Time Budgets of Wyoming Ground Squirrels, Spermophilus Elegans

Great Basin Naturalist

Volume 41 Number 2 Article 9

6-30-1981

Time budgets of Wyoming ground squirrels, Spermophilus elegans

David A. Zegers University of Colorado, Boulder

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Recommended Citation Zegers, David A. (1981) "Time budgets of Wyoming ground squirrels, Spermophilus elegans," Great Basin Naturalist: Vol. 41 : No. 2 , Article 9. Available at: https://scholarsarchive.byu.edu/gbn/vol41/iss2/9

This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. TIME BUDGETS OF WYOMING GROUND SQUIRRELS, SPERMOPHILUS ELEGANS

David A. Zegers'

.\bstract.— Time budget of free-living adult Spermophiltts elegans differed significantly from that of juveniles in the Front Range of the Rockies during 1974-1975. No differences were found between males and females. Hour of day. day since emergence, air temperature, cloud cover, and presence of predators all correlated with the frequency of various components of the time budget.

Study of time budgets is important in com- binocular, and a 20X telescope to observe the prehending the roles of animals in ecosystems squirrels from a blind. The animals were as well as understanding their basic patterns marked for individual recognition from a dis- of behavior. Time budgets constructed for a tance using a unique combination of freeze few ground .squirrels [the Columbian ground brands (Hadow 1972) located at one or two squirrel, Spemiophihis columbianus (Betts of the spots on the animal's body. 1976); the thirteen-lined ground squirrel, S. The behavior of these ground squirrels was tridecemlineatus, and the spotted ground divided into 13 categories (i.e., activities) (Ze- .squirrel, S. (Streubel spilosoma 1975); and gers 1977). This classification scheme is sim- Belding ground squirrel, S. belding (Morton ilar to those previously used for this squirrel 1975)] illu.strate the .significant effects exo- (Clark and Denniston 1970) and for the close- genous factors and endogenous have on the ly related Richard.son's ground squirrel, S. time allotted to various activities. My objec- richardsonii (Quanstrom 1968 and 1971). tives were (1) to produce time budgets for These 13 activities and their definitions are the Wyoming ground squirrel, Spennophihis as follows: elegans {sensu Nadler, Hoffmann, and Greer 1. The basic posture is a resting and observation posi- 1971; (2) to document differences in time tion with all four paws on the ground. budgets due to age and sex; (3) to correlate 2. Semi-alert posture is a resting and observation posi- variation in time budget with several envi- tion in which the forepaws are off the ground and ronmental factors: weather, day since emer- the back is arched. gence, hour of day, and presence of pre- 3. The alert position is a resting and observation position in which the forepaws are off the ground and dators; and (4) to assess the ecological and the back is straight, not arched. evolutionary correlates of these variations in 4. The down feeding posture is a variation of the basic time budget. posture in which the squirrel is eating. Food is ma- nipulated using the teeth and lips without the aid of the forepaws.

Methods 5. The upright feeding posture is a variation of either

the semi-alert or alert postures in which food is han- A colony of free-ranging Wyoming ground dled with the forepaws. squirrels was observed from 18 May 1974 to 6. Running is a rapid locomotor activity in which the 24 August 1974 and from 20 April 1975 to 20 animal is moving > 1.0 m/s and is not involved in a chase. August 1975 in a montane meadow (2440 m 7. Chasing is running in which the individual is chas- elevation) in the Front Range of the Rocky ing another.

Mountains approximately 16 km southwest of 8. Chased is running in which the individual is being Boulder, Colorado (Zegers and Williams chased. 1979). 9. Walking is relatively slow (compared to running) lo- comotion of < 1.0 m/s. Using the technique of Wiens et al. (1970), 10. Hay-gathering involves stuffing herbaceous stems I employed an electronic metronome. and leaves into the mouth without chewing and

'Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, Colorado 80309. Present address: Department of Biology, Millersville State College, Millersville, Pennsylvania 17551.

