Observations on Torpidity in Captive Chipmunks of the Genus Eutamias Author(S): Tom J

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Observations on Torpidity in Captive Chipmunks of the Genus Eutamias Author(s): Tom J. Cade Reviewed work(s): Source: Ecology, Vol. 44, No. 2 (Apr., 1963), pp. 255-261 Published by: Ecological Society of America Stable URL: http://www.jstor.org/stable/1932172 . Accessed: 24/12/2011 11:52

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http://www.jstor.org Spring 1963 CAPTIVE EUTAMIAS CHIPMUNKS 255 the red-legged frog (Rana aurora aurora). Herpeto- of development in Bufo vallicepts. Physiol. Zobl. 30: logica 16:251-259. 164-176. Straw, R. M. 1958. Experimental notes on the Deep Wright, A. H. 1932. Life histories of the frogs of Springs toad, Bufo exsul. Ecology 39:552-553. Okefinokee Swamp, Georgia. New York: Macmillan. Stuart, L. C. 1951. The distributional implications of Zeuthen, E. 1942. The ventilation of the respiratory temperature tolerance and hemoglobin values in the tract in birds. Danske Vidensselskab. Biol. Med. 17: toads Bufo marines (linnaeus) and Bufo bocourti 1-51. Brocchi. Copeia 1951: 220-221. Zweifel, R. G. 1955. Ecology, distribution, and syste- Thorson, T. B. 1955. The relationship of water econ- matics of frogs of the Rana boylei group. Univ. Calif. omy to terrestrialism in amphibians. Ecology 36: Publ. Zo6l. 54:207-292. 100-116. . 1957. Studies on the critical thermal maxima Volpe, E. P. 1953. Embryonic temperature adaptations of salamanders. Ecology 38:64-69. and relationships in toads. Physiol. Zol. 26:344-354. - 1959. Effect of temperature on call of the frog, . 1957. Embryonic temperature tolerance and rate Bombania variegate. Copeia 1959: 322-327.

OBSERVATIONS ON TORPIDITY IN CAPTIVE CHIPMUNKS OF THE GENUS EUTAMIAS TOMJ. CADE Department of Zoology, Syracuse University, Syracuse, New York

INTRODUCTION and talus slopes at timber line in the Sierra Nevada Hibernation is well known in a number of sciu- (E. alpinus) ; and some kind of chipmunk lives in rid rodents in the tribe Marmotini, and there have the understory or in the brush fields of all the been many excellent studies dealing with various forested zones lying between these extremes. species of marmots and ground squirrels. Some Other species have ventured into arid pin6n- work has also been done on hibernation in the juniper scrub forests (E. panamintinus; E. qua- eastern chipmunk, Tamias striatus (Allen 1938; drivittatus hopiensis), sage brush desert (E. mini- Woodward and Condrin 1945; Engels 1951; mus), and dry chaparral associations (E. mer- Yerger 1955; Lyman and Blinks 1959; Panuska riami). 1959), but surprisingly little attention has been Such a "plastic" group, containing populations given to patterns of activity and torpidity among readily modified to take advantage of subtle en- species of the related genus Eutamias. No physi- vironmental opportunities, may well encompass a ological studies have been reported, and the brief wide spectrum of physiological adaptations re- records by Svihla (1936) and by Broadbooks lated to periods of activity and torpidity. It is (1958) on a few captive specimens of E. amoenus this likelihood of divergence in the physiological seem to be the only laboratory observations. adaptations of closely related species that makes The literature in natural history and ecology the genus Eutamias such an attractive group for also contains few references to torpidity in west- study. ern chipmunks, a fact which has not changed This study presents some exploratory findings appreciably since Howell (1923) first called at- on several aspects of torpidity in 3 species of tention to it nearly 40 years ago. Only twice have Eutamias, with the hope of stimulating others to descriptions been published of naturally hiber- undertake the detailed physiological investigations nating chipmunks (E. townsendii) found torpid so interestingly posed by the ecological distribu- in their nests (Walker 1923; Anthony 1924). tion of this genus. The work was carried out Grinnell and Storer (1924: 81) mention a trap- during the tenure of a postdoctoral fellowship injured individual of E. specious which became from the National Science Foundation in conjunc- torpid and subsequently aroused in captivity, and tion with a program of study at the Museum of Criddle (1943) gives some information on E. Vertebrate .Zoology, University of California, minimum. Broadbooks (1958) has summarized a Berkeley. few other field observations; otherwise little seems to be known. MATERIALS AND METHODS Western chipmunks occupy a diversity of basi- On 18 October 1958, 35 live traps were set in cally chaparral-like habitats in North America. 