Life History of the Kangaroo Rat

Part 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

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

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). 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).

Part 2

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. 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.

IDENTIFICATION.

There are only three groups of mammals in the Southwest having external cheek pouches. These are (a) the pocket gophers (Geomyidae), 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.

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