. That the voles are not monogamous in habits was +demonstrated when the same female was often trapped in association +with either of two males. Other trap associates taken together +repeatedly often were two males, or two females. Voles that are nest +mates or "neighbors" may tend to move about together in their +foraging, or one confined in a trap may attract the other +sufficiently to cause it to force an entrance by lifting the heavy +door of a trap.</p> + +<p><span class="pagenum"><a name="Page_134" id="Page_134">[Pg 134]</a></span> +When a new vole, caught at a different location, is added to a +container in which one or more are already confined, there is mutual +circumspection between the original occupants and the newcomer. At +first, each vole is intimidated by movements of the other, and as a +result, the original occupants huddle in their established corner +while the newcomer cowers in the most remote part of the container. +Gradually the voles become less timid and one may approach another +slowly and cautiously, to sniff at it. The vole approached may react +with a show of hostility which is largely defensive. In the +characteristic posture of threat for defense, the vole crouches, or +rears back on its haunches, with snout elevated and incisors +prominently displayed. If the warning posture is unheeded, or if the +vole is made unusually aggressive by having young to defend, or for +some other reason, it attacks with a sudden forward lunge, striking +the adversary simultaneously with both forefeet and with the +incisors. The lunge is so rapid that when I have observed it, I have +been unable to discern whether the attacker bit its opponent. The +attack serves to force back the other animal, throwing it off +balance and intimidating it. The attacked animal may dodge nimbly to +avoid the lunge, but whether or not it is actually struck, it +usually retreats, avoiding or postponing further hostilities. Voles +that have been kept in containers for periods of hours or days tend +to be more hostile and aggressive toward a newcomer than are those +newly introduced. After series of meetings resulting from the +exploratory behavior of the newcomer and the curiosity or normal +activity of those longer confined, hostility gradually subsides. +Within a few hours a newcomer is usually accepted, and thenceforth +he huddles with other members of the group when at rest, and +hostility is rarely evident.</p> + +<p>This ready acceptance on short acquaintance of strange voles into +the family or social group suggests that lack of territoriality +extends even to the use of the nest burrows, and that groups of +voles may share the same nest, huddling together and deriving mutual +benefit from the association, such as warmth in cold weather. +Schmidt (1931: 113), studying this vole in Clark County, Wisconsin, +noted its colonial habits. He found isolated small mounds that were +riddled with burrows, and little sign in intervening areas. At one +mound he trapped two adult males, one adult female, and two young; +at another mound, two adult males, two adult females, and four young +were trapped. My individuals that were released from live-traps were +on many occasions trailed by means of a stiff wire collar with spool +of thread attached, to holes that presumably +<span class="pagenum"><a name="Page_135" id="Page_135">[Pg 135]</a></span> +were their home burrows. Data obtained in this manner indicated that +ordinarily several or many individuals use the same burrow system. +The histories of individual voles on the study area at the +Reservation indicate shift of home base from time to time, usually +for short distances within the area already included in the home +range, but occasionally to new areas relatively remote from the +original home range.</p> + +<p>Severe fighting between adult prairie voles occurs at times. +Occasionally, sharp squeaks accompanied by brisk rustling in the +grass suggesting pursuit or conflict, are heard in their habitat. An +unusually large adult male, long resident on a study area, suddenly +lost weight and deteriorated in condition over a period of several +days, then was found dead in a nest-box attached to a trap. +Dissection revealed numerous punctures in the skin and flesh of the +neck and back, probably made by the incisors of another vole. +Extensive hemorrhage and swelling had occurred, and obviously these +injuries were the cause of death.</p> + +<p>Although it was not feasible to study the home life of the voles +underground, clues were gained from those uncovered in runways and +nests beneath large boards and strips of tarpaper, previously +distributed for this purpose. Nests were constructed by the voles +beneath several such pieces of tarpaper and runways appeared beneath +all the pieces that were placed in habitat favorable to the voles. +In summer, however, the high daytime temperatures beneath these +shelters made them uninhabitable to the voles, and they were used +mainly in spring. From February 15 to May 1, 1953, 14 voles were +caught 19 times beneath five of the tarpaper strips, and many other +voles that were seen beneath them escaped. Upon turning one of the +strips I often discovered voles in close proximity. Sometimes two or +more darted from the same nest. The disturbance of repeatedly +raising the strips and exposing the voles' shelters soon caused them +to desert the sites; consequently the information obtained by this +means was limited.</p> +<br /> + +<div class="caption2"><a name="SEXUAL_BEHAVIOR" id="SEXUAL_BEHAVIOR"></a> +SEXUAL BEHAVIOR</div> + +<p>There is sexual activity in every month of the year, but its +incidence varies greatly from one season to another. As has been +indicated by various authors, male voles reach sexual maturity later +than females. It seems that ordinarily the availability of sexually +active males is not a limiting factor, however. While males that are +still well below average adult size produce mature spermatozoa, and +are probably capable of breeding (Jameson, 1947: 145), certain +<span class="pagenum"><a name="Page_136" id="Page_136">[Pg 136]</a></span> +large old males may sire a disproportionately large percentage of the +litters produced. Observations on males in confinement indicated +that sexual activity tended to be directly proportional to the size +of the testes. Occasional individuals, having much enlarged scrotal +testes were more readily stimulated to sexual activity and more +aggressive toward females than were those in which the testes were +of more nearly typical size or abdominal or were smaller than +normal. The combination of factors controlling size of testes is not +well understood, but males having unusually large testes were caught +most often when food supply was optimum, for instance after a period +of heavy precipitation when an abundant supply of new grass provided +succulent and nutritious food.</p> + +<p>In confinement sexual activity was largely inhibited and attempts to +establish a laboratory colony met with failure. Sexual activity was +observed mainly in recently captured males, and their interest was +aroused chiefly by females that had given birth to litters within a +few hours previously. Oestrus is known to follow closely after +parturition. Females found in live-traps with newborn young often +were brought to the laboratory for observation. An apparent instance +of hostility between rival males competing for an oestrus female was +observed on September 2, 1950. The female was found in a trap with +four newborn young, and since the young had not yet attached to her +teats, she was temporarily returned to the trap after recording, to +prevent desertion of the litter. Returning twenty minutes later I +found another adult vole at this trap. It would suddenly emerge from +dense grass nearby, and would move over the trap or around it, with +jerky, halting movements, then would dart back under cover. The +female emerged from the nest box into the trap runway, and sniffed +at the other, and both pressed against the intervening wire barrier. +There was gnawing on the wire by one or both. A third adult vole +appeared. As it moved toward the trap, all three suddenly took alarm +and darted back under cover, the female hiding in the trap nest box. +In a few seconds they again appeared. The two outsiders, presumably +both males, were not individually recognizable, but several times +one was seen to dart at the other, chasing it away momentarily. They +were seldom both in sight at once.</p> + +<p>Males confined with post-partum females usually evinced sexual +interest, following them about persistently and nuzzling their +genitalia. The females, however, were often unreceptive perhaps +because they were disturbed by strange surroundings and by the +presence of their litters, so that they usually attempted to escape, +<span class="pagenum"><a name="Page_137" id="Page_137">[Pg 137]</a></span> +or to rebuff the male's attention. At first the female might flee, +squeaking in protest at the male's pursuit. If he still continued to +follow, she would turn on him, rearing back in the characteristic +threatening pose, and would lunge at him, striking him sharply or +driving him back. After such rebuff, males were usually intimidated +or discouraged so that they temporarily or permanently abandoned +their advances, and small males were more easily rebuffed than were +larger individuals. On several occasions large males having enlarged +testes were not readily rebuffed by females but continued to follow +them. When the female turned upon him, such a male might lunge +against her, throwing her off balance, and causing her to attempt to +escape, and then continuing the pursuit until it ended in copulation +or in more severe fighting. Although not accepted sexually, a +rebuffed male might be readily accepted as a nest-mate, huddling +along with the female and perhaps other individuals of both sexes. +In huddling voles, the most frequently observed type of social +behavior was grooming; one individual would slide its chin or muzzle +through the other's fur with a stroking movement consisting of a +series of rapid forward jerks and the stroking movements might +continue for periods of minutes. The recipient of the grooming +usually made no evident response indicative of either pleasure or +displeasure. Often it seemed to be sleeping while the grooming was +performed. Individuals of both sexes performed this grooming and the +recipient might be of either the same sex or the opposite sex. This +grooming may have some significance as a search for ectoparasites +such as fleas, or mites that often infest the voles. However, after +prolonged grooming by a companion, a vole's fur was of mussed and +disarranged appearance. Although the grooming that occurs between +voles that are resting in nests seems to have no direct significance +as sexual behavior, somewhat similar actions constitute part of the +mating pattern. A sexually aroused male overtaking a receptive +female, slides his chin forward along her back with jerky, stroking +movements. In some observed instances this behavior continued +intermittently for several minutes before actual copulation. In some +other instances it was almost lacking.