Chapter 1

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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

WASHINGTON GOVERNMENT PRINTING OFFICE 1922

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_).

_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).

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: