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diff --git a/17966-8.txt b/17966-8.txt new file mode 100644 index 0000000..9a526db --- /dev/null +++ b/17966-8.txt @@ -0,0 +1,2650 @@ +The Project Gutenberg EBook of Life History of the Kangaroo Rat, by +Charles T. Vorhies and Walter P. Taylor + +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: Life History of the Kangaroo Rat + +Author: Charles T. Vorhies and Walter P. Taylor + +Release Date: March 11, 2006 [EBook #17966] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK LIFE HISTORY OF THE KANGAROO RAT *** + + + + +Produced by David Starner, Sigal Alon and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + +UNITED STATES DEPARTMENT OF AGRICULTURE + +BULLETIN No. 1091 + +Also Technical Bulletin No. 1 of the Agricultural Experiment Station +University of Arizona + +Washington, D. C. PROFESSIONAL PAPER September 13, 1922 + +LIFE HISTORY OF THE KANGAROO RAT +_Dipodomys spectabilis spectabilis_ Merriam + +BY + +CHARLES T. VORHIES, Entomologist +Agricultural Experiment Station, University of Arizona; and + +WALTER P. TAYLOR, Assistant Biologist +Bureau of Biological Survey, U. S. Department +of Agriculture + + + + +CONTENTS + + +Importance of Rodent Groups 1 +Identification 3 +Description 5 +Occurrence 7 +Habits 9 +Food and Storage 18 +Burrow Systems, or Dens 28 +Commensals and Enemies 33 +Abundance 36 +Economic Considerations 36 +Summary 38 +Bibliography 40 + + +[Illustration] + + +WASHINGTON +GOVERNMENT PRINTING OFFICE +1922 + + +[Illustration: PLATE I.--Banner-tailed Kangaroo Rat (Dipodomys spectabilis +spectabilis Merriam). + +From _Dipodomys merriami_ Mearns and subspecies, which occur over much +of its range, this form is easily distinguished by its larger size and +the conspicuous white brush on the tail.] + + + + +UNITED STATES DEPARTMENT OF AGRICULTURE + +BULLETIN No. 1091 + +Also Technical Bulletin No. 1 of the +Agricultural Experiment Station, University of Arizona + +Washington, D. C. PROFESSIONAL PAPER September, 1922 + +LIFE HISTORY OF THE KANGAROO RAT, + +_Dipodomys spectabilis spectabilis_ Merriam. + +By CHARLES T. VORHIES, _Entomologist, Agricultural Experiment Station, +University of Arizona_; and WALTER P. TAYLOR, _Assistant Biologist, +Bureau of Biological Survey, U. S. Department of Agriculture_. + + + + +CONTENTS. + + + Page + +Importance of rodent groups 1 + Investigational methods 2 +Identification 3 +Description 5 + General characters 5 + Color 6 + Oil gland 6 + Measurements and weights 7 +Occurrence 7 + General distribution 7 + Habitat 7 +Habits 9 + Evidence of presence 9 + Mounds 9 + Runways and tracks 10 + Signals 11 + Voice 12 + Daily and seasonal activity 12 + Pugnacity and sociability 13 + Sense developments 14 + Movements and attitudes 15 + Storing habits 15 + Breeding habits 16 +Food and storage 18 +Burrow systems, or dens 28 +Commensals and enemies 33 + Commensals 33 + Natural checks 34 + Parasites 35 +Abundance 36 +Economic considerations 36 + Control 37 +Summary 38 +Bibliography 40 + + +NOTE.--This bulletin, a joint contribution of the Bureau of Biological +Survey and the Arizona Agricultural Experiment Station, contains a +summary of the results of investigations of the relation of a subspecies +of kangaroo rat to the carrying capacity of the open ranges, being one +phase of a general study of the life histories of rodent groups as they +affect agriculture, forestry, and grazing. + + + + +IMPORTANCE OF RODENT GROUPS. + + +As the serious character of the depredations by harmful rodents is +recognized, State, Federal, and private expenditures for their control +increase year by year. These depredations include not only the attacks +by introduced rats and mice on food materials stored in granaries, +warehouses, commercial establishments, docks, and private houses, but +also, particularly in the Western States, the ravages of several groups +of native ground squirrels and other noxious rodents in grain and +certain other field crops. Nor is this all, for it has been found that +such rodents as prairie dogs, pocket gophers, marmots, ground squirrels, +and rabbits take appreciable and serious toll of the forage on the open +grazing range; in fact, that they reduce the carrying capacity of the +range to such an extent that expenditures for control measures are amply +justified. Current estimates place the loss of goods due to rats and +mice in warehouses and stores throughout the United States at no less +than $200,000,000 annually, and damage to the carrying capacity of the +open range and to cultivated crops generally by native rodents in the +Western States at $300,000,000 additional; added together, we have an +impressive total from depredations of rodents. + +The distribution and life habits of rodents and the general +consideration of their relation to agriculture, forestry, and grazing, +with special reference to the carrying capacity of stock ranges, is a +subject that has received attention for many years from the Biological +Survey of the United States Department of Agriculture. As a result of +the investigations conducted much has been learned concerning the +economic status of most of the more important groups, and the knowledge +already gained forms the basis of the extensive rodent-control work +already in progress, and in which many States are cooperating with the +bureau. If the work is to be prosecuted intelligently and the fullest +measure of success achieved, it is essential that the consideration +largely of groups as a whole be supplemented by more exhaustive +treatment of the life histories of individual species and of their place +in the biological complex. The present report is based upon +investigations, chiefly in Arizona, of the life history, habits, and +economic status of the banner-tailed kangaroo rat, _Dipodomys +spectabilis spectabilis_ Merriam (Pl. I). + + +INVESTIGATIONAL METHODS. + +Some 18 years ago (in 1903) a tract of land 49.2 square miles in area on +the Coronado National Forest near the Santa Rita Mountains, Pima County, +southern Arizona, was closed to grazing by arrangement between the +Forest Service and the Agricultural Experiment Station of the University +of Arizona. Since that time another small tract of nearly a section has +been inclosed (Griffiths, 1910, 7[1]). This total area of approximately +50 square miles is known as the United States Range Reserve, and is +being devoted to a study of grazing conditions in this section and to +working out the best methods of administering the range (Pl. II, Fig. +1). + +For some years an intensive study of the forage and other vegetative +conditions of this area has been made, the permanent vegetation quadrat, +as proposed by Dr. F. E. Clements (1905, 161-175), being largely +utilized. During the autumn of 1917 representatives of the Carnegie +Institution and the Arizona Agricultural Experiment Station visited the +Reserve and were impressed with the evidence of rodent damage to the +grass cover. The most conspicuous appearance of damage was noted about +the habitations of the banner-tailed kangaroo rat (_Dipodomys +spectabilis spectabilis_ Merriam), although it was observed also that +jack rabbits of two species (_Lepus californicus eremicus_ Allen and _L. +alleni alleni_ Mearns), which were very abundant in some portions of the +reserve, were apparently affecting adversely the forage conditions in +particular localities. Accordingly, the Biological Survey, the +Agricultural Experiment Station of the University of Arizona, the +Carnegie Institution of Washington, and the U. S. Forest Service have +undertaken a study of the relation of the more important rodents to the +forage crop of the Range Reserve in Arizona. + +The present paper is a first step in this larger investigation.[2] In +this work the authors have made no attempt to deal with the taxonomic +side of the kangaroo rat problem. It is not unlikely that intensive +studies will show that the form now known as _Dipodomys spectabilis +spectabilis_ is made up of a number of local variants, some of them +perhaps worthy of recognition as additional subspecies. But it is felt +that the conclusions here reached will be little, if at all, affected by +such developments. + +Color descriptions are based on Ridgway's Color Standards and Color +Nomenclature published in 1912. + + [Footnote 1: References in parentheses are to the Bibliography, p. + 40 (the last figure being to the page of the publication). + References to authorities where no citation of literature is + appended relate for the most part to manuscript notes in the files + of the Biological Survey or the University of Arizona Agricultural + Experiment Station.] + + [Footnote 2: In addition to assistance rendered by officials of the + Biological Survey and the University of Arizona, which is hereby + acknowledged, the authors are indebted to the following persons for + helpful suggestions and assistance: G. S. Miller and J. W. Gidley, + of the U. S. National Museum; Dr. Frederic E. Clements and Gorm + Loftfield, of the Carnegie Institution; Morgan Hebard, of the + Academy of Natural Sciences of Philadelphia; James T. Jardine and + R. L. Hensel, both formerly connected with the U. S. Forest Service; + and R. R. Hill, of the Forest Service. They are also indebted to + William Nicholson, of Continental, Ariz., for many courtesies + extended in connection with work on the Reserve.] + + + + +IDENTIFICATION. + + +There are only three groups of mammals in the Southwest having external +cheek pouches. These are (_a_) the pocket gophers (Geomyidæ), which have +strong fore feet, relatively weak hind feet, and short tail, as compared +with weak fore feet, relatively strong hind feet, and long tail in the +other two; (_b_) the pocket mice (_Perognathus_), which are considerably +smaller than the kangaroo rats and lack the conspicuous white hip +stripe possessed by all the latter; and (_c_) the kangaroo rats +(_Dipodomys_). + +[Illustration: FIG. 1.--Range, east of the Colorado River, of _Dipodomys +spectabilis spectabilis_ compared with that of _Dipodomys merriami_. +Cross hatching indicates area of overlapping of the two forms. The range +of _Dipodomys deserti_, not shown on the map, is west of that of +_spectabilis_, and so far as known the two do not overlap.] + +_Dipodomys spectabilis spectabilis_ Merriam requires comparison with +three other forms of kangaroo rats in the same general region, namely, +_D. deserti_ Stephens, of approximately the same size, and _D. merriami_ +Mearns and _D. ordii_ Woodhouse, the last two of decidedly smaller size. +The range of _deserti_ lies principally to the west of that of +_spectabilis_, and the two do not, so far as known, overlap. On the +other hand, _merriami_ and _ordii_, and subspecies, occur over a large +part of the range of _spectabilis_, living in very close proximity to +its burrows; _merriami_ is even suspected of pillaging the stores of +_spectabilis_. The range of _merriami_, however, is much more extensive +than that of _spectabilis_ (Fig. 1), which argues against a definite +ecological dependence or relationship. Separation of the four forms +mentioned may be easily accomplished by the following key: + +_Key to Species of_ Dipodomys _in Arizona._ + +_a^1_. Size much larger (hind foot and greatest length of skull more +than 42 millimeters); tail tipped with white. + + _b^1_. Upper parts dark brownish buffy; tail dark brownish or + blackish with more sharply contrasted white tip; interparietal + broader, distinctly separating mastoids (range in Arizona mainly + southeastern part) =Dipodomys spectabilis.= + + _b^2_. Upper parts light ochraceous-buffy; tail pale brownish with + less sharply contrasted white tip; interparietal narrower, reduced + to mere spicule between mastoids (range in Arizona mainly + southwestern part) =Dipodomys deserti.= + +_a^2_. Size much smaller (hind foot and greatest length of skull less +than 42 millimeters); tail not tipped with white. + + _b^1_. Hind foot with four toes =Dipodomys merriami.= + + _b^2_. Hind foot with five toes =Dipodomys ordii.= + +On account of the small size, _merriami_ and _ordii_ do not require +detailed color comparison with the other two. The general color of the +upperparts of _spectabilis_ is much darker than that of _deserti_; +whereas _spectabilis_ is ochraceous-buff or light ochraceous-buff +grizzled with blackish, _deserti_ is near pale ochraceous-buff and lacks +the blackish. + +The color of the upperparts alone amply suffices to distinguish +_spectabilis_ and _deserti_; but the different coloration of the tail is +the most obvious diagnostic feature. The near black of the middle +portion of the tail, the conspicuous white side stripes, and the pure +white tip make the tail of _spectabilis_ stand in rather vivid contrast +to the pale-brown and whitish tail of _deserti_. + +The dens of the two larger species of _Dipodomys_--_spectabilis_ and +_deserti_--can be distinguished at a glance from those of the two +smaller--_merriami_ and _ordii_--by the fact that the mounds of the +former are usually of considerable size and the burrow mouths are of +greater diameter. On the Range Reserve _merriami_ erects no mounds, but +excavates its burrows in the open or at the base of _Prosopis_, +_Lycium_, or other brush. The mounds of _spectabilis_ are higher than +those of _deserti_, the entrances are larger, and they are located in +harder soil (Pl. III, Fig. 1). The dens of _deserti_ are usually more +extensive in surface area than those of _spectabilis_, and have a +greater number of openings (Pl. III, Fig. 2). + + +[Illustration: PLATE II. FIG. 1.--WINTER VIEW OF AREA INHABITED BY +KANGAROO RATS. + +A water-hole scene on the U. S. Range Reserve at the base of the Santa +Rita Mountains, Ariz., where cooperative investigations are being +conducted to ascertain the relation of rodents to forage. This is +typical of a large section of country occupied by _Dipodomys spectabilis +spectabilis_ and _Dipodomys merriami_. The brush is mesquite +(_Prosopis_), cat's-claw (_Acacia_), and paloverde (_Cercidium_).] + +[Illustration: PLATE II. FIG. 2.--KANGAROO RAT COUNTRY FOLLOWING SUMMER +DROUGHT. + +An area of the U. S. Range Reserve in the autumn of 1918, showing the +result of failure of summer rains. Such a condition is critical not only +for the stockmen but also for kangaroo rats and other desert rodents, +and results in competition between them as to which shall benefit by +what the range has to offer.] + + +[Illustration: PLATE III. FIG. 1.--KANGAROO RAT MOUND (DIPODOMYS S. +SPECTABILIS). + +Typical _Dipodomys s. spectabilis_ mound on the Range Reserve, under +shelter of desert hackberry (_Celtis pallida_). Most dens on the reserve +are located in the shelter of brush plants, the more important being +mesquite (_Prosopis velutina_), cat's-claw (_Acacia_ spp.), and the +desert hackberry. (See also Pl. VIII Fig. 2.)] + +[Illustration: PLATE III. FIG. 2.--KANGAROO RAT MOUND (DIPODOMYS DESERTI). + +Den of _Dipodomys deserti deserti_, showing typical wide, low mound with +numerous entrance holes. This species excavates its den in soft, sandy +soil. The tree is a species of _Dalea_.] + + + + +DESCRIPTION. + + +GENERAL CHARACTERS. + +Size large; ears moderate, ear from crown (taken in dry skin) 9 or 10 +millimeters; eyes prominent; whiskers long and sensitive; fore feet +short and weak; hind feet long and powerful, provided with four +well-developed toes; tail very long, usually 30 to 40 per cent longer +than the body. Cranium triangular, the occiput forming the base and the +point of the nose the apex of the triangle, much flattened, auditory and +particularly mastoid bullae conspicuously inflated. + + +COLOR. + +General color above, brownish buffy, varying in some specimens to +lighter buffy tints, grizzled with black; oblique hip stripes white; +tail with dark-brown or blackish stripes above and below, running into +blackish about halfway between base and tip, and with two lateral side +stripes of white to a point about halfway back; tail tipped with pure +white for about 40 millimeters (Pl. I). Underparts white, hairs white to +bases, with some plumbeous and buffy hairs about base of tail; fore legs +and fore feet white all around; hind legs like back, brown above, hairs +with gray bases, becoming blackish (fuscous-black or chætura-black) +about ankles, hairs on under side white to bases; hind feet white above, +dark-brown or blackish (near fuscous) below. + +Color variations in a series of 12 specimens from the type locality and +points widely scattered through the range of _spectabilis_ consist in +minor modifications of the degree of coloration, length of white tip of +tail, and length of white lateral tail stripes. In general the color +pattern and characters are remarkably uniform. Young specimens, while +exhibiting the color pattern and general color of adults, are +conspicuously less brown, and more grayish. + +There appears to be little variation in color with season. In the series +at hand, most specimens taken during the fall, winter, and spring are +very slightly browner than those of summer, suggesting that the fresh +pelage following the fall molt is a little brighter than is the pelage +after being worn all winter and into the following summer. But at most +the difference is slight. + + +OIL GLAND. + +Upon separating the hairs of the middle region of the back about a third +of the distance between the ears and the rump, one uncovers a prominent +gland, elliptical in outline, with long axis longitudinal and about 9 +millimeters in length. The gland presents a roughened and granular +appearance, and fewer hairs grow upon it than elsewhere on the back. The +hairs in the vicinity are frequently matted, as if with a secretion. In +worn stage of pelage the gland may be visible from above without +separating the hairs. Bailey has suggested that this functions as an oil +gland for dressing the fur, and our observations bear out this view. +Kangaroo rats kept in captivity without earth or sand soon come to have +a bedraggled appearance, as if the pelage were moist. When supplied with +fine, dusty sand, they soon recover their normal sleek appearance. +Apparently the former condition is due to an excess of oil, the latter +to the absorption of the excess in a dust bath. The oil is doubtless an +important adjunct to the preservation of the skin and hair amid the +dusty surroundings in which the animal lives. + + +MEASUREMENTS AND WEIGHTS. + +External measurements include: _Total length_, from tip of nose to tip +of tail without hairs, measured before skinning; _tail vertebræ_, length +of tail from point in angle when tail is bent at right angles to body to +tip of tail without hairs; and _hind foot_, from heel to tip of longest +claw. + +The following are measurements of a series from the U. S. Range Reserve: + + [Transcriber note: Next line was corrected per erratum. The + original text was of the following paragraph (_Averages for 17 + adult females: Total length, 326.4 millimeters_).] + +Average measurements of 30 adult specimens of both sexes: Total length, +326.2 millimeters (349-310); tail vertebræ, 188.4 (208-180); hind foot, +49.5 (51-47); the average weight of 29 adult specimens of both sexes was +114.5 grams (131.9-98.0). + +Averages for 17 adult females: Total length, 326.4 millimeters +(349-310); tail vertebræ, 188.8 (208-179); weight (16 individuals), +113.7 (131.9-98.0); excluding pregnant females, 13 individuals averaged +112.9 grams (131.9-98.0). + +Averages for 13 adult males: Total length, 326 millimeters (345-311); +tail vertebræ, 187.8 (202-168); weight, 116.8 grams (129-100). + +There appears to be no significant difference in the measurements and +weights of males and females, with the possible exception of the +comparison of adult males and adult nonpregnant females. + + + + +OCCURRENCE. + + +GENERAL DISTRIBUTION. + +_Dipodomys spectabilis spectabilis_ is found in southeastern Arizona, in +northwestern, central, and southern New Mexico, in extreme western +Texas, in northern Sonora, and in northern and central Chihuahua (Fig. +1). A subspecies, _D. s. cratodon_ Merriam, has been described from +Chicalote, Aguas Calientes, Mexico, the geographic range of which lies +in central Mexico in portions of the States of Zacatecas, San Luis +Potosi, and Aguas Calientes. + + +HABITAT. + +In the Tucson region _spectabilis_ is typically a resident of the Lower +Sonoran Zone. This is perhaps the principal zone inhabited over its +entire range, but the animal is often found in the Upper Sonoran also, +and in the Gallina Mountains of New Mexico Hollister found it invading +the yellow pine Transition where the soil was dry and sandy and the pine +woods of open character. The same observer found it common in grassy and +weed-grown parks among the large junipers, pinyons, and scattering +yellow pines of the Bear Spring Mountains, N. Mex. Bailey calls +attention to the fact that the animal apparently does not inhabit the +lower half of the Lower Sonoran Zone, as it extends neither into the Rio +Grande Valley of Texas nor the Gila Valley of Arizona. In extreme +western Texas it is common at the upper edge of the arid Lower Sonoran +Zone, and in this region does not enter the Upper Sonoran to any extent. + +In July, 1914, Goldman found this kangaroo rat common on the plain at +4,600 feet altitude, near Bonita, Graham County, Ariz., and noted a few +as high as 5,000 feet altitude on the warm southwestern slopes of the +Graham Mountains, near Fort Grant. Apparently _spectabilis_ reaches its +upper altitude limit in the Burro Mountains, N. Mex., where Bailey has +found it sparingly on warm slopes up to 5,700 feet, and at the western +base of the Sandia Mountains, east of Albuquerque, N. Mex., where dens +occur at approximately 6,000 feet. + +About Tucson it is undoubtedly more common in the somewhat higher +portions of the Lower Sonoran Zone, above the _Covillea_ association, +than elsewhere (Pl. IV, Figs. 1 and 2). A few scattered dens are to be +seen in the _Covillea_ belt, but as one rises to altitudes of 3,500 to +4,000 feet, and the _Covillea_ is replaced by the cat's-claws (_Acacia_ +sp. and _Mimosa_ sp.) and scattered mesquite (_Prosopis_), with the +_Opuntia_ becoming less abundant, kangaroo rat mounds come more and more +in evidence. Here is to be found the principal grass growth supporting +the grazing industry, and the presence of a more luxuriant grass flora +is probably an important factor in the greater abundance of kangaroo +rats, both _spectabilis_ and _merriami_. In this generally preferred +environment the desert hackberry (_Celtis pallida_) is one of the most +conspicuous shrubs; clumps of this species are commonly accompanied by +kangaroo rat mounds. + +In order to ascertain whether the banner-tailed kangaroo rat has any +marked preference for building its mounds under _Celtis_ or some other +particular plant, all the observable mounds were counted in a strip +about 20 rods wide and approximately 4 miles long, an area of +approximately 160 acres, particular note being taken of the kind of +shrub under which each mound was located. Of 300 mounds in this area, 96 +were under _Prosopis_, 95 under _Acacia_, 65 under _Celtis_, 11 under +_Lycium_, 31 in the open, 1 about a "cholla" cactus (_Opuntia +spinosior_), and 1 about a prickly pear (_Opuntia_ sp.). There is +apparently no strongly marked preference for any single species of +plant. While both desert hackberry and the cat's-claws afford a +better protection than mesquite--since cattle more often seek shade +under the latter, and in so doing frequently trample the mounds +severely--it appears that the general protection of a tree or shrub of +some sort is sought by kangaroo rats, rather than the specific +protection of the thickest or thorniest species. + +The following records indicate particular habitat preferences of +_spectabilis_ as noted at different points in its range: + + Occurs on open bare knolls exposed to winds, also on gravelly + places at lower edge of foothills (Franklin Mountains, Tex., Gaut); + here and there over the barest and hardest of the gravelly mesas + (Bailey, Tex., 1905, 147); on open creosote-bush and giant-cactus + desert (Tucson, Ariz., Vorhies and Taylor); on firm, gravelly, or + even rocky soil on the grassy bajada land along the northwest base + of the mountains, either in the open or under _Celtis_, _Prosopis_, + _Lycium_, _Acacia greggii_, or other brush (Santa Rita Mountains, + Ariz., Vorhies and Taylor); mounds usually thrown up around a bunch + of cactus or mesquite brush (Magdalena, Sonora, Bailey); in heavy + soil (Ajo, Ariz., A. B. Howell); loamy soil (Gunsight, Ariz., A. B. + Howell); in mesa where not too stony (Magdalena, Sonora, Bailey); + grassy plain (Gallego, Chihuahua, Nelson); in open valley and high + open plains (Santa Rosa, N. Mex., Bailey); in grassy and weed-grown + parks among the larger junipers, pinyons, and scattering yellow + pines (Bear Spring Mountains, N. Mex., Hollister); on sand-dune + strip (east side of Pecos River, 15 miles northeast of Roswell, N. + Mex., Bailey); among _Ephedra_ patches (San Juan Valley, N. Mex., + Birdseye); in open sandy soil along dry wash (Rio Alamosa, N. Mex., + Goldman); on sides and crests of bare, stony hills (Mesa Jumanes, + N. Mex., Gaut); in open, arid part of the valley and stony mesas + (Carlsbad and Pecos Valley, N. Mex., Bailey); about the edges of + the plains of San Augustine and the foothills of the Datil and + Gallina Mountains, and in the Transition Zone yellow-pine forest of + the Gallina Mountains (Datil region, N. Mex., Hollister); on hard + limy ridges (Monahans, Tex., Cary). + +A. Brazier Howell notes that _spectabilis_ occurs in harder soil than +does _deserti_. This observation is confirmed by others, and seems to +afford a conspicuous habitat difference between the two, for _deserti_ +is typically an animal of the shifting aeolian sands. + +Usually, as on the Range Reserve, the rodents are widely distributed +over a considerable area. Occasionally, as in the vicinity of Rio +Alamosa, N. Mex., as reported by Goldman, they occur only in small +colonies. + + +[Illustration: PLATE IV. FIG. 1.--RANGE CONDITIONS FAVORING KANGAROO RATS. + +View on higher portion of Range Reserve, showing type of country where +_Dipodomys s. spectabilis_ is most abundant. Good growth of grama and +needle grasses in October, following summer growth and before grazing +off by cattle and rodents.] + +[Illustration: PLATE IV. FIG. 2.--RANGE CONDITIONS LESS FAVORABLE TO +KANGAROO RATS. + +View on lower portion of Range Reserve, where _Dipodomys s. spectabilis_ +is less abundant. Vegetation consists principally of _Lycium_, mesquite, +rabbit brush, and cactus, there being very little grass.] + + + + +HABITS. + + +EVIDENCE OF PRESENCE. + + +MOUNDS. + +One traveling over territory thickly occupied by the banner-tailed +kangaroo rat is certain to note the numerous and conspicuous mounds so +characteristic of the species, particularly if the region is of the +savannah type, grassy rather than brushy. These low, rounded mounds +occupy an area of several feet in diameter, and rise to varying heights +above the general surface of the surrounding soil, the height depending +rather more upon the character of the soil and the location of the mound +as to exposure or protection than upon the area occupied by the burrow +system which lies within and is the reason for the mound. + +A den in sandy soil in the open may be of maximum size in area occupied +and yet scarcely present the appearance of a mound in any sense, due +probably both to the fact that the sandy soil will not heap up to such a +height over a honeycomb of tunnels as will a firmer or rocky soil, and +also to its greater exposure to the leveling action of rains and the +trampling of animals. These mounds are in themselves large enough to +attract some attention, but their conspicuousness is enhanced by the +fact that they are more or less completely denuded of vegetation and are +the centers of cleared areas often as much as 30 feet in diameter (Pl. +V, Fig. 1); and further that from 3 to 12 large dark openings loom up in +every mound. The larger openings are of such size as to suggest the +presence of a much larger animal than actually inhabits the mound. Add +to the above the fact that the traveler by day never sees the mound +builder, and we have the chief reasons why curiosity is so often aroused +by these habitations. + +On the Range Reserve the mounds are usually rendered conspicuous by the +absence of small vegetation, but Nelson writes that in the vicinity of +Gallego, Chihuahua, they can be readily distinguished at a distance +because of a growth of weeds and small bushes over their summits, which +overtop the grass. In the vicinity of Albuquerque, N. Mex., Bailey +reports (and this was recently confirmed by Vorhies) that the mounds +about the holes of _spectabilis_ are often hardly noticeable. Hollister +writes that in the yellow-pine forests of the Gallina Mountains the +burrows are usually under the trunk of some fallen pine, both sides of +it in some cases being taken up with holes, there being some eight or +ten entrances along each side, the burrows extending into the ground +beneath the log. In the vicinity of Blanco, N. Mex., Birdseye says that +occasionally _spectabilis_ makes typical dens but more often lives in +old prairie-dog holes (_Cynomys_), or in holes which look more like +those of _D. ordii_. + + +RUNWAYS AND TRACKS. + +Still other features add to the interest in the dwelling places of +_spectabilis_. Radiating in various directions from some of the openings +of the mounds well-used runways are to be seen, some of them fading out +in the surrounding vegetation, but others extending 30, 40, or even 50 +or more yards to neighboring burrows or mounds (Pl. V, Fig. 2; Pl. VI, +Fig. 1). These runways and the entrances to the mounds are well worn, +showing that the inhabitants are at home and are at some time of day +very active. The worn paths become most conspicuous in the autumnal +harvest season, when they stand out in strong contrast to surrounding +grass. One usually finds not far distant from the main habitation one or +more smaller burrows, each with from one to three typical openings, +connected by the trail or runway system with the central den, and these +we have called "subsidiary burrows" (Pl. VI, Fig. 2). These will be +again referred to in discussing the detailed plan of the entire shelter +system. + +Examination of the runways and of the denuded area about a mound +discloses an abundance of almost indecipherable tracks. The dust or sand +is ordinarily much too dry and shifting to record clear footprints, and +there are no opportunities to see footprints of this species recorded in +good impressionable soil. Very characteristic traces of kangaroo rats +may be readily observed in the dust about the mounds, however, and these +are long, narrow, sometimes curving, furrows made by the long tails as +the animals whisk about their work or play. + + +[Illustration: PLATE V. FIG. 1.--CLEARING ABOUT A MOUND. + +A typical clearing about a mound of _Dipodomys s. spectabilis_, showing +the autumnal denudation of the mound and surrounding areas. In this +instance about 30 feet in diameter.] + +[Illustration: PLATE V. FIG. 2.--MOUND AND RUNWAYS. + +A small mound of _Dipodomys s. spectabilis_ in early autumn, showing +runways radiating from the den. Evidences of activity may be noted in +and about the surface of the mound.] + + +[Illustration: PLATE VI. FIG. 1.--RUNWAY OF DIPODOMYS S. SPECTABILIS. + +Well-traveled path leading from the main den, in the foreground, to a +subsidiary burrow (see Fig. 2, below), about 30 feet distant, at +apparent end of runway.] + +[Illustration: PLATE VI. FIG. 2.--SUBSIDIARY BURROW OF DIPODOMYS S. +SPECTABILIS. + +Located at the end of the 30-foot runway shown in Figure 1, above. This +has three openings, two in the foreground and the third a little to the +rear and indicated by an arrow.] + + +SIGNALS. + +If a scratching or tapping sound be made at the mouth of a burrow, even +in the daytime, one is likely to hear a muffled tapping in response, and +this may at times be heard while one is engaged in excavating a mound. +It has a chirring or fluttering quality, described by Fisher as +resembling the noise of a quail flying. Bailey (1905, 148) is of the +opinion that it is used as a signal of alarm, call note, or challenge, a +view which the present authors believe to be correct. During the winter +of 1920-21, however, both Bailey and Vorhies discovered that this sound, +or a very similar one, is made by the rapid action of the forefeet in +digging. On one occasion in the laboratory the sound was given by one of +a pair and was responded to at once by the other, the two being in +separate but contiguous cages. This observation, however, could not be +repeated. (Vorhies MS.) + +One evening, while working in the vicinity of the Burro Mountains, N. +Mex., Goldman heard a kangaroo rat near camp making this thumping noise. +Taking a lantern, he approached the den, very cautiously, until within +10 feet. The kangaroo rat was just outside the entrance of one of its +burrows, and though moving about more or less restlessly at first showed +little fear, and kept up the thumping or drumming at intervals. When +making the noise the animal was standing with the forefeet on the ground +and the tail lying extended. The noise seemed to be made with the hind +feet only, and the vibration of the feet could be seen. The tapping was +kept up for a second or two at a time, the sounds coming close together +and being repeated rhythmically after a very short interval, suggesting +the distant galloping of a horse. After continuing in this way for a +short time, the animal turned quickly about, with its head in the +opposite direction, and began tapping. It appeared to pay little +attention to the light, but finally gave a sudden bound and entered one +of its holes about 4 feet from the one in front of which it had been +standing. + +Vorhies has repeatedly noted when watching for the appearance of a +kangaroo rat at night that this sound invariably precedes the rodent's +first emergence into the open, and often its appearance after an alarm, +though when the storage season has begun and the kangaroo rat is +carrying loads of grass heads or other material into its den, it +regularly comes out without preliminary signaling. Vorhies has also +observed it making the sound while on top of the mound, and certainly +not digging, but was unable to see how it was made. + + +VOICE. + +No data concerning any call notes or sounds other than those described +above are at hand, with the following exception: Price (in Allen, 1895, +213), who studied the habits of the animal in the moonlight, at Willcox, +Ariz., says that a low chuckle was uttered at intervals; and Vorhies has +had one captive female that would repeatedly utter a similar chuckle in +a peevish manner when disturbed by day, and one captive male which, when +teased into a state of anger and excitement, would squeal much like a +cornered house rat. Vorhies has spent many moonlight hours observing +kangaroo rats, but without ever hearing a vocal sound uttered by free +individuals. + + +DAILY AND SEASONAL ACTIVITY. + +The kangaroo rat is strictly nocturnal. An observer watching patiently +by a den in the evening for the animal's first appearance is not +rewarded until darkness has fallen completely, and unless the moon is +shining the animal can hardly be seen. Were it not for the white +tail-brush of _spectabilis_ and its white belly when upright on the hind +legs and tail, one could not as a rule see the animal at all when it +makes its first evening appearance. With the first streak of dawn +activity usually ceases completely and much more abruptly than it began +with the coming of darkness, but on a recent occasion Vorhies observed +that a kangaroo rat which did not appear until near morning remained +above ground until quite light, but not fully daylight. On removal of +the plug from the mouth of a kangaroo rat burrow, one may sometimes see +a fresh mass of earth and refuse shoved into the opening from within. As +often as not, however, even this unwelcome attention does not elicit any +response by day, the great majority of the burrow openings of this +species, as observed by the authors, remaining permanently open. + +The ordinary activities of the kangaroo rat in southern Arizona can +scarcely be said to show any true seasonal variation. The animals are +active all the year in this region, there being neither hibernation nor +estivation, both perhaps being rendered unnecessary by the storage +habit, to be discussed in full later (pp. 15-16), and by the mildness of +the winter climate. On any particular night that the weather is rainy, +or the ground too wet and cold, activity is confined to the interior of +the burrow system, and for this reason one has no opportunity to see a +perfect imprint of the foot in freshly wet soil or in snow. On two or +three of the comparatively rare occasions on which there was a light +fall of snow on the Range Reserve a search was made for tracks in the +snow. At these times, however, as on rainy nights, the only signs of +activity were the pushing or throwing out of fresh earth and food refuse +from within the burrow. This is so common a sight as to be complete +evidence that the animals are active within their dens during stormy +weather but do not venture outside. Trapping has again and again proved +to be useless on rainy nights, unless the rain is scant and a part of +the night favorable, in which case occasional individuals are taken. +These statements apply to the Range Reserve particularly; the facts may +be quite different where the animals experience more winter, as at +Albuquerque, N. Mex., although in November, 1921, Vorhies noted no +indications of lessened activity in that region. + + +PUGNACITY AND SOCIABILITY. + +So far as their reactions toward man are concerned, kangaroo rats are +gentle and make confiding and interesting pets; this is especially the +case with _merriami_. This characteristic is the more surprising in view +of the fact that they will fight each other so readily and so viciously, +and yet probably it is explained in part by their method of fighting. +They do not appear to use their teeth toward each other, but fight by +leaping in the air and striking with the powerful hind feet, reminding +one most forcibly of a pair of game cocks, facing each other and +guarding in the same manner. Sometimes they carry on a sparring match +with their fore feet. Biting, if done at all, is only a secondary means +of combat. When taken in hand, even for the first time, they will use +their teeth only in the event that they are wounded. The jaws are not +powerful, and though the animals may lay hold of a bare finger, with the +apparent intention of biting, usually they do not succeed in drawing +blood. As Bailey says (1905, 148), they are gentle and timid, and, like +rabbits, depend upon flight and their burrows for protection. + +The well-traveled trails elsewhere described (p. 10) indicate a degree +of sociability difficult to explain in connection with their pugnacity +toward each other. While three or four individuals may sometimes be +trapped at a single mound, more than two are seldom so caught, and most +often only one in one night. Trapping on successive nights at one mound +often yields the larger number, yet in some cases the number is +explained by the fact that two or three nearly mature young are taken, +and the capture of several individuals at a single mound can not be +taken to indicate that all are from the one den. Our investigations tend +strongly to the conclusion that only one adult occupies a mound, except +during the period when the young are in the parental (or maternal) den. +In the gassing and excavating of 25 or more mounds we have never found +more than one animal in a den, except in one instance, and then the two +present were obviously young animals. + + +SENSE DEVELOPMENTS. + +Without making special investigations through a study of behavior or +other special methods, one can speak in only general terms regarding +what appear to be the special sense developments of kangaroo rats. The +eyes are large, as is very often the case in nocturnal animals, and when +brought out into the bright light of day the rats perhaps do not see +well. Yet, if an animal leaves a den which is in process of excavation, +and follows one runway, even