</p> +<br /> + +<div class="caption2"><a name="CHANGES_IN_FEMALE_GENITALIA" id="CHANGES_IN_FEMALE_GENITALIA"></a> +CHANGES IN FEMALE GENITALIA</div> + +<p>In female voles that are sexually quiescent, both those that have +not yet attained breeding maturity, and those that have undergone +regression after attainment of sexual maturity, the vaginal orifice +is not evident. The canal is sealed externally by a membranous +<span class="pagenum"><a name="Page_138" id="Page_138">[Pg 138]</a></span> +layer of epithelium. Presence of a vaginal orifice indicates that the +individual is in some active stage of the breeding <ins title='Correction: was "cyle"'>cycle</ins>. +The appearance of the orifice varies between different females, and +it changes in the same female from day to day or even from hour to +hour. Presumably these changes in the vaginal orifice are cyclical +and are closely correlated with oestrus, but attempts to trace them +were unsuccessful largely because the normal cycle was rapidly +suppressed in captive voles, which soon became sexually quiescent. +Individual voles living under natural conditions were not trapped +with sufficient regularity to permit tracing the details of changes +in their genitalia.</p> + +<p>In those females having the vaginal orifice most developed, the +margins are turgid and slightly inflamed. The circular opening gapes +1.0 to 1.5 mm. in diameter when the tail is raised. A female may +remain in this condition for two days or more. Vaginal smears at +this stage often showed nucleated cells characteristic of oestrus. +Subsequently the margins of the orifice become less prominent and +the opening becomes smaller. The dorsal and ventral walls adhere +until an opening is no longer evident unless the adjacent skin is +stretched.</p> + +<p>In pregnancy the orifice is occasionally sealed, but usually is +evident. It is, however, less prominent than in oestrus, and does +not gape. The margins are less turgid than in oestrus, and the +opening is in the form of a transverse slit through which the +purplish epithelial lining of the dorsal wall of the vagina can be +seen. After parturition, placentae and bloody discharge often are in +evidence in the vaginal canal. Females that have not given birth to +young recently may also have bloody mucous discharge. Its +significance has not been determined. In females that are undergoing +sexual regression, the margins of the vaginal orifice become +shrunken and pale, and the orifice becomes partly or wholly sealed.</p> + +<p>Bodenheimer and Sulman (1946:255) concluded from their study of +<i>Microtus guentheri</i> that in this species, as in "the cat," "the +rabbit," "the ferret," and a few other mammals, ovulation is induced +by copulation, and that there is no regular vaginal cycle. Hoyte +(1955:412) disagreed with these conclusions for other species of +<i>Microtus</i>, as he trapped individuals of <i>M. oeconomus</i> that had +recently ovulated without copulation (at least no sperm were found +in the genital tracts). In <i>M. ochrogaster</i> oestrus seems to be +controlled largely by the food supply, at least the incidence of +perforate females was found to fluctuate irregularly tending to +follow the trend of rainfall, and, probably in more direct +correlation, the amount +<span class="pagenum"><a name="Page_139" id="Page_139">[Pg 139]</a></span> +of new grass present (see <a href="#Table_1">Table 1</a>, and Martin, 1956:383-384). It +therefore seems unlikely that in this species ovulation is dependent +on copulation.</p> + +<p>In females that have not yet produced young the teats are minute and +well concealed in the fur, so that they are difficult to find, but +in lactation they become conspicuous. In early lactation the teats +are typically about 1 mm. in diameter and 2.5 mm. in length. As +lactation progresses, they become thickened to nearly twice the +original diameter. After lactation, as inversion occurs, they shrink +to scabrous low prominences, 2 mm. to 3 mm. in diameter, surrounded +by bare skin. There are three pairs of mammae, one pair pectoral and +the other two abdominal. As mentioned by Jameson (1947:146), the +pectoral mammae show little evidence of use in lactating prairie +voles. Probably they are not used at all except in females with more +than the four young in a litter accommodated by the abdominal +mammae. As in various other rodents, the suckling young may cling to +the female's teats and may be dragged over the ground as she moves +about. When the female forages near the nest, she may drag the young +with her instead of leaving them, but she can detach them instantly +if she so desires. On many occasions females found in live-traps had +young that were several days old clinging to their teats. In some +instances young that had their eyes open may have followed the +female into the trap and attached afterward.</p> +<br /> + +<div class="caption2"><a name="SEASONAL_INCIDENCE_OF_BREEDING" id="SEASONAL_INCIDENCE_OF_BREEDING"></a> +SEASONAL INCIDENCE OF BREEDING</div> + +<p>In the region of my study the prairie vole breeds the year round, +but the rate of breeding changes continually. There is no regularity +in the trend of the breeding season from year to year. It is obvious +that the species is responsive to environmental changes and is so +well attuned that its breeding is speedily initiated or inhibited by +changes to favorable or unfavorable weather. The incidence of +breeding is highest when temperature is moderate and both water and +foods of preferred sorts are plentiful.</p> + +<p><a href="#Table_1">Tables 1 and 2</a> and <a href="#Fig_1">Fig. 1</a>, based on 11,109 records representing each +month over a four-year period, show the changing trends from month +to month. The perforate condition recorded in <a href="#Table_1">Table 1</a> may represent +any of several stages in oestrus or pregnancy, but is regarded as a +crude index of rate of breeding, since voles in the anoestrus stage +lack the vaginal orifice. Highest percentages of perforate females +occurred in the months of February, March, April, May, and June, +while by far the lowest percentages were recorded in the drought +summers of 1952 and 1953. Even in mid-winter a substantial +proportion of the females trapped were perforate.</p> + +<p><span class="pagenum"><a name="Page_140" id="Page_140">[Pg 140]</a></span></p> +<div class="fig_center" style="width: 424px;"> +<a name="Fig_1" id="Fig_1"></a> +<img src="images/fig_1.png" width="424" height="635" alt="" title="" /> +<div class="fig_caption">Fig. 1. Average catch per day in a three-acre field, in a grid of 100 live-traps, +over a four-year period. For each year, solid line represents total and dashed +line represents number of young up to 30 grams in weight. Numbers caught +are roughly indicative of population density, but many variables distort this +relationship. Young are never represented in the catch in their true ratio to +adults, since on the average they are less vagile and less attracted to traps.</div> +</div> +<br /> + +<p><span class="pagenum"><a name="Page_141" id="Page_141">[Pg 141]</a></span></p> +<div class="center"> +<div class="tbl_cap"><a name="Table_1" id="Table_1"></a> +Table 1. Percentages of Adult Females Recorded as Perforate<br /> + in the Monthly Samples From 1950 Through 1953.</div> + +<table summary="Percentage of Perforate Females"> +<tr> + <td> </td> + <td class="center brdtp2 brdlf brdbt">Jan.</td> + <td class="center brdtp2 brdlf brdbt">Feb.</td> + <td class="center brdtp2 brdlf brdbt">Mar.</td> + <td class="center brdtp2 brdlf brdbt">Apr.</td> + <td class="center brdtp2 brdlf brdbt">May </td> + <td class="center brdtp2 brdlf brdbt">June</td> + <td class="center brdtp2 brdlf brdbt">July</td> + <td class="center brdtp2 brdlf brdbt">Aug.</td> + <td class="center brdtp2 brdlf brdbt">Sept.</td> + <td class="center brdtp2 brdlf brdbt">Oct.</td> + <td class="center brdtp2 brdlf brdbt">Nov.</td> + <td class="center brdtp2 brdlf brdbt">Dec.</td> +</tr> +<tr> + <td>1950</td> + <td class="center brdlf">....</td> + <td class="center brdlf">....</td> + <td class="center brdlf">40.6</td> + <td class="center brdlf">76.0</td> + <td class="center brdlf">84.0</td> + <td class="center brdlf">67.7</td> + <td class="center brdlf">57.3</td> + <td class="center brdlf">43.1</td> + <td class="center brdlf">47.0</td> + <td class="center brdlf">44.8</td> + <td class="center brdlf">24.4</td> + <td class="center brdlf">31.1</td> +</tr> +<tr> + <td>1951</td> + <td class="center brdlf">27.3</td> + <td class="center brdlf">47.7</td> + <td class="center brdlf">38.5</td> + <td class="center brdlf">41.9</td> + <td class="center brdlf">40.0</td> + <td class="center brdlf">41.5</td> + <td class="center brdlf">45.5</td> + <td class="center brdlf">52.2</td> + <td class="center brdlf">56.5</td> + <td class="center brdlf">48.9</td> + <td class="center brdlf">45.0</td> + <td class="center brdlf">45.0</td> +</tr> +<tr> + <td>1952</td> + <td class="center brdlf">41.7</td> + <td class="center brdlf">53.1</td> + <td class="center brdlf">77.0</td> + <td class="center brdlf">51.9</td> + <td class="center brdlf">52.0</td> + <td class="center brdlf">19.3</td> + <td class="center brdlf">12.7</td> + <td class="center brdlf">5.4</td> + <td class="center brdlf">51.6</td> + <td class="center brdlf">43.4</td> + <td class="center brdlf">24.1</td> + <td class="center brdlf">37.5</td> +</tr> +<tr> + <td>1953</td> + <td class="center brdlf">33.3</td> + <td class="center brdlf">72.9</td> + <td class="center brdlf">50.0</td> + <td class="center brdlf">73.0</td> + <td class="center brdlf">58.2</td> + <td class="center brdlf">16.6</td> + <td class="center brdlf">15.4</td> + <td class="center brdlf">31.3</td> + <td class="center brdlf">56.2</td> + <td class="center brdlf">60.0</td> + <td class="center brdlf">61.5</td> + <td class="center brdlf">41.6</td> +</tr> +</table> +</div> +<br /> + +<div class="center"> +<div class="tbl_cap"><a name="Table_2" id="Table_2"></a> +Table 2. Percentages of Adult Females Recorded to Be in Late Pregnancy<br /> +in the Monthly Samples From 1950 Through 1953.</div> + +<table summary="Percentage of Perforate Females"> +<tr> + <td> </td> + <td class="center brdtp2 brdlf brdbt">Jan.</td> + <td class="center brdtp2 brdlf brdbt">Feb.</td> + <td class="center brdtp2 brdlf brdbt">Mar.</td> + <td class="center brdtp2 brdlf brdbt">Apr.</td> + <td class="center brdtp2 brdlf brdbt">May </td> + <td class="center brdtp2 brdlf brdbt">June</td> + <td class="center brdtp2 brdlf brdbt">July</td> + <td class="center brdtp2 brdlf brdbt">Aug.</td> + <td class="center brdtp2 brdlf brdbt">Sept.</td> + <td class="center brdtp2 brdlf brdbt">Oct.</td> + <td class="center brdtp2 brdlf brdbt">Nov.</td> + <td class="center brdtp2 brdlf brdbt">Dec.</td> +</tr> +<tr> + <td>1950</td> + <td class="center brdlf">....</td> + <td class="center brdlf">....