5 localities on the west side of Lake Almanor, Some live in the brushy understory and log- Plumas County, California, between the Almanor littered floor of humid coastal forests (E. town- postoffice and the southwest corner of the lake. sendii); others in rock-bordered, alpine meadows Seven chipmunks were captured as follows: one 256 TOM J. CADE Ecology, Vol. 44, No. 2 adult male E. quadrinaculatus, one adult male E. sunning, and chasing each other were the main speciosus, one adult male and 4 adult female E. activities. Typically a chipmunk would go to the a-noenus. In addition to these captured indi- food tray soon after emerging from its sleeping viduals, at least 3 other E. speciosus and 20 E. box, fill its cheek pouches with shelled seeds, and amnoenus were seen during the day. Tevis (1953) then retire to the top of one of the sleeping boxes also found E. townsendii around Lake Almanor. to sit and eat at its leisure. Or if it showed a That same day, the chipmunks were transported tendency to hoard seeds, it would eat a few, then down from the mountains to Lafayette, Contra enter one of the boxes, store the rest, and con- Costa County, California, where they were placed tinue to make trips with filled cheek pouches from together in an outdoor cage with a floor space of the food tray to the sleeping box for a good part 36 square feet and a volume of 72 cubic feet. The of the day. Idle chipmunks usually perched atop cage was provided with 6 sleeping boxes made of the sleeping boxes, where they often sat in the one-inch thick, unfinished redwood boards with typical upright posture on their haunches or inside dimensions of 6" by 12" by 5" high. Each stretched out in various relaxed postures to doze had a 2-inch square entrance near the top of one in the sun. At other times, particularly when end and a removable lid for convenience in ex- several chipmunks were trying to collect seeds at amining the occupants. Cotton was provided at the same time, they chased each other vigorously intervals for nesting material. The cage was all about the cage and in and out of the sleeping always provided with water and food, which con- boxes. sisted of sunflower seed, cracked corn, milo maize, The animals were strictly diurnal, never emerg- barley, and occasionally pieces of apple and lumps ing from the sleeping boxes until the sun was well of peanut butter mixed with oatmeal. up and always retiring for the night before sun- Permanently fastened around the neck of each down. They were reluctant to move about in the chipmunk was a collar made of differently colored dark inside their sleeping boxes and seldom at- porcelain beads strung on copper wire. General tempted to escape from a box at night even when observations on activity and behavior were made disturbed. at a distance of 15 feet from inside quarters by All of the chipmunks showed a strong prefer- looking through a glass door leading onto the ence for sunflower seeds. Apple was readily sundeck where the cage was located. Body tem- eaten, and so was the peanut butter-oatmeal mix- peratures and weights, unless otherwise indicated, ture, but sunflower seeds were the only food were all taken at least 2 hours after dark, usually stored in the sleeping boxes. The stored seeds between 2200 and 2300 hours. The animals were were always shelled and placed in the bottom of weighed on a triple beam balance accurate to one the cotton lining of the nest. tenth of a gram, and all temperatures were esti- mated to a tenth of a degree C, using a Schultheis BODY TEMPERATURE AND TORPIDITY rapid registering thermometer inserted