A Study of the Golden-Mantled Ground Squirrel (Citellus Lateralis) in a Sagebrush-Grass Community
Brigham Young University BYU ScholarsArchive
Theses and Dissertations
1967-05-01
A study of the golden-mantled ground squirrel (Citellus lateralis) in a sagebrush-grass community
Dennis E. Peterson Brigham Young University - Provo
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BYU ScholarsArchive Citation Peterson, Dennis E., "A study of the golden-mantled ground squirrel (Citellus lateralis) in a sagebrush- grass community" (1967). Theses and Dissertations. 7849. https://scholarsarchive.byu.edu/etd/7849
This Thesis is brought to you for free and open access by BYU ScholarsArchive. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. ',.,..., { ,,,l ptl 2 ··1 1 I A STUDY OF THE GOLDEN-MANTLED GROUND SQUIRREL
(CITELLUS LATERALIS) IN A SAGEBRUSH-GRASS COMMUNITY
A Thesis
Presented to the
Department of Zoology and Entomology
Brigham Young University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
by
Dennis E. Peterson
Mayl967 This thesis by Dennis E. Peterson is accepted in its present form by the Department of Zoology and Entomology of Brigham Young University as satisfying the thesis requirement for the degree of Master of Science.
Date
Typed by Sonja W. Peterson iii
ACKNOWLEDGMENTS
To Dr. C. Lynn Hayward, who served as committee chairman, and Dr. Joseph R. Murdock, committee member, I express sincere appre- ciation for much valuable assistance during the research and preparation of the manuscript for this thesis.
Grateful acknowledgment is also extended to other individuals who contributed to the successful completion of this work: Dr. Kenneth
E. Duke, Duke University, for financial assistance; Dr. Stephen D.
Durrant, University of Utah, for his cooperation, helpful suggestions , and for making available the University of Utah mammal collection;
Dr. D Elden Beck and Selby Herrin, Brigham Young University, for identification of the ectoparasites; Richard H. Weissert and Donald J.
Proctor, U. S. Forest Service, for their generous cooperation. iv
TABLE OF CONTENTS
Page
ACKNOWLEDGMENTS ••• iii
LIST OF TABLES •••••• vi
LIST OF ILLUSTRATIONS .... vii
INTRODUCTION •••••••• ...... 1
REVIEW OF THE LITERATURE 5
Taxonomy • • • • • • • •• 5 Biology and Seasonal Changes • 6 Reproduction and Development •••••• 7 Feeding Habits and Economic Importance 7 Behavior and Natural History •• 9
STUDY AREA •••• 0 • • • • • • • • 10
Location ••••••••• 0 e O O O • O O 0 10 Historical Background 10 Description ••••••• 14
METHODS AND PROCEDURES 21
Field Studies ••••• • • • • • • 0 • 21
0 bservations of Animal Activity 21 Trapping 23 Burrows 25 Vegetation 25
Laboratory Studies • •••••••••••••• 0 • • • • • • • • 2 6
Captive Animals 2 6 Preparation and Study of Preserved Materials 27
RESULTS ...... 29
Trapping ...... 29 Description of _Q_.lateralis Specimens •• 29 0 ther Animals ••••••••••••• 33 Population Density and Dynamics ••••••• 38 V
Page
Activity Periods •• 40 Food and Drink. •• 43 Elimination • • 46 Economic Importance and Relationship With Man • 4 7 Sounds ...... •• 49 Climbing Behavior ••••••••••••• • • 5 0 Home Range ••••••• • • 51 Burrows •••• . . . . 51 Reproduction 59
Growth and Development • • • o O O O O O o • 65
D !SC USS ION . . • . . • . • . • . • . . • . . . . • . • • • ...... o • • • • • 7 7
SUMMARY AND CONCLUSIONS ••••••••••••••••••••••••••• 92
LITERATURE CITED ••••••••••••••••••••••••••••••••••• 9 7 vi
LIST OF TABLES
Table Page
1 Monthly Means and Ranges of Temperatures and Amounts of Precipitation •••••• •• 17
2 Vegetation Cover and Composition Percentages •• 18
3 Body Measurements of Adult C. lateralis •••• • • 3 1
4 Cranial Measurements of Adult _g_.lateralis •• •••• 31
5 Checklist of Principal Vertebrate Species •••. • • 34
6 Ectoparasites Taken From Mantled Squirrel Specimens ••.••. 3 8
7 Dates of Birth and Sizes of Captive Litters •.• • •• 6 3
8 Mean Growth Rates of Young Mantled Squirrels •• 7 5 vii
LIST OF ILLUSTRATIONS
Figure Page
1. Distribution of Citellus lateralis and Allies • 2
2. Aerial View of the South End of Sheep Creek Canyon and Vicinity ..•••• 11
3. Distribution of .Q_. lateralis in Utah 12
4. Study Area •• 15
5. Study Area •• 15
6. Diagram of the Study Area • ••• 2 2
7. Types of Cages and Traps Used in This Study .•••••.•.• 24
8. Burrow Location in the Stream Bank •• . • 53
9. Burrow Location in the Road-cut .••• • ••• 5 3
10. Burrow Location Under a Rock Pile •• 54
11. Burrow Location on Rocky Hillside Near Alfalfa Field •• 54
12. Burrow Location Under Serviceberry Plant •• • ••• 5 5
13. Burrow Location Under Sagebrush • • • 5 5
14. Burrow Location Under Sagebrush ••• • • 5 6
15 . Excavated Burrow •••••••• 56
16. Diagrams of Burrow Patterns . . . 58
17. Diagram of Mating Cage . . . 60
18. New-born .Q_. lateralis . . • . . . 66
19. Three-day-old Litter of _g_.lateralis 66
20. New-born and 16-day-old Squirrels . . . 70
21. A 23-day-old C. lateralis •••••.•• 70 viii
Figure Page
22. Weight Increase Curve for Young _g_.lateralis •. •• 76
23. Comparative Specimens of C. lateralis ••••.• • ••• 7 8 INTRODUCTION
The golden-mantled ground squirrel (Citellus lateralis Say) is a
common inhabitant of the mountainous areas of the Western United States
and Southwestern Canada. It ranges from British Columbia and Western
Alberta south to Central New Mexico, Central Arizona, and to Southern
California. Figure 1 indicates approximately the known distribution of
this group of rodents.
Ci tell us lateralis attains its greatest abundance in open, sunny
coniferous forests, or at the edges of mountain meadows bordered by timber.
The open forest habitat is considered to be characteristic for the species.
However, it is also known to occur sparsely in dense forests, in certain
desert shrub areas of the Great Basin, and has been observed 2,000 feet
above timber line on Mt. Las sen, an isolated volcanic peak in California
(McKeever, 1964).
Despite the fact that _Q_.lateralis occurs so abundantly in Western
North America, relatively little is known regarding many of the aspects of
its natural history. Information is particularly lacking with regard to the
ecology of this species as it occurs in certain marginal habitats, or in
communities apart from the normally preferred open-forest or forest-edge
environment. 2
01 t:::=~~~- scale of miles
39
·7 I---·--·- ·-· / I ! i:=.·=··7 -·-· .I I. I I
Fig· 1. . of Citellus latera 1is, and allies• Distribution d Kelson, 1959) (after Hall an
C. l. an 'zonensis. 1 cinerascens 12. C. 1 • trepidus . 1 • C 1. cary1 . 7. C. 1 · connectens 8 C. • 1· 13. C. l • trinitat1s i 2 • • 1 bernardrnus 9 • c. 1 . latera is 14. C. l • wortman 3. C • • t nurus 4 C. 1. cas a lo • c. l . mitratus 15. C. saturatu~ • 1 certus 11 .• C. l • tescorum 16. C. madrens1s 6.5. c. C. l: chrysodeirus 3
Although it is known that mantled ground squirrels occasionally inhabit portions of the desert shrub communities, little has been done to investigate populations of these animals specifically in this environment.
This study was conducted for the purpose of observing a population of mantled squirrels in a sagebrush-grass community, and to compare these observations with similar ones made by workers who investigated _Q_.lateralis population centers in coniferous forests. Particular emphasis was placed upon observations of daily and seasonal activity patterns, burrowing habits, reproductive behavior, and upon growth and development of the young.
Possible adaptations to the arid, desert environment were also especially noted.
A study of this type is desirable from an economic standpoint. In certain areas of heavy squirrel population, the mantled ground squirrel damages grain crops, is detrimental to reforestation in coniferous forests, and is implicated as a host in the life cycle of possible disease-carrying parasites. On occasion it has become a nuisance in recreational areas by carrying away food supplies of campers. Citellus lateralis was one of several rodent species considered detrimental to the success of a rangeland reseeding project conducted by the U. S. Forest Service near the area chosen for this study. If _Q_.lateralis is a possible destructive nuisance in econom- ically important regions, it would be of value to determine as much as pos- sible concerning its life history and habits so that the most efficient control measures might be utilized.
Owing to the particular location of the study area chosen for this 4
work, it was considered important to determine the subspecies on which the observations were made. The study site is situated between the ranges of two subspecies.
A considerable amount of research by other workers has been con- ducted with regard to hibernation of .Q_. lateralis. Therefore, the subject of hibernation was not investigated in this study. 5
REVIEW OF THE LITERATURE
Taxonomy
The first generally recognized observations of mantled ground
squirrels were noted in Long's (1823) account of an expedition from
Pittsburgh to the Rocky Mountains in 1819 and 1820. S(ciurus). lateralis
Say was the name originally applied to the species at that time. Thomas
Say, a member of that expedition, also recorded information concerning their findings (Say, 1823). Harlan (1825), however, states that some of these animals were observed as early as 1804-1806 at the base of the
Rocky Mountains by Lewis and Clark. Since the time of those early initial observations, mantled ground squirrels have been found throughout the mountainous areas of Wes tern North America.
Merriam (1897) first applied the name Callospermophilus to this group of animals in a subgeneric designation. A short time later (1901) he advanced Callospermophilus to generic rank. For nearly 40 years this was the generic name most frequently used in the literature. Then, in 1938,
Howell revised the classification of the North American ground squirrels, placed this species, along with all of the other ground squirrels, within the more inclusive generic designation of Citellus, and reduced Callospermo- philus again to a subgeneric rank. Thus, Citellus lateralis has come to be 6 the more generally accepted binomen for the species. Some workers (Hall and Kelson, 1959; Hall, 1965), however, still prefer to use the generic designation of Spermophilus, which was first proposed by Cuvier (1825).
There are presently 14 subspecies listed for _g_.lateralis (Howell,
1938; Miller and Kellogg, 1955; Hall and Kelson, 1959). The subspecies initially observed by the Long expedition has been designated as Citellus lateralis lateralis Say. The type locality was established by Merriam (1905) as being on the Arkansas River about 2 6 miles below Canyon City, Colorado.
According to Howell (1938) no type specimen is designated for C. l- lateralis, but the description is apparently based on a specimen taken by Long's expedition and preserved in the Philadelphia Museum (Say, 182 3 :4 7). The study which is reported in the following thesis deals with members of this subspecies.
Biology and Seasonal Changes
In his work on the Sciuridae, and particularly the ground squirrels,
Howell (1938) discussed some biological and economic aspects of _g_.lateralis and each of its subspecies.
A more extensive investigation of the biology of mantled squirrels was reported by Hatt (1927). He made particular mention of two glandular areas; the spatulate area in the skin of the back, which he had first des- cribed in 1926, and the anal glands.
Tevis (1955) conducted a study aimed at gaining a better under- standing of the biology of diurnal rodents which, due to their seed-eating 7 habits, were thought to hinder reforestation. He observed 1,340 chipmunks and mantled squirrels and wrote a detailed report relating to their life histories.
Another study of the biology of mantled squirrels gave special emphasis to the relationship between variation in size of the endocrine glands and popu- lation density, and between size of the glands and reproductive condition and hibernation (McKeever, 1964).
Reproduction and Development
Such factors as the time and length of the breeding season, length of gestation period, litter size, endocrine involvement in the reproductive cycle, and growth rates of the young mantled squirrels were observed by
McKeever (19 65). One of the few works dealing specifically with the development of Sciuridae from the ovarian egg to the establishment of the germ layers was that of Schooley (1934).
Feeding Habits and Economic Importance
Tevis (1952) made extensive investigations of the feeding habits of .Q_. lateralis in Northern California. He found that when a failure of the seed crop of conifers and shrubs occurred, the mantled squirrels turned to hypogeous fungi for food. Later he reported (1953b) that grasses and forbs were the principal spring food, and that during the summer and fall hypo- geous fungi were the most important food item of mantled squirrels. During an extensive outbreak of the caterpillar Nymphalis californica, Tevis (1953a) found that _g_.lateralis ate many of those migrating across the ground. 8
Mrosovsky (19 64) tested the reaction of mantled ground squirrels to an adulterated diet by feeding them sugary and salty foods. He noted that the squirrels ate relatively less of the salty diet during the season in which weight increase occurs. Carleton (19 66) performed a detailed investigation of the food habits of the mantled ground squirrel and the least chipmunk, which are sympatric species in Colorado. He revealed a profound dependence by both species upon the common dandelion for summer food.