</td> + <td class="center brdlf">5.8</td> + <td class="center brdlf">8.0</td> + <td class="center brdlf">21.0</td> + <td class="center brdlf">13.3</td> + <td class="center brdlf">57.3</td> + <td class="center brdlf">43.8</td> + <td class="center brdlf">40.4</td> + <td class="center brdlf">45.2</td> + <td class="center brdlf">7.0</td> + <td class="center brdlf">0</td> +</tr> +<tr> + <td>1951</td> + <td class="center brdlf">2.3</td> + <td class="center brdlf">0</td> + <td class="center brdlf">0</td> + <td class="center brdlf">19.4</td> + <td class="center brdlf">37.1</td> + <td class="center brdlf">14.9</td> + <td class="center brdlf">6.7</td> + <td class="center brdlf">15.2</td> + <td class="center brdlf">15.0</td> + <td class="center brdlf">21.9</td> + <td class="center brdlf">8.9</td> + <td class="center brdlf">0</td> +</tr> +<tr> + <td>1952</td> + <td class="center brdlf">0</td> + <td class="center brdlf">10.4</td> + <td class="center brdlf">22.6</td> + <td class="center brdlf">22.6</td> + <td class="center brdlf">29.5</td> + <td class="center brdlf">16.5</td> + <td class="center brdlf">7.9</td> + <td class="center brdlf">10.8</td> + <td class="center brdlf">20.3</td> + <td class="center brdlf">18.9</td> + <td class="center brdlf">3.3</td> + <td class="center brdlf">0</td> +</tr> +<tr> + <td class="brdbt">1953</td> + <td class="center brdlf brdbt">0</td> + <td class="center brdlf brdbt">9.1</td> + <td class="center brdlf brdbt">13.3</td> + <td class="center brdlf brdbt">27.5</td> + <td class="center brdlf brdbt">39.4</td> + <td class="center brdlf brdbt">5.5</td> + <td class="center brdlf brdbt">3.8</td> + <td class="center brdlf brdbt">12.5</td> + <td class="center brdlf brdbt">6.2</td> + <td class="center brdlf brdbt">10.0</td> + <td class="center brdlf brdbt">23.0</td> + <td class="center brdlf brdbt">8.3</td> +</tr> +</table> +</div> +<br /> + +<p>Usually pregnancy can be recognized only in the last week before +birth of the litter, when the female's abdomen is noticeably +distended by the enlarged fetuses. Palpating to detect embryos +was not attempted because of the danger of injuring them or the +female. Because gestation is of approximately three weeks duration, +the figures in <a href="#Table_2">Table 2</a> represent roughly perhaps one-third, +or a little less, of the adult females actually pregnant. At most +times of year a substantial proportion of adult females (sometimes +nearly all) are pregnant. Only in the winter (including March +in 1951) were samples taken in which no recognizably pregnant +females were found. Incidence of pregnancy was notably high in +July, August, September, and October of 1950, May, 1951, May, +1952, and April and May, 1953. A high rate of breeding was not +necessarily followed by an increase in the population. A relatively +low rate of breeding was adequate to maintain the population +level, provided that environmental factors remained favorable. +<a href="#Fig_1">Fig. 1</a> shows the average catch per day (with approximately 100 +live-traps) over the four-year period, 1950 through 1953. The +young (including all those weighing 30 grams or less, and corresponding +roughly with the part of the population less than two +months old) are shown separately. It is noteworthy that throughout +<span class="pagenum"><a name="Page_142" id="Page_142">[Pg 142]</a></span> +the entire period the ratio of young to adults tended to be +fairly stable—usually fluctuating between ten and thirty per cent +of the total catch. Ratios of young to adults were notably high +in March and May, 1950; April, June and July, 1952; and April, +May and June, 1953. Ratios of young were notably low in June and +December, 1950; January, February, March, and June through +October, 1951; January, February, and March, 1952; and November, +1953.</p> + +<p>In <a href="#Fig_1">Fig. 1</a> the catch per day of voles, varying from month to +month, reflects chiefly the changing population density. However, +other factors also have important effects on the catch. For example, +bait acceptance is better in the winter when natural foods, especially +greens, are scarce, with the result that a higher catch can be made +with the same population density. Interference with the trap line +by other animals also affected the catch of voles. In warm weather +the traps were checked in both morning and evening, and the +catch was correspondingly greater than it was in cool weather +when the traps were checked only once daily. The ratios obtained +of young to adult voles cannot be accepted at face value as the +true ratios in the population, either. For the first several days of +each trapping period, the voles caught were mostly adults previously +marked and, presumably, conditioned to the grain bait. +Later, young voles not previously recorded, came to the traps in +increasing numbers. The young, being at first not conditioned to +the bait, and also having relatively small home ranges, would +generally be less well represented in the catch than would the +adults.</p> +<br /> + +<div class="caption2"><a name="GESTATION" id="GESTATION"></a> +GESTATION</div> + +<p>In other species of <i>Microtus</i>, so far as known, a 21-day gestation +period seems to be the rule (Bailey, 1924:528; Hamilton, 1941:13; +Hatfield, 1935:264). <i>M. ochrogaster</i> seems to conform to this +pattern, but the data obtained were meager, because breeding +activity was usually inhibited in voles kept in confinement.</p> + +<p>A female live-trapped on July 23, 1951, appeared to be in +breeding condition. When trapped two days later, she had a +copulatory plug, and 21 days after this she was found with a newborn +litter in a trap. A female thought to have given birth to a +litter between successive captures on July 20, and July 21, 1951 +(on the basis of appearance of genitalia, and reduction in weight +from 53 to 46 grams), appeared to have just completed parturition +<span class="pagenum"><a name="Page_143" id="Page_143">[Pg 143]</a></span> +when she was examined on August 10. A female that gave birth to +a litter in confinement on May 18, 1954, bred and was released the +same day. She was recorded as pregnant in the first week of June, +but on June 7 was no longer pregnant. If this pregnancy terminated +normally, a gestation of 20 days or less is indicated.</p> + +<p>Greenwald (1956:221) suggested that in <i>M. californicus</i>, oestrus +might occur in the period of lactation, because he found recently +formed corpora lutea in lactating females. In the course of my +field work on <i>M. ochrogaster</i>, I obtained precise or approximate +dates of successive litters born at intervals of somewhat more than +21 days apart. In different females, intervals of 23, 23, 24, 26, +and approximately 27 (between 26 and 28) days were recorded +between successive litters. In four other females intervals between +litters were known only approximately because one of two records +was based on a capture in late pregnancy judged to be within +two or three days of parturition. For these females, intervals of +23, 24, 24, and 26 days were recorded. From the trend of these +records, it seems that females often became pregnant within a +few days after birth of a litter. Pregnancy from post-partum +oestrus would seem to be less frequent than pregnancies beginning +a few days after birth of the previous litter, and within the period +of lactation.</p> +<br /> + +<div class="caption2"><a name="NUMBER_OF_YOUNG_PER_LITTER" id="NUMBER_OF_YOUNG_PER_LITTER"></a> +NUMBER OF YOUNG PER LITTER</div> + +<p>Jameson (1947:146) found an average of 3.4 young per litter +in 58 litters of <i>M. ochrogaster</i> from northeastern Kansas, mostly +from Douglas County. Martin (1956:386) recorded a somewhat +lower mean of 3.18 ± 0.24 in 65 litters on the Reservation in 1950, +1951, and 1952. For a total of 82 litters recorded from 1950 through +1956, inclusive, I obtained an average of 3.37 ± .075 young per +litter. Several litters that were recorded were excluded from this +computation as in each instance there was reason to suspect that +they were incomplete. These included instances of females found +in traps with young several days old, females that may not have +completed parturition when they were released with newborn +young, and those litters that might have sustained losses through +cannibalism by the mother or her trap-mates.</p> + +<p>Mean numbers of young per litter were found to vary from year +to year and from month to month, as shown by the following lists: +1950, 3.0 (13 litters); 1951, 3.5 (23 litters); 1952, 3.5 (11 litters); +1953, 3.4 (5 litters); 1954, 3.4 (15 litters); 1955, 4.1 (7 litters); +1956, 3.8 (5 litters); January 2.0 (1 litter); February 3.5 (4 litters); +<span class="pagenum"><a name="Page_144" id="Page_144">[Pg 144]</a></span> +March 4.5 (4 litters); April 3.9 (12 litters); May 3.3 (25 litters); +June 3.0 (9 litters); July 2.7 (4 litters); August 2.9 (7 litters); September +2.8 (6 litters); October 3.4 (7 litters); November 5.0 (2 litters); +December 4.0 (1 litter).</p> + +<p>These differences can be logically explained on the basis of +changes in the average age of the breeding females in the population. +On the average, with greater length, weight and age, females +produced progressively larger litters, although individuals +did not necessarily conform to this general trend. For 24 females +recorded in 1954-1956 and measured within a few days of birth of +their litters, average length was correlated with number of young as +follows: 6 young, 163.5 mm.; 5 young, 158.0 mm.; 4 young, 157.7 mm.; +3 young, 154.6 mm.; 2 young, 160.5 mm.</p> + +<p>For 48 other females, recorded in 1950-1953, that were not measured, +but that were mostly assignable to broad age groups on the +basis of their individual histories in the trapping records, the following +well defined trend was demonstrated.</p> + +<div class="center"> +<div class="tbl_cap"><a name="Table_3" id="Table_3"></a> +Table 3. Number of Young per Litter Correlated <br /> +with Age or Size of Female.</div> + +<table summary="Number of Young per Litter"> +<tr> + <td class="center brdtp2 brdbt smcap">Age or Size Group <br />of Female</td> + <td class="center brdtp2 brdlf brdbt">Number of females <br />in sample</td> + <td class="center brdtp2 brdlf brdbt">Average number of young <br />per litter</td> +</tr> +<tr> + <td>More than one year old</td> + <td class="center brdlf">4</td> + <td class="center brdlf">4.25</td> +</tr> +<tr> + <td>6 to 12 months old</td> + <td class="center brdlf">16</td> + <td class="center brdlf">3.50</td> +</tr> +<tr> + <td>Large (age indeterminate)</td> + <td class="center brdlf">9</td> + <td class="center brdlf">3.44</td> +</tr> +<tr> + <td>2 to 5 months old</td> + <td class="center brdlf">9</td> + <td class="center brdlf">2.90</td> +</tr> +<tr> + <td class="brdbt">Small and medium (age indeterminate)</td> + <td class="center brdlf brdbt">10</td> + <td class="center brdlf brdbt">2.80</td> +</tr> +</table> +</div> +<br /> + +<p>It seems that the exceptionally high average numbers of young +per litter in March and April result from the breeding females in +those months being nearly all fully mature survivors of the previous +year. In summer, when many females that are only a few weeks +old become pregnant, the average litter declines to less than three +young. The small average litter of 3.0 young for 1950 probably +resulted from the fact that the population on the Reservation was +then expanding rapidly in the newly favorable habitat created by +one year's crop of vegetation after discontinuance of grazing, and +had an unusually high percentage of breeding females that were +not fully adult.