to a depth A number of rectal temperatures taken under of 15 mm rectally, orally, or into a cheek pouch. various external and internal conditions are sum- After cautiously removing the lid of a sleeping marized in Figure 1. The body temperatures of box, it was often possible to get resting or sleep- these nontorpid chipmunks were conspicuously ing rectal temperatures by gently lifting up a labile, ranging from a low of 310C during sleep chipmunk's tail and inserting the thermometer. to a high of 40.6? C following vigorous activity. The chipmunks showed remarkably little resist- After moderate to heavy activity, the body tem- ance to this procedure so long as they were left perattures were typically above 380C; during inside their sleeping boxes. To obtain active periods of rest, rectal temperatures were usually body temperatures, the chipmunks were allowed in the range of 36 to 370C, but during sleep, tem- to run freely in a small room for several minutes. peratures were frequently down to 34WCand often From time to time individuals were placed in lower. No significant differences were noted be- plastic boxes and kept for variable periods in a tween the resting or sleeping body temperatures refrigerator at 3 to 40C in attempts to induce at ambient temperatures of 3 to 4VC in the re- hibernation. Observations ended 7 February frigerator and those taken at 10 to 20'C out- 1959. doors, although the samples taken at the low range of air temperature are small. Thus the body RESULTS temperatures of these nontorpid chipmunks fluc- GENERAL BEHAVIOR AND ACTIVITY tuated normally through a range of 9 to 100C The chipmunks quickly adjusted to caged life during their daily cycle of activities. and settled into a predictable routine of activities No chipmunk in the outdoor cage entered deep in the first 2 or 3 days. Feeding, hoarding seeds, hibernation under the moderate winter conditions Spring 1963 CAPTIVE EUTAMIAS CHIPMUNKS 257 * AMBIENT TEMP 10?-20? C. inactivity, although their body temperatures re- 42 - AMBIENT TEMP 3?-4?C. (ALL RESTING mained above 300C. ?OR SLEEPING) These changes in the activity of quadrimaculatuis first became o 40 ACTIVE obvious 20 November, when he did not emerge from his z RANGE sleeping box until 0945, a full _ s~~~- 2 hours after the other chipmunks had become ! 8 ! - .- .'i-.-.----- :. .... active. His first appearances were noted as often RESTING as possible thereafter. On 25 November, for instance, he did not appear until 1300 and remained outside for only an hour. He was not seen outside his sleeping box at all 2 December, RANGE although a check that night revealed that he still held a rectal temperature of 340C. From this date until 9 January quadrimaculatus often remained 30 inside his sleeping box all day, and if he came out at all it was only for a brief period of 30 to 45 minutes in the middle of the afternoon, around E. QUADRIMACULATUS E. AMOENUS 1400 to 1500 hours. During these brief exits he E. SPECIOSUS seemed more interested in drinking than in col- FIG. 1. Lability of body temperature in chipmunks lecting seeds. under various external conditions and different metabolic All during this period he kept a states. large store of 200 to 300 g of shelled sunflower seeds in the bottom of his nest. After 9 January, at W~~~~~~~Lafayette. Furthermore, only 2 animals be- he began to appear regularly for short periods came fat as most hibernating sciurids do (Table each afternoon, but never for more than an hour I ). The weight of quadrimaculatus was quite or 2 at a time. Although he was observed fre- constant with observed extremes of 85.1 and quently at night during this time, he was never found in a torpid condition, and the lowest rectal TABLE I. Body weights of captive chipmunks (Eutamias) temperature recorded was 32.6?C. A similar but less ANIMALS well-marked reduction in activity was also noted for amoenus-1, beginning Daequadri- amoenusamoenus amoen us amoenusamoenus 25 November when this animal first started to maculatusspeciosus 1 2 3 4 5 hoard seeds and to sleep in isolation. During the I Nov. 85.1 81.6 56.8 52 .0 58.1 60.3 49.1 latter half of December there