Inasmuch as the mantled ground squirrel is closely associated with forested areas, Wahlenburg (1925) and Taylor and Gorsuch (1932) considered them to be an important consumer of conifer seeds. They reported that the mantled ground squirrel was responsible for the complete depredation of yellow pine seedlings. Smith and Aldous (194 7) discussed the large quantities of seeds eaten by other squirrels and chipmunks, but merely mentioned that the mantled ground squirrel is responsible for seed consumption. Tevis (1956) had also stated that _g_.lateralis was a threat to reforestation owing to their seed-eating habits. He had shown previously
(Tevis, 1952), however, that Eutamias townsendii is more detrimental than are other kinds of chipmunks, and that the mantled squirrel, at least in the
Sierra Nevadas, did not gather or eat pine seeds unless they occurred abundantly.
In camping areas, mantled squirrels soon lose their fear of humans, and often become a nuisance by getting into food supplies (Merriam, 1890).
In some areas the mantled squirrel damages grain crops by carrying away the 9 heads of wheat, oats and barley (Birdseye, 1912).
Citellus lateralis is also possibly implicated in the transmission of diseases, particularly Rocky Mountain spotted fever, since they serve as a host for intermediate stages of ticks and other ectoparasites (Birdseye,
1912; Kohls, 1937; Hubbard, 1947; Arthur, 1962).
Behavior and Natural History
Colton (1933) studied the behavior of mantled squirrels in activity wheels and reported that the peak of activity was attained in mid October and was at a minimum in July. Most of the work which has been done with regard to behavioral patterns of mantled squirrels was carried out in the laboratory or possibly in semi-natural conditions. Gordon (193 6, 193 8 and
1943), with his classical approach to behavioral studies under natural conditions, is one of the few who has done any work on the social structure of these animals. Wirtz (1961) followed Gordon's lead in studying behavior and social and community interactions.
Some of the known predators of mantled ground squirrels are weasels
(Follett, 1937; Boyer, 1943), and red-tailed and Cooper's hawks (Hall, 1946).
All of the studies dealing with mantled squirrels were performed with animals from the characteristic coniferous forest habitat. Some workers
(Grinnell and Storer, 1924; Svihla, 1931; Gordon, 1943; Miller and Kellogg,
1955; Olin, 1961; McKeever, 1964) have mentioned that mantled ground squirrels may occur sparsely in the upper edge of the northern desert shrub biome. It is within an isolated section of this biome that the present study was conducted. 10
STUDY AREA
Location
Most of the field observations and trapping for this study were
conducted in an area located at the south end of Sheep Creek Canyon, 9. 5
miles east of Thistle Junction in Utah County, Utah. The area is immediately
north of Highway 6-50, at approximately 39° 58' north latitude and 111° 20' west longitude, and at an elevation of 5,750 feet (Gazeteer of Utah Locali-
ties and Altitudes, 1952 :110). South of the highway is the junction of Sheep
Creek with Soldier Creek. The northern portion of the study area lies within the southern boundary of the Uinta National Forest (Fig. 2). This particular
location places the study area at a position intermediate between two sub-
species of _Q_.lateralis. It is at the southeast corner of _g_.l- castanurus range and at the western limit of _Q_.l• lateralis distribution (Fig. 3).
Historical Background
The past history of the general area of Sheep Creek and surround- ing vicinity has been one of destructive grazing by sheep, cattle, and deer (U. S. Forest Service, 19 64). At the present time much of the vegeta- tion shows the effects of intense grazing by having browse-lines, branched and forked terminal growth of shrubs, and an abundance of non-palatable 11
Fig. 2. Aerial view of the south end of Sheep Creek Canyon and vicinity. 12
,,. 113 112 Ill 110 100 L
25 0 25 50 15 MtLE.5 • Location of the study area ~· 41
0
30 31
3&
i i 31 Jr·-· -··-··-r:·-··-··-·,
------114 113 112 ------~--·---Ill 110 -- IOI
Fig. 3 • Distribution of _g_.lateralis in Utah. (Durrant, 19 52) 1. C. 1. trepidus 2. C. 1. castanurus 3. C. 1. lateralis 13 species. Grazing has occurred in this area since the 1850' s, but since the 187 O's it has been very extensive, and a peak was reached in the late
189 O's for numbers of grazing domestic animals, most of which were sheep.
Most of the range damage was done by the early 1900' s and very little recovery has taken place on much of the area since that time.
The general area was homesteaded in 1899, at which time it was cleared of a thick growth of big sagebrush (Artemisia tridentata) by plowing.
The livestock of early homesteaders and settlers and large herds of sheep from other areas used these lower elevation lands for lambing grounds and early spring grazing. Later, cattle were grazed in common with the sheep in gradually increasing numbers. The use of the Sheep Creek area proper for grazing of sheep was terminated in the 1940' s. Cattle continued to graze from the 1940's until 1962. In 1962, cattle use was also eliminated south of Sheep Creek, although cattle are still trailed through to higher areas in June, and sheep are trailed through during the first part of July.
This area is part of the big game winter range for Utah herd unit
18. The deer population began to increase during the 192 O's and reached its peak in the late 1940' s. The heavy losses during the extreme winters of 1948-49 and 1951-52 substantially reduced deer numbers. Since then, there has been a gradual increase again. In the Tank Hollow area special deer hunts have been held during the past three years in order to keep the deer populations under control. In 1962 there were 203 does taken in the special hunt. 14
In 1939 the U. S. Department of Agriculture purchased much of the land in this location, and has subsequently made numerous efforts toward reclamation of the rangeland. In 1940 approximately 600 acres were re-
seeded to crested wheatgrass (Agropyron desertorum) in a fenced pasture in
Tank Hollow, and it currently supports a good stand of wheatgrass along with reinvading big sagebrush. It was in conjunction with the crested wheatgrass reseeding project in Tank Hollow that the Fish and Wildlife
Service poisoned the area with 1080 grain for rodent control (U. S. Forest
Service, 1964). At that time a number of the mantled ground squirrels in the Tank Hollow area were killed.
Description
The study area is O. 9 mile in length and about O. 2 mile at the widest part. Sheep Creek, which carries water throughout the year, flows
southward through the length of the site. A dirt road, which connects with
Strawberry Reservoir 21 miles to the north, also longitudinally bisects the area. Slopes of the eastern Wasatch foothills rise on either side of the creek and road. Within the boundaries of the area there are some farm buildings and cultivated pasture land (Figs. 4 and 5).
The soil parent material is mostly Green River Formation composed of lacustrine shale and siltstone. Conglomerate outcropping occurs in some areas. Relatively younger alluvial deposits also occur chiefly along the
active stream. The soil itself is generally rocky or gravelly, described as 15
Fig. 4. Study area. Looking northeast into Sheek Creek Canyon from south of Highway 6-50.
Fig. 5. Study area. Looking southwest toward Highway 6-50, which can be seen running horizontally at center of picture. 16 an unconsolidated regolith, although near the stream it is more of a sandy clay loam material.
The climatological data, which are summarized in Table 1, were obtained from the Birdseye weather station located about 14 miles to the southwest at an elevation of 5 , 7 0 0 feet.
The climate of the area is generally characterized by hot, dry summers and cold winters. The prevailing winds are from the southwest.
The length of the growing season is from approximately the last of April to the first of September, with maximum growth obtained by the middle of
July. There is an average total of 115 frost-free days per year with approxi- mately 7 5 consecutive frost-free days, ranging from the middle of June until the first of September. Frost occasionally interrupts this consecutive pattern, although these frosts usually last one night only, are not severe, and are accompanied by high daytime temperatures.
On a long-term basis, the average annual precipitation is about
12 inches; although, as Table 1 indicates, in 1965 there was an unusually plentiful supply. Mr. Dancy, whose farm is located in the study area, reported (personal communication) that a great deal of snow does not accumulate on the ground in the area. The maximum that he recalls is approximately three feet.
The dominant plant species in most of the area is the big sagebrush
(Artemisia tridentata), with several grasses and various other herbaceous forms (Table 2) interspersed among the sage. 17
TABLE 1
MONTHLY MEANS AND RANGES OF TEMPERATURES AND AMOUNTS OF PRECIPITATION
Year Temeerature in Degrees Fahrenheit Precieitation (inches} and Maximum Minimum Rain or Month Mean Range Mean Range Snowfall Melted Snow 19 64 January 30 16-43 1 (-) 24-22 10.54 0.95 February 32 24-45 0 (-) 17-19 4.50 0.45 March 38 25-57 8 (-) 18-27 23.00 1. 25 April 54 41-70 27 20-35 6.30 1.2 8 May 67 44-83 32 19-45 11. 00 1.40 June 74 61-85 39 30-51 1.27 July 88 83-99 41 31-53 0.05 August 84 68-91 42 23-58 0.63 September 74 60-91 28 19-46 0.47 October 71 55-78 21 9-41 0.10 November 43 22-58 15 (-) 6-2 8 4.00 1.30 December 36 12-48 14 (-) 19-36 24.00 3.59 For the year 58 12-99 22 (-) 24-58 83.34 12.74 1965 January 35 22-49 11 (-) 14-35 19.00 2.48 February 36 2-51 9 (-) 13-27 9.00 0.67 March 45 28-65 17 (-) 4-38 11. 00 1.38 April 58 40-76 28 18-39 5.00 1.05 May 64 41-78 31 17-45 3.00 1.42 June 74 64-83 36 29-50 0.79 July 84 76-91 44 35-57 1.93 August 83 64-93 42 24-54 2.58 September 68 45-82 30 15-44 10.00 1.94 October 73 50-84 23 14-32 0 .14 November 55 32-71 21 5-38 8.00 2.53 December 42 28-56 10 (-) 8-25 6.00 1.63 For the year 1966 January 36 21-50 2 (-) 15-22 9.00 0.60 February 37 27-48 3 (-) 18-20 29.00 1.67 March 53 23-72 18 (-) 12-36 6.00 0.49 April 63 44-75 21 (-) 2-31 2.00 0.59 May 74 56"'.'."84 29 21-38 0.69 June(lst half)76 70-83 28 24-33 18
TABLE 2
VEGETATION COVER AND COMPOSITION PERCENTAGES
% Cover % Composition
Trees Juniperus osteosperma 0.5 0.7 Pinus edulis 0.2 0.3
Shrubs Amelanchier utahensis 0.3 0.5 Artemisia tridentata 25.5 37.3 Chrysothamnus nauseosis 8.5 12.4 Rhus trilobata 1.4 2.0 Rosa woodsii 0.2 0.3 Salix sp. 0.1 0.2 Symphoricarpos sp. 0.2 0.3
Grasses Agropyron desertorum 0.5 0.8 A. smithii 0.3 0.4 A. spicatum 2.8 4.0 A. trachycaulum x Setanion hystrix 0.1 0.2 Bromus tectorum 8.6 12.6 Oryzopsis hymenoides 4. 1 6.0 Sporobolus cryptandrus 1.0 1.5
Other Herbs Achillea millefolium 0.3 0.5 Artemisia ludoviciana 0. 1 0.2 Astragalus utahensis 0.2 0.3 Castilleja sp. 0.1 0.2 Chrysopsis villosa 0.3 0.5 Circium undalatus 0.1 0.1 Convolvulus arvensis 0.1 0.1 Cryptantha fulvocanescens 0.7 1.0 Cyanoglossum officinalis 2.4 3.5 Cymopterus longipes 0.2 0.3 Descurainia pinnata 0.2 0.3 Eriogonum sp. 0.2 0.3 Helotropium convolvulaceum 0.1 0.1 Lactuca pulchella 0.1 0.1 Melilotus officinalis 1.9 2.8 19
TABLE 2 (continued)
% Cover % Composition
Other Herbs
Mentha sp. 0.3 0.5 N epeta cataria 0.1 0.1 Oenothera caespitosa 0.1 0.2 0 puntia fragilis 0.2 0.3 Phlox caespitosa 1.5 2.3 Phys aria sp. 0.1 0.2 Rananculus testiculatus 0.2 0.3 Rumex crispus 0.5 0.7 Sisymbrium altissimum 0.1 0.1 Sphaeralcea coccinea 0.2 0.3 Taraxacum offininale 0.7 1.1 Verbascum thapsus 1.4 2.0 20
A few isolated clumps of serviceberry (Amelanchier utahensis) and
squawbush (Rhus trilobata) occupy portions of the lower slopes, while higher on the slopes are scattered junipers (Juniperus osteosperma) and a few pinyon pines (Pinus edulis). In the center of the area are some cultivated fields containing crested wheatgrass and alfalfa. The percentages of cover and
composition of the principal plant species are summarized in Table 2. 21
METHODS AND PROCEDURES
Field Studies
The field work for this study was conducted periodically from
July, 1963 until July, 1966. A total of 280 hours was devoted to field studies. Most of the observations took place during the months of March to August.