</p> + + +<p><span class="pagenum"><a name="Page_145" id="Page_145">[Pg 145]</a></span></p> +<div class="caption2"><a name="SIZE_AT_BIRTH" id="SIZE_AT_BIRTH"></a> +SIZE AT BIRTH</div> + + +<p>In four newborn young, total lengths, in mm., were 47, 45, 45, +and 42. From the length-weight relationships shown in <a href="#Fig_2">Fig. 2</a>, it +seems that a length of approximately 47 mm. is typical of newborn +young of average weight. Martin (1956:388) found a mean +weight of 2.8 ± 0.36 grams in sixteen newborn prairie voles from +the Reservation. For a series of 67 other newborn voles representing +27 different litters in seven different years, I found an average +of 2.9 ± .05 grams. Young ranged in weight from 3.8 to 2.0 grams. +Weights of the newborn voles could not be correlated with season, +size, age of females, or food conditions. However, a distinct trend +toward larger size in those litters that contained fewer young was +evident, as shown in <a href="#Table_4">Table 4</a>.</p> + +<div class="center"> +<div class="tbl_cap"><a name="Table_4" id="Table_4"></a> +Table 4. Weight of Newborn Young, Correlated with <br /> +Number of Young per Litter.</div> + +<table summary="Newborn Weights"> +<tr> + <td class="center brdtp2 brdbt smcap">Known Young <br />Per Litter</td> + <td class="center brdtp2 brdlf brdbt">Mean weight <br />in grams</td> + <td class="center brdtp2 brdlf brdbt">Number of litters <br />in sample</td> + <td class="center brdtp2 brdlf brdbt">Number of young <br />in sample</td> +</tr> +<tr> + <td class="center">2</td> + <td class="center brdlf">3.1 ± .09</td> + <td class="center brdlf">7</td> + <td class="center brdlf">13</td> +</tr> +<tr> + <td class="center">3</td> + <td class="center brdlf">3.0 ± .17</td> + <td class="center brdlf">11</td> + <td class="center brdlf">28</td> +</tr> +<tr> + <td class="center">4</td> + <td class="center brdlf">2.7 ± .22</td> + <td class="center brdlf">6 </td> + <td class="center brdlf">17</td> +</tr> +<tr> + <td class="center brdbt">5</td> + <td class="center brdlf brdbt">2.6 ± .42</td> + <td class="center brdlf brdbt">3</td> + <td class="center brdlf brdbt">9</td> +</tr> +</table> +</div> +<br /> + + +<div class="caption2"><a name="EARLY_GROWTH" id="EARLY_GROWTH"></a> +EARLY GROWTH</div> + +<p>Voles less than 100 mm. in total length were seldom captured, +because those less than this size are dependent on the female, +and rarely venture far enough from the nest to be caught in a trap. +A further difficulty in obtaining growth records on the smallest +young is that of making accurate measurements. During their +first few days they partially retain the fetal posture, usually lying +on one side, with the head, body and tail flexed in an arc almost +completed by the tail approximating the muzzle. Straightening +the animal by stretching it and holding it with sufficient firmness +to obtain a measurement might have involved injury to it. Therefore, +in most instances the newborn voles examined were merely +weighed or an approximate measurement was estimated without +stretching the young to its full length.</p> + +<p>Newborn voles were obtained when females that were caught +in live-traps produced their litters before they were found and released. +<span class="pagenum"><a name="Page_146" id="Page_146">[Pg 146]</a></span> +In some instances, females caught while in late pregnancy +were retained in the laboratory for a day or more until parturition +occurred. Many of the newborn voles were marked by toe-clipping, +according to the same system used for adults. Early growth +was measured in some instances by keeping the female with her +litter in confinement, measuring and weighing the young at intervals. +In most instances, the female was released at the point of +capture (presumably near her nest burrow) with the young clinging +to her teats. For the young so released, the incidence of recovery +was remarkably low, seeming to indicate that they were +subject to decimating losses. Perhaps such losses are normal, +at least on the study area where voles are live-trapped regularly. +Holding of adults and partly grown young in live-traps ordinarily +has no harmful effects on them, but the resultant separation of females +from newly born litters may often result in death of the +young either from hunger and exposure, or from attack by other +voles and natural enemies.</p> + +<p>During the first ten days the increase in length from an original +47 mm. is from three to four mm. per day. Figs. <a href="#Fig_2">2</a>, +<a href="#Fig_5">5</a>, and <a href="#Fig_8">8</a> show +length and weights of voles whose ages in days were definitely +known because they were born in the laboratory, or in a live-trap +after the female was caught there. Young voles marked at birth +and released with the female were rarely recovered in the period +of suckling, as they ordinarily remain in the nest burrow when +the female ventures out to forage. Litters retained in the laboratory +therefore have provided most of the records of growth in suckling +young. Growth varied greatly between litters. It was not +clearly correlated with size of female, size of young at birth, or +number of young in litter, but probably was influenced by attentiveness +of the female, her adjustment to captivity, and her productivity +of milk. Within each litter there were usually persistent differences +in development, but these were minor (except for those of occasional +runts) compared with the differences between litters. In +several litters of five young, one was usually smaller than the others +at birth and therefore could not compete successfully with its +litter mates, so that it never gained possession of a teat other than +one of the pectoral pair, and always succumbed within a few days, +after failing to gain weight as its litter mates did. The relatively +few voles marked at birth and recovered after developing under +natural conditions, did not deviate from the trend of those in confinement.</p> +<br /> + +<p><span class="pagenum"><a name="Page_147" id="Page_147">[Pg 147]</a></span></p> +<div class="caption2"><a name="CARE_OF_YOUNG" id="CARE_OF_YOUNG"></a>CARE OF YOUNG</div> + +<p>Females in confinement were attentive to young, and, soon after +parturition, licked them clean and huddled over them protectively. +Ordinarily, the newborn young soon attached to a teat, and spent a +large part of its time attached during its early development. Females +found in live-traps with their litters of young less than a day +old, often had some or all of the young clinging to their teats. Females +with newborn litters, when released from live-traps, always +left without attempting to retrieve any young that were unattached. +Such young usually were permanently deserted, but in some instances +disappeared within an hour or less, perhaps rescued by +the female returning for them.</p> + +<p>Females with newborn young were made far more aggressive +than most other voles by their tendency to protect their young +from possible danger. In captivity such females usually took the +offensive in attacking or rebuffing any other voles confined with +them. Post-partum females obviously in oestrus were prevented +from being fully receptive by their hostility toward males whose +presence might endanger the young. Such a female has been seen +to turn on a pursuing male and attack him viciously, several times +within a few minutes, before copulation occurred. In captivity, +at least, such attacks would soon discourage a male so that unless +he was exceptionally active sexually, mating was prevented.</p> + +<p>Cannibalism, involving destruction of the newborn, is probably +an important factor in the population dynamics of the prairie vole. +Only a small percentage of the young known to have been born +on an area ever survived to be live-trapped; this small percentage +was indirect evidence of decimating losses in the young. Under +unfavorable conditions each of several females killed and ate her +own litter, but the degree of provocation varied greatly among +individuals. Females that gave birth to young in live-traps occasionally +ate one or more of their newborn young, as evidenced +by discarded remnants. Perhaps other instances passed unnoticed +because no remnants were found. That need for food or moisture +as well as psychological stress often motivated such cannibalism +was suggested by the fact that surviving litter mates might be +accepted and cared for by a female that had already eaten one or +more of her young. Although cannibalism is most likely to occur +within a few hours after birth of the young, they may be killed +and eaten at any stage of development. One female that had probably +<span class="pagenum"><a name="Page_148" id="Page_148">[Pg 148]</a></span> +eaten one or more of her litter, soon after parturition, nursed +the two survivors. When these were two weeks old, all were +"pastured out" in a wire mesh cage in tall brome grass. When +the supply of grass had become scarce (though some was still available), +the female killed and partly ate both her remaining young.</p> + +<p>One female was captured with three young attached that were +several days old. The young were detached from the female's teats +with great difficulty. When these young were returned to the female +a few minutes later, after they had been measured, weighed +and marked, she attacked them viciously, and within a few seconds +had killed all of them by biting their heads. In this instance the +dead young were not eaten, although they were temporarily left +with the female.</p> + +<p>Females with young have ample cause for their circumspective +demeanor toward adult males, which are especially inclined to eat +the newborn. A male engaged in sexual pursuit has been observed +to grasp a young dangling behind the female, pull it from her teat, +and pausing momentarily, nibble its head off, before continuing +to follow the female. Like the genitalia of the post-partum female, +the newborn young seem to have an odor that attracts and excites +the male.</p> + +<p>To a lesser degree, adult females also display marked interest in +the newborn young of other individuals, which is liable to result +in cannibalism. The incidence of cannibalism is affected by the +condition, collectively, of the population of voles, and the availability +of nutritious food and moisture. In periods of summer +drought the grass becomes coarse and fibrous, and its protein +content declines. Under such conditions many voles appear to be +undernourished, and some are actually emaciated. Dehydration +may be an important factor at times when dew is unavailable for +drinking and the green vegetation remaining is exceptionally low in +moisture content. Voles caught at such times and brought to the +laboratory, drank avidly, and gained several grams soon after being +offered water or succulence. Cannibalism by adults on newborn +young in times of drought may be motivated by the acute +need for moisture and nutritious food. In times of drought the +birth rate is at low ebb.</p> + +<p>Adult males have never been observed to display paternal solicitude +toward young, but some individuals, kept with females and +their litters, did not molest the young and were accepted by the +females as members of the family group.</p> + +<p><span class="pagenum"><a name="Page_149" id="Page_149">[Pg 149]</a></span> +Other things being equal, cannibalism involving the young might +be expected to be greater at times of high population density. Then, +young left in the nest by a female in the course of her foraging +would more often encounter adults and partly grown young, both +those that lived in the same burrow system and exploring intruders +from other areas.