were a few days 11 Nov. 85.9 87.5 58.7 55.2 69.5 65.5 51.5 20 Nov. 88.6i 87.7 65.9 58.0 77.0 66.4 51.2 when this individual did not emerge from her 1iDec. 88.3 95.3 60rO.0 57.1 73 .3 60.7 54.6 sleeping box, but usually she did come out for a 10Dec. 87.6 - _ _ _ _O - few minutes each day. 12 Dec. - 91E.2 - _ _ _ Like quadrimaculatus, she 14Dec. - 94.1 - - _ _c was never found torpid at night with a low body 20 Dec. 86.7 - 52.1 53 .2 - 56 .1 50.9 temperature. uJan. 85.3 80.7 47.1 52.2 63.2 - 50.6 25 Jan. 89.1 84.4 49.0 52.0 62.8 - 49.6 Both these chipmunks were very gentle and easy Mean 89 .1 87.8 55.9 54.3 67.3 61.8 51 .1 to handle during this time. When taken out of their sleeping boxes at night and held in the hand, 89.1 g. Only specious and amoenns-3 gained they did not try to escape or move about very appreciable weight. The heaviest weight of spe- much, and if left sitting undisturbed they would cisus, 95.3 g, amounted to an increase of 13.8 g often go to sleep. If forced to move about, they or a little better than 18% of its initial weight, quickly warmed up to rectal temperatures of 370C, whereas the heaviest weight of ahmoenks-3, 77.0 g, after which they became more responsive, but if amounted to an increase of 18.9 g or a little less left alone their temperatures soon dropped back than 35%0 of its initial weight. down to 340C or lower. None of the other chip- The patterns of daily activity revealed some munks showed clear-cut reductions in the amount interesting features for qubadrimaculatuhs and of their activity as winter progressed, and none amoenus- 1. These were the only 2 animals which of them acted lethargic, although their rectal tem- consistently hoarded seeds and slept in isolation peratures, too, were frequently around 330 to from the other chipmunks. Both of these chip- 340C at night. munks became progressively less active as the Figure 2 shows the change in body weight of winter advanced, and they tehded to become lethar- several chipmunks held without food in a re- gic in behavior during the prolonged periods of frigerator at 30 to 40C. During a 9-day fast, 258 TOM J. CADE Ecology, Vol. 44, No. 2

900 ESOPHAGUS OR CHEEK POUCH 90 0 s sTORPID7 RECTAL 40 -- ESOPHAGUS OF DEAD ANIMAL 80 N

35 - _70 SPECIOSUS

60N AMvENUS-3 (TORPID) W 30 ,

n50 AMOENUS-I Z 25 40 w AMOENUS-4 (DEAD AT END)

30 0 1 2 3 4 5 6 7 8 9 10 2~~~~~~~~~~~ DAYS OF FOOD DEPRIVATION a.11 FIG. 2. Decline in body weights of chipmunks kept without food in a refrigerator at 30 to 40C. 20

speciosus lost a total of 43 g, starting at an ini- w5 4 tially heavy weight of 94.1 g, or an average of w . . . .* . 4.8 g per day. The rate of weight loss was fairly uniform during the 9 days, except for the 4th andl 5th days when the rate of loss was only one granm per day. Unfortunately, the animal was not observed on these 2 days. On the 3d day, however, I- 10 2 30 40 50 60 70 MINUTES FROM BEGINNING OF AROUSAL the animal had been observed curled up in a ball FIG. 3. Rate of arousal of E. amoenus from with a respiratory rate of 10 breaths in 10 seconds deep hibernation, as indicated by increase in rectal and oral tem- and a rectal temperature of 26.6?C. On the 6th peratures, at a room temperatureof 200C. day the animal was active with a rectal temperature of 370C, and he was never again found with 3. For comparison, the passive increase in tem- a rectal temperature lower than 30'C. At the perature, of a dead chipmunk, amoenus-4, is also end of 9 days, speciosus weighed only 51.1 g, or indicated. The initially slightly faster rate of 30.5 g less than his first recorded weight a few increase for the dead animal may be explained by days after capture. Since he was in a weak con- the fact that the dead individual had a slightly dition and clearly could not have survived much smaller mass than did the live chipmunk. Cn- longer, the animal was returned to the outdoor ceivably it might also reflect a physiological. dif- cage with the other chipmunks. Seven days later ferenlce resulting from some sort of circulatory he again weighed 80.7 g, a gain of more than 4 g shunting of the heat in the live animal to critical per day. organs. Rectal temperature lagged somewhat be- During their short periods in the refrigerator, hind oral temperature, particularly during the amoenus-1 and amoenus-4 remained active-often middle part of the arousal. The actual difference hyperactive-and the lowest rectal temperature is probably greater than indicated by the measure- recorded for these individuals was 340 C. Both menlts, because the rectal temperature was taken lost weight rapidly, and ctmoenus-4 died on the 3d about half a minute after each oral temperature.