OBSERVATIONS OF ANIMAL ACTIVITY
Mantled ground squirrels lend themselves well to field study because of their diurnal and open habits of activity. The field observa- tions were generally made during the periods of mantled squirrel activity outside the burrows. In 1964 and 1966 the field observations began the last of March in order that a determination could be made of the time of emergence from hibernation.
For all field observations of animal activities, a 40-power spotting telescope and 35 x 7 field glasses were extensively used. The study area was divided into seven stations. An outline map of the study area was prepared and locations of observed squirrel activities, trapped animals, and burrow sites were plotted on the map as each observation was made.
The information was subsequently consolidated on a composite map (Fig. 6). 22
...• TANK HOLLOW
STATION 4
STATION 5
, 6 STATION 3 -·
STATION 2
• OBSERVED SQUIRRELS , TRAPPED SQUIRRELS • BURROW STATION BOUNDARY ------HOME RANGE
11111111 ,I 1 0 0.1 MILE N SCALE
FIG. 6. DIAGRAM OF THE STUDY AREA. 23
These data were used to help establish distributional patterns, population densities, and home range.
Observations were also made of other animals present in the area to more completely describe the community and possible community inter- actions. From these observations a checklist of principal vertebrate species was compiled.
TRAPPING
The trapping of squirrels was performed primarily to provide a supply of captive animals which could be taken to the laboratory and studied in more detail, either as live captives or animals from which study specimens could be prepared. Secondarily, the trapping data provided information which was helpful in the determination of population densities and distribution. In view of the principal purpose of the trapping, no attempt was made to place traps in particular patterns throughout the area. Instead, the trapping pro- cedure was the one which most effectively harvested the desired animals.
The traps used for mantled squirrels were 6" x 6" x 19" National wire live traps (Fig. 7). A variety of bait was utilized, including oats, apples, peanut butter, bacon, cheese, bread, and raisins. None seemed particularly more effective than the other.
The most effective means of obtaining squirrels was to place the open end of the trap at the opening of an active burrow, so that when an animal emerged from the burrow it would walk directly into the trap. The 24
Fig. 7. Types of cages and traps used in this study. 25 best time to place the traps was in the early morning shortly before the squirrels emerged from the burrows.
Smaller rodents were trapped for purposes of identification by using museum special snap traps. The traps were placed at ten-foot intervals in trap lines. A total of 25 traps comprised each line.
BURROWS
Assuming that approximately 80 percent or more of a mantled squirrel's lifetime may normally be spent in its burrow, investigation of the burrowing habits received considerable attention in this study. Loca- tions and numbers of burrows were noted throughout the area and ten different burrows were excavated. Measurements and drawings were made of the burrow structures. Photographs were taken of excavated as well as undisturbed burrows.
VEGETATION
Inasmuch as the vegetation is utilized both as food and shelter by the mantled ground squirrels, analysis of the vegetation was made during the seasons when _g__.lateralis was active outside the burrow. Plant specimens were collected and pressed in a standard 12" x 18" plant press so that identification could be made. In addition, a line-point sampling procedure was employed. This consisted of a series of 5 0-foot transect lines within each segment of the study area. The plant species encountered at one-foot intervals along each transect was recorded. Five transects, 26 spaced ten feet apart, were observed for each of the seven segments of the study area. It was possible from these data to determine the percentage of cover and composition of each plant species (Table 2).
Laboratory Studies
CAPTIVE ANIMALS
A total of 16 (seven in 1964 and nine in 19 66) of the animals trapped in the field were maintained alive in captivity for periods of time ranging from three days to 13 months. They were housed in cages in an animal room at a temperature of abou 70°F to 72°F. The cages measured
28 inches across the front, 20 inches from front to back, 13 inches high, and were divided by wire into two compartments (Fig. 7). These compart- ments could be used as two separate cages, or the center partition could be opened to provide a nesting chamber on the one side and a feeding area in the other half. Cotton batting was provided as nesting material in each cage.
Food and water were supplied ad libitum. The food consisted of a variety of items. Dandelion greens generally comprised the bulk of the diet, but were supplemented at various times with such items as sunflower seeds, hampster food, rabbit pellets, laboratory chow pellets, apples, acorns, melon rinds, bread and meat scraps. The water was placed within each cage in open, clear glass finger bowls. This was done so that the drinking behavior could be observed more nearly as it would occur in natural 27 conditions, where an open stream provides the water supply.
Many hours were spent observing activities of the captive animals.
Some of the observations were made from behind a blind so that the animals were not aware of the presence of anyone in the room. Use of the blind made possible, in three instances, observation of the mating behavior of these animals. Observations were usually made without the use of the blind.
The observations generally took place during the months of April through
September.
The growth and development of two litters of squirrels born in captivity were followed carefully. For the first month following birth they were weighed and measured approximately every two days. Thereafter the weights and measurements were determined at one-week intervals. Weights were recorded to the nearest O. I g and measurements to the nearest milli- meter.
PREPARATION AND STUDY OF PRESERVED MATERIALS
The captive animals were periodically sacrificed, at which time they were weighed, measured, and examined for ectoparasites. Any para- sites found were placed into 7 0 percent ethyl alcohol. Study skins and skulls of the squirrels were prepared for future examination. The skulls were measured with calipers to the nearest O .1 mm. Investigation of the internal organs of the squirrels was also made, and reproductive tracts were excised and preserved with Bouin' s preservative. Fleas and mites which were removed from the animals were subsequently mounted on glass 28
slides so that species identification could be made.
Inasmuch as the study area is located near the border between the ranges of .Q__.l- castanurus and C . .J... lateralis, squirrel specimens were
examined to determine if intergradation has occurred in members of this population. Therefore, the study skins and skulls of animals prepared for this study were compared with those present in the mammal collections of
Brigham Young University and University of Utah. More than 3 00 specimens
of mantled squirrels were examined. Skull measurements made by Durrant
(1952) and Howell (1938) were used for comparison. 29
RESULTS
Trapping
A total of 72 live traps, placed primarily during April and May of
1964 and 1966, resulted in the capture of 21 (nine male and 12 female) adult mantled ground squirrels. This was 29 percent trapping success. A total of 15 other rodents were trapped in 64 snap traps during April, May and
June, 19 66, for 2 3 percent success.
Description of C. lateralis Specimens
In the spring pelage of an adult squirrel the top of the head, the nape, and the dorsal surface between the stripes are a mixture of black, grayish white and rufous; medial pair of black stripes greatly reduced or absent; a pair of light stripes a yellowish rusty white and extend from the
shoulder to the hip; outer black stripes well defined and wider than the light stripes but not more than two-thirds as long; flanks and sides of neck deep bright chestnut; upper surface of the feet a pale yellowish rusty color
slightly lighter than eye ring; ventral surface rufous with black bases of hairs showing through; dorsal tail surface mixed black and chestnut with a chestnut border; ventral tail surface chestnut, with black border and chest- nut again outside of black. In the worn and faded pelage of winter and early 30
spring the colors have more of a gray appearance. After molt occurs in July
the top of the head is chestnut. Measurements of adult mantled squirrel
specimens are summarized in Tables 3 and 4.
Five pairs of mammary nipples are present, but they are not equally
spaced. From anterior to posterior they are arranged in the following manner.
The most anterior pair is at the level of the front legs. The second pair is
approximately 23 mm posterior to the first. Then a space of approximately
45 mm separates pairs 2 and 3. The three pairs of posterior nipples (3, 4
and 5) are somewhat clustered together into a space of 30 mm; 15 mm from
3 to 4 and 15 mm between pairs 4 and 5. The fifth pair is only 15 mm from
the urogenital orifice. The milk lines are approximately 2 0 mm lateral of
the midline except at the posterior end where they curve slightly toward the
midline.
Two other external glandular structures were observed in these
animals. Frequently when captive animals were greatly disturbed, three white, flat-topped, straight-sided nipples would protrude from the anus.
A thick, milky substance was extruded from each nipple.
The other glandular area could be most clearly observed when the animal was skinned and the skin reversed. A darkly pigmented, spatulate
shaped area about 40 mm long and 12 mm wide was easily distinguishable in marked contrast to the otherwise light skin surface. This glandular area is situated on the dorsal surface between the shoulders, and a slightly oily fluid is secreted from it.
Compared to the size of its body, a mantled ground squirrel has 31
TABLE 3
BODY MEASUREMENTS OF ADULT .Q_. LATERALIS (in mm)
Total Tail Hind Length Vertebrae Foot
Six Males
Mean 266 92 42 Range 250-275 89-94 40-44
Four Females
Mean 279.5 98 42.5 Range 275-285 94-102 42-43
TABLE 4
CRANIAL MEASUREMENTS OF ADULT _g_.LATERALIS (in mm)
Greatest Length Length of Zygomatic of Skull Nasals Breadth
Four Males
Mean 45.0 15.8 27.0 Range 44.7-45.3 15.4-16.0 26.5-27.4
Five Females
Mean 43.9 15.6 26.8 Range 43.0-44.9 15.3-16.0 26.6-27.0 32
TABLE 4 (continued)
Alveolar Length of Mastoid Interorbital Postorbital Palatilar Upper Molarform Breadth Breadth Breadth Length Tooth Row
21. 6 10 12.8 2 0. 3 8.5 21.2-22.0 9.7-10.3 12.5-13.0 19.9-20.6 8.2-9.0
21. 5 9.9 12.6 2 0. 2 8.5 21.0-21.8 9.6-10.1 12.3-12.9 19.8-20.7 8.3-8.8 33
an unusually capacious stomach and caecum. A 51-day-old juvenile animal, which weighed 89 g and measured 15 0 mm from snout to rump, had a stomach weighing 9 g and measuring 40 mm long x 35 mm wide x 20 mm broad. The
most conspicuously large portion of the intestinal tract is the caecum.
Unusually large cheek pouches, which are not noticeable except when filled, occupy the sides of the face and extend posteriorally to the
level of the ears.
0th er Anima 1s
Interspecific influences may occur directly or indirectly between
C. lateralis and certain other vertebrate species in this community. Some of the species which have been observed during this study are listed in
Table 5.
The least chipmunk (Eutamias minimus) was found to occupy a niche very similar to that of the mantled ground squirrel.
The farmer who owns the hay and grain fields within the study area reported (personal communication) that previously Uinta ground squirrels
(Citellus armatus) were extremely numerous within the study area. They were very detrimental to the crops. Several years ago he began to place poisoned oats each spring along the creek banks located in his fields.
One spring he gathered 2 88 .Q_. armatus which had died from the poison.
Another year 170 dead animals were found. The control methods have been
so effective that during the entire period of field observations for this study only two _g_.armatus were observed. 34
TABLE 5
CHECKLIST OF PRINCIPAL VERTEBRATESPECIES
*Relative Frequency Reptiles Sagebrush Swift (Sceloporus graciosus) 1
Birds Cooper• s Hawk (Accipiter cooperii) 1 Red-winged Blackbird {Agelaius phoeniceus) 1 Red-tailed Hawk (Buteo jamaicensis) 2 Swainson 1 s Hawk (Buteo swainsoni) 2 House Finch (Capodacus mexicanus) 2 Green Ta.iled Towhee (Chlorura chlorura) 2 Common Nighthawk (Chordeiles minor) 3 Red Shafted Flicker (Colaptes cafer) 2 Killdeer (Charadrius vociferus) 3 Audubon• s Warbler (Dendroica auduboni) 3 Brewer's Blackbird (Euphagus cyanocephalus) 1 Sparrow Hawk (Falco sparverius) 3 Barn Swallow (Hirundo ru stica) 3 Scott's Oriole (Icterus parisorum) 4 Black-billed Magpie (Pica pica) 1 Say's Phoebe (Sayornis saya) 1 Broad-tailed Hummingbird (Selasphorus platycercus) 3 Mountain Bluebird (Sialia currucoides) 1 Chipping Sparrow (Spizella passerina) 1 Western Meadowlark (Sturnella neglecta) 4 Starling (Sturnus vulgaris) 1 Robin (Turdus migratorius) 1 Mourning Dove (Zenaidura macroura) 3 White Crowned Sparrow (Zonotrichia leucophrys) 2
Mammals Deer Mouse (Peromyscus maniculatus) 1 Long-tailed Meadow Vole (Microtus longicaudus) 1 Least Chipmunk (Eutamias minimus) 3 Uinta Ground Squirrel (Citellus armatus) 3 Northern Pocket Gopher (Thomomys talpoides) 5 Black-tailed Jackrabbit (Lepus californicus) 1 Nuttall' s Cottontail (Sylvilagus nuttalli) 3 Porcupine (Erethizon dorsatum) 5 Bobcat (Lynx rufus) 5 Coyote (Canis latrans) 5 Mountain Lion (Felis concolor) 5 Mule Deer (Odocoileus hemionus) 5 35
TABLE 5 (continued)
*Key to frequency symbols.