</p> + +<p>The eyes open at an age of nine or ten days. Then the young +enter upon an exploratory period, when each wanders out of the +nest, emerges from the burrow, and wanders through the adjacent +surface runways in frequent short forays, sometimes following the +female and sometimes alone. Such forays usually cover only a +few inches at first, but as the young vole grows, becomes familiar +with its surroundings, and takes more plant food, its sphere of +activity gradually widens, and family ties are dissolved. Voles +reared to an age of three weeks in the laboratory and then released, +survived just as well if the female was not released with +them demonstrating that they were fully capable of shifting for +themselves at this age. In confinement, however, young voles of +greater age continued to suckle and remained closely associated +with the female. Females in confinement evinced much uneasiness +because of their inability to evade the young when the latter were +old enough to walk. The young then followed the female continually +and suckled whenever she stopped or even while she +moved about, unless she paused to remove them from her teats, +but they would not remain detached for more than a few seconds. +When a young followed the female away from the nest and then attached +to a teat, the female after pulling the young from her teat, +would usually carry it, grasped between her incisors, back to the +nest and deposit it there. On one occasion a young vole caught in +a live-trap was partly plucked and eventually killed by the female +on the outside trying to pull it through the wire mesh.</p> + +<p>On several occasions, young were successfully transferred from +the mother to another lactating female in confinement, which accepted +them as part of her own litter. Young, up to the time of +weaning, appeared not to differentiate between the mother and +other adult voles. They would follow any larger individual indiscriminately, +and would huddle against it or nuzzle its undersurface +searching for a teat.</p> +<br /> + + +<div class="caption2"><a name="EARLY_DEVELOPMENT_OF_YOUNG" id="EARLY_DEVELOPMENT_OF_YOUNG"></a> +EARLY DEVELOPMENT OF YOUNG</div> + + +<p>The following notes are based upon many different litters, and +give some idea of the sequence of events in their early development.</p> + +<p><span class="pagenum"><a name="Page_150" id="Page_150">[Pg 150]</a></span> +Newborn: The skin is pinkish gray dorsally and pink ventrally. +In profile, sparse and exceedingly fine hairs less than 1 mm. in length +are discernible. The vibrissae are approximately 2 mm. long. The +skin is thin and partly transparent, much wrinkled, with some +deeper folds, notably one between the knee and the heel. The +young lie on their sides making violent convulsive respiratory +movements. When not attached to the female's teats, they may +make faint squeaking sounds.</p> + +<p>One day old: Little changed in appearance or behavior except +that the dorsal surface has become darker because of growth of +hair.</p> + +<p>Two days old: Covering of fine brown hair readily discernible +on dorsal surface; lower incisors protruding about .5 mm. from the +gum; upper incisors have barely pierced the gum.</p> + +<p>Four days old: Pale brown hair averaging about 1 mm. in length +over the dorsal surface gives the young a sleek, seallike appearance. +The young have gained greatly in muscular co-ordination. +Part of the time they may still lie on their sides, but they are able +also to gain an upright sprawling posture. In crawling, they are +unsteady and often topple over on their sides after taking a few +halting steps. They make frequent jerky lateral flexions of the +body, probably to search for a teat. Their eyes and ears still are +sealed shut.</p> + +<p>Five days old: Young have changed but little in appearance +since the preceding day, but they have become notably more active, +with movements better co-ordinated. When placed on a level +surface they can crawl briskly.</p> + +<p>Eight days old: Young are able to stand erect, with bodies held +clear of the ground, and they can even run, but the gait is slow +and clumsy, and the forequarters and hind quarters are poorly co-ordinated, +so that the voles tend to fall on their sides. The fur +averages approximately 3 mm. in length.</p> + +<p>Nine days old: At this stage all young have their eyes open or +beginning to open.</p> + +<p>Ten days old: All young of this age have their eyes open, but +not to their fullest extent, and the eyes are still slitlike in appearance. +The young have become rather gopherlike in appearance and gait. +They walk briskly but unsteadily, with bodies held high off the +ground. When handled, they struggle vigorously, and try to bite. +These young are similar in size and appearance to the smallest +voles caught in live-traps apart from their mothers.</p> + +<p>Thirteen days old: Hair on back has grown to an average length +of 8 mm. (shorter on ventral surface, head, and limbs).</p> + +<p><span class="pagenum"><a name="Page_151" id="Page_151">[Pg 151]</a></span> +Seventeen days old: The young have become alert, and almost +as quick in their movements as adults. They have molariform teeth, +and are taking plant food. When a family group was examined, +the young instantly detached from the female's teats and scattered. +The hair on the back averages 10 mm. long and the vibrissae average +20 mm. long.</p> + +<p>There is intense competition among the young of a litter, especially +if the litter has more than the average number of young. In +litters with more than four young, there is competition for the +inguinal teats, since, in most females at least, the pectoral teats +seem to have an inadequate milk supply. As a result, it is doubtful +whether more than four young to a litter are ever able to survive. +From the time their eyes open, the young compete actively. +When litters in confinement were fed with fresh greens, there was +nearly always quarrelsome squeaking and scuffling, as the young +competed for food. At such times, they have been seen to chase +and attack each other.</p> +<br /> + + +<div class="caption2"><a name="GROWTH_FROM_WEANING_TO_MATURITY" id="GROWTH_FROM_WEANING_TO_MATURITY"></a> +GROWTH FROM WEANING TO MATURITY</div> + +<p>No individual vole was recaptured with sufficient regularity, +from birth to maturity, to provide a complete growth curve. The +curve in <a href="#Fig_7">Fig. 7</a> is a composite based on all available records of +voles that were recorded as making growth in length and were recaptured +before they were fully grown, so that growth rates could +be computed. The figure shows that growth is extremely rapid +for the first three weeks, and thereafter slows gradually but steadily, +until in individuals of adult size, the increment per day is much +less than that in the small young.</p> + +<p>Since rate of growth changes rapidly, with a slowing trend, +only those young voles that were recaptured within a few weeks +showed the approximate growth rate for any specific portion of +the ontogenetic curve. <a href="#Table_5">Table 5</a> summarizes the records of 98 such +young sorted into size groups representative of several stages in +development. The slowing trend of growth in voles that are nearing +subadult size is well shown by these records. Throughout +the greater part of the growth curve no difference could be found +in rate between the sexes. It is only after sexual maturity has +been attained and growth has become relatively slow that males +become noticeably larger than females. This tendency for continued +growth in the adult males results in a much more marked +disparity in size between the sexes in the oldest voles, as evident +in <a href="#Fig_2">Fig. 2</a>.</p> +<br /> + +<p><span class="pagenum"><a name="Page_152" id="Page_152">[Pg 152]</a></span></p> + +<div class="fig_center" style="width: 503px;"> +<a name="Fig_2" id="Fig_2"></a> +<img src="images/fig_2.png" width="503" height="387" alt="" title="" /> +<div class="fig_caption">Fig. 2. Size distribution of prairie voles in a year-around sample, including +all the measurements of voles taken over a three-year period. Young are not +represented in their actual ratio to the total population in this sample, because +they are less attracted to the bait, and range less widely than adults. The +higher ratios of males than of females in the three largest size groups is well +shown, as is the higher ratio of females among those voles of small adult size.</div> +</div> +<br /> +<br /> + +<div class="center"> +<div class="tbl_cap"><a name="Table_5" id="Table_5"></a> +Table 5. Average Growth (in Over-all Length) in Young Voles of +Several Sizes.</div> + +<table summary="Newborn Weights"> +<tr> + <td class="center brdtp2 brdbt smcap">Average lengths in mm. <br />at beginning and end <br />of growth period</td> + <td class="center brdtp2 brdlf brdbt">Average length, in days, <br />of growth periods</td> + <td class="center brdtp2 brdlf brdbt">Average increment <br />per day in mm.</td> + <td class="center brdtp2 brdlf brdbt">Total, and number <br />of each sex in sample</td> +</tr> +<tr> + <td class="center">97.0 to 126.6</td> + <td class="center brdlf">in 16.8</td> + <td class="center brdlf">1.76</td> + <td class="center brdlf">5 (1 ♂, 4 ♀ ♀)</td> +</tr> +<tr> + <td class="center">103.3 to 127.3</td> + <td class="center brdlf">in 14.9</td> + <td class="center brdlf">1.61</td> + <td class="center brdlf">9 (3 ♂ ♂, 6 ♀ ♀)</td> +</tr> +<tr> + <td class="center">107.5 to 123.4</td> + <td class="center brdlf">in 11.0</td> + <td class="center brdlf">1.44</td> + <td class="center brdlf">8 (5 ♂ ♂, 3 ♀ ♀)</td> +</tr> +<tr> + <td class="center">114.0 to 132.3</td> + <td class="center brdlf">in 17.5</td> + <td class="center brdlf">1.05</td> + <td class="center brdlf">6 (5 ♂ ♂, 1 ♀)</td> +</tr> +<tr> + <td class="center">118.5 to 136.0</td> + <td class="center brdlf">in 19.7</td> + <td class="center brdlf">.88</td> + <td class="center brdlf">6 (3 ♂ ♂, 3 ♀ ♀)</td> +</tr> +<tr> + <td class="center">122.1 to 135.8</td> + <td class="center brdlf">in 16.2</td> + <td class="center brdlf">.85</td> + <td class="center brdlf">15 (5 ♂ ♂, 10 ♀ ♀)</td> +</tr> +<tr> + <td class="center">129.3 to 145.5</td> + <td class="center brdlf">in 22.8</td> + <td class="center brdlf">.71</td> + <td class="center brdlf">4 (all ♂ ♂)</td> +</tr> +<tr> + <td class="center">130.6 to 146.1</td> + <td class="center brdlf">in 19.8</td> + <td class="center brdlf">.78</td> + <td class="center brdlf">12 (all ♀ ♀)</td> +</tr> +<tr> + <td class="center">139.8 to 147.5</td> + <td class="center brdlf">in 29.5</td> + <td class="center brdlf">.26</td> + <td class="center brdlf">10 (all ♂ ♂)</td> +</tr> +<tr> + <td class="center brdbt">141.2 to 148.8</td> + <td class="center brdlf brdbt">in 26.2</td> + <td class="center brdlf brdbt">.29</td> + <td class="center brdlf brdbt">23 (all ♀ ♀)</td> +</tr> +</table> +</div> +<br /> + +<p><span class="pagenum"><a name="Page_153" id="Page_153">[Pg 153]</a></span></p> +<div class="fig_center" style="width: 313px;"> +<a name="Fig_3" id="Fig_3"></a> +<a href="images/fig_3_lg.png"><img src="images/fig_3_sm.png" width="313" height="614" alt="" title="" /></a><br /> +<div class="smaller center">Click on graph to view larger version.