in bright sunlight, it makes excellent +speed to the next opening, often a distance of several yards. Whether +this is accomplished chiefly by the aid of sight or in large measure by +a maze-following ability, such as experiments have shown some rodents to +have, can not be stated without precise experimentation. Marked ability +to follow a maze would not be at all surprising in view of the +labyrinthine character of the underground passages which make up the +normal habitation. + +When watching beside a mound by moonlight one is impressed with the fact +that the rats possess either a very keen sense of hearing or of sight, +probably both. The very slightest movement or noise on the part of the +observer results, with a timid individual, in an instantaneous leap for +safety, a disappearance into the burrow so sudden as to be almost +startling. All attempts to obtain flashlight photographs at the mounds +were failures, the animal either having gotten completely out of the +field before the light flashed following the pull of the trigger, or +leaving merely an indistinguishable blur on the plate as it went, and +this in spite of carefully hiding the trigger chain behind a screen. A +slight noise accompanying the trigger action gave the alarm in one case, +and in another the length of time of the flash was sufficient for the +get-away. The marvelous quickness of the animal clearly indicates a +remarkably short reaction time. Occasionally a bold individual is +found, as in the case of one which came out repeatedly, even after being +flashed twice in the same night. + +Certain peculiar physical characteristics suggest a relationship to +sense reactions. On these, however, the authors are not prepared to do +more than offer suggestions for future work. The extremely large +mastoids found in kangaroo rats suggest a connection in some way with +special developments of the sense of hearing or of balance. It may be +noted that an intermediate condition between the kangaroo rats and the +majority of rodents in respect to this character is to be found in the +pocket mice (_Perognathus_), which belong to the same family. Herein +lies a field for some interesting experimentation and discovery. + +The small, pointed nose might suggest a not overkeen sense of smell, and +there appears no reason to believe that this sense is particularly well +developed. However, the turbinals are very complex. The vibrissæ are +long and sensitive, and may indicate a special development of the sense +of touch as an adaptation to nocturnal habits and to life in an +underground labyrinth. The long, well-haired tail doubtless serves as an +important tactile organ as well as a balance. + + +MOVEMENTS AND ATTITUDES. + +Movements and attitudes are characteristic. As a kangaroo rat emerges +from the burrow a reason for the relatively large size of the opening is +seen in the fact that, kangaroolike, the animal maintains a partially +upright position. Its ordinary mode of progression is hopping along on +the large hind legs, or, when in the open and going at speed, leaping. +When moving slowly about over the mound, as if searching for food, it +uses the fore legs in a kind of creeping movement. It appears to be +creeping when pocketing grain strewn about, but close observation shows +that the fore feet are then used for sweeping material into the pockets, +reminding one somewhat of a vacuum cleaner. When it assumes a partially +upright position the fore limbs are usually drawn up so closely that +they can be seen only by looking upward from a somewhat lower level than +that occupied by the animal. The slower movements of searching or +playing about the mound are occasionally interrupted by a sudden leap +directly upward to a height of 1-1/2 to 2 feet, often with no apparent +reason other than play. This is, however, a fighting or guarding +movement, though indulged in for play. The play instinct seems to be +well developed, and in evidence on any moonlight night when actual +harvesting operations are not going on. + + +STORING HABITS. + +Probably no instinct is of greater importance to the kangaroo rat than +that of storing food supplies. When a crop of desirable seeds is +maturing the animal's activities appear to be concentrated on this work. +During September, 1919, when a good crop of grass seed was ripening +following the summer rains, a kangaroo rat under observation made +repeated round trips to the harvest field of grass heads. Each outward +trip occupied from 1 to 1-1/2 minutes, while the unloading trip into the +burrow took only 15 to 20 seconds. + +One individual in a laboratory cage, which had not yet been given a nest +box, busied itself in broad daylight in carrying its grain supply into +the darkest corner of the cage. When a nest box is supplied the +individual will retreat into its dark shelter, and will only come forth +after darkness has fallen unless forcibly ejected, but will store the +food supplied. + +In another case an animal escaped while being handled, and sought refuge +behind a built-in laboratory table, where it could not be recovered +without tearing out the table. For four days and nights it had the run +of the laboratory. On the first night of its freedom it found and +entered a burlap bag of grass seed that had been taken from a mound. A +trail of seed and chaff next morning showed that it had been busily +engaged in making its new quarters comfortable with bedding and food. +After four nights of freedom it was captured alive in a trap, and later +it was found that it had moved from the corner behind the table to the +space beneath a near-by drawer, where it had stored about 2 quarts of +the grass seed and a handful of the oatmeal used for trap bait. + + +BREEDING HABITS. + +Observations on breeding habits have consisted mainly in taking records +from the females trapped at all seasons of the year throughout the +course of the investigation, and from examinations made during poisoning +operations, and yet from this source the number of pregnant females +taken or of young discovered is disappointingly small. The records +indicate a breeding period of considerable length, extending from +January to August, inclusive. It is possible that the length of the +period may be increased by a second litter from the earliest breeding +females in summer, but the large percentage of nonpregnant or +nonbreeding animals which occurs throughout the season would indicate a +wide variation in the time of breeding of different individuals. + +Trapping in February and March for the purpose of securing greater +numbers of female specimens, begun with the idea that these months were +most likely to be the breeding months, has invariably yielded an +unsatisfactory number of nonbreeding specimens and males. Unfortunately, +the numbers of females secured in some months were not sufficient to be +significant if worked out in percentages of breeding and nonbreeding +individuals, and this, coupled with the fact that the importance of +recording carefully all nonbreeders was not at first recognized, makes +it impossible to tabulate such information reliably. The total of +females taken in April, for example, is only 3, of which 1 was breeding; +while in June, during the course of poisoning operations, 45 females +were examined, of which 21 were breeding. + +Five breeding females were taken in January, all during the last three +days of the month. One of these was a suckling female, the young of +which were secured alive and were probably at least a week old when +taken. This must have been exceptionally early for young, since of a +number of adult kangaroo rats taken during the first week of January +none have been found to be breeding. Two records from Vernon Bailey are +as follows: May 19-June 8, 1903, young specimen in nest (Santa Rosa, N. +Mex.); June 12, 1889, one female, two embryos (Oracle, Ariz.). + +The considerable proportion (which we believe to be more than 50 per +cent) of nonbreeding females taken during all those months in which +breeding has been found to occur may also indicate an extended period of +breeding, with a small percentage breeding at any one time. This period +also furnishes ample time for the rearing of two litters a year by some +females, but we have no evidence as to the occurrence of two litters. +Young of the year, practically grown, are taken during and after the +month of April. + +The mammae are arranged in three pairs, pectoral, 1/1; inguinal, 2/2. + +Kangaroo rats are among those rodents in which the vagina becomes +plugged with a rather solid material, translucent, and of the +consistency of a stiff gelatine, after copulation. This must occur very +soon after coitus, since in those individuals taken in this condition no +definite evidence of the beginning of development of embryos could be +detected by examination. + +The length of the gestation period of _spectabilis_ is unknown. The +young are born naked, a fact inferred by failure to find any fetus +showing noticeable hair development, and from the conditions observed in +such young as have been seen. A suckling female was taken by Vorhies, +January 31, 1920, and her den immediately excavated in the hope of +securing the young. Two juveniles were found in a special nest chamber +(see p. 30). These were estimated to be perhaps two weeks old. A serious +effort was made to raise the little animals by feeding milk with a +pipette and keeping them warm with a hot water bottle, but they survived +only 10 days, without the eyes having opened. The uneven temperature as +well as the character of the food was probably responsible for their +deaths. On February 3 they were measured and weighed, with the following +results: + +--------------------------------------------------- + | | Measurements (in millimetres). + | Weight |------------------------------- + | (in | Total | Tail | Hind + | grams). | length. | vertebrae. | foot. +---------|---------|---------|------------|-------- +No. 1 | 13.3 | 90 | 38 | 24 +No. 2 | 12.6 | 93 | 38 | 24 +--------------------------------------------------- + +At this stage the young were partially clothed with a coat of fine +velvety fur, more especially on the bodies, the tails being still nearly +naked. The body color was dark plumbeous, just the color of the dark +underfur of the adult, or a shade darker, while the characteristic white +markings of the adult stood out sharply as pinkish-white areas against +the dark background (see Pl. IX, Fig. 2, at p. 32). The proportions were +much as in the adult, except that the tails were relatively much shorter +and the feet relatively longer. + +Only one other record of young is at hand, that by Bailey, who secured +the young after capture of a suckling female at Santa Rosa, N. Mex. In +this case the litter contained only one. This was squeaking when found, +but was not large enough to crawl away. Its eyes and ears were closed, +and its soft, naked skin was distinctly marked with the pattern of the +adult, the colors being as given for the other two. This juvenile lived +only a week. Young less than half grown were not trapped or noted in our +poisoning operations outside the dens. + +Kangaroo rats, if _spectabilis_ be representative, reproduce at a slow +rate as compared with many other small rodents. We have records of 67 +females with embryos or scars showing the number produced, and of the +two litters of young described above. Of the 69 females thus recorded, +15, or 21.7 per cent, had but one offspring each; 52, or 75.3 per cent, +but two each; while only 2 individuals, or 2.9 per cent, had three. +Three young is the maximum litter recorded. This, taken in connection +with the protracted breeding season and lack of sure evidence of the +production of two broods a year, gives a surprisingly low rate of +reproduction, indicating relative freedom from inimical factors. + +Our breeding records for _merriami_ are fewer than for _spectabilis_, +but are very similar in every way so far as they go, both as to the time +of year and number of young. + + + + +FOOD AND STORAGE. + + +_Dipodomys s. spectabilis_ does not hibernate, so must prepare for +unfavorable seasons by extensive storage of food materials. There are +two seasons of the year, in southeastern Arizona at least, when storage +of food takes place, namely, in spring, during April or May, and in +fall, from September to November, the latter being the more important. +For the periods between, the animal must rely largely on stored +materials. Not infrequently a season of severe drought precludes the +possibility of any storage. The summer and fall of 1918 was such a +season on the Range Reserve (Pl. II, Fig. 2). If food stores are +inadequate at such a time the kangaroo rats must perish in considerable +numbers. Fisher found many deserted mounds in the vicinity of Dos +Cabezos, Ariz., in June, 1894, which may be accounted for in this way. +In 1921 Vorhies found all mounds within 4 or 5 miles of Albuquerque, N. +Mex., deserted by _spectabilis_, resulting probably from overgrazing by +sheep and goats during a succession of dry years. In the arid Southwest +natural selection probably favors the animals with the largest food +stores, and it is not surprising that the storing habit has been +developed to a remarkable degree. + +Some stored material is likely to be found at any time of year in any +mound examined, the largest quantity usually in fall and winter, the +smallest in July or August (Table 1, dens 1, 2, 14, and 24). Amounts +found by different observers vary from a few