1 Very common throughout the period of the study.
2 Quite frequent during certain portions of the study period.
3 Only occasionally observed.
4 Rarely observed.
5 Presence determined by indirect evidence. 36
The farmer also stated that gophers (Thomomys talpoides) were usually flooded out of their burrows when the fields were irrigated. On one such occasion 2 5 drowned gophers were found.
The Predator and Rodent Control Division of the Fish and Wildlife
Service has men working in Sheep Creek Canyon to locate and kill coyotes
(Canis latrans). On April 23, 19 66, for example, eight coyotes were located in a den a short distance up the canyon from this study area.
The U. S. Forest Service and Utah Fish and Game Department have estimated that approximately 3 00 head of resident deer (Odocoileus hemionus) are present in the general vicinity of Sheep Creek. Deer tracks were found regularly on the banks of the creek.
Different kinds of hawks were frequently observed soaring over the study area. It is very probable that there were other species than those listed, but identification could not be made.
Mantled ground squirrels compete with each other as individuals for food, shelter, territory, homesites, and for mates. On one occasion a squirrel chased two intruding squirrels from its territory. Captive animals were frequently found struggling with one another over a bit of food. Some- times one animal would steal a piece of food from the grasp of another.
Adult females compete with their young for. food after the young are weaned.
In several instances when young animals would attempt to take food from the female, she would push them aside with a forepaw.
The mantled squirrel was the principal diurnal mammal in this habitat, and there was apparently little interspecific competition. The 37 least chipmunk is also a possible competitor for home sites. There is a likelihood that deer, which browse in the area, offer some competition for food.
During the field observations no mantled squirrels were observed to fall victim to predators. On one occasion, however, a Cooper's hawk was seen on top of a trap attempting to get the mantled squirrel which was inside. In another instance, a mantled squirrel scampered into the pro- tection of a burrow just as a Red-tailed hawk soared past a few feet above the ground.
The mantled squirrels were constantly alert for the appearance of predatory birds. Many different kinds of birds flew over the area without eliciting any response from the squirrels, but as soon as a hawk appeared, the squirrels would give warning calls and immediately assume a position of attention ready to dive into a nearby burrow. A large black bird, identified as a white-faced ibis (Plegadis chihi), once flew over the area and caused the squirrels to respond as if a hawk had appeared.
Besides several kinds of hawks, there are other possible enemies of mantled squirrels in this habitat. The coyote and bobcat are among the carnivores which may be involved. In one instance, a squirrel butrow dis- played evidence that some larger animal had been attempting to excavate the burrow.
Various arthropod parasites were found to afflict the squirrels
(Table 6). Sometimes they occurred in sufficiently large numbers to impair the vigor of the squirrel host. 38
TABLE 6
ECTOPARASITES TAKEN FROM MANTLED SQUIRREL SPECIMENS
Number of Parasites Removed Squirrel Fleas Ticks Mites Collection (Oropsylla (Dermacentor (Haemolaelops Number idahoensis) andersonii) glasgowi)
4-4 5 26 14 6-4 4 50 7 6-5 4 15 6-6 41 12 6-9 32
The figures in Table 6 do not imply that these were the total numbers of ectoparasites present on the animals. These represent the numbers of parasites which were readily found, removed and preserved for identification purposes. Young squirrels, from the time they were a few days old, were rather heavily infested with mites.
Population Density and Dynamics
As of July, 19 66 it was estimated that the mantled ground squirrel population within this community did not exceed 5 0 animals. In the summer of 19 63 when the initial observations were made, the population was at its peak level (not much in excess of the present population). Then in the
early spring of 1964, the first trapping was done. During that time 12
squirrels were captured, eight of which were gravid or lactating females.
Based upon the average litter size for these animals (p. 63), that would
amount to a total potential of 55 animals which were suddenly removed 39 from the population.
Eight of the 12 trapped animals, including five pregnant females, were taken from stations 1 and 2 (Fig. 6). This included an area extending
425 yards from the south end of the study area along each side of the road and stream. During the remainder of the observations in 19 64, throughout all of 19 65, and until July, 19 66, not a single mantled squirrel was observed in stations 1 and 2. Burrows which had been used previously were aban- doned during that period. In the absence of the squirrels in these sites, chipmunks occupied at least one of the homesites previously inhabited by the squirrels. Only July 6, 1966 mantled squirrels were observed in these stations for the first time since May, 19 64. The trapping had apparently depleted the squirrels from these segments of the study area.
As a consequence of the 19 64 trapping, the population density in
1965 was at the low point for the study period. In order to allow the popu- lation to recover somewhat from the previous year, additional trapping was not done in 19 65.
In the spring of 1966 the population was still rather sparse. By
July, however, the density had increased significantly, despite the fact that nine adult animals, including four gravid females, had been trapped and removed from the population during April. During July squirrels were present in previously uninhabited sites within the community.
The lowest level of population density was noted in the spring of each year, and the peak density was attained by the first part of July when the young of the year greatly increased the numbers of observed animals. 40
During the last part of June and early July of 19 66, approximately three juvenile animals were observed to each adult that was seen.
The most heavily populated portion of the community was station
6. Even in this station, however, the density probably did not exceed one squirrel per acre. This is primarily a steep hillside adjacent to the stream and the alfalfa field. Besides abundant sage, it also contains junipers, the few pinyon pines which are present in the study area, several service- berry bushes and a diversity of grasses.
Activity Periods
In 19 64 the mantled squirrels emerged from hibernation during the third week in April. Several burrows which had been used by squirrels during the summer of 19 63 were covered by loose soil and rocks during the winter. These burrows were still covered on April 14 but had been opened by the squirrels when again observed on April 18. Some squirrel activity was observed at station 6 on April 14. The activity which commenced dur- ing April was somewhat interrupted by late snow storms on May 2-5. In the spring of 1966, squirrel activity began the first week in April and continued throughout the spring. Squirrels were never observed outside the burrows until well after sunrise, and their activity terminated before dusk. During very overcast or stormy weather their activities are markedly curtailed.
General patterns of daily extraburrow activities were discernible during the various spring and summer months. These patterns could be somewhat modified by existing weather conditions.
The squirrels normally were not active out of the burrows until 41
9 :30 or 10:00 a. m. during April. They would then remain active during
most of the hours between 10:00 a.m. and 4:00 p.m. A slight decline in
activity was noted between 1:30 and 2:00 p.m., but animals were active
during all of the midday hours. By 4:00 p.m. the activity would usually
cease.
In May the pattern was quite similar to April. However, the
animals began to appear a little earlier in the morning, and the activity
would continue until 5:00 or 5:30 p.m. Again, there was a slight diminish-
ing of movement in the early afternoon, but some animals were active during
any hour between 9:00 a.m. and 5:30 p.m.
During June the activities began to be more confined to the early
morning and late afternoon hours, with a marked decline during the early
afternoon. This was especially noticeable during periods of warmer weather.
The pattern which became manifest in June was more accentuated
during July. The activity would begin as early as 7:30 a.m. with consider-
able activity occurring until about noon or 1:00 p.m. Frequently there would then be an almost complete absence of squirrel movement between noon and
4:00 p.m. A resumption of activity would usually occur between 4:00 and
6:00 p.m.
The schedule of activity during August was often very similar to
that of June or July, although there was an indication of a slightly later
onset of activity in the morning and earlier termination of afternoon move-
ments. 42
Mantled ground squirrels appeared quite sensitive to temperature
extremes. Late in the afternoon on May 1, 1964 1 some traps were placed in the area. The next morning there was an unseasonably late snow storm and the traps could not be checked. During the afternoon of May 2 the weather cleared and warmed up considerably so that the snow was soon gone. By the morning of May 3, when the traps were checked, two of the trapped squirrels were dead, and a third animal died three days later in
captivity. During stormy I overcast, or cold weather these animals remain in the burrows until warmer conditions prevall.
They also are seriously affected by very high temperatures, and their activities are noticeably curtailed during periods of very warm
weather. They are decidedly sun-loving animals I but they will pass the hot part of the day in the cool protection of a burrow.
The effects on these animals of exposure to heat were illustrated in the following instances. On July 11, 1964, the captive animals (seven adults and 16 young) were placed in a small wooden garage which had one end open. The animals were continuously shaded, but the temperature in the garage would get very high during the day. The daytime temperatures during the next two weeks were in the high 90' s and a few days exceeded
100. By July 26, nine of the animals (three adults and six young) had died.
In order to substantiate that the heat had been the causative factor in the deaths, the animals were again placed into the animal room at a temperature which did not exceed 7 5°F. From that time on they were healthy and active.
On June 15 1 19 65 a female squirrel which had been maintained in 43 captivity for 13 months was placed in an automobile. It was a warm day, and after a period of one hour the animal was nearly dead.
Accumulation of fat in mantled squirrels normally occurs in August or September in preparation for hibernation. However, three female animals, which were sacrificed on June 17, 1966, had accumulated considerable amounts of creamy white fatty tissue, both subcutaneously and within the abdominal cavity. The subcutaneous fat was rather generally distributed, but was more concentrated in the posterior portions of the body, particularly in the inguinal and anal regions. Fatty tissue also extended anteriorally in large amounts along the sides of the body and under the forelimbs. Within the abdominal cavity there were large concentrations surrounding the ovi- ducts, ovaries and kidneys, as well as in the folds of the intestines.
Fat was removed with scissors and forcepts and weighed. One of the animals weighed 89. 3 g and was a 51-day-old juvenile which had been born in captivity. From this animal 1. 5 g of subcutaneous fat were removed. The other two were adult animals which had been in captivity for two months. The one weighed 153. 3 g and the other 210 .2 g at the time they were sacrificed. From the first one 5. 4 g of subcutaneous fat were removed, and from the latter one 25 g of subcutaneous and 12 g of abdominal fat were removed.
Food and Drink
The diet of mantled squirrels consisted mainly of vegetative material. However, these animals were very adaptable, and would eat 44
almost any food available to them. They were omnivorous if meat became
available. In the early spring when they first emerged from hibernation
there was not an abundant supply of green vegetation available in this
habitat. At that time dandelion (Taraxacum officinale) leaves and stems
were the most commonly chosen food item. They would not eat the flowers
of dandelions. Leaves of yellow sweet clover (Melilotus officinalis) and
blossoms of Phlox caespitosa also made up a portion of the early spring
diet.
If they had equal access to several different kinds of food items,
they displayed decided preferences. S·eeds, when available, were pre-
ferred by captive animals over most other items. When sunflower seeds were provided along with succulent vegetation, such as dandelions, apples
or clover, the seeds were always eaten first. In the natural habitat this
preference for seeds was also observed. As seeds of grasses and other
herbs ripened these comprised a large part of the diet. Squirrels were
observed eating the seeds of Bromus tectorum, Oryzopsis hymenoides,
Agropyron spicatum, Rumex crispus, and Penstemon. When the berries of
squawbush (Rhus trilobata), serviceberry (Amelanchier utahensis) and other
shrubs ripened they were also preferred items in the squirrel diet.
These squirrels were prodigious eaters. One animal which was observed on April 21, 1966 foraged around over a wide area picking up bits of food for three hours. Then, after the three hours, it stationed itself in a patch of dandelions and ate steadily for another hour. Its feeding activity ceased then only because it was disturbed and retreated to its burrow. 45
The captive squirrels consumed huge quantities of food for such small animals. A pile of dandelion greens which would almost fill the cage, would be consumed within a 24-hour period. Three large handfulls of sun- flower seeds, and a dozen small apples were placed into a cage with two
2 1/2 month-old squirrels. Twenty-four hours later they had consumed all of the food that had been given them, and when more food was placed into the cage they ate as though they were very hungry.
The cheek pouches were frequently used when an animal attempted to quickly gather a large quantity of seeds. Succulent vegetation was eaten directly and not packed into the pouches. The full capacity of the pouches was not determined, but captive animals were observed to pack 2 0 or more unshelled sunflower seeds into their pouches.
Three separate instances of cannibalism were observed with captive animals. On two occasions females ate their new-born litters.