</div><br /> +<div class="fig_caption">Fig. 3. Changing numbers and composition (according to size of individual) +in a population of voles on an area of approximately one half an acre that +was intensively sampled with live-traps over periods of months. The population +as a whole and the ratio of young to adults tended to be higher in spring +and summer, but with little regularity from one year to the next. Weather was +far more important than season in determining the population trend. Many of +the voles recorded on the half-acre area ranged more or less beyond its +boundaries.</div> +</div> +<br /> +<br /> + +<p><span class="pagenum"><a name="Page_154" id="Page_154">[Pg 154]</a></span></p> +<div class="fig_center" style="width: 614px;"> +<a name="Fig_4" id="Fig_4"></a> +<img src="images/fig_4.png" width="614" height="698" alt="" title="" /> +<div class="fig_caption">Fig. 4. Weight in free-living prairie voles in a year-around sample from juveniles +to large adults (grouped in length-classes of 6 mm. range, separate for +each sex). In each sample mean, standard error, standard deviation, and extremes +are shown. Note that mean weight is proportional to length, that in +each size class females average heavier (because of pregnancy in some) and +have a much wider range of variation in weight.</div> +</div> +<br /> +<br /> + +<p>Martin (1956:389) stated that growth in young prairie voles +was, in general, most rapid in the period April-May-June and +least rapid in mid-winter. However, his data were based entirely +on weights. The high incidence of pregnancy in the larger young +females in spring and early summer may have caused the trend. +Measurements taken by me of lengths do not bear out the idea of +more rapid growth in the spring and summer, but, indeed, show the +opposite. In most instances, voles of comparable sizes made significantly +more rapid growth in the colder half of the year (mid-October +to mid-March) than in the warmer half. Dividing the +young voles in eight size groups and separating each group into +comparable summer and winter samples, I found more rapid average +growth in the summer sample in only two instances. These +<span class="pagenum"><a name="Page_155" id="Page_155">[Pg 155]</a></span> +deviations from the general trend probably resulted from inadequately +small sizes of some samples. On the average, the +growth rate in summer was 92 per cent of that in winter.</p> + +<div class="fig_center" style="width: 447px;"> +<a name="Fig_5" id="Fig_5"></a> +<img src="images/fig_5.png" width="447" height="665" alt="" title="" /> +<div class="fig_caption">Fig. 5. Over-all length plotted against weight in young prairie voles, from +newborn to the minimum size at breeding maturity. The range of variation increases +as development proceeds, especially after the age of weaning is attained.</div> +</div> +<br /> + +<p><span class="pagenum"><a name="Page_156" id="Page_156">[Pg 156]</a></span></p> +<div class="caption2"><a name="SIZE_AND_AGE_AT_SEXUAL_MATURITY" id="SIZE_AND_AGE_AT_SEXUAL_MATURITY"></a> +SIZE AND AGE AT SEXUAL MATURITY</div> + +<p>Greenwald (1956: 220) found that in females of <i>Microtus californicus</i> +some individuals are extremely precocious sexually, and +might, at an age of as little as two weeks, produce corpora lutea and +have sperm in the uterus. Greenwald mentioned one perforate +female which weighed only 10 grams, but most reached a weight +of at least 30 grams before their first pregnancies. The sterile +cycles passed through earlier seemed to represent a "tuning-up" +stage before establishment of the pituitary-gonad relationship.</p> + +<div class="fig_center" style="width: 425px;"> +<a name="Fig_6" id="Fig_6"></a> +<img src="images/fig_6.png" width="425" height="475" alt="" title="" /> +<div class="fig_caption">Fig. 6. Weight plotted against age in young voles, from birth up to 25 +days. The range is wide at the start and increases as development proceeds.</div> +</div> +<br /> + +<p>Although females of <i>M. ochrogaster</i> are much less precocious +in their manifestations of puberty, they may become perforate +<span class="pagenum"><a name="Page_157" id="Page_157">[Pg 157]</a></span> +well before impregnation can occur, and seem to pass through +sterile cycles before becoming pregnant. The 18 smallest females +recognized as being pregnant were of the following over-all lengths, +in mm.: 149, 149, 149, 148, 148, 148, 147, 146, 145, 145, 144, 144, +143, 143, 143, 142, 135, and 134. As pregnancy is ordinarily recognized +only in the last four days the females must have been impregnated +from 20 to 17 days earlier—when they were in most instances +7 to 11 weeks old and 135 to 145 mm. in length. The two smallest individuals, +recorded as pregnant at 135 and 134 mm., must, if they +were of typical size for their age, have become pregnant at an +age of approximately one month, when they were only 119 and +122 mm. in length. The smallest lactating females (some of them +pregnant also) were recorded at lengths of 149, 148, 148, 147, 147, +146, 144, 144, 143, 143, and 142 mm. Occasionally females of less +than 120 mm. were found to be perforate, and seemingly had begun +oestral cycles. Records of a female of definitely known age, +typical of many of the same size in her development, are cited +below:</p> + +<div class="smaller"> +<p>March 19, 1956 Born in captivity.</p> + +<p>April 7, 1956 (19 days old) Released on study area at site of mother's +capture; length 102 mm., weight 11.1 gms. +</p> + +<p><span class="pagenum2"><a name="Page_158" id="Page_158">[Pg 158]</a></span> +April 15, 1956 (27 days old) Recaptured; perforate with a copulatory +plug; length 113 mm., weight 13.4 gms.</p> + +<p>April 27, 1956 (39 days old) Recaptured; imperforate; length 131 mm., +weight 24.3 gms.</p> + +<p>May 12, 1956 (54 days old) Recaptured; perforate and in late pregnancy; +length 146 mm.</p> + +<p>May 25, 1956 (67 days old) Recaptured; imperforate, in an advanced +state of lactation; length 150 mm., weight 33 gms.</p> +</div> + +<div class="fig_center" style="width: 501px;"> +<a name="Fig_7" id="Fig_7"></a> +<img src="images/fig_7.png" width="501" height="372" alt="" title="" /> +<div class="fig_caption">Fig. 7. Growth curve in the prairie vole; dots are based on means of +series of definitely known age (born in captivity); circles are based on mean +lengths of recaptured marked young whose ages were not precisely known.</div> +</div> +<br /> + +<div class="fig_center" style="width: 497px;"> +<a name="Fig_8" id="Fig_8"></a> +<img src="images/fig_8.png" width="497" height="564" alt="" title="" /> +<div class="fig_caption">Fig. 8. Over-all length in young prairie voles of definitely known ages, +up to 40 days. All were born in captivity. Some were released with the +female and developed under natural conditions, but their growth rate did +not differ discernibly from that of those kept in the laboratory. Dots indicate +individual records; circles are means for ages at which four or more records were +obtained.</div> +</div> +<br /> + +<p>When captured on May 12, at an age of 54 days, this female +appeared to be within two or three days of parturition, and hence +<span class="pagenum"><a name="Page_159" id="Page_159">[Pg 159]</a></span> +must have become pregnant at an age of approximately 35 or 36 +days. Pregnancy in the more precocious females probably occurs +at a length of approximately 130 mm. and an age of a little +less than 40 days. Such females are still growing so rapidly that +by the time their litters are born, they have grown to more than +140 mm.</p> +<br /> + + +<div class="caption2"><a name="GROWTH_IN_SUBADULTS_AND_ADULTS" id="GROWTH_IN_SUBADULTS_AND_ADULTS"></a> +GROWTH IN SUBADULTS AND ADULTS</div> + +<p><a href="#Table_6">Table 6</a> is a summarization of 73 records of individuals that made +substantial growth as adults, after they were marked and measured. +These records show the slowing trend of growth with advanced age. +Also, they show the wide range of individual variation in growth +rate, and difference between the sexes. With advanced age, growth +in females lags behind that in males to an increasing extent. Exceptionally +large individuals, of either sex, are many months old, +but some individuals live to be a year old or more without growing +much beyond average adult size. The average growth rate of +more than 1 mm. per day in young has slowed to less than .1 mm. +per day, on the average, in adults exceeding 160 mm., and has +slowed to less than .05 mm. per day, on the average, in those exceeding +165 mm.</p> +<br /> + +<div class="center"> +<div class="tbl_cap"><a name="Table_6" id="Table_6"></a> +Table 6. Size Groups (Over-all Length) in Recaptured Voles That +Were Marked Before Maturity and Therefore Were of Approximately +Known Ages.</div> + +<table summary="Size Groups"> +<tr> + <td class="center brdtp2 brdbt smcap" rowspan="2">Size Group Length in mm.</td> + <td class="center brdtp2 brdlf brdbt" colspan="3">Estimated age, in days</td> + <td class="center brdtp2 brdlf brdbt" rowspan="2">Number in sample</td> +</tr> +<tr> + <td class="center brdlf brdbt">Average</td> + <td class="center brdlf brdbt">Maximum</td> + <td class="center brdlf brdbt">Minimum</td> +</tr> +<tr> + <td class="center">171 to 175</td> + <td class="center brdlf">♂ 435</td> + <td class="center brdlf">.....</td> + <td class="center brdlf">.....</td> + <td class="center brdlf">1</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">♀ 324</td> + <td class="center brdlf">338</td> + <td class="center brdlf">310</td> + <td class="center brdlf">2</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">All 361</td> + <td class="center brdlf">435</td> + <td class="center brdlf">310</td> + <td class="center brdlf">3</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> +</tr> +<tr> + <td class="center">166 to 170</td> + <td class="center brdlf">♂ 304</td> + <td class="center brdlf">523</td> + <td class="center brdlf">179</td> + <td class="center brdlf">9</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">♀ 398</td> + <td class="center brdlf">597</td> + <td class="center brdlf">158</td> + <td class="center brdlf">6</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">All 346</td> + <td class="center brdlf">597</td> + <td class="center brdlf">158</td> + <td class="center brdlf">15</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> +</tr> +<tr> + <td class="center">161 to 165</td> + <td class="center brdlf">♂ 227</td> + <td class="center brdlf">465</td> + <td class="center brdlf">104</td> + <td class="center brdlf">15</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">♀ 257</td> + <td class="center brdlf">394</td> + <td class="center brdlf">134</td> + <td class="center brdlf">18</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">All 243</td> + <td class="center brdlf">465</td> + <td class="center brdlf">104</td> + <td class="center brdlf">33</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> + <td class="center brdlf"> </td> +</tr> +<tr> + <td class="center">156 to 160</td> + <td class="center brdlf">♂ 188</td> + <td class="center brdlf">349</td> + <td class="center brdlf">107</td> + <td class="center