ounces to several quarts or +pecks, and stored materials taken from 22 mounds on the Range Reserve +vary in weight from 5 to 4,127 grams (more than 9 pounds). This is +exceeded by one lot from New Mexico, which totaled 5,750 grams (12.67 +pounds). It is fairly evident that in seasons of scanty forage for stock +the appropriation of such quantities of grass seeds and crowns and other +grazing materials by numerous kangaroo rats may appreciably reduce the +carrying capacity of the range. Studies of cheek-pouch contents and food +stores taken from dens show that the natural food of _spectabilis_ +consists principally of various seeds and fruits, particularly the seeds +of certain grasses. The study of burrow contents has been especially +illuminating and valuable. + +All of the stored material from 22 dens on the Range Reserve and from 2 +near Albuquerque, N. Mex., has been saved and analyzed as to species as +carefully as the conditions of storage would permit. Within the mound +the food stored is usually more or less segregated by plant species, +though the stores of material of any one kind may be found in several +places through the mound, and often the material is mixed. In the latter +case the quantities of the various species can only be estimated, but in +the former the species may be kept separate by the use of several bags +for collecting the seeds, and a fairly accurate laboratory weighing can +be made later. Very frequently, the explanation of this separation of +species lies in the different seasons of ripening, but sometimes where +two species are ripe at the same time near the mound, one is worked upon +for a time to the exclusion of the other. The one kind is often packed +in tightly against the other, but with a very abrupt change in the +character of the material. + +A number of the more interesting and representative results of the +weighing and analyses of burrow contents are presented herewith in +tabular form. The data for each den, or lot, shows in grams the quantity +of stored material removed and the best estimate it was possible to make +of the percentages or weights of the various species. When the weight +was less than 5 grams, the mere trace of the species frequently is +indicated in the following tables by the abbreviation "Tr." + +TABLE 1.--_Analyses of plants stored by _Dipodomys spectabilis +spectabilis_ Merriam, obtained from examination of representative dens +(all except Den 24 from U. S. Range Reserve, near the Santa Rita +Mountains, Ariz.)._ + + +DEN 1. + +February 7, 1918. Burrow typical, located on bank of wash in partially +denuded grass-land, _Bouteloua rothrockii_ and weed type; soil sandy; +burrow photographed in section (Pl. VII, Fig. 1). + + Species stored. Grams. + +Bouteloua rothrockii 2,205 +Bouteloua aristidoides (B. eriopoda and B. rothrockii, Tr.) 1,445 +Plantago ignota 442 +Eriogonum polycladon 35 + ----- + Total 4,127 + +Four species of plants represented in burrow contents (Pl. VII, Fig. 2). +Maximum quantity for single burrow in series of 22 from Range Reserve. + + +DEN 2. + +March 9, 1918. Surroundings overgrazed and partially restored by +complete protection. Red soil, with much coarse rough gravel and stone. + + Species stored. Grams. + +Bouteloua rothrockii (nearly pure) 1,460 +Bouteloua rothrockii (mixed with Aristida spp.) 945 +Boerhaavia wrightii 660 +Bouteloua rothrockii } +Bouteloua aristidoides } 525 +Aristida divaricata } +Aristida bromoides } +Kallstroemia laetevirens Tr. +Heterotheca subaxillaris Tr. +Plantago ignota 15 +Fleshy fungi 10 + ----- + Total 3,615 + +Eight species of plants represented by seeds. One species of fleshy +fungus in addition. + + +DEN 4. + +September 20, 1918. In _Calliandra_ type. Stony or gravelly soil, red, +nearly denuded of grass. + + Species stored. Grams. + +Prosopis velutina 190 +Mollugo verticillata (pure) 90 +Anisolotus trispermus (mixed, but mostly of this genus) 50 +Solanum elaeagnifolium (12 fruits) 2 + Per cent. +Mollugo verticillata (inseparable) 50 } +Bouteloua rothrockii 1 } +Bouteloua aristidoides 10 } +Lepidium lasiocarpum Tr. } +Polygala puberula Tr. } +Ayenia microphylla 2 } +Portulaca suffrutescens 1 } 400 +Aplopappus gracilis Tr. } +Alternanthera repens 1 } +Tridens pulchella 1 } +Plantago ignota 33 } +Panicum hallii Tr. } +Fleshy fungi (puffballs) 2 + --- + Total 734 + +Fifteen species represented in addition to the fleshy fungi. No +perceptible grass growth from the summer rains here, therefore dependent +on a wide variety of scattering plants. + + +DEN 6. + +October 17, 1918. Mixed type, partially denuded, no growth from summer +rains. Sandy soil. + + Species stored. Grams. + +Bouteloua rothrockii (crowns) (heads 1 to 2 per cent) 1,435 +Bouteloua rothrockii (heads and crowns, about 50 per cent of each) 325 +Bouteloua rothrockii (with small percentage of crowns) 315 +Boerhaavia wrightii (with a few grass crowns) 150 +Prosopis velutina 90 +Solanum elaeagnifolium (3 fruits) Tr. + ----- + Total 2,315 + +Four species represented. Count of 100 grams of stored _Bouteloua_ +crowns gives 1,700, or 17 crowns per gram. At this rate there were at +least 27,000 crowns stored in this burrow. If a density of 250 plants to +the square yard be assumed (a high estimate) these crowns represent the +total _B. rothrockii_ on 104 square yards of range surface. Further +examination of the vicinity of this den showed that the surrounding area +was not completely cleared, but was devoid of _B. rothrockii_, while +still having _B. eriopoda_ with crowns undisturbed. + + +DEN 11. + +April 9, 1919. In partially denuded land where good spring growth of +_Eschscholtzia_ was in bloom at time of excavation. Stomach of +_spectabilis_ killed in this burrow contained a mass of fresh but +finely comminuted green material, probably poppy leaves, strongly +colored with yellow from blossoms. No summer growth here in 1918. + + Species stored. Grams. + +Bouteloua rothrockii (crowns) (miscellaneous chaff, etc.) 107 +Eschscholtzia mexicana (buds and flowers) } +Anisolotus trispermus (leaves and pods) } +Gaertneria tenuifolia (leaves) } 10 +Lupinus sparsiflorus (flowers) } +Solanum elaeagnifolium (2 fruits) Tr. + --- + Total 117 + +Six species represented, some only by leaves or flowers and not by +seeds. _Such storage is never in large quantity._ The fresh storage +material was weighed after becoming air dry. This illustrates a late +spring condition, storage running low. + + +DEN 14. + +August 8, 1919. Excellent summer growth all over range. This burrow in +mixed growth, grasses and weeds. + + Species stored. Grams. + +Miscellaneous portions of _green plants_ of mixed species, + _no seeds_ 5 + +Representing minimum for any one of the 22 burrows studied. Active +storage does not begin until September. + + +DEN 16. + +October 17, 1919. In good grass, but mound overrun by a large +_Apodanthera_ vine. + + Species stored. Per cent. Grams. + +Aristida divaricata 90 to 95 } +Chamaecrista leptadenia 10 to 5 } 58 +Bouteloua rothrockii Tr. } +Prosopis velutina 200 +Apodanthera undulata 55 + --- + Total 313 + +Five species represented. Two species, _Apodanthera_, and _Chamaecrista +leptadenia_, new to storage records. Several whole fruits of +_Apodanthera_, about 2 inches in diameter, stored in addition to seeds +alone; seeds of this form not previously noted in burrows, but very +abundant in this one, indicating importance of the factor of +accessibility in storage. + + +DEN 19. + +October 31, November 1, 1919. In good grass. Entire burrow system mapped +(Fig. 2, p. 29). + + Species stored. Per cent. Grams. + +Aristida spp. (probably mostly _divaricata_) 98 } +Eriogonum sp Tr. } +Bouteloua rothrockii 1 } 1,813 +Bouteloua aristidoides 1 } +Panicum sp Tr. } +Prosopis velutina 1,213 + ----- + Total 3,026 + +Five species represented, in addition to those of _Aristida_. Largest +storage of _Prosopis_ found. Mound was near a good-sized mesquite tree. +No storage in subsidiary burrows. + + +DEN 21. + +January 31, 1920. Male trapped here night of January 29, and suckling +female trapped at same place and same opening of mound, night of January +30. Burrow excavated to secure young, which were found in special nest +chamber. + + Species stored. Grams. + +Aristida spp. (intimate mixture of undetermined species) 1,115 +Eschscholtzia mexicana (from spring of 1919) 48 +Opuntia (prickly pear, seeds only, no fruits) 10 + ----- + Total 1,173 + +Three species represented. Prickly pear hitherto found as fruits only. + + +DEN 22. + +January 1, 1921. Rather good grass growth here in summer of 1920. Burrow +typical, sandy soil. Two skulls of former residents unearthed. + + Species stored. Grams. + +Aplopappus gracilis (some B. rothrockii) 1,030 +Astragalus nuttallianus 630 +Bouteloua rothrockii (some A. gracilis) 530 +Sida diffusa 30 +Solanum elaeagnifolium (282 fruits) 53 +Loeflingia pusilla Tr. +Bouteloua aristidoides Tr. +Plantago ignota Tr. +Lupinus sparsiflorus Tr. +Old storage (mostly Bouteloua aristidoides with traces of B. + rothrockii and Aristida divaricata) 60 + ----- + Total 2,333 + +Eleven species represented. First instance of quantity storage of +_Aplopappus gracilis_. First occurrence of _Loeflingia pusilla_ and +_Astragalus nuttallianus_. + + +DEN 24. + +November 8, 1921. On mesa northeast of Albuquerque, N. Mex., near base +of Sandia Mountains. Fair grass growth here during preceding summer. + + Species stored. Grams. + +Sporobolus cryptandrus strictus 5,455 +Salsola pestifer 295 + ----- + Total 5,750 + +Two species represented. The heads of _Sporobolus cryptandrus strictus_ +are retained to a great extent within the leaf sheaths. This +necessitates the cutting of the stems into suitable lengths for +carrying, and the stored material appears to be merely cut sections of +the stems. Close examination, however, discloses the heads within, and +shows that as in other instances seed storage is the end sought. These +pieces are packed beautifully parallel like so many matches, and vary +from a minimum length of 20 to a maximum of 37 millimeters, averaging +about 30. Count of 2 grams of the above _Sporobolus_ material shows that +there are 125 separate cut sections per gram, or a total of +approximately 680,000 pieces in this one lot of storage, indicating a +remarkable activity on the part of the individual rat (Pl. VIII, Fig. +1). + + +[Illustration: PLATE VII. FIG. 1.--DEN EXCAVATED ON RANGE RESERVE. + +Vertical section through Den No. 1, of Table 1 (p. 20), showing the +complex system of burrows, some of them plugged with closely packed +storage (outlined in white), the depth of the den, and the widened +chambers centrally located.] + +[Illustration: PLATE VII. FIG. 2.--CONTENT OF EXCAVATED DEN. + +Storage content of Den No. 1 (Fig. 1, above), showing the separate +species of plants listed in Table 1. The rod is 1 meter long. The large +pile on the left is composed of seed-laden heads of crowfoot grama +(_Bouteloua rothrockii_), the large pile on the right consists of heads +of six-weeks grama (_Bouteloua aristidoides_), the pile of heads in the +center is desert plantain (_Plantago ignota_), and the smallest heap is +composed of buckwheat-bush seeds (_Eriogonum polycladon_).] + + +The number of lots of storage (24) studied in detail, extending as it +does over a period of three years with seasons of varying growth +conditions, is not sufficient to permit the construction of a curve +showing increase and decrease in quantity of stored material with +growing seasons and intervals between; but the results indicate a very +decided increase during the autumn storing season, and continuing large +well into the winter, since some outside material can still be obtained +until midwinter. From about February to April a decrease may be noted, +followed, if the spring growth of annuals be good, by a slight increase; +and we can very nearly predict the general character of the increases +and decreases by the precipitation and consequent growth conditions. + +TABLE 2.--_Quantity of storage per den correlated with time of year and +growth conditions of preceding season (chiefly from United States Range +Reserve near the Santa Rita Mountains, Ariz.)._ + +------------+-----------+-----------+----------- + | | | + Den No. | Date. | Quantity. | Preceding + | | | season. + | | | +------------+-----------+-----------+----------- + | 1918. | _Grams._ | + | | | + 1 | Feb. 7 | 4,127 | Good. + 2 | Mar. 9 | 3,615 | Do. + 3 | July 25 | 401 | Poor. + 4 | Sept. 20 | 734 | Do. + 5 | Sept. 21 | 2,520 | Do. + 6 | Oct. 17 | 2,315 | Do. + 7 | Dec. 20 | 1,247 | Do. + | | | + | 1919. | | + | | | + 8 | Feb. 7 | 1,600 | Do. + 9 | Mar. 13 | 370 | Do. + 10 | Apr. 7 | 180 | Do.[3] + 11 | Apr. 9 | 117 | Good.[3] + 12 | May 7 | 298 | Do.