Animals which had died from the heat were eaten by other squirrels that were in the cages with them. A young chipmunk happened to get into a trap with a mantled squirrel and the squirrel killed the chipmunk, but did not eat it.
Both captive and free animals stored food. Captive animals frequently packed food into a corner of the cage. One squirrel stored seeds in the nesting material. Attempts to store food were observed as early as
June 15 and during July, August and September the storage of food was common practice with all of the captive animals. Animals as young as two months of age formed food caches. Food storage chambers containing 46 various kinds of seeds were also found in the excavated burrows.
Sheep Creek provides a continuous supply of water, and all of the
home sites of the squirrels were within range of the creek. As long as the
diet consisted mainly of succulent vegetation there appeared to be no need
for the squirrels to drink. This was verified through observations of captives.
However, when the captive animals were fed only sunflower seeds they
drank frequently. When they drank they dipped the lips and tip of the chin
into the surface of the water and sucked the water into the mouth with a
scooping motion of the jaws. The tongue helped to hold the water in the
mouth. They did not lap up the water with the tongue. When young animals
first began to drink they often dipped their noses too far into the water. As
a consequence, they would suddenly jerk their heads away from the water
and sneeze a few times to clear the water from their noses.
Elimination
During the last two weeks of April, 1966, the captive squirrels
were fed abundant quantities of succulent dandelion leaves. In the day-
time periods of activity they would urinate an average of approximately
once each hour. During a six-hour period from 9:00 a.m. to 3:00 p.m. they
would normally urinate six or seven times. Elimination was not as frequent
during the less active periods of the day. In an 11-hour period between
9:00 p.m. and 8:00 a.m. one animal urinated five times and another six
times, for an average of once about every two hours. In a 15-hour period
from 5:00 p.m. to 8:00 a.m. urination occurred once each 1.5 hours. 47
Most of the animals which were sacrificed had full urinary bladders.
The capacity of the bladder was 2-3 ml.
At the time when the diet consisted of succulent vegetation the
fecal pellets were very moist and large. Occasionally they were so moist
that they would adhere to one another and form chain-like strings of pellets.
With this succulent diet the fecal pellets measured about 9 x 4 mm and
weighed O. 06 g per pellet.
When the diet consisted exclusively of sunflower seeds, the
frequency of urination was significantly reduced. The animals urinated less than half as frequently as they had done with a succulent diet, although
they often drank water. The fecal pellets were very markedly drier in texture and smaller in size with the dry diet. They measured 6 x 3 mm or
smaller and weighed 0. 014 g per pellet. They were also significantly fewer in number.
Elimination nearly always occurred outside of the nesting chamber.
The squirrels would generally defecate in a corner of the cage farthest away
from the nest. This was also somewhat the case with urination, although there was more of a tendency for urination to occur anywhere outside the nest.
Economic Importance and Relationship With Man
Mantled squirrels did not range into the cultivated fields of crested wheatgrass or alfalfa located within the study area. Occasionally they were observed at the edges of the fields. There were no squirrel burrows in the 48 open fields, and these animals would do their foraging only within close proximity to a burrow. It was also noted that in the Tank Hollow area where the range reseeding project was conducted, the mantled squirrels did not venture into the open rangelands.
It was previously indicated (Table 6) that mantled squirrels serve as hosts for ectoparasites which are known to be disease vectors. In this regard, as with any organism which may help to perpetuate disease, C. lateralis poses a possible threat to the well being of man and his domestic livestock.
These squirrels were extremely cautious, wild and easily frightened animals. Any unusual movement would cause them to be alert and ready to retreat into hiding. In captivity they normally did not become tame or ac- customed to the presence of humans. They would usually bury themselves in the nesting material and remain in that position as long as a human was moving around in the animal room. However, one captive female, which had borne a litter in captivity, began to leave the nest to eat even though a human was near. Gradually she became less frightened, and eventually would take sunflower seeds from the fingers of a person as the seeds were handed through the wire of the cage. If the cage were opened, however, she would hide. Her offspring also became tame enough to hand feed inside of the cage. They never became so tame that one could hold them without the danger of being bitten. 49
Sounds
Mantled squirrels are normally silent animals as they carry on the routine daily activities. The most noticeable sound is an alarm call which is a single, shrill bird-like whistle. The effectiveness of this call was aptly demonstrated in the following incident. A squirrel had been foraging on a hillside for about 45 minutes when suddenly a single alarm call brought the animal to an immediate halt in its activities. It stopped near a small bush where a burrow opening was located. The call came from a second squirrel which was on the edge of a burrow 3 00 feet away. The first squirrel remained motionless for 15 minutes, as the second squirrel repeated the warning call approximately once each minute. Suddenly the first squirrel dived into the burrow just as a red-tailed hawk swooped over the spot where the squirrel had been sitting. As soon as the hawk had gone, the squirrel was out foraging around again. Shortly the squirrel again be- came alert as the alarm call was again heard. In a few minutes the hawk once more soared over the area.
The alarm call was the only sound heard from mantled squirrels in the natural habitat, but captive animals were heard to also make a variety of other sounds. After mating had occurred and the female no longer desired the attention of the male, she would respond to his approach with a harsh, snarling or buzzing sound.
A female with a Jitter, which was able to venture out of the nest, would attempt to frighten an intruder. To do this she would first charge at 50 the intruder and then stare intently while rapidly vibrating the jaws in a grinding motion and making a low chattering sound.
The new-born and very young squirrels would utter almost con- tinuous squeeking, grunting sounds, especially as they were nursing.
When the young were about three weeks of age they developed an aggres- sive behavior and they would emit a growling sound whenever something touched them. At about seven weeks of age the young began to engage in sex play, and this was usually accompanied by a squeal of protest on the part of one of the animals involved. A low snarl was sometimes heard from the young as they contended over a morsel of food.
Climbing Behavior
Although much of the activity of mantled squirrels takes place upon or beneath the surface of the ground, this is not indicative of a lack of climbing ability. These animals are adept climbers when the need arises.
Squirrels in this community spent a considerable portion of time climbing whatever prominent object was accessible. One squirrel was observed for a 45-minute period, during which time it spent 40 minutes climbing or sitting on the branches of a serviceberry bush. Others were observed climbing among the branches of a huge squawbush gathering the ripe berries.
In the course of their foraging, these squirrels paused every few seconds to survey their surroundings. Sometimes they would sit motion- less for as long as 15 minutes. Most often when they did so they would climb to a prominent position which afforded them a more encompassing 51 view of the area. Squirrels were frequently observed atop fence posts.
They could ascend the sheer side of a six-foot fence post with no apparent difficulty. When they descended a post they would go with the head down- ward, and climb down with ease. One animal took cover by running into the hollowed-out trunk and branches of an old juniper. The squirrel could be heard climbing inside of a branch eight feet above the ground.
Captive animals, especially young ones, spent much time climb- ing on the sides or tops of the cages. One animal was kept in a large cage measuring 6 x 4 x 4 feet. This animal frequently climbed up the sides of the cage, across the top, and down the opposite side.
Home Range
A few of the home ranges of the squirrels in this community have been indicated in Figure 6. One animal was observed as it ranged over an area which measured 350 feet in length and more than 200 feet wide.
Several animals were known to move at least 300 feet from their homesites as they foraged. Considerable overlapping of ranges occurred within this area.
Burrows
The distribution and approximate locations of many of the burrows are shown in Figure 6.
Burrows were found in the following locations: 52
1. In the stream bank beside a protruding rock (Figure 8).
2. In the bank of the road-cut, usually beneath or beside a
rock (Figure 9) •
3. Beneath a large rock pile near the road (Figure 10).
4. In the bare face of a rocky hillside 10 feet above the
alfalfa field (Figure 11) •
5. Beneath serviceberry plants (Figure 12).
6. Beneath juniper trees.
7. The majority of the burrows were located under sage bushes
(Figures 13 and 14), and were usually well concealed.
Burrow openings were always situated on the down slope side when they were near a bush, rock or tree.
Mantled squirrels constructed their own burrows. A squirrel was observed from 10:50 to 11:20 a.m. on April 30, 1966 as it began the construction of a burrow. It first dug a shallow depression seven inches in width. It would loosen the soil with the forefeet and then elevate the body and throw the loose dirt back between the hind legs. It threw loose soil a distance of nearly two feet down the hill. Its normal pattern was to dig for no more than about one minute at a time. Then it would pause and look around for about 15 seconds before resuming its digging. Before the squirrel would resume digging, it would flip the loosened soil away from the burrow entrance. It would then move down into the tunnel, loosen more soil, push the soil toward the entrance, come back out of the hole, look around, chew the dirt off its forepaws, and flip the loose dirt down the hill. 53
------
Fig. 8. Burrow location in the stream bank.
Fig. 9. Burrow location in the road-cut. 54
Fig. 10. Burrow location under a rock pile.
Fig. 11. Burrow location on a rocky hillside near alfalfa field. 55
Fig. 12. Burrow location under serviceberry plant.
Fig. 13. Burrow location under sagebrush. 56
Fig. 14. Burrow location under sagebrush.
Fig. 15. Excavated burrow. (See Fig. 16b) 57
The burrow entrance narrowed from seven down to two inches. One of the burrows which was excavated is shown in Figure 15, and diagrams of the tunnels and chambers of this one and others are shown in Figure 16.
There appeared to be at least three different kinds of burrows.
The following types have been identified:
1. Food storage burrows. These were of two types:
a. Temporary storage. In several instances squirrels formed very shallow (two or three inches deep) non-branching holes into which they placed items of food (generally seeds) for only a few days or weeks. Pin yon nuts, for example, were found in this type of storage burrow.
b. More permanent winter food storage chambers. These were generally a portion of a large, more complex burrow system. Three burrow chambers were found to contain numerous seeds mixed with loose soil.
2. Emergency or escape burrows. These were the most numerous and were scattered throughout the home range. This allowed the squirrels to forage over large areas without having to venture many yards away from a burrow. The structure of an emergency burrow usually consisted of a single shallow tunnel not more than 18 inches in length. One squirrel which was pursued ran into a burrow located beneath a sage plant. After a couple of minutes it left this burrow and ran across the road to a second burrow. When the first burrow was excavated it extended at a shallow angle to a distance of 18 inches and ended in a small blind chamber. The second 58
Top View Nest Chamber
Ground Level Side View
12
24
36 a.
b. c.
Fig. 16. Diagrams of burrow patterns.
Scale: 1/32 "=l" 59 burrow was considerably more complex. It will be described under the following burrow type.
3. Nesting burrows {Fig. 16a). A nesting chamber was usually a side branch of a more extensive network of tunnels and chambers. One such nesting chamber was seven inches in diameter and two feet below the surface of the ground. It contained nesting material which consisted of shredded sage bark and dried grass.
In conjunction with the more extensive burrow systems there were also several chambers which had been filled with loose soil. A consider- able amount of soil was also found in the bottom of the nesting chamber and mixed with the seeds in the food storage chamber.
On one occasion when the air temperature at ground level was
91 °F, the temperature 11 inches down in one of the tunnels of a burrow was 73°F.
Reproduction
Mating occurs soon after the squirrels have aroused from hiberna- tion. In view of the times that litters were born {Table 7) , it appears that in 19 64 mating occurred as early as April 11 or 12, and as late as April 2 5.
In 19 66, mating probably occurred as early as March 31, and was still taking place on April 16.
At the time the male squirrel emerges from hibernation the testes are large and have descended into the scrotal sac. There is an abundant
supply of viable sperm available. By the first part of May the testes have 60 ascended into the body cavity and have begun to atrophy slightly.
Three instances of the mating behavior were observed in captive
animals. These occurred on April 18 1 April 2 6 and May 17, 19 66. Since the pattern was quite similar in each case, an account of the instance on
April 18 will be related. A cage (Figure 17) was prepared for the purpose of observing the mating behavior.
A B C
Fig. 17. Diagram of mating cage.
A nesting box (A) was attached to one of the regular double- compartmented (B and C) cages described previously. A female animal had been housed in cage B for 11 days. The nesting chamber was attached and the female was allowed time to become accustomed to it so that she would take refuge in A when disturbed. While the female was hidden in the nesting material, a male animal was placed into cage C along with
some nesting material, food and water. An opening was made between B and C. This permitted free access between all three of the compartments.
The observer was then positioned behind a blind I so that the animals were unaware of his presence. The following sequence of events was then
observed.
Within one minute the male came out of hiding in the nesting
material in C. The female was in the nest in A. The male spent the next 61
two minutes exploring around in C. He then located the opening into B,
entered that cage and continued his explorations. Within another minute
he located the entrance to A and climbed into that box where the female was
still lying quietly in the nesting material. The male soon located the female.
She remained quiet and passive as the male sniffed at her for a short while.