221 222 Great Basin Naturalist Vol. 41, No. 2

swallowing. These materials are cut or pulled up by Few time budgets of other sciurids are of the forepaws and teeth and placed in the use available for comparison. Betts (1976) found mouth perpendicular to the sagittal line and then that feeding consumed from 49 to 86 per- deposited somewhere underground. 11. Grooming includes self- and allogrooming as well as cent, and "alertness" occupied from 6 to 26 dusting, in which a squirrel rolls from side to side percent of the total time above ground of while prostrate in the dirt of an entrance mound. Spermophilus cohimbianus. Tamiasciunis, 12. Digging is the behavior in which a squirrel removes the red squirrel, spent approximately .35 per- soil from a tunnel entrance by using either or both hind limbs and forelimbs. cent of its total time above ground feeding, 13. Fighting is similar to fighting among other rodents, although this percentage ranged from 9 to 60 and involves rolling, biting, clawing, and yelping. percent (Smith 1968). Streubel (1975) found Spermophilus tridecemlineotiis spent 42.4 Other data were collected for each of 1125 percent and S. spilosoma spent 45.6 percent observation periods, which lasted from 5 to of its time feeding, but only 11.6 percent and 15 minutes. These data included date, time of 15 percent, respectively, in some alert pos- observations, animal identification number, tures. Sexual and agonistic behavior com information about predators (i.e., whether or prised less than 5 percent of the total budget not a predator was visible, and, if so, its spe- for these species. When above ground, cies), and weather conditions. Air temper- Wyoming ground squirrels spent a smaller ature was measured at 0.5 m above ground proportion of their time feeding, and more every half hour. Sky cover was divided into time in sedentary observation than these four cloud categories: clear (no clouds), part- other species. This may be due to a greater ly cloudy (less than 50 percent of sky cov- predators, or to prevailing habi- ered), mostly cloudy (more than 50 percent threat from differences in so- of sky covered) and overca,st (complete cloud tat conditions resulting in cover). cial system or foraging strategy. Differences in time budget due to age and These differences in time budget also re- sex were tested via chi-square analysis. The flect differences in territorial maintenance relationship between five environmental fac- strategy. For example, Tamiasciunis, a squir- tors and the components of time budget were rel that defends a food supply, uses a strategy analyzed by multiple regression. Air temper- that spends little time on actual territorial ature, day since emergence, hours of day, sky defense (0.25 to 1.85 percent of active time. conditions, and presence of predators served Smith 1968). Complete defense is probably as independent variables, and the frequencies difficult if not impossible in the spatial com- of each of the 13 activities for each of the ob- plexity of the coniferous forest. It appears to servation periods were the dependent be energetically adaptive to use warning calls variables. and to tolerate some intrusion rather than to spend considerable time and energy chasing other squirrels. Spermophilus spilosoma and

FIesults and Discussion S. tridecemlineatus do not defend food sup- plies. Their territoriality can be described as

Although the behavior of S. elegans has core monopolization (Streubel 1975), in been studied (Clark 1970a, Clark and Dennis- which individual distance and the tendency ton 1970, Pfeifer 1980), a time budget has to remain near the home burrow spaces indi- never before been constructed. Aboveground viduals. No cooperative or extended familiar

time budget for all individuals is shown in behavior and little agonistic behavior occur

Figure 1. Note that the two feeding activities (Streubel 1975). In contrast, S. richardsonii were the most protracted, combining to con- and S. elegans do not defend food territories sume 39.3 percent of all time spent above but do defend reproductive territories. Dur- ground. The three sedentary but watchful po- ing mating individual males occupy terri- sitions (basic, semi-alert, and alert) were the tories that contain the home ranges of several next most frequent, followed by the five pos- females (Yeaton 1972). These are succeeded tures labeled "individual maintenance." Note by female territories during gestation and that the three agonistic activities were the lactation (Quanstrom 1968, Yeaton 1972). My least frequent. observation of female territories for S. June 1981 Zegers: Wyoming Ground Squirrels 223

35r

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Fig. 1. Time budget of a population of Wyoming ground squirrels during the summers of 1974 and 1975. 224 Great Basin Naturalist Vol. 41, No. 2 elegans revealed them to be essentially used of hibernation essentially full grown and to protect the burrow entrance, (and there- must only consume sufficient energy to re- fore the young) against intrusion by con- produce successfully and to deposit enough specifics rather than for defending an area of fat to survive hibernation. Juveniles, how- open ground. ever, grow at a rate of 11.4 percent per day The differences in time budget between during the first weeks after birth until full sexes for adults and between age groups are length is achieved at about 63 days of age shown in Figures 2 and 3. Time budgets of (Clark 1970a). In addition, the juveniles must adults differed significantly from those of then put on enough fat to survive hiberna- juveniles (X2 = 38.67; df = 12; p < 0.05) tion. Moreover, for both S. richardsonii and but sex did not have a significant effect on S. elegans a temporal difference exists be- time budget (X^ = 0.73; df = 12; p > 0.05). tween adults and juveniles in their activities. The effects of age and sex on time budgets Adults are finished with aboveground activi- have not been studied extensively for sciurids. ties before juveniles start prehibernatory fat-