[3] + 13 | May 11 | 1,590 | Do. + 14 | Aug. 8 | 5 | Good. + 15 | Sept. 4 | 151 | Do. + 16 | Oct. 17 | 313 | Do. + 17 | Oct. 18 | 583 | Do. + 18 | Oct. 25 | 3,410 | Do. + 19 | Nov. 1 | 3,026 | Do. + 20 | Dec. 13 | 2,816 | Do. + | | | + | 1920. | | + | | | + 21 | Jan. 31 | 1,173 | Do. + | | | + | 1921. | | + | | | + 22 | Jan. 1 | 2,333 | Fair. + 23[4] | Nov. 7 | 1,685 | Good. + 24[4] | Nov. 8 | 5,750 | Do. + | | | +------------+-----------+-----------+----------- + + [Footnote 3: Changing from poor summer season of 1918 to excellent + spring growth of 1919.] + + [Footnote 4: From near the Sandia Mountains, N. Mex.; others from + United States Range Reserve, near the Santa Rita Mountains, Ariz.] + +In presenting Table 2, showing quantity of storage per burrow correlated +with the time of year and the character of the preceding growing season, +the fact may be emphasized that the growing seasons in southern Arizona +are two in number--early spring and midsummer. The spring season is the +less important, the plants consisting chiefly of a variety of small +annuals, while the important range grasses make their chief growth and +head out almost exclusively in the July-August rainy season. It may be +noted also that the actual increases in storage appear somewhat after +the growth period proper, since storing does not get well under way +until the seed crop is mature. The banner-tailed kangaroo rat shows a +marked adaptability to different foods available in the neighborhood of +its burrows. It must, perforce, adapt itself and its storage program to +the food that it can get, and this varies enormously with the climatic +conditions of successive seasons. The large numbers present in suitable +localities clearly indicate that the animal is successful in meeting the +changing and sometimes extremely adverse conditions of its environment. + + +[Illustration: PLATE VIII. FIG. 1.--CONTENT OF DEN EXCAVATED IN NEW MEXICO. + +Storage content of Den No. 24, of Table 1, from Sandia Mountains, N. +Mex. This is the largest lot of storage taken in the course of the +investigations. The larger pile consists wholly of a valuable grass, +_Sporobolus cryptandrus strictus_: the smaller of Russian thistle +(_Salsola pestifer._)] + +[Illustration: PLATE VIII. FIG. 2.--GROWTH FOLLOWING ELIMINATION OF +KANGAROO RATS. + +The same mound as shown in Plate III, Figure 1, after three years of +protection, the rodents having been killed out. Nearly as good grass +recovery following poisoning operations occurred in the single excellent +season of 1921.] + + +At times, more especially in the seasons of active growth, some of the +green and succulent portions of plants are eaten. This was very +noticeable in the spring of 1919, when a most luxuriant growth of +Mexican poppy (_Eschscholtzia mexicana_) occurred. Stomachs at this time +were filled with the yellow and green mixture undoubtedly produced by +the grinding up of the buds and flowers of this plant. Small caches of +about a tablespoonful of these buds were also found in the burrows at +this time. Occasionally in spring one may find a few green leaves of +various plants, _Gaertneria_ very commonly, tucked away in small pockets +along the underground tunnels, indicating that such materials are used +to some extent. As has been shown in detail, however (Table 1), the +chief storage, and undoubtedly the chief food, consists of air-dry +seeds. + +The character of the storage, the absence of rain for months at a time +in some years, and the consequent failure of green succulents show that +without doubt _spectabilis_ possesses remarkable power, as to its water +requirements, of existing largely if not wholly upon the water derived +from air-dry starchy foods, i.e., metabolic water serves it in lieu of +drink (Nelson, 1918, 400), this being formed in considerable quantities +by oxidation of carbohydrates and fats (Babcock, 1912, 159, 170). During +the long dry periods characteristic of southern Arizona, no evidence +that the animal seeks a supply of succulent food, as cactus, is found; +and if it may go for two, three, or six months without water or +succulent food, it is reasonable to suppose that it may do so +indefinitely. In the laboratory _spectabilis_ ordinarily does not drink, +but rather shows a dislike for getting its nose wet. During the periods +of drought the attacks upon the cactuses by other rodents of the same +region, as _Lepus_, _Sylvilagus_, _Neotoma_, and _Ammospermophilus_, +become increasingly evident. The list of plant species thus far found +represented in the storage materials of _spectabilis_ on the Range +Reserve is shown in Table 3. + +TABLE 3.--_List of all plant species found in 22 dens of _Dipodomys +spectabilis_ on the United States Range Reserve, near the Santa Rita +Mountains, Ariz., with approximate total weights._ + + GRASSES. + Grams. +Aristida bromoides (six-weeks needlegrass) 536 +Aristida divaricata (Humboldt needlegrass) 9,412 +Aristida scabra (rough needlegrass) 344 +Bouteloua aristidoides (six-weeks grama) 3,093 +Bouteloua radicosa (grama) 1,269 +Bouteloua eriopoda (black grama) Tr. +Bouteloua rothrockii (seeds, 8,495; crowns, 3,517 grams) + (crowfoot grama) 12,012 +Festuca octoflora (fescue grass) 70 +Panicum arizonicum (Arizona panic-grass) 11 +Panicum hallii (Hall panic-grass) Tr. +Pappaphorum wrightii Tr. +Tridens pulchella Tr. +Valota saccharata Tr. + + OTHER PLANTS. + +Alternanthera repens Tr. +Anisolotus trispermus (bird's-foot trefoil) 186 +Aplopappus gracilis 1,030 +Apodanthera undulata (melon loco) 55 +Astragalus nuttallianus (milk vetch) 630 +Ayenia microphylla Tr. +Boerhaavia wrightii 885 +Chamaecrista leptadenia (partridge pea) 5 +Echinocactus wislizeni (visnaga) 5 +Eriogonum polycladon 35 +Eschscholtzia mexicana (Mexican poppy) 250 +Gaertneria tenuifolia (franseria) Tr. +Collomia gracilis (false gilia) Tr. +Heterotheca subaxillaris Tr. +Kallstroemia laetevirens Tr. +Lupinus sparsiflorus (lupine) Tr. +Martynia altheaefolia (small devil's-horns) 12 +Mollugo verticillata (carpetweed) 324 +Oenothera primiverus (evening primrose) 15 +Opuntia discata (prickly pear) 15 +Loeflingia pusilla Tr. +Lepidium lasiocarpum (peppergrass) Tr. +Plantago ignota (plantain) 818 +Polygala puberula (milkwort) Tr. +Portulaca suffrutescens (purslane) Tr. +Prosopis velutina (mesquite) 1,570 +Sida diffusa (spreading sida) 30 +Solanum elaeagnifolium (742 fruits) (trompillo, prickly solanum) 156 +Puffballs and fleshy fungi (undetermined) 12 + + Total species, exclusive of fungi, 41. + +It will be seen from Table 3 that while a large number of species of +plants are represented in the totals from so many dens, a majority of +them are of very minor importance, and that the seeds of grasses are the +principal storage and probably therefore the principal food material. +Six of the most important species of grasses (disregarding species +furnishing less than 5 grams) comprise 85.6 per cent of the total weight +of storage from 22 dens. Crowfoot grama (_Bouteloua rothrockii_) stands +first in quantity in the total, forming 39.4 per cent of all stored +material, 46 per cent of the six important grasses, and 45 per cent of +all grasses. The largest amount of storage of any one species of grass +in any one den on the Range Reserve also is of this species, 2,205 +grams[5] (Table 1, den 1, p. 20, and Pl. VII, Fig. 2). This is exceeded +by a dropseed grass, _Sporobolus cryptandrus strictus_, which amounted +to 5,455 grams in a lot from Albuquerque, N. Mex. (Table 1, den 24, and +Pl. VIII, Fig. 1). + + [Footnote 5: This amount of dry grama grass seed (heads) amounts to + approximately a bushel.] + +Of the species other than grasses found stored in these dens, mesquite +beans (_Prosopis velutina_) are most important both by weight and number +of dens containing them. The total for the 22 Range Reserve dens is +1,570 grams, or 35.9 per cent of the seeds other than grasses, but only +5.1 per cent of the total storage. In bulk mesquite beans do not loom up +large, as they are probably the heaviest material stored. Sections of +pods which must have been dragged into the burrows are found, some of +them certainly being much too long for carriage in the pouches. The +species of plant other than grass found in the largest quantity in any +one den, however, was _Aplopappus gracilis_, not recorded in quantity +from any den until the excavation of the twenty-second, and then found +in a very large bulk of soft, fluffy material, with most of the seeds +separated from the heads, and weighing 1,030 grams (Table 1, den 22). + +Any of the food materials above listed are likely to be found in the +cheek pouches, while in addition such extraneous matter as stones and +feces have also been found. All species of plants stored are accessible +in the immediate vicinity of the mound, and when any particular plant is +found seeding in abundance in the vicinity of the den it is likely to be +represented in the storage. Usually the animals can be readily trapped +with almost any kind of grain bait, as oats, rolled oats, rolled barley, +and wheat; and nut meats also are attractive, though we have no record +of the storing of any true nut in the dens, such not being available in +the range of the animal on the Range Reserve. + +The following plants not represented in the list stored by the kangaroo +rat on the Range Reserve have been found in the cheek pouches or mounds +of _spectabilis_ in other localities: + + _Amaranthus palmeri_, _Sesuvium portulacastrum_, and _Atriplex + wrightii_ (alluvial soil of Santa Cruz Valley, Continental, Ariz., + Bailey). + + Cut leaves and stems of a small sagebrush (Franklin Mountains, + Tex., Gaut). + + _Gutierrezia_ heads (San Juan Valley, N. Mex., Birdseye). + + _Verbesina enceliodes_, _Portulaca oleracea_, _Bouteloua gracilis_, + and _Munroa squarrosa_ (Rio Alamosa, N. Mex., Goldman). + + Tops of buds of _Artemisia filifolia_ (Mesa Jumanes, N. Mex., + Gaut). + + Tumbleweed (_Amaranthus graecizans_), Russian thistle (_Salsola + pestifer_), _Munroa squarrosa_, and _Sporobolus cryptandrus + strictus_ (Sandia Mountains, Albuquerque, N. Mex., Vorhies). + + + + +BURROW SYSTEMS, OR DENS. + + +The burrow system, or den, in which _spectabilis_ stores its caches of +food materials, has its nest, and remains throughout the hours of +daylight is a complicated labyrinth of tunnels. Ejection of refuse and +soil from this retreat builds up the mound frequently referred to. These +mounds are, as Bailey says, characteristic of the species, and are as +unmistakable as muskrat houses or beaver dams, and as carefully planned +and built for as definite a purpose--home and shelter. They are, +furthermore, the most notable of all kangaroo rat dwelling places +(Nelson, 1918, 400). They range in height from 6 inches to approximately +4 feet and from 5 to 15 feet in diameter. + +The mound is built up not only through the cleaning out of chaff and +other food refuse, but through extension and modification of the +tunnels; old tunnels, entrances, and caches of musty food material are +from time to time closed up and others excavated, repair and rebuilding +being especially necessary after the collapse of portions of the den as +a result of heavy rains or trampling by cattle. Ejected material is most +commonly simply thrown out fan-wise from the openings, without much +apparent effort to add to the height of the mound. + +There are usually from 6 to 12 entrance holes in each mound opening into +the subterranean burrow system, each hole from 4 to 5-1/2 inches in +diameter. These holes are nearly all situated a little above the surface +of the surrounding soil, and as Price has suggested (in Allen, 1895, +213), this is doubtless a wise provision against flooding, as torrential +rains sometimes occur in the kangaroo rat country. + +Both Bailey and Nelson state that as a rule several of the holes are +closed with sand or miscellaneous earth and old storage material during +the daytime, but our observations on the Range Reserve are that such +closing is only occasional. Many occupied dens have not a single +opening closed. Further, night observations disclose that the inhabitant +of the mound will appear from some one of the two or three most-used +openings when night falls, and not necessarily from one which has been +closed by day. Recently an opening closed one day was observed in use +during the night, but was left open all the next day. + +In attempting to determine whether there exist similarities of plan or +system in the dens, it was considered advisable to map them with some +degree of accuracy. This we were enabled to do by laying off a square +about a given mound, 2-1/2 or 3 meters each way, and subdividing it into +a series of small squares of half a meter on each side by drawing +cross-lines on the surface of the ground over the top of the mound. One +person then did the digging and exploring of the tunnels, as to +direction and depth, while the other noted the results on coordinate +paper (Figs. 2 and 3); the proper excavation and mapping of one of these +workings occupied from four to eight hours for the two. + +[Illustration: FIG. 2.