He explored a little further into other parts of the next box, then returned
to the nest, smelled at the female, and quickly mounted her. He grasped
her in front of her hind legs with his forepaws and placed his head on her
back so that his nose was at the level of the female's shoulders. The male
arched his back, curled his tail over the back, and with a few very rapid thrusts, accompanied by a flicking of the tail, copulation was completed.
The male then sat on his haunches, bent forward and groomed his genitalia.
He shortly left the nest and jumped down into B. The female remained in the nest.
In a few moments the male returned to the nest and copulation occurred again. He then left the nest, moved into the other chambers, only to return a third time to the nest where once again the very brief copulatory process took place. Almost immediately the male again moved down into the other cages, but this time he displayed a great deal more excitement than he had previously shown. He ran around the cage very excitedly, and pushed at the top of the cage as if attempting to find a means of escape. At this time the female left the nest for the first time and entered cage C where the male had started to eat. Whereas previously the female had sown a completely docile and passive behavior when the 62 male was near her, she now responded to his presence with a very aggres- sive reaction. When the male now attempted to mount her she would growl and bite at him, and not allow him to get close to her. The male responded to this sudden display of aggression on the part of the female by very rapidly packing the nesting material from cage C into his cheek pouches and transporting it as quickly as he could into the nest in A. He would then return to C, stuff his pouches and mouth with a quantity of nesting material twice the size of his head, run very rapidly from C to A, and place the material into the nest.
This procedure was repeated about 15 times, as quickly as he could move. Twice he tried to carry so much that he tripped on it. While he was carrying the material to the nest, the female sat in C eating. Soon the male stopped transporting the material and began to eat. Again, when he would approach the female, she would growl and nip at him. The female then returned to the nest and began to arrange the materials into a well- formed nest. The male ate for a few minutes, then he also returned to A and began to help form the nest. The male picked up the loose pieces of material lying around the nest and would either jump into the nest with them or thrust his head into the nest and place the material inside. The female remained inside arranging the materials into the desired shape. One hour and 35 minutes from the time the male was first placed into cage C, the entire process of mating and nest formation was completed.
0 ne of the noticeable differences between the mating that took place April 18 and that on May 17 was the much longer period that elapsed, 63 on May 17, from the time the male first contacted the female until he
attempted to mount her. On April 18 copulation occurred within a few
minutes after they were together, but on May 17 they had been together for 2 0 minutes or more before the first copulatory attempt was made.
The dates of birth for seven captive litters, and the sizes of five of them, are given in Table 7.
TABLE 7
DATES OF BIRTH AND SIZES OF CAPTIVE LITTERS
Collection Number of Female Bearing Litter Date of Birth Number of Young
4-2 May 9, 1964 (eaten by female) 4-7 May 15, 1964 5 4-8 May 20, 1964 5 4-10 May 22, 1964 6 6-1 April 2 7 , 19 6 6 5 6-7 May 13, 1966 6 6-9 May 3, 1966 (eaten by female)
For those litters where the number of young were known, the mean number per litter was 5. 4 Two other gravid animals had died before giving birth to their litters. One of these had five embryos and the other had six.
Therefore, of seven known litter sizes, four consisted of five young and three had six.
These animals are capable of bearing only a single litter each year. An attempt was made to mate animals after the normal breeding period, but it was unsuccessful.
The female squirrel is normally an attentive and solicitous parent. 64
In the two instances where the females ate their new-born offspring, they were subjected to undesirable conditions for the bearing of young. The one animal was still in a trap with inadequate nesting materials or space to form a proper nest. She had also been subjected to frequent observations since her capture. The other female had been transferred from one cage to another a short time before she gave birth to her litter. She had also been under observation about the time she was to give birth.
In five other cases the females bore their litters and cared for them until the young were capable of leading an independent existence.
From the time of birth until the young are weaned the female spends most of her time in the nest nursing and caring for the young. In the usual nursing position the female lies on her side, but occasionally the young will nurse while she lies on her back or on her ventral side.
As long as the young are unable to leave the nest, the female remains with them if an intruder approaches. When the young begin to be active outside the nest the female often displays a protective behavior.
On one occasion the young animals were climbing on the sides of the cage taking sunflower seeds that were being offered. They appeared unafraid of the presence of a human. The female suddenly grasped with her teeth a young one which was hanging on the side of the cage, and jerked it off.
This startled all five of the young so that they ran into the nest. On several occasions females with litters have charged at an intruder who was near the cage and made the vibrating, chattering motions with their jaws. 65
Growth and Development
One gravid female squirrel contained six embryos, three in each uterine horn. The spacing of the embryos within the uterus indicated that the birth sequence would probably alternate between the young in the two sides of the uterus. Each of the embryos was enclosed in a separate embryonic sac. The average size of each sac was 34 x 22 mm. Another female contained five embryos, distributed three and two in the uterus.
The average size of these sacs was 29 x 22. 5 mm.
Summarized in the following paragraphs are some of the observed physical and behavioral stages of development of young mantled squirrels.
This includes the period from shortly after birth until l O weeks of age, when the young squirrels have nearly attained the appearance and behavioral patterns of adult squirrels.
DAYOF BIRTH (Figure 18)
They are altricial animals. The dark dried umbilicus is present.
They are completely pink in color except where the dark eye pigment and the internal organs can be seen through the transluscent pink skin. The eyes and ears are sealed. There are prominent eye bulges, and the ears are merely small buds on each side of the head. The eye slit is barely discernible. The only detectable hair is on the anterior portion of the face, and consists of minute vibrissae (less than l mm) and a bit of white fuzz on the chin. The anterior part of the body is noticeably better 66
Fig. 18. New-born .Q_. lateralis.
Fig. 19. Three-day-old litter of C. lateralis. 67 developed than the posterior portion. The head is disproportionately large,
comprising more than one-third of the body length.
The toes on all four feet are fused. There are five toes on each hind foot and four on each forefoot. The thumbs are mere vestiges • The
claws on the forefeet are noticeable, but are virtually non-existent on the hind feet. The pads on the soles of the feet, especially the forefeet,
are pronounced.
A small lump can be seen where the lower incisors will eventually
erupt. It is possible to distinguish the sexes on the day of birth. The male genital swelling is situated more anteriorally from the anus than that of the female. The young produce an incessant squeeking, grunting sound.
SECOND DAY
They begin to show a slight darkening of the skin on the dorsal
surface.
THIRD DAY (Figure 19)
By this time the darkening pigmentation on the dorsal surface is quite noticeable, especially on the head. A streak of dark fuzz begins to
appear along the median portion of the dorsal surface. The ear pinna is
upright and projects 1 mm above the crown. The eyes are prominent, dark
oval bulges measuring 6 x 5 mm. The animals turn in circles when placed
on a bare surface. The hind part of the body drags when they move. 68
FOURTH DAY
The light stripe on each side of the body is barely distinguishable from the darkening pigmentation of the dorsal and lateral surfaces. The lower incisor lump is enlarging. The front claws have become darkly pig- mented, but those on the hind feet are non-pigmented.
FIFTH DAY
The front toes begin to separate slightly, but the hind ones are completely fused.
SIXTH DAY
The light stripes are quite evident by this time in contrast to the dark pigmentation on the entire dorsal surface. There is very short, dark hair on much of the dorsal head and body. The ventral surface, however, is nearly the same pink color it was at birth, and no hair is present.
EIGHTH DAY
A few light hairs have appeared on the pink ventral surface.
There is a vestige of a dark nail on each thumb. The white testes can be readily distinguished through the light skin of the abdomen.
TENTH DAY
The eye ring is distinct. 69
TWELFTH DAY
The chestnut color of the mantle is beginning to be distinguishable with the sides of the head and shoulders appearing quite golden. The dorsal surface is darker than that of an adult animal. The stripes are very distinct. The ventral surface is still pink with not much hair present. The front toes are separated, but the hind ones are still fused more than half their length. The claws on the hind feet are beginning to darken.
FOURTEENTH DAY
Small lumps, which appear to be mammary nipples, can be detected along the ventral surface.
SIXTEENTH DAY (Figure 20)
The hair on the dorsal surface is 2 mm long.
NINETEENTH DAY
The ventral surface is well covered with huffy hair. The hind toes are nearly separated. The hind quarters still drag when the animal crawls. They now tend to back away when something touches them.
TWENTIETH DAY
The lower incisors have erupted. 70
Fig. 20. New-born and 16-day-old squirrels.
Fig. 21. A 23-day-old .Q_. lateralis. 71
TWENTY-FIRST DAY
The hind toes are separated. They can grip well with the forefeet.
The hind quarters are beginning to develop better coordination, but they
still drag somewhat when the animal moves. They have begun to display
an aggressive behavior when something touches them. They growl and snap
at each other. The hair on the back is 4 mm long.
TWENTY-THIRD DAY (Figure 21)
The aggressive behavior is more pronounced. They are able to
move about rather rapidly.
TWENTY-FOURTH DAY
They crawl out of the nest occasionally, although their eyes are
not yet opened •
TWENTY-SIXTH DAY
The upper incisors are beginning to form a lump, but they have
not erupted.
TWENTY-EIGHTH DAY
Their eyes have begun to open. It begins as a narrow opening toward the anterior part of the eye slit. Their coloration and markings are
quite similar to that of an adult, but the colors are somewhat darker and 72 brighter than an adult. They appear very sleek and colorful. The tail hairs are still very short. They are able to give the bird-like warning chirp now, and they do so frequently.
THIRTIETH DAY
The upper incisors have erupted. They are 1 mm in length as
compared with the 4 mm length of the lower incisors. Now that the eyes are open they move freely around the cage. They do not display any fear when handled.
THIRTY-FIFTH DAY
They have begun to eat solid food.
FORTY-FIFTH DAY
They are weaned by this time. Some of the young engage in sex play where they attempt to mount one another. They could not have learned this sex behavior from observing adult animals, since there has been no opportunity for them to do so.
FORTY-SEVENTH DAY
The pelage has now become very faded and dull looking. They no longer have the smooth, sleek, colorful appearance they had two or three weeks ago. They appear to be rather fuzzy and uniformly dull brownish gray. The stripes and mantle are not very distinct. 73
FORTY-EIGHTH DAY
When they are given sunflower seeds they take them one at a time, and crack and eat them. They do not pack them into the cheek pouches.
They also attempt to store seeds in a corner of the cage.
FIFTY-FIRST DAY
They have begun to pack seeds into their cheek pouches. Sex play is very common.
FIFTY-FIFTH DAY
They spend a considerable amount of time running up the sides of the cage, then flipping themselves backward and landing on their feet.
SIXTIETH DAY
They have now acquired the very attractive coloration which an adult has following molt. The mantle is bright and there is sharp contrast between the light and dark stripes.
SIXTY-EIGHTH DAY
They appear very much like adults now, .except they have not yet reached full adult size.
Normally the young animals attain nearly full growth by their first winter. One of the young had attained more than 9 0 percent of its adult 74 size by the time it was 65 days old. In contrast to this, two animals of the 1964 litters, which were 14 months of age, were only about two-thirds adult size.
The average rates of growth of 11 animals for the first 28 days are
summarized in Table 8, and the average weight increases for 30 days are plotted on the curve in Figure 22. The average weight increase of five animals for the first 30 days was 1. 2 g per day. One young animal at 31 days of age weighed 42 g and at 82 days of age weighed 174 g, for an average weight increase of 2. 6 g per day. That same animal at 82 days of age had the following measurements: total length, 244 mm; tail vertebrae,
77 mm; hind foot, 40 mm; ear, 19 mm. 75
TABLE 8
MEAN GROWTH RATES OF YOUNG MANTLED SQUIRRELS
(measurements in mm) Age Weight Snout to Tail Hind (days) {g) Rump Length Vertebrae Foot Ear
Birth 5.2 45.0 10.8 7.2 2.0 l 5.9 48.0 11. 6 8.0 2.2 2 6.8 50.8 12.0 8.1 2.4 3 7.9 53.0 12. 8 8.4 2.5 5 8.9 58.4 14.6 9.4 3.0 6 10.0 60.8 15.0 10. 2 3.2 8 14.0 66.0 18.2 11.2 4 .1 12 16.4 74.8 23.0 14.0 5.0 14 18. 2 78.0 25.2 15.0 6.0 16 20.5 81.2 27.2 17.0 6.4 19 24.6 87.8 30.8 18.6 7.3 21 28.4 91. 4 33.0 19.8 7.8 23 32.3 95.2 35.4 22.0 8.6 26 36.9 102.0 40.8 24.6 9.7 28 40.0 106.4 43.0 26.4 11. 0 76
50
40
Weight in 30 Grams
20·
10
10 20 30
Age in Days
Fig. 22. Weight increase curve for young .Q_. lateralis. 77
DISCUSSION
Due to the reduction of the medial pair of black stripes, the lighter coloration of the lower tail surface, and the cranial measurements, the mantled squirrels in this population are assigned to the subspecies _Q_.l. lateralis. These animals, however, are considerably darker on the dorsal body than many members of this subspecies at other locations in the state.