I know of only one other study of sciurids tening (Clark 1970b, Dorrance 1974, Mich- that presents time budget data by age and sex ener 1972 and 1974, Quanstrom 1968, and groups. Although the data were not statistic- Zegers 1977). This removes adults from the ally analyzed, the time budgets of adult and area when the juveniles are preparing for hi- yearling S. columhianus appear to be sub- bernation and, by reducing intraspecific com- stantially different from those of juveniles petition, probably increases survival of juve- (Betts 1976). Moreover, differences between niles (Yeaton 1969). Likewise, early adults and yearlings and between males and immergence of adults into hibernacula may females existed. Likewise, my data indicate a increase adult survivorship by reducing pre- significant difference between age groups, al- dation pressure (Morton 1975). though the difference between sexes was not Several sciurids are known to modify activ- significant. The apparent time budget differ- ity periods in response to environmental fac- ences between sexes of the Columbian tors (Yeaton 1969, Clark 1970b, Quanstrom ground squirrel suggest that that species has a 1971, Baudinette 1972, G. R. Michener more pronounced division of labor than S. 1973). Multiple regression of environmental elegans. factors on the 13 components of the time Differences in time budget between adults budget of Wyoming ground squirrels re- and juveniles are important and obvious. vealed some interesting relationships to that Feeding to support growth is not as impor- budget (Table 1). None of the independent tant to adults as to juveniles. Adults come out variables correlated with frequency of

Table 1. Independent variables which were significant predictors of the frequency of 13 activities of Spermo- phihis elegans. Presence of predator (Pred), hour of day, day since emergence, air temperature, and sky conditions were analyzed for their effect on the frequency of each activity. Direction of the correlation is indicated by the sign (+ or -). n.s. = not significant

Independent variables (p<0.05 for beta)

Activity Pred Zegers: Wyoming Ground Squirrels 225

FEMALES 30 i

MALES

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the sum- Fi^. 2. Comparison of time budgets of adult male and adult female Wyoming ground squirrels during mers of 1974 and 1975. 226 Great Basin Naturalist Vol. 41, No. 2

ADULTS 30

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UJ cr < UJ CD UJ CO June 1981 Zegers: Wyoming Ground Squirrels 227 fighting. This reflects the obvious social na- and cloudiness also affect specific behaviors, ture of fighting; social situation was ob- although this conclusion must be qualified. viously the most important factor in in- Many behaviors were not influenced by itiating fighting, which went on regardless of weather conditions (Table 1). Although run- the hour, date, or weather. ning decreased on sunny days, digging in- The presence of a predator was the most creased. As air temperature increased squir- recurring significant variable (Table 1), cor- rels walked and dug less. This may reflect relating with the frequency of 11 activities. generally lower activity when temperatures The most casual observer of these squirrels are high. Although this could be a thermore- would agree that behavior is greatly modified gulatory response, the data in Table 1 gener- once a predator is detected by the squirrels. ally support the idea that specific behaviors All feeding, social activity, grooming, etc., of ground squirrels tend not to be greatly in- stopped as the squirrels, using either the bas- fluenced by weather conditions. These squir- ic, semi-alert, or alert postures, intently ob- rels were above ground apparently for a pur- served the predator. pose (e.g., feeding, territorial defense, Day since emergence correlated with feed- predator detection). If weather conditions ing postures, chasing, chased, walking, and were unfavorable enough to seriously inter- fere with these activities, the grooming activities. This indicates chronolog- animals re- turned to their burrows. If, however, condi- ical changes in the time budget (Zegers tions were less than ideal but not sufficient to 1977). As the season proceeded, adults be- force them into burrows, the squirrels may came progressively more sedentary and spent have responded with slight modifications of less time feeding, although they continued to (1) the frequency of some behaviors or gain weight (Zegers and Williams 1977). This (2) posture. For example, on cold, sunny days the quiescence could be due to diminished meta- squirrels used postures that maximized their bolic rate during prehibernatory fattening heat gain from the sun, whereas on hot, sun- (Armitage and Schulenberger 1972). In addi- ny days they used postures that minimized tion, the squirrels might have been able to heat gain from the sun (Zegers 1977). In gen- spend less time feeding and still gain weight eral, activity level (i.e., number of individuals because the energy drain of reproduction and above ground at any one time) decreased territorial defense was no longer present. Re- during cool and cloudy periods and during gardless of the cause of their quiescence, the hot and sunny periods. Likewise Baudinette alertness of these individuals probably aided (1972) found that the California ground in predator detection and thereby contrib- squirrel, S. heecheiji, avoided the warmest pe- uted to the survival of juveniles. This inter- riods of summer days by remaining in the fa- pretation is supported by the fact that in the vorable environment of the burrow. The last two weeks before disappearing into hi- blacktail prairie dog, Cynomys ludovicianus, bernacula these adults stopped gaining (Althen 1975) also showed peak activity weight and on the average actually lost above ground synchronous with times of op- weight (Zegers and Williams 1977). Some timal microenvironmental thermal factor other than insufficient body fat was conditions. preventing these adults from hibernating two weeks earlier. Perhaps this factor was paren- tal care. Acknowledgments The effects of ambient temperature, cloud cover, and hour of the day on sciurid time Sigma Xi and the Kathy Lichty Memorial budgets are generally interpreted as ther- Fund of the University of Colorado provided moregulatory and water balance mechanisms. financial support. Dr. Olwen Williams gave