brdlf">12</td> +</tr> +<tr> + <td class="center"> </td> + <td class="center brdlf">♀ 187</td> + <td class="center brdlf">284</td> + <td class="center brdlf">93</td> + <td class="center brdlf">11</td> +</tr> +<tr> + <td class="center brdbt"> </td> + <td class="center brdlf brdbt">All 188</td> + <td class="center brdlf brdbt">349</td> + <td class="center brdlf brdbt">93</td> + <td class="center brdlf brdbt">23</td> +</tr> +</table> +</div> +<br /> + +<p><span class="pagenum"><a name="Page_160" id="Page_160">[Pg 160]</a></span></p> +<div class="caption2"><a name="SUMMARY" id="SUMMARY"></a> +SUMMARY</div> + + +<p>The prairie vole is non-territorial and somewhat social. Several +or many individuals of both sexes and various sizes may use the +same system of surface runways and burrows and even the same +nest. In general, members of such a group are mutually tolerant. +A strange vole may provoke some hostility at first, but may soon +be accepted as a member of a new group. Consequently, there +are frequent shifts from one home base to another. Sexual relations +are probably more or less promiscuous, although a male and +female may rest and travel together in a semi-permanent association. +In confinement only those males having markedly enlarged +scrotal testes showed interest in females that were in oestrus. +Post-partum females especially were eagerly pursued by such males. +Anoestrus females are imperforate, and a vaginal orifice is present +only during an active oestral cycle or in pregnancy. The perforate +condition therefore, is a crude index of breeding activity in the +population. In adult females the ratio of those that were perforate +usually fluctuated between one-fourth and three-fourths +of the total. Only in severe summer drought did the numbers +decline below 24 per cent. Normally, breeding continues the +year around, but it is temporarily inhibited in unusually cold +weather or drought. The highest incidence of pregnancy normally +is in late spring and early summer. The ratio of juveniles in the +population from month to month and year to year is far more stable +than the actual population density.</p> + +<p>Gestation is 21 days or a little less. The mean litter is 3.37 ± .075 +young. Three is the most frequent number per litter, with four, +two, and five in that order of frequency. Larger and older females +have more young per litter, on the average. Average size is greater +in those litters having fewer young. At birth, young are between +40 and 50 mm. in length (typically, 47 mm.), and weigh 2.9 ± .05 +grams.</p> + +<p>At an age of nine days the young have their eyes open, and +they may be weaned at an age of approximately three weeks. +Young suckle chiefly from the four abdominal teats. The pectoral +mammae seem to be inadequately developed, with the result that +in exceptionally large litters of five, six or seven young, usually +no more than four survive. Until weaning the young spend much +of their time attached to the female's teats. She may even drag +them behind as she forages. Females that have suckling young +<span class="pagenum"><a name="Page_161" id="Page_161">[Pg 161]</a></span> +become much less tolerant of other voles. Attacks on young, and +cannibalism, are common. Adult males, especially, are liable to +eat the newborn young. The acquisition of cannibalistic habits +by individuals, and seasonal lack of adequately nutritious plant +foods may result in the killing off of young in such numbers that +the population level is held down.</p> + +<p>In young females sterile oestral cycles often begin at about the +time of weaning. Earliest pregnancies occur when females are +approximately one month old, but most are several weeks older +before they become pregnant. Rate of growth declines steadily +from a length increment of approximately 2 mm. per day in voles +less than two weeks old to an increment of approximately one-fourth +mm. per day in subadults. Growth rate is highly variable +among individuals at all stages, and especially in those that have +attained adult size. Even adults tend to gain in length, slowly, +as well as in weight, and the largest individuals are all many months +old.</p> +<br /> + + +<div class="caption2"><a name="LITERATURE_CITED" id="LITERATURE_CITED"></a> +LITERATURE CITED</div> + + +<div class="smcap">Bailey, V.</div> +<div class="reference">1924. Breeding, feeding and other life habits of meadow mice. Jour. +Agric. Res., 27: 523-536.</div> +<br /> + +<div><span class="smcap">Bodenheimer, F. S.</span>, and <span class="smcap">F. Sulman</span>.</div> +<div class="reference">1946. The estrous cycle of <i>Microtus guentheri</i> D. and A. and its ecological +implications. Ecol., 27: 255-256.</div> +<br /> + +<div class="smcap">Greenwald, G. S.</div> +<div class="reference">1956. The reproductive cycle of the field mouse, <i>Microtus californicus</i>. +Jour. Mamm., 37: 213-222, 2 figs., 1 pl.</div> +<br /> + +<div class="smcap">Hamilton, W. J., Jr.</div> +<div class="reference">1941. The reproduction of the field mouse, <i>Microtus pennsylvanicus</i>. +Cornell Univ. Agric. Exp. Sta. Mem., 237: 1-23.</div> +<br /> + +<div class="smcap">Hatfield, D. M.</div> +<div class="reference">1935. A natural history of <i>Microtus californicus</i>. Jour. Mamm., 16: 261-271.</div> +<br /> + +<div class="smcap">Hoyte, H. M. D.</div> +<div class="reference">1955. Observations on some small mammals of Arctic Norway. Jour. +Animal Ecology, 24: 412-425.</div> +<br /> + +<div class="smcap">Jameson, E. W.</div> +<div class="reference">1947. Natural history of the prairie vole. Univ. Kansas Mus. Nat. Hist. +Publ., 1: 125-151.</div> +<br /> + +<div class="smcap">Martin, E. P.</div> +<div class="reference">1956. A population study of the prairie vole (<i>Microtus ochrogaster</i>) in +northeastern Kansas. Univ. Kansas Mus. Nat. Hist. Publ., 8: 361-416.</div> +<br /> + +<div class="smcap">Schmidt, F. J. W.</div> +<div class="reference">1931. Mammals of western Clark County, Wisconsin. Jour. Mamm., 12: +99-117.</div> +<br /> +<br /> +<br /> +<br /> + +<div class="center"> +<img src="images/square.png" width="16" height="17" alt="" title="" /> +<br /> +26-7561<br /> +</div> +<br /> +<br /> + + + + +<p><span class="pagenum"><a name="Page_i" id="Page_i">[Pg i]</a></span></p> + +<div class="caption2">UNIVERSITY OF KANSAS PUBLICATIONS<br /> +MUSEUM OF NATURAL HISTORY</div> + +<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. +Nevertheless, 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> + +<div > +<table summary="UKMNH_Pubs"> +<tbody> +<tr> + <td class="text_rt"> Vol. 1.</td> + <td colspan="2">Nos. 1-26 and index. Pp. 1-638, 1946-1950.</td> +</tr> +<tr> + <td class="text_rt vtop">*Vol. 2.</td> + <td colspan="2" class="pub_list">(Complete) Mammals of Washington. By Walter W. Dalquest. Pp. 1-444, 140 + figures in text. April 9, 1948.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 3.</td> + <td class="text_rt vtop">*1.</td> + <td class="justify">The avifauna of Micronesia, its origin, evolution, and distribution. By Rollin + H. Baker. Pp. 1-359, 16 figures in text. June 12, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">*2.</td> + <td class="justify">A quantitative study of the nocturnal migration of birds. By George H. + Lowery, Jr. Pp. 361-472, 47 figures in text. June 29, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">Phylogeny of the waxwings and allied birds. By M. Dale Arvey. Pp. 473-530, + 49 figures in text, 13 tables. October 10, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">Index. Pp. 651-681.</td> +</tr> +<tr> + <td class="text_rt vtop">*Vol. 4.</td> + <td colspan="2" class="pub_list">(Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41 plates, 31 + figures in text. December 27, 1951.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 5.</td> + <td class="text_rt vtop">1.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">2.</td> + <td class="justify">Two new moles (Genus Scalopus) from Mexico and Texas. By Rollin H. + Baker. Pp. 17-24. February 28, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">Two new pocket gophers from Wyoming and Colorado. By E. Raymond + Hall and H. Gordon Montague. Pp. 25-32. February 28, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">5.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">6.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">7.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">8.</td> + <td class="justify">A new pocket gopher (Genus Thomomys) from eastern Colorado. By E. + Raymond Hall. Pp. 81-85. October 1, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">9.</td> + <td class="justify">Mammals taken along the Alaskan Highway. By Rollin H. Baker. Pp. 87-117, + 1 figure in text. November 28, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">*10.</td> + <td class="justify">A synopsis of the North American Lagomorpha. By E. Raymond Hall. Pp. + 119-202, 68 figures in text. December 15, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">11.</td> + <td class="justify">A new pocket mouse (Genus Perognathus) from Kansas. By E. Lendell + Cockrum. Pp. 203-206. December 15, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">12.</td> + <td class="justify">Mammals from Tamaulipas, Mexico. By Rollin H. Baker. Pp. 207-218. +December 15, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">13.</td> + <td class="justify">A new pocket gopher (Genus Thomomys) from Wyoming and Colorado. + By E. Raymond Hall. Pp. 219-222. December 15, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">14.</td> + <td class="justify">A new name for the Mexican red bat. By E. Raymond Hall. Pp. 223-226. + December 15, 1951.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">15.</td> + <td class="justify">Taxonomic notes on Mexican bats of the Genus Rhogeëssa. By E. Raymond + Hall. Pp. 227-232. April 10, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">16.</td> + <td class="justify">Comments on the taxonomy and geographic distribution of some North American + woodrats (Genus Neotoma). By Keith R. Kelson. Pp. 233-242. April 10, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">17.</td> + <td class="justify">The subspecies of the Mexican red-bellied squirrel, Sciurus aureogaster. By + Keith R. Kelson. Pp. 243-250, 1 figure in text. April 10, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">18.</td> + <td class="justify">Geographic range of Peromyscus melanophrys, with description of new subspecies. + By Rollin H. Baker. Pp. 251-258, 1 figure in text. May 10, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">19.</td> + <td class="justify">A new chipmunk (Genus Eutamias) from the Black Hills. By John A. + White. Pp. 259-262. April 10, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">20.</td> + <td class="justify">A new piņon mouse (Peromyscus truei) from Durango, Mexico. By Robert + B. Finley, Jr. Pp. 263-267. May 23, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">21.</td> + <td class="justify">An annotated checklist of Nebraskan bats. By Olin L. Webb and J. Knox + Jones, Jr. Pp. 269-279. May 31, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">22.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">23.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">24.