--Diagram of a typical den of _Dipodomys +spectabilis spectabilis_. Double shading indicates where one portion of +tunnel lies above another and solid black a three-story arrangement; +_A_, _B_, _C_, etc., active openings to surface; figures without arrows, +depths in centimeters to tunnel roofs; figures with arrows, tunnel +widths in centimeters; _N._ nest chamber; _S_, storage; _OS_, old +storage; _Y_, probably an old nest chamber; _Z_, old, unused, or +partially plugged openings.] + +While there is greater complexity in the larger, and probably older, +mounds than in the smaller, all are extremely complicated and can only +be described as labyrinthine in character. The tunnels wind about +through the mound, rising and falling in vertical depth, +intercommunicating frequently, but with occasional cul-de-sacs, and in +places expanding into chambers, of which there may be three or four +large ones. The stored materials are found in some, but not necessarily +all, of these chambers, and may also occupy considerable lengths of +ordinary tunnel, especially when the quantity present is large. Small +evaginations of the tunnels frequently contain lesser caches, and it is +in such pockets that bits of fresh material are placed during a growing +season, or that grain supplied the previous night for bait is usually +found. + +The main masses of storage are most often found centrally located at +depths of from 15 to 57 centimeters, although at times one may find a +cache near the periphery of the system and as near the surface as 2 or 3 +centimeters. In the latter case the materials are subject to wetting +from rains, and consequent spoilage. + +The major portion of the whole tunnel system is within about 50 +centimeters of the surface of the mound, but usually some one branch +tunnel goes to somewhat greater depth, and this is likely to be the one +containing the nest; this is also likely to extend toward or beyond the +periphery of the main system, and always ends blindly. Such a one, from +which two young were taken on January 31, 1920, was at a depth of about +65 centimeters, and about 1-1/2 meters beyond the periphery of the mound +itself. + +The individual tunnels average about 8 centimeters in height, and about +11 centimeters in width, though the variation, especially in width, is +considerable. The expansions mentioned as being the chief places of +storage are from 15 to 25 centimeters in diameter, and may or may not +involve a considerable increase in height. They are frequently located +at junction points of two or more branches of the tunnel system. + +The nest cavity is a chamber of approximately spherical shape and from +17 to 23 centimeters in diameter. Chambers of this character were +observed and noted as "old storage" in a number of cases. They were +sometimes cut off from the rest of the habitation, and at first were +supposed to contain abandoned musty storage. As experience in excavating +and interpreting results has been gained we have concluded that these +chambers in fact represent abandoned nests. + +[Illustration: FIG. 3.--Diagram of the system of surface runways and +subsidiary dens of _Dipodomys spectabilis spectabilis_. The underground +tunnels of the main den were too complicated to illustrate on this +scale, being very similar to those of Figure 2. The underground tunnels +of the subsidiaries are shown in solid black. Some runways fade out in +the grass in a manner that can not be indicated in a line drawing.] + +Bailey gives the dimensions of nest chambers observed in New Mexico as +about 6 by 8 inches to 8 by 10 inches. The nest is composed of finer, +softer, and more chaffy material than the regular storage. The chaff +refuse from the food probably contributes largely to it, though some +leaves of grasses not stored for food may also be found, and a nest, +especially the one in use, may be distinguished, if excavating is +carefully done, by the distinct cavity about the size of a fist in its +interior (Pl. IX, Fig. 1). One may sometimes find this cavity distinctly +warm from the recent presence of the inhabitant. + +The walls or partitions between the chambers and tunnels are in places +surprisingly thin, and it is no wonder that one is almost certain to +break through in stepping on a mound, since the whole is a honeycomblike +structure of from two to four stories in vertical plan, as shown by the +transect of a mound in Plate VII, Figure 1. As Bailey writes, these +partition walls are a mixture of earth and old food and nest material +discarded years ago, resembling the adobe walls of the Mexican houses +built of chopped earth and straw. This is the result of the continual +ejection of refuse and earth as before mentioned, combined with the +caving action of rains and disturbances from larger animals. + +Apparently there are no special pockets for deposit of feces in +_Dipodomys_ burrows; such matter may be found throughout the den, and is +more or less mixed with the food refuse which carpets practically the +entire tunnel system. The nest and food stores are, however, clean and +neat, the droppings being dry and, though present on the floor of a +storage chamber, not actually mingled with the food. Evidently the +animal does not clean up the floor litter before storing food material. + +The entire system for any one den seems to consist not only of the +burrows within the mound itself, as described, but of those small +outlying ones which we have referred to as subsidiary burrows. These are +two to four in number, and are connected with the main mound by the +runways already mentioned. They often seem to be way stations on the +runways connecting main mounds, and there is seldom any mound of earth +whatever in connection with them. One entire den system, the home mound +and three subsidiaries, was mapped after being excavated (Fig. 3), all +having been carefully gassed with carbon bisulphide. The subsidiaries +were simple and contained no storage. Two of them were shallow, while in +the third a depth of 48 centimeters was reached. They appear to be +merely places of refuge, though the well-worn trails connecting them +with the main mound indicate regular use. These runways are conspicuous +on the Range Reserve, and are apparently characteristic of mounds +throughout the range of the animal. Dwellers in different mounds must +have rather extensive social contacts, notwithstanding the enmity of +individuals toward each other in captivity. The main mound, in this +instance very complicated, was in one place three stories high, and we +have found as many as four utilized stories; but as a rule there are two +or three only. + +Since collapses are rather frequent during rainy seasons, aside from the +trampling previously referred to, the kangaroo rats, where abundant, +as on the Range Reserve, may well be a factor in increasing soil +porosity and fertility; for in the course of time they probably have +succeeded in plowing and cultivating the whole surface layer of the +soil. They may thus be a factor in ecologic succession, tending to +improve the character of the soil and adapt it to another stage. + +Doubtless their own workings afford the only shelter the animals know. +In the course of our digging in one mound, the occupant, an adult male, +did not forsake the den until the excavation was three-fourths +completed; and even then it did not leave by a burrow leading away from +our operations, but came toward us, escaped the active efforts of four +individuals bent on its capture, and ran speedily along a used runway +toward another burrow several meters distant. A sack had been stuffed in +the mouth of this, however, and, baffled, the rat then returned to the +original burrow and was captured. Observations on other rats thus driven +from the home mound indicate that they are very familiar with the +runways of the vicinity of the mound and the various subsidiary burrows, +and it is a question whether they need to see clearly to follow these +runs. Apparently they never attempt to escape by forsaking their +well-traveled runways. Tests of the maze-running ability of these +animals by animal-behavior experts would be of extraordinary interest, +in view of the character of the homes which they always inhabit and the +network of runs on the outside. + + +[Illustration: PLATE IX. FIG. 1.--KANGAROO RAT NEST AND YOUNG. + +Nest and the two young, the ordinary number in the litter, of _Dipodomys +s. spectabilis_, taken from den on January 31, 1920.] + +[Illustration: PLATE IX. FIG. 2.--YOUNG OF THE KANGAROO RAT. + +The same young as shown in Figure 1, above. They were probably about two +weeks old, the pelage being short but with the white markings of the +adult; the tails are relatively short and with scarcely any hair.] + + + + +COMMENSALS AND ENEMIES. + + +COMMENSALS. + +It is doubtful whether any animals live in a truly commensal +relationship with _spectabilis_, but of not unfriendly associates there +are a great number. It is the experience of Bailey, corroborated by +observations of Vorhies on living animals, that these kangaroo rats are +active in defending their caches of food, and will even fight +individuals of the same species savagely and to the death. One moonlight +night a strange individual was liberated on a mound. It deliberately +entered one of the openings, but after about two minutes' time made an +exceedingly rapid exit, running rapidly out of sight as if pursued, +though the owner of the home did not appear outside of the burrow. There +can be little doubt that the stranger was precipitately ejected by the +owner. We suspect, though this is a point difficult to prove +satisfactorily, that _merriami_ does not always store food supplies for +itself, but visits the burrows of _spectabilis_ regularly to pilfer the +seed stored therein. The observed facts thus far recorded which suggest +this are that in no _merriami_ burrow examined has a store of food been +found, and also that in trapping for _spectabilis_ on its own +characteristic mounds one catches a large percentage of _merriami_. + +On two separate occasions Vorhies has observed the smaller species +running over the mounds of the larger, actually carrying away the grain +which had been placed to entice the larger when it might appear. (In +these cases the larger species did not put in an appearance until near +morning.) Furthermore, the dens of _merriami_ are often connected by +distinct runways with those of _spectabilis_, indicating much traveling +or visiting. That this is probably not friendly visiting is suggested by +the certainty with which an individual of the larger species will strike +and kill one of the smaller when they are placed together in the same +inclosure. The word "thief" expresses this suspected relationship better +than would the term "parasite." + +It is not to be expected that such obvious shelter retreats as the +mounds of _spectabilis_ should fail to attract the attention of other +animals. We have found a small gecko (_Coleonyx variegatus_), scorpions +of two or three undetermined species, and certain insects (of the Order +Orthoptera) to be very common inhabitants of the dens. With the +exception of the parasitic insects the most common are wingless +locustids (_Ceuthophilus_ spp.) and the peculiar wingless females of a +species of cockroach (_Arenivaga erratica_). These two are seldom absent +when a burrow is excavated, the female cockroaches being abundant, +although the winged males have never been taken in the burrows. + +Cary's observations at Monahans, Tex., and those of others at numerous +localities, combined with our own, show that at various times the dens +furnish protection and shelter for various species of cottontail rabbits +(_Sylvilagus_), ground squirrels (_Citellus_ and _Ammospermophilus_), +wood rats (_Neotoma_), grasshopper mice (_Onychomys_), rattlesnakes +(_Crotalus_), and most of the common lizards. Of these the ground +squirrels _Citellus tereticaudus_ and _Ammospermophilus harrisii_ are +most often noted on the Range Reserve using the dens as a retreat, the +_Ammospermophilus_ seldom being observed to enter any other kind of +burrow. It should be added that the total observations include dens +which have been deserted by their rightful owners. + + +NATURAL CHECKS. + +The enemies of the kangaroo rat are not determined in detail, or as to +relative importance, but the badger (_Taxidea taxus berlandieri_) and +the kit fox, or swift (_Vulpes macrotis neomexicana_), may well be +foremost. Dens which have been deeply excavated by badgers are +frequently seen, and sometimes two or three badger tunnels penetrate one +burrow system. Dens thus despoiled are probably soon reoccupied even if +the original owner is captured, and in the course of a few months the +reworking of the abode obliterates the signs of destruction. + +Droppings of the kit fox show an abundance of bones of small mammals of +kangaroo rat size, among them those of _spectabilis_. + +Bobcats (_Lynx baileyi_) and coyotes (_Canis mearnsi_) probably are a +prejudicial factor. Skunks may sometimes be able to surprise the +kangaroo rats, but probably not often. The western horned owl (_Bubo +virginianus pallescens_), the barn owl (_Tyto alba pratincola_), and +perhaps others may well be among the most feared enemies, but no special +investigation of owl pellets on the reserve has been possible. In 592 +barn-owl pellets from California were found remains of 230 kangaroo +rats, only one other rodent being represented by a larger number +(McAtee, 1921, 258). + +Much more information on enemies is needed. The relatively low rate of +reproduction (see p. 18) indicates comparative freedom from inimical +factors. + + +PARASITES. + +_Dipodomys s. spectabilis_ is regularly infested with a species of flea, +_Ctenophthalmus_ sp. Seldom or never is a specimen taken in reasonably +fresh condition without some of these parasites present on its body, +though of course they desert the body of the host after it becomes cold, +and hence dead specimens left too long may be free from them. The den +conditions are ideal for the breeding of this parasite, because of the +great quantities of fine, dusty, organic refuse littering the tunnels +and furnishing food and refuge for the larvæ. As demonstrated to us by +F. C. Bishopp, of the Bureau of Entomology, a handful of this refuse +taken from the floor of a burrow within arm's length of the entrance is +almost certain to contain these larvæ. + +Less regularly present, perhaps because of its different life history, +is a small tick, _Trombicula_ sp. At times this parasite is very common, +being present on nearly every individual rat, and at other times +specimens are difficult to find; it appears to be more commonly present +in summer and fall