- day at a body weight of 39.3 g or after a loss of Other individuals of amoenuss and qua~drimacu- 16.7 g. latus were kept in the refrigerator at 3 to 4? C The other chipmunk of this group, anOvenus-3, f rom- 2 to 5 days with food available. None of began fasting at the heavy weight of 69 g and these anii-nals became torpid, none lost weight, and during a 4-day period lost 15.5 g. On the 3d day rectal temperatures below 30'C were not recorded this individual became torpid; at 2135 on that ally case. day it was found curled up in the typical hibernation posture with only 15 respirations in 25 to DISCUSSION 30 seconds, interspersed with short periods of HIBERNATIONIN SPECIESOF Eutamias apnea. On the 4th day this animal was artificially Tile fact that so few western chipmunks have aroused by placing it at a room temperature of b~eeti foul-id inl a dormant state raises a question 200C. about the nature of hibernation in these squirrels. The rate of arousal, as indicated by increase in Tile question is further emphasized by the fact that rectal and oral temperatures, is shown in Figure seNveral observers have reported species of Eulta- Spring 1963 CAPTIVE EUTAMIAS CHIPMUNKS 259 mias to be active above ground at various times Although active chipmunks are likely to be seen during every month of the winter season (Walker on occasions throughout the winter, there is no 1923; Taylor and Shaw 1927; Criddle 1943). question that these animals do undergo profound In the San Bernardino and San Gabriel mountains seasonal changes in the amount of activity they of southern California, E. speciosus has been ob- carry on above ground in their natural habitat. served around public camp grounds in every month Such a seasonal change was clearly reflected in of the year; it appears to become inactive for the pattern of activity shown by 2 of the captive periods of several days only during times of rela- chipmunks,E. quadrimaculatus and E. anoenius, tively deep and sustained snow cover and is likely but the inactive state was not accompanied by to be active on bright sunny days even in Decem- entrance into deep hibernation in either case. ber and January (Cade, unpublished). Tevis Svihla (1936), keeping animals in outdoor cages (1955) is the only writer who has reported pro- near Pullman, Washington, and Broadbooks longed inactivity of chipmunks during the winter. (1958), keeping animals indoors at 680F, noted a Despite a mild winter with much thawing of snow similar tendency for captive individuals of E. and little frozen ground, he neither saw nor heard amoenus to become less and less active as winter a chipmunk from 29 November to 19 March in progressed without ever entering deep hibernation. the Lake Almanor region. Emergence was grad- Criddle (1943) observed the same gradual de- ual, and chipmunks did not appear in conspicuous crease in the above-ground activity of a wild popu- numbers until the middle of April. lation of E. minimus in Manitoba. In the present series of observations, one indi- Available evidence from the field and from the vidual of E. amoenus entered a state of "deep few captives studied supports the notion that spe- hibernation" with an oral temperature of 4.60C cies of Eutamias are not typical hibernators in the and subsequently aroused from that condition. sense that they easily and regularly allow deep The performance of this animal during recovery body temperature to drop down to values ap- seemed typical of the arousal of a hibernator proaching low ambient temperatures for long rather than of the slow return to normalcy of a periods of time. The information available on nonhibernator