</td> + <td class="justify">The subspecific status of two Central American sloths. By E. Raymond Hall + and Keith R. Kelson. Pp. 313-337. November 21, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">25.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">26.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">27.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">28.</td> + <td class="justify">The pocket gophers (Genus Thomomys) of Coahuila, Mexico. By Rollin H. + Baker. Pp. 499-514, 1 figure in text. June 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">29.</td> + <td class="justify">Geographic distribution of the pocket mouse, Perognathus fasciatus. By + J. Knox Jones, Jr. Pp. 515-526, 7 figures in text. August 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">30.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">31.</td> + <td class="justify">Four new pocket gophers of the genus Cratogeomys from Jalisco, Mexico. + By Robert J. Russell. Pp. 535-542. October 15, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">32.</td> + <td class="justify">Genera and subgenera of chipmunks. By John A. White. Pp. 543-561, 12 + figures in text. December 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">33.</td> + <td class="justify">Taxonomy of the chipmunks, Eutamias quadrivittatus and Eutamias umbrinus. + By John A. White. Pp. 563-582, 6 figures in text. December 1, + 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">34.</td> + <td class="justify">Geographic distribution and taxonomy of the chipmunks of Wyoming. By + John A. White. Pp. 584-610, 3 figures in text. December 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">35.</td> + <td class="justify">The baculum of the chipmunks of western North America. By John A. + White. Pp. 611-631, 19 figures in text. December 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">36.</td> + <td class="justify">Pleistocene Soricidae from San Josecito Cave, Nuevo Leon, Mexico. By + James S. Findley. Pp. 633-639. December 1, 1953.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">37.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">Index. Pp. 647-676.</td> +</tr> +<tr> + <td class="text_rt vtop">*Vol. 6.</td> + <td colspan="2" class="pub_list">(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.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 7.</td> + <td class="text_rt vtop">*1.</td> + <td class="justify">Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73 figures in + text, 37 tables. August 25, 1952.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">2.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">The silky pocket mice (Perognathus flavus) of Mexico. By Rollin H. Baker. + Pp. 339-347, 1 figure in text. February 15, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">North American jumping mice (Genus Zapus). By Philip H. Krutzsch. Pp. + 349-472, 47 figures in text, 4 tables. April 21, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">5.</td> + <td class="justify">Mammals from Southeastern Alaska. By Rollin H. Baker and James S. + Findley. Pp. 473-477. April 21, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">6.</td> + <td class="justify">Distribution of Some Nebraskan Mammals. By J. Knox Jones, Jr. Pp. 479-487. + April 21, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">7.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">8.</td> + <td class="justify">A new subspecies of bat (Myotis velifer) from southeastern California and + Arizona. By Terry A. Vaughn. Pp. 507-512. July 23, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">9.</td> + <td class="justify">Mammals of the San Gabriel mountains of California. By Terry A. Vaughn. + Pp. 513-582, 1 figure in text, 12 tables. November 15, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">10.</td> + <td class="justify">A new bat (Genus Pipistrellus) from northeastern Mexico. By Rollin H. + Baker. Pp. 583-586. November 15, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">11.</td> + <td class="justify">A new subspecies of pocket mouse from Kansas. By E. Raymond Hall. Pp. + 587-590. November 15, 1954.</td> +</tr> +<tr> + <td> <span class="pagenum"><a name="Page_iii" id="Page_iii">[Pg iii]</a></span></td> + <td class="text_rt vtop">12.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">13.</td> + <td class="justify">A new cottontail (Sylvilagus floridanus) from northeastern Mexico. By Rollin + H. Baker. Pp. 609-612. April 8, 1955.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">14.</td> + <td class="justify">Taxonomy and distribution of some American shrews. By James S. Findley. + Pp. 613-618. June 10, 1955.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">15.</td> + <td class="justify">The pigmy woodrat, Neotoma goldmani, its distribution and systematic position. + By Dennis G. Rainey and Rollin H. Baker. Pp. 619-624, 2 figs. in + text. June 10, 1955.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">Index. Pp. 625-651.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 8.</td> + <td class="text_rt vtop">1.</td> + <td class="justify">Life history and ecology of the five-lined skink, Eumeces fasciatus. By Henry + S. Fitch. Pp. 1-156, 26 figs. in text. September 1, 1954.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">2.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">An ecological study of the collared lizard (Crotaphytus collaris). By Henry + S. Fitch. Pp. 213-274, 10 figures in text. February 10, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">5.</td> + <td class="justify">Check-list of the birds of Kansas. By Harrison B. Tordoff. Pp. 307-359, 1 + figure in text. March 10, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">6.</td> + <td class="justify">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.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">7.</td> + <td class="justify">Temperature responses in free-living amphibians and reptiles of northeastern + Kansas. By Henry S. Fitch. Pp. 417-476, 10 figures in text, 6 tables. June 1, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">8.</td> + <td class="justify">Food of the crow, Corvus brachyrhynchos Brehm, in south-central Kansas. By + Dwight Platt. Pp. 477-498, 4 tables. June 8, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">9.</td> + <td class="justify">Ecological observations on the woodrat, Neotoma floridana. By Henry S. + Fitch and Dennis G. Rainey. Pp. 499-533, 3 figures in text. June 12, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">10.</td> + <td class="justify">Eastern woodrat, Neotoma floridana: Life history and ecology. By Dennis G. + Rainey. Pp. 535-646, 12 plates, 13 figures in text August 15, 1956.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">Index. Pp. 647-675.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 9.</td> + <td class="text_rt vtop">1.</td> + <td class="justify">Speciation of the wandering shrew. By James S. Findley. Pp. 1-68, 18 + figures in text. December 10, 1955.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">2.</td> + <td class="justify">Additional records and extension of ranges of mammals from Utah. By + Stephen D. Durrant, M. Raymond Lee, and Richard M. Hansen. Pp. 69-80. + December 10, 1955.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">A new long-eared myotis (Myotis evotis) from northeastern Mexico. By Rollin + H. Baker and Howard J. Stains. Pp. 81-84. December 10, 1955.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">Subspeciation in the meadow mouse, Microtus pennsylvanicus, in Wyoming. + By Sydney Anderson. Pp. 85-104, 2 figures in text. May 10, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">5.</td> + <td class="justify">The condylarth genus Ellipsodon. By Robert W. Wilson. Pp. 105-116, 6 + figures in text. May 19, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">6.</td> + <td class="justify">Additional remains of the multituberculate genus Eucosmodon. By Robert + W. Wilson. Pp. 117-123, 10 figures in text. May 19, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">7.</td> + <td class="justify">Mammals of Coahulia, Mexico. By Rollin H. Baker. Pp. 125-335, 75 figures + in text. June 15, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">8.</td> + <td class="justify">Comments on the taxonomic status of Apodemus peninsulae, with description + of a new subspecies from North China. By J. Knox Jones, Jr. Pp. 337-346, + 1 figure in text, 1 table. August 15, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">9.</td> + <td class="justify">Extensions of known ranges of Mexican bats. By Sydney Anderson. Pp. + 347-351. August 15, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">10.</td> + <td class="justify">A new bat (Genus Leptonycteris) from Coahulia. By Howard J. Stains. + Pp. 353-356. January 21, 1957.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">11.</td> + <td class="justify">A new species of pocket gopher (Genus Pappogeomys) from Jalisco, Mexico. + By Robert J. Russell. Pp. 357-361. January 21, 1957.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">More numbers will appear in volume 9.</td> +</tr> +<tr> + <td class="text_rt vtop">Vol. 10.</td> + <td class="text_rt vtop">1.</td> + <td class="justify">Studies of birds killed in nocturnal migration. By Harrison B. Tordoff and + Robert M. Mengel. Pp. 1-44, 6 figures in text, 2 tables. September 12, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">2.</td> + <td class="justify">Comparative breeding behavior of Ammospiza caudacuta and A. maritima. + By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1 figure. December 20, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">3.</td> + <td class="justify">The forest habitat of the University of Kansas Natural History Reservation. + By Henry S. Fitch and Ronald R. McGregor. Pp. 77-127, 2 plates, 7 figures + in text, 4 tables. December 31, 1956.</td> +</tr> +<tr> + <td> </td> + <td class="text_rt vtop">4.</td> + <td class="justify">Aspects of reproduction and development in the prairie vole (Microtus ochrogaster). + By Henry S. Fitch. Pp. 129-161, 8 figures in text, <ins title='Correction: was "4 tables"'>6 tables</ins>. December + 19, 1957.</td> +</tr> +<tr> + <td> </td> + <td colspan="2" class="justify">More numbers will appear in volume 10.</td> +</tr> + +</tbody> +</table> +</div> +<br /> +<br /> + +<div class="trans_notes"> +<div class="caption2">Transcriber's Notes</div> + +<p>With the exception of the typographical corrections listed below and +minor corrections not noted here, the text presented here is the same +as in the original printed version. The list of UKMNH publications was +compiled at the end of the article's text.</p> +<br /> + +<div class="caption2">Typographical Corrections</div> + +<table summary="typos"> +<tr> + <td class="brdbt2">Page(s)</td> + <td> </td> + <td class="brdbt2">Correction</td> +</tr> +<tr> + <td><a href="#Page_129">129</a>, <a href="#Page_130">130</a>, <a href="#Page_iii">ii</a></td> + <td>This publication: 4 tables ⇒ 6 tables</td> +</tr> +<tr> + <td><a href="#Page_138">138</a></td> + <td>cyle ⇒ cycle</td> +</tr> +</table> +</div> +<br /> +<br /> +</div><!-- End article --> + + + + + + + + +<pre> + + + + + +End of the Project Gutenberg EBook of Aspects of Reproduction and +Development in the Prairie Vole (Microtus ochrogaster), by Henry S. 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