Michener (1968) demonstrated that S. rich- valuable suggestions and guidance. Dr. Ste- ardsonii modified overall activity in response ven Telleen helped with some of the field work. to Drs. Merritt, to air temperature and light intensity (i.e., Thanks James Ha, J. F. cloudiness) in ways that promoted overall D. McCracken, and S. Ha and two anony- maintenance of body temperature and water mous reviewers for their helpful suggestions balance. My data show that air temperature concerning this manuscript. 228 Great Basin Naturalist Vol. 41, No. 2

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behavior of the Richardson ground squirrel ciiirus. Ecol. Monog. 38: 31-63. {Spermopliilus richanlsoni clcg,ans). Amer. Midi. Streubel, D. p. 197.5. Behavioral features of svmpatrv of Nat. 83: 197-205. Spennopliihis .^pilosoma and Spermophilus tridc- squirrel 1970b. Richardson's ground (Spermo- cemlineattis and some aspects of the life history phihis richarclsoni) in the Laramie Basin, Wyom- of S. spilosoma. Unpublished dissertation, Univ. ing. Great Basin Nat. .30: 55-70. of Northern Colorado. 1.30 pp. Clark, T. W., and R. H. Denniston. 1970. On the de- A., S. R. Holthaus, and F. A. Wiens, J. G. Martin, W. scriptive ethologv of Richardson's ground squir- IwEN. 1970. Metronome timing in behavioral rel. Southw. Nat.' 15: 193-200. ecology studies. Ecology 51: 350-352. Dt^RRANCE, M. 1974. The annual cycle and population J. Yeaton, R. I. 1969. Social behavior, .social organization, dynamics of Richardson's ground squirrel. Un- daily and seasonal activity patterns in the Rich- published dissertation, Univer. of Wisconsin. ardson's ground squirrel, Spermophilus richard- Hadow, H. H. 1972. Freeze-branding: a permanent sonii. Unpublished thesis, Univ. of Saskatchewan. marking technique for pigmented mammals. J. 106 pp. Wildl, Manage. .36: 645-641). 1972. Social behavior and social organization in Mic;hener, D. 1968. A study of the ecology of Richard- Richardson's ground squirrel (Spermophihis rich- son's ground squirrels, Citellus richardsonii, with 53: ardsonii) in Saskatchewan. J. Mamm. special reference to effects of meteorological var- 1.39-147. iables on activity. Unpublished thesis, Waterloo Zegers, D. a. 1977. Energy dynamics and role of Rich- Univ., Waterloo. 88 pp. ardson's ground squirrel {Spermophihis richard- 1972. Population dynamics of Richardson's sonii elegans) in a montane meadow ecosystem. groiuid squirrels. Unpublished dissertation, Univ. Unpublished dissertation, Univ. of Colorado. 177 of Saskatchewan. 110 pp. pp. 1974. Annual cycle of activity and weight Zegers, D. A., and O. Williams. 1977. Sea.sonal cycles changes in Richardson's groimd squirrel, Spcrmo- of bodv weight and lipids in Richardson's groimd philiis richardsonii. Can. Field-Nat. 88: 409-413. squirrel, Spermophihis richardsoni elegans. Acta MicHENER, G. R. 1973. Climatic conditions and breed- Theriol. 22: 380-383. ing in Richardson's ground stjuirrel. |. Mamm. 1979. Energy flow through a population and 54: 499-503. Richardson's ground squirrels. .\cta Theriol. 24: 221-2.35.