Specimens of _g_• .!_. lateralis from the southern part of the range are consider- ably lighter in color. They have less black on the dorsal parts of the body and tail. The outer pair of black stripes on animals of the present community are distinct, whereas in other members of this subspecies marked reduction of both pairs of black stripes is evident. The darker body coloration and the distinct black stripes are more characteristic of _Q_.l- castanurus. In
Figure 2 3 typical specimens of _g__.l. castanurus and _g__• .!_. lateralis from other localities are compared with a specimen from the present study area.
Comparison of specimens from this marginal community with 300 specimens of mantled squirrels from other localities, indicates that some intergradation is manifest in members of this population. Howell (1938) had indicated that intergradation between _g__.l- lateralis and _g__.l. castanurus does not occur. However, Durrant (19 52) cites examples of six animals from Santaquin Canyon, north of Mount Nebo, which are intergrades.
Adjacent populations of these two subspecies also occur in Wyoming (Long, 78
Fig. 2 3. Comparative specimens of _Q_.lateralis. Top: _Q_.l- castanurus from Summit County. Middle: Specimen from the present study area . Bottom: C. l- lateralis from Kane County . 79
1965}, and instances of intergradation have been noted in that area.
The vegetation which characterizes this community marks it as a
habitat of the Upper Sonoran Life Zone. The Transition, Hudsonian and
Canadian Zones are the ones in which _g_.l, lateralis is normally found
(Cary, 1911; Howell, 1938; Miller and Kellogg, 1955). The only subspecies
which have previously been listed as occurring in the Upper Sonoran are
C.J. wortmani (Cary, 1911; Howell, 1938) and C. l• trepidus (Hall, 1946;
Miller and Kellogg, 1955}.
The particular habitat in which this study was made is considered
to be a marginal situation in at least four regards.
1. It is intermediate between _Q_.l• lateralis and C. l• castanurus
distributions.
2. A sagebrush community is atypical and rather an extreme
habitat for C. l, lateralis.
3. It is situated at the lower elevational limits for mantled
squirrels in Utah.
4. Durrant (1952) had stated that _Q_.l• lateralis has been known to occur in all of the mountains and foothills of the state except in the
Wasatch Mountains and the mountains of the basin of Lake Bonneville.
This community is in a southeastern portion of the Wasatch Mountains.
Reports of other workers indicate that this not only approaches the lower altitudinal limit for Utah, but also for the general range of the
species. Specimens listed for Utah were taken from 6,000 to 11,000 feet
(Durrant, 1952). Borell and Ellis (1934) found that mantled ground squirrels 80 were recorded at altitudes as low as 6,000 feet in the Ruby Mountains in
Nevada, but that squirrels were much more numerous above 8,500 feet.
They were more common at 9,700 feet than at any other location. In the
Toyabe Mountains of Nevada, Lins dale (193 8) found them at localities ranging from 7,000 to 11,000 feet. Lowe (19 64) indicates that the mantled ground squirrels in Arizona occur above 6,500 feet. Specimens collected from several locations in Wyoming (Long, 19 65) were located from 6,600 feet to 10,800 feet.
In a few instances records of mantled squirrels from lower eleva- tions are noted, but in these cases they inhabit coniferous forests which extend down to lower altitudes. Grinnell and Storer (1924) found squirrels in the forests of Yosemite National Park as low as 5,500 feet. On Mt.
Rainier mantled squirrels occur in the Hudsonian Zone between 4,500 and
6,500 feet (Taylor and Shaw, 192 7).
There was an inadequate number of animals trapped to justify formation of any conclusions concerning the sex ratios of trapped animals during particular periods, but the data do give an indication that will be considered. In the earliest spring trapping on April 6 and 8, 19 66, five of the six trapped animals were males. In contrast, the three animals trapped three weeks later on April 26 and 2 8 were females, and during May 1-19 in
19 64, eight out of the 11 trapped animals were females. There is at least an indication that male animals, more frequently than females, may be found above ground shortly after emergence from hibernation, and that females become more active during the latter part of April and the first 81 part of May. These possible trends will be correlated with the information that was presented concerning the mating behavior.
It was noted in the observations of mating that the female remained in the nest until after mating had occurred. The male left his homesite and explored until he located the female in her nesting chamber, where copula- tion occurred. The male left the nest temporarily between repetitions of the mating act. The male was also the one that made frequent trips outside the nest to gather nesting material. Later the female was occupied within the nest while the male either ate or gathered other nesting materials. In each of these instances, there was a greater tendency for the male to be outside of the burrow while the female was primarily in close proximity to the nest. Inasmuch as the mating and nest-building activities occur shortly after emergence from hibernation, this would tend to clarify the reason that a greater number of male animals are trapped during the first two weeks of
April. Not until after mating had occurred and the nest was properly pre- pared did the female carry on any extensive amount of activity outside the burrow. This idea tends to be substantiated by the fact that 11 of the 12 females that were trapped in the spring were gravid or lactating.
During the gestation period the female usually spends consider- able time engaged in feeding outside of the burrow. Gestation occurs during the latter part of April and the first two weeks of May; so again, there is a correlation between the breeding season and the tendency for a predominance of activity by one of the sexes.
The survival of an organism depends on its physiological and 82
morphological adaptation to the environmental conditions to which it is
subjected or to its ability to escape those conditions not favorable to its
existence. Morphological and physiological adaptations may occur in
animals but they are greatly augmented by adaptive behavior which enables
them to evade the critical environmental extremes to which they are subject-
ed (Fautin, 19 46). The mantled squirrels of this community are subjected
to several environmental extremes, and they appear to manifest physiological
adaptations which enhance their chances for survival, as well as adaptive
behavior which allows them to evade the extremes. Subsequent portions of
this discussion will elucidate some of these adaptive features.
Hatt (1927), in discussing the spatulate-shaped glandular area
on the back of mantled squirrels, stated that no observations on these
animals indicate the use of the glands, and one is forced to speculation
if an explanation of their function is to be given. He suggests that the
glands, by being rubbed against objects in the environment and leaving
characteristic odors, may convey information from one individual to another.
It was noted during the observations of mating behavior that the
male frequently smelled the back of the female at the location of the
spatulate glands just prior to mounting her. During copulation he would
place his nose directly on this area, and at times it appeared as if he took the skin of that region in his mouth. These glands may, therefore, serve
as a means of causing sexual stimulation.
It has also been noted that the glands of this spatulate area
secrete an oily substance. Secretions from oil glands may play a part in 83 preventing water losses from the surface of the body. It would be of con-
siderable importance for animals in this arid habitat to employ ev~ry possible means of conserving body water. Here, then, may be another function of the spatulate glandular area.
Even though the least chipmunk and mantled squirrel occupy:
similar niches, they are not necessarily competitive for food. Carleton
(1966) pointed out in his studies that although both species were greatly dependent upon dandelions for food, they displayed decided preferences for different parts of the plant. The squirrel preferred the leaves and
stems, while the chipmunk chose the flowers and roots. In the present
study site mantled squirrels and chipmunks also relied on dandelions for the bulk of their spring diet, and the same kind of preference for the different plant parts was manifest here as in Carleton's study.
In this community there appeared to be little direct competition for the mantled squirrels. Even though at one ti.me _Q_.armatus was very abundant, it is doubtful that this species offered competition to _g_. lateralis inasmuch as they occupy different niches. Uinta ground
squirrels were confined to the stream banks in the center of the cultivated fields, and they relied on the hay and grain crops for their food. Mantled
squirrels did not utilize the fields for home sites, and they were not dependent on the cultivated crops for a food supply.
The fact that the mantled squirrels responded to the low-flying, white-faced ibis in the same way they did for a hawk would seem to indicate that they may react to the size of a bird. The smaller birds 84 did not elicit responses from the squirrels.
The findings from this study agree with those of Hubbard (1947) wherein he concluded that mantled ground squirrels are generally only moderately infested with fleas, the numbers of any one animal are usually few, and at times many of the squirrels can be examined and found without them. Fleas, however, are known vectors of Pasteurella pestis, the bacterium responsible for bubonic plague. Mantled squirrels are the favored hosts of the flea Oropsylla idahoensis.
A greater possible threat exists because of the ticks (Dermacentor andersoni) which infest these squirrels, The ticks not only occurred in far greater abundance than the fleas, but the ticks also are known vectors for a wider variety of diseases. The bacillus Pasturella tularensis is the causative agent for tularemia, and under natural conditions ticks, particu- larly Q. andersoni, appear to be the primary transmitters (Arthur, 19 62).
Tick paralysis in the Northwestern United States and adjoining South- western portion of Canada is caused by the bite of D. andersoni. This tick species has also been reported as a vector of Anaplasma, the causa- tive agent of anaplasmosis. In its acute stages this disease may kill the infected animal within 24-72 hours, and the mortality rate is from 30-50%.
Rocky Mountain spotted fever rickettsiae and also the causative rickettsiae in Q-fever (Coxiella burnetii), have been found to occur in D. andersoni<
The viruses which cause Colorado tick fever and encephalitis japonica are also transmitted by D. andersoni. 85
The small size of the mantled squirrel population and the apparent ease with which they might be completely eliminated from the community were demonstrated by the trapping and removal of animals in 19 64. The removal of only eight mantled squirrels from stations 1 and 2 completely depleted the population in those stations, and it required more than two years before squirrels reinhabited the vacated areas. Tevis (1956) indi- cates how members of a population of mantled squirrels radiated two and a half miles through continuous virgin forest, and established themselves in a logged area. The squirrels of the present study area only had to move several hundred feet to fill in the vacated sites.
There is evidence that the onset of activity in the spring may be somewhat determined by the prevailing weather conditions. In 19 64 the winter had been unusually long and moist, and warm spring weather arrived late. The first warm period occurred in the middle of April and during that period the first sign of squirrel activity was observed. The litters of the animals captured in 19 64 were not born before May 9, which would indicate that mating took place about the middle of April.
In 19 66 a different situation prevailed. The early spring weather was unseasonably warm and dry, and the winter had been less severe than in 19 64. Considerable squirrel activity was observed beginning the first week in April. During 1966 litters of captured animals were born as much as two weeks earlier than in 19 64. Mating must have occurred as early as
March 31 in order for the litters to have been born when they were. 86
Mantled squirrels are definitely intolerant of prolonged exposure to the high daytime temperatures to which this community is frequently sub- jected, but they effectively utilize the cool protection of the burrows to escape the temperature extremes. This was evidenced by the lack of activity during the hot portions of the summer days. Vorhies (1945) clearly showed that the high air and soil surface temperatures are not transmitted very far beneath the surface of the ground. The cool, moist conditions which prevail in the burrow would help to reduce the rate of respiration and loss of water from the body surface. Their activities were restricted to that part of the day when it was coolest and the evaporating power of the air lowest.
Diet is also a factor which would be of considerable importance in the water economy of these animals. The end product of protein metabolism is urea, which requires considerable amounts of water for its elimination. Therefore, a diet low in nitrogenous constituents would be desirable for animals in an arid habitat. Since carbohydrates and fats furnish large amounts of metabolic water, a diet high in these constituents would be advantageous. The diet of these mantled squirrels consisted pre- dominantly of carbohydrates and fats.
Storage of food was not found to occur among the mantled squirrels studied by McKeever (1964). With the squirrels of the present study, how- ever, food storage was of general occurrence.
The capacity of the pouches may be indicated from the following examples. Merriam (1890) found 39 unbroken seed pods of Penstemon 87 barbatus in the pouches of one animal. Birdseye (1912) shot a squirrel which had 357 kernals of whole oats. Howell (1938) tells of one animal which had 410 weed seeds and another which carried 360 grains of barley.
From the pouches of another squirrel Warren (1942) removed 27 scrub oak acorns.
A study of Pengelley (19 64) demonstrated that .Q_. lateralis, at
23 °c and being fed "Purina chow" will survive during the active season only about 2 0 days without free water. In the present study it appeared that when these animals are fed a diet of succulent vegetation they can conceivably survive for longer periods without taking free water. They are capable of deriving their needed water from the vegetation. However, the fact that the homesites of the squirrels were all located within easy range of the water supply would indicate that they are reliant upon a water supply, at least during a portion of the season, for their survival in this habitat.