than at other seasons, and is found attached chiefly +to the ears. + +No internal parasites have been detected. The nocturnal and fossorial +habits of the animal seem to give complete protection against a form of +parasite which is very common among some other rodents of the Range +Reserve, notably _Lepus_ and _Sylvilagus_. Nearly all rabbits are +infested with "warbles," the larvæ of a species of bot-fly, _Cuterebra_ +(family Oestridae). Other small mammals also are occasionally +parasitized by the _Cuterebra_, but in the handling and examination of +perhaps 200 or more individuals of _spectabilis_ and _merriami_, we have +yet to find a single case of infestation by an oestrid fly. + + + + +ABUNDANCE. + + +One's first impression of a well-occupied _spectabilis_ area is that a +large family must inhabit each den, but, as previously mentioned, we +have gradually been compelled to shift from this conception to the idea +of but a single animal to a mound, except when the young are present. +Therefore a census of the adult kangaroo rat population can readily be +made, simply by counting the mounds. Such a census affords at least a +conservative estimate of the number of adult individuals occupying a +given area. + +The first estimates of abundance on the Range Reserve were from actual +counts of dens on areas measured off for experimental fencing, and gave +the figure of about two mounds to the acre. From time to time rough +estimates were made on different portions of the pastures, and these +checked well with the above. Later still, a careful count showed 300 +mounds on approximately 160 acres (see p. 8), or 1.87 mounds per acre. +Nine areas of 2 acres each, representing different environmental +conditions, were later selected in different portions of the Range +Reserve, and the dens accurately counted. The number of dens per 2 acres +varied from none to a maximum infestation of 12, neither extreme +occurring over large areas. The total number of dens was found to be 43 +on the 18 acres, or an average of 2.38 dens per acre. + +From all these estimates it may fairly be concluded that two mounds, or +two animals, per acre is a conservative estimate for the infestation of +the entire Range Reserve, with the possible exception of small areas at +its upper edges, where the altitude limit of _spectabilis_ is passed. It +is, however, impossible to estimate the area of the State infested with +kangaroo rats, for some large stretches of fine grassland show no +kangaroo rats whatever, while others have more than are present on the +reserve; and we have no estimates of the extent of either type. + + + + +ECONOMIC CONSIDERATIONS. + + +In May, 1894, Fisher found a ranchman at Willcox, Ariz., who complained +more bitterly of the depredations of _spectabilis_ than of those of any +other mammal. + +On the United States Range Reserve the food material appropriated by the +kangaroo rat during good years is inappreciable. There is such an excess +of forage grass produced that all the rodents together make very little +difference. But with the periodic recurrence of lean years, when drought +conditions are such that little or no grass grows, the effects of rodent +damage not only become apparent, but may be a critical factor +determining whether a given number of domestic animals can be grazed on +the area (Pl. VIII, Fig. 2). + +With two kangaroo rats to the acre (1,280 per square mile), there would +be 64,000 animals on the 50 square miles of the Range Reserve. If each +rat stores 4 pounds of grass seeds and crowns and other edible forage +during the season (and in severe seasons we find that more crowns are +stored than under ordinary conditions), a total of 256,000 pounds, or +128 tons, of edible forage are rendered unavailable to stock. In dry +years it is probable that this amount of forage would be of critical +importance. Allowing 50 pounds of food a day for each steer, the forage +destroyed would be sufficient to provide for the needs of one steer for +5,120 days, or for the needs of 14 steers for one year. On a stock ranch +the size of the Range Reserve this might mean the difference between +success and failure. + +It seems not unlikely, therefore, that during seasons of drought the +banner-tailed kangaroo rat, where it is abundant on the grazing ranges +of the Southwest, may be a factor of critical importance in relation to +forage production and carrying capacity. It must be remembered, +moreover, that the stored material consists largely of seeds, so that +this loss is of greater importance than would be the case were it +ordinary forage. Some of the range grasses of this region found in +greatest quantity in the stored material depend in large part, under +certain conditions, upon seed reproduction. Rehabilitation of a depleted +range after severe drought and consequent close grazing and trampling is +retarded by the heavy toll of seed taken by the kangaroo rats. + + +CONTROL. + +Kangaroo rats may be easily eradicated by the use of the poisoned grain +used for prairie-dog control by the Biological Survey and the University +of Arizona Extension Service. This can be obtained by application to the +State representative of the Biological Survey or to the local county +agricultural agent, or may be mixed as follows: + + _Formula for poisoned bait._--Dissolve 1 ounce of strychnine + sulphate in 1-1/2 pints of boiling water. Add 1 heaping + tablespoonful of gloss starch, previously mixed with a little cold + water, and boil until a clear paste is formed. Add 1 ounce of + baking soda and stir to a creamy mass. Add 1/2 ounce of glycerine + and 1/4 pint of corn sirup and stir thoroughly. Pour over 16 quarts + of rolled barley and mix well until every grain is evenly coated. + Allow to dry before using. + + In bushel quantities use as above directed, 2 ounces of strychnine, + 2 ounces of soda, 1 ounce of glycerin, 1-1/4 ounces of starch, + 1-1/2 quarts of boiling water, and 5/8 pint of corn sirup. + + Scatter poison, when the natural food of the kangaroo rat is + scarce, on clean hard places near the holes, 1 quart to 50 holes. + + If powdered strychnine alkaloid is used, prepare the hot starch + paste first. Then sift strychnine and baking soda, previously + thoroughly mixed, into the hot starch paste and stir to a creamy + mass. Proceed as in the above directions with sirup, glycerin, + etc. + + Use this poison within five days after mixing or retain in + air-tight containers. + + _Caution._--All poison containers and all utensils used in the + preparation of poison should be kept _plainly labeled_ and _out of + reach of children_, irresponsible persons, and live stock. + + A spoonful of the poisoned grain scattered about the used entrances + of a mound is sufficient, and prebaiting is not necessary, as with + prairie dogs. + +A word of caution should perhaps be offered in connection with control +measures. As man has come to occupy a greater portion of the earth's +surface, and as he has become more and more the master of his +environment, he has inevitably disturbed the relationships of the birds +and mammals about him, has upset the balance of nature. If he kills the +carnivorous species because of their depredations on game and live stock +he must be prepared to cope with the increased hordes of rodents which +feed on vegetation and on which the carnivorous animals act as a check. +If he destroys the rodents, he may remove the checks on certain noxious +plants or insects. One control measure often necessitates the adoption +of another. + +This is not to argue against control measures, for if our harmful +species were not controlled, agriculture in many sections would be +impossible. Control measures, however, should be scientifically founded +and applied. The indiscriminate slaughter of supposedly harmful species +of birds and mammals in the guise of benefiting agriculture may do far +more harm than good. Many of the species which do some harm do far more +good. The exact status of each suspected species should be carefully +determined through an adequate scientific investigation. If the species +is condemned, sound control measures should be thoroughly applied. + +In grazing districts or in areas devoted to intensive agriculture the +death sentence should probably be passed on the banner-tailed kangaroo +rat. It should be recalled, however, that this is the largest and one of +the handsomest of all its family, and that it is one of the most +characteristic and interesting of all the desert fauna; where extensive +grazing or agricultural operations are not undertaken, therefore, we +feel that the kangaroo rat should be let alone, unless its presence +threatens infestation of valuable agricultural or grazing lands. + + + + +SUMMARY. + + +(1) Kangaroo rats may be separated with ease from all other mammals; the +long tail and short and weak fore feet separate them from the pocket +gophers; the white hip-stripe distinguishes them from the pocket mice. +The decidedly larger size and the white-tipped tail separate _Dipodomys +spectabilis spectabilis_ and _D. deserti_ from _D._ _merriami_ and _D. +ordii_. The darker color and vividly contrasted black-and-white tail of +_spectabilis_ distinguish it from _deserti_. + +(2) _Dipodomys s. spectabilis_ occurs in the open arid country of +portions of the Lower and Upper Sonoran Zones of Arizona, New Mexico, +Texas, Sonora, and Chihuahua. It lives in harder soil than does +_deserti_, and builds more conspicuous mounds. + +(3) There is no evidence of intergradation or hybridization between +_spectabilis_ and _deserti_. + +(4) _Dipodomys s. spectabilis_ is nocturnal; it is gentle, and does not +offer to bite when taken in the hand; is silent for the most part; +active; somewhat sociable with its fellows, but fights in defense of its +food stores; progresses chiefly by leaping; signals by a drumming or +tapping on the ground with its hind feet. + +(5) The breeding season of _spectabilis_ begins in January and continues +into August. Whether more than one litter is raised in a single season +is unknown. The number of young in each litter varies from 1 to 3, +averaging 2. + +(6) _Dipodomys s. spectabilis_ does not hibernate, but provides food +stores, mostly seeds, for use during seasons when food would be +otherwise unavailable. Storage in each den varies in quantity from 5 +grams (about 1/6 ounce) to 5,750 grams (12.67 pounds). Materials stored +include several important forage plants; for example, various species of +_Bouteloua_ and _Aristida_, with _B. rothrockii_ (crowfoot grama) the +most important. Accessibility and abundance of different plants have +much to do with the kinds of storage found. + +(7) The dens of _spectabilis_ are the most notable of all kangaroo rat +dwelling places. They range from 6 inches to 4 feet in vertical height, +and from 5 to 15 feet in diameter. Here the kangaroo rat has its home, +shelter, and food-storage chambers. Within the den is found a tortuous +network of burrows, with many storage and some nest chambers, the whole +arranged so as to be two to four stories high. + +(8) _Dipodomys s. spectabilis_ is not of great economic significance, +except locally, in ordinary seasons. During periods of extreme drought +it may be of critical importance on grazing areas from the standpoint of +the carrying capacity of the range. + +(9) Kangaroo rats are easy to poison by following the same formula as +that used by the Biological Survey for destroying prairie dogs. + +(10) In many places unsuited to extensive grazing or agriculture +_spectabilis_ does no appreciable damage. It is one of the most +interesting of all the rodents peculiar to our Southwestern deserts, and +should not be molested except where it is destructive. + + + + +BIBLIOGRAPHY. + + +ALLEN, J. A. + +1895. On a collection of mammals from Arizona and Mexico, made by Mr. +W. W. Price, with field notes by the collector. Bull. Amer. Mus. Nat. +Hist., vol. 7, art. 6, pp. 193-258. 17 figs. in text. + +BABCOCK, S. M. + +1912. Metabolic water: Its production and rôle in vital phenomena. +Research Bull. No. 22, Univ. Wisconsin Agr. Exp. Station, pp. 159 and +170, March. + +BAILEY, V. + +1905. Biological survey of Texas. North Amer. Fauna No. 25, Biol. Surv., +U. S. Dept. Agr., pp. 222, 16 pls., 24 figs. in text. + +CLEMENTS, F. E. + +1905. Research methods in ecology. Lincoln, Univ. Pub. Co., pp. xvii, +334, 85 figs. in text. + +GRIFFITHS, D. + +1910. A protected stock range in Arizona. Bull. No. 177, Bur. Plant +Ind., U. S. Dept. Agr., pp. 28, 6 pls., 1 fig. in text. + +GRINNELL, JOSEPH. + +1921. Revised list of the species in the genus _Dipodomys_. Journal of +Mammalogy, vol. 2, No. 2, pp. 94-97, May 2. + +MCATEE, W. L. + +1921. Farm help from the birds. In Yearbook of the U. S. Dept. Agr. for +1920, pp. 253-270; unnumbered figs. in text. + +MERRIAM, C. H. + +1890. Description of three new kangaroo rats, with remarks on the +identity of _Dipodomys ordii_ of Woodhouse. In North Amer. Fauna No. 4, +Div. Ornith. and Mamm. (Biol. Surv.), U. S. Dept. Agr., 41-49. + +NELSON, E. W. + +1918. Smaller mammals of North America. Nat. Geog. Mag., vol. 33, No. 5, +pp. 371-493; numerous unnumbered figs. and colored pls. in text. + + +ADDITIONAL COPIES +OF THIS PUBLICATION MAY BE PROCURED FROM +THE SUPERINTENDENT OF DOCUMENTS +GOVERNMENT PRINTING OFFICE +WASHINGTON, D. C. +AT +15 CENTS PER COPY + + + + + + +End of the Project Gutenberg EBook of Life History of the Kangaroo Rat, by +Charles T. Vorhies and Walter P. 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