This area is generally of little agricultural importance. The only two areas which might be of any consequence are the range reseeding project and the fields of hay and grain. The mantled squirrels do not forage in the midst of the open fields either in Tank Hollow or in the cultivated fields. Occasional foraging which may occur along the edges of the fields would not prove to be a serious detriment, since the population size is small. The farmer who had done the poisoning of squirrels in his field had not found mantled squirrels among the dead animals. It is, therefore, doubtful that mantled squirrels pose any threat to agriculture or to the reseeding project. 88
The dry feces of these animals and the marked reduction of urinary elimination during times of dry diet, indicate an ability to conserve body water when necessary. The dry fecal pellets are indicative of efficient reabsorption of water within the large intestine. It was shown by Howell and Gersh (19 35) that water in the urine may be conserved for reutilization by kangaroo rats fed on dry diets. Mantled squirrels do not display the ability to reabsorb water to the degree that desert dwelling animals such as the kangaroo rat are capable of doing, but there is a definite indication that when the need arises the squirrels have the capacity to conserve con- siderable amounts of water by diminishing the quantity which is eliminated.
This would be another factor in helping to assure their survival under these arid conditions.
Hall (1931) indicated that the golden-mantled ground squirrel was so thoroughly established in his mind as a fossorial rodent that it was an unexpected event when he first found them climbing in trees. He saw one
15 feet above the ground on the limb of a white pine and another took refuge in a tree. From some of the statements which have been made concerning the lack of climbing ability or climbing tendency on the part of mantled squirrels, it appears that others also regard mantled squirrels as strictly fossorial. There are some observers, however, who have found that these animals display considerable climbing dexterity. Howell (193 8), for example, stated that they occasionally climb into bushes or trees to a height of 20 or 30 feet in search of food. From observations made with the present group of animals, it appears that they not only possess the 89
ability to climb very well, but they frequently use this ability.
Burrows were situated in virtually all possible types of conditions within the study area and there was no indication that the squirrels were dependent upon a particular type of soil or plant species for their burrowing
habits.
By the simple expedient of digging their burrows on the lower slope
side under the base of a rock or bush, the squirrels not only provided a
means of protecting the burrow entrance from sliding rocks, soil and water, but they also provided themselves with a protected spot of ground at the burrow opening where snow would melt away before it would at other locations.
The question was posed by Gordon (1943) concerning the disposi- tion of the soil which was removed from the burrows as the squirrels
excavated. He stated that he had not found mounds of dirt around the entrances of squirrel burrows. A conclusive answer is not forthcoming here, but some suggestions are presented. After the initial burrowing
effort, there is a mound of soil present, but it was found that the squirrels aided by wind and weather, can effectively spread much of the loose soil over a wide area so that it is not readily noticeable. When some of the large burrows were excavated, several large chambers were found to be
completely filled with loose soil. The function of these chambers was not apparent, other than that they contained soil. The nesting and seed stor-
age chambers also accommodated considerable amounts of soil.
Squirrels in this community dug their own burrows, but others 90
have found that mantled squirrels may occupy burrows which were made by
other animals. Taylor and Shaw (192 7) noted that on Mt. Rainier squirrels
occasionally utilized the abandoned burrows of marmots. On the Kaibab
Plateau in Arizona C. lateralis occupied burrows made by pocket gophers
(Rasmussen, 1941). There were numerous gopher burrows within the fields
of this community, but they were not occupied by squirrels.
Walker (1964) states that the burrows of mantled squirrels are about 10 inches deep and 14 inches in length. McKeever (1964) also indicated that the burrows are very simple and shallow. A burrow of the dimensions given by Walker appears to be comparable to one of the numerous emergency burrows described earlier. The larger type of burrow found in this area (Fig. 16a) was something more than shallow and simple
as attested to by the five separate openings, the five different chambers, a system of interconnecting tunnels that covered an area of approximately
5 0 square feet and the depth of more than two feet.
In a population studied by McKeever (1965) there were sexually
active .Q_. lateralis for about two months, from mid March to May. This
information coincides with the findings of the present study. The attempt to breed the two animals on May 17 did not result in the production of a
litter. The animals attempted to mate, but the breeding season had most
likely passed. The testes of the male had ascended into the body cavity.
This inability to produce offspring late in the season is a protective
measure. The offspring of such a late mating would not have been active
outside the burrow until nearly the first of August and this would not have 91 allowed them sufficient time to develop or to accumulate the necessary fat to carry them through the period of dormancy.
The average litter size of this study agrees with Asdell (1964) who places the mean number of young per litter at 5. 5. Asdell also states that embryo counts have varied from two to eight. The gestation period is at least 2 7 days (McKeever, 1965).
In two of the instances where mating behavior was observed, the female was apparently already gravid at the time she was captured.
One female, which was captured April 7, was placed with the male on
April 18, and she bore her litter nine days later. The other female was captured April 26 and placed with the male the same day. Her litter was born on May 13. Despite the fact that they were gravid, they had permit- ted copulation to occur. This may have been an unnatural occurrence brought about by confinement in the cage with a male animal. It is of interest, however, that both of these pregnant females would allow the male to copulate and not display any aggressive behavior toward him until after the third or fourth repetition of the copulatory act. 92
SUMMARY AND CONCLUSIONS
This was an ecological study of a population of golden-mantled ground squirrels (Citellus lateralis) in a sagebrush-grass community. Its primary purpose was to observe the activities of the squirrels and to deter- mine some factors which contribute to their success in this habitat.
Observations were made of both free and captive squirrels. Other biotic and physiographic features of the environment were also investigated.
Mantled squirrels of this community were assigned to the sub- species C. l. lateralis, but slight intergradation between typical .Q_. l. lateralis and _g_.l- castanurus was evident.
The location of this community renders it a marginal _g_.l• lateralis habitat in at least four regards: (1) It is located between the ranges of ------C. 1. lateralis and -- C. 1. castanurus, (2) sagebrush habitat is not typical for this subspecies, (3) it is situated at the lower elevational limit for _g_.lateralis in Utah, and (4) it is in the Wasatch Mountains, where .Q_. l• lateralis was thought not to occur.
Mantled ground squirrels are presently the principal diurnal mammals in the community, but they occur sympatrically with least chipmunks. The community sustains only a sparse population of mantled squirrels (not more than 50). The population density is lowest in early spring and greatest in July. 93
Periods of squirrel activity are considerably affected by weather conditions. The time of emergence from hibernation may be altered as much as two or three weeks by prevailing spring weather, however, the animals normally emerge about the first part of April. Daily activities are notice- ably curtailed during either hot or cold temperature extremes, and during heavy overcast or stormy conditions. By remaining in the burrows during weather extremes, the squirrels greatly increase their chances for survival.
Mantled squirrels can subsist on a wide variety of food items.
They are usually adaptable in this regard, and will eat almost whatever food is available to them. This is another factor which contributes to their success in these harsh conditions. Shortly after emergence from hiberna- tion the diet usually consists of dandelions and a few other early spring plants. Later in the season grass and weed seeds and berries of woody plants comprise the bulk of the diet. Three instances of cannibalism were observed. On two occasions females ate their new-born litters, and the third instance resulted when several squirrels died from exposure to heat.
The water requirements of the squirrels could apparently be provided by eating succulent vegetation. However, when the diet con- sisted only of dry food items, the squirrels drank water frequently. They sucked up the water when they drank. Home sites of the squirrels were always located within range of a water supply.
These squirrels displayed the ability to conserve their body water, when necessary, by reducing the amount of water that was eliminated.
When they were fed a dry diet, the frequency and amount of urination were 94 considerably reduced, and feces became much drier than with a succulent diet. It was suggested that a glandular area located on the back and which secretes an oily substance, may also serve in water conservation by prevent- ing water loss from the skin.
Even though mantled squirrels are normally silent animals, they are capable of producing a variety of sounds under certain conditions.
Despite their normally fossorial habits, the squirrels in this community displayed remarkable climbing ability, and a definite tendency to spend considerable time engaged in climbing.
Burrow locations were not dependent upon a particular type of soil or vegetation. Burrows were found in many different situations, but the majority were located beneath woody shrubs. At least three kinds of burrows were observed: (1) Food storage, (2) emergency or escape, and
(3) nesting and hibernation.
A predominance of extraburrow activity by one of the sexes during certain portions of the spring season was likely related to the breeding and nesting behavior. Mating takes place soon after the animals emerge from hibernation. It appears that the female waits in the nesting chamber while the male leaves his own home site and goes to the female in her burrow.
With captive animals copulation occurred in the nesting chamber. The copulatory act lasted a few seconds, and was repeated a number of times within a short period. During mating the female was very docile and sub- missive, but as soon as mating was completed she suddenly became very defensive and belligerent toward the male. The male collected nesting 95 materials and carried them to the nesting chamber where the female arranged them in the desired form. The male, therefore, made frequent excursions outside the burrow during mating and nest-building, whereas the female spent more time underground until after completion of these activities.
Captive gravid females permitted coitus to occur.
The squirrels were capable of bearing only a single litter each year, and the mean number per litter was 5. 4. At the time of birth the young were naked, helpless, and pink in color. Their eyes and ears were sealed.
Captive litters gained weight during the first month at: the rate of 1. 2 g per day. During the next two months, after they had begun to eat solid food, the weight increase was about 2. 6 g per day. Dark pigmentation and hair began to appear on the dorsal surface by the third day, and by the fourth day the light stripes on the sides of the body began to be discernible. By the
12th day the chestnut color of the mantle was barely distinguishable. The lower incisors erupted by the 20th day. The young occasionally crawled out of the nest by the 24th day, but their eyes were not open until the 28th day.
On the 30th day the upper incisors had erupted, by the 35th day the young began to eat solid food, and they were weaned at six weeks of age. By the time they were three months of age they may have attained as much as 9 0 percent of adult size.
Some of the contributions made by this study are as follows:
It is an initial effort to specifically study mantled ground squirrels in a desert shrub habitat. This subspecies had not previously been shown to occur in the Upper Sonoran Zone, nor in the Wasatch Mountains. It is the 96 lowest altitude at which mantled squirrels have been found in Utah. Their method of drinking was previously unknown. It was demonstrated that
mantled squirrels are capable of conserving body water by various means, thus rendering them more capable of survival in arid habitats. This study provided detailed descriptions of the burrowing, mating and nest-building behaviors, and of the development of young animals. 97
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Wirtz, J. H. 19 61. The golden-mantled ground squirrel Ci tell us lateralis chrysodeirus (Merriam) its social and community interactions. Unpublished Doctoral thesis, Oregon State Univ., Corvallis. A STUDY OF THE GOLDEN-MANTLED GROUND SQUIRREL
(CITELLUS LATERALIS) IN A SAGEBRUSH-GRASS COMMUNITY
An Abstract of a Thesis
Presented to the
Department of Zoology and Entomology
Brigham Young University
In Partial Fulfillment
of the Requirements for the Degree
Master of Science
by
Dennis E. Peterson
May 1967 P,BSTRACT
Golden-mantled ground squirrels (Citellus lateralis Say) typically
inhabit coniferous forest regions, but they occasionally occur in desert
shrub habitats. The principal purpose of this study was to observe activi- ties of mantled squirrels in a sagebrush community, and to ascertain factors which contribute to their success in an unusually arid habitat.
Squirrels of this community belong to the subspecies _g__.1_. lateralis; however, intergradation between typical _g__.l, lateralis and _g__.l, castanurus is evident. This community is in the Wasatch Mountains at an elevation of
5,750 feet, and in the Upper Sonoran Zone. These three conditions were not previously recorded for members of this subspecies.
These animals can subsist on a variety of food items, but their diet is usually low in nitrogenous substances which require considerable amounts of water for elimination, and high in carbohydrates and fats which provide high proportions of metabolic water. This hleps to conserve body water. They can derive much of their water requirement from succulent vegetation; however, their homesites are located near a water supply and they drink freely when the diet is dry. They suck lfp the water when they drink. When the diet is dry their urine output is markedly diminished, and they produce unusually dry feces. Water loss from the skin may be dimin- ished by the oily secretions of glands on the backs of these squirrels. They remain in the burrows during extremely hot weather. Three kinds of burrows were found: (1) food storage, (2) emergency escape, and
{3) nesting and hibernation. They dig their own burrows, and a description of the burrowing behavior is given in this paper.
There is indication that mating occurs in the burrow of the female.
The copulatory act is extremely brief, but repeated a number of times. Nest building takes place soon after mating has occurred, and the male gathers the nesting material while the female forms the nest. The female displays remarkably contrasting behavior toward the male before and after mating.
Prior to and during the mating process the female is submissive and docile, but as soon as mating is completed she becomes very belligerent toward the male.
The altricial young begin to display pigmentation and growth of hair by the third day after birth. Their eyes open about the 28th day, they begin to take solid food by the 3 5th day, and are weaned by the sixth week.
During the first month, the young gain weight at the rate of approximately
1. 2 g per day, and during the next two months at the rate of 2. 6 g per day.
They may attain as much as 9 0 percent of adult size by the age of three months.