forced into a hypothermic state. Tanias stratus indicates that it is similar to Euta- The average rate of arousal, 0.50C per minute, is mias in this characteristic (Woodward and Con- quite fast for an animal of its size. By compari- drin 1945; Panuska 1959). According to Pear- son, the average rate of arousal of a smaller hiber- son's (1960) useful classification, these chipmunks nator, such as Perogncathus longimembris weigh- are "stubborn homeotherms," capable of main- ing about 8 grams, is around 0.60C per minute taining a warm body temperature in a wide range (Bartholomew and Cade 1957), and for a larger of environmental temperatures and resorting to one, Citellus mohavensis weighing about 250 deep hibernation only when faced with severe grams. the rate varies between 0.4 and 0.10C per stresses such as exhaustion of the winter food minute (Bartholomew and Hudson 1960). cache. Compared with some other hibernators Other indications of some kind of hiberation in in this category, western chipmunks appear to be this group are fat accumulation in the fall and the much more stubborn than pocket mice (Bartholo- tendency of captive individuals to become inactive mew and Cade 1957), considerably more stubborn in the winter. Tevis (1955) found "hiberation than most species of ground squirrels that hiber- fat" in specimens of all species occurring around nate, and are perhaps about comparable to that Lake Almanor, except E. amoenus, of which no most stubborn of all hibernators, the domesticated specimens were collected at the right time of the hamster (Lyman 1954), which is also a notable year. The average gain in weight of these chip- food hoarder. munks in the fall was 20%. In contrast to these Since it is known that chipmunks store their findings, Broadbooks (1958), studying E. a-moe- food in the lining of their nests in the hibernaculum nmisin eastern Washington, observed no signifi- (Broadbooks 1958), it is consistent with the point cant seasonal increase in the live weights of a of view being developed here that the only chip- large series of animals. In the present study only munks found in deep torpor in nature were dug 2 out of 7 captive chipmunks gained appreciable out of nests which contained no food (Walker weight. By comparison, other species of hiber- 1923; Anthony 1924). A further point of con- nators, such as Zapus spp. and some species of sistency may relate to Tevis's (1955) observations Citellus, that depend primarily upon body fat as that no chipmunks were active above ground dur- their source of energy during hibernation, typi- ing the winter of his studies in the Lake Almanor cally gain an amount of fat equal to their fat-free region. His studies were carried out during a body weight ( Morrison 1960). period of widespread failure in the seed crops most 260 TOM J. CADE Ecology, Vol. 44, No. 2 commonly used by chipmunks for their winter munks in any physiological condition are un- stores. In the fall of that year before their dis- available, but an approximation can be made by appearance below ground, the chipmunks in this employing a number of reasonable assumptions. area fed heavily on subterranean fungi, a bulky, Consider a small chipmunk such as E. amoenus perishable food not usually stored but nutritious with a fat-free weight of 50 g. The calculated enough to allow the chipmunks to build up con- standard or resting metabolic rate for such a mam- siderable reserves of fat. With only residual stores mal according to Kleiber's (1947) formula- of seeds in their hibernacula but possibly more 70 X W4, where W equals the body weight in body fat than is typical of Eutacmias when they kilograms-is about 7.4 kcal per day. Assume become inactive, it is possible that these chipmunks that the average metabolic rate of a chipmunk in switched over to a kind of physiological prepara- shallow hibernation is slightly substandard and, tion that permitted many of them to spend the further, that the chipmunk does not have to ex- winter season in a state of deep hibernation, since pend any extra energy to keep its body tempera- it has now been shown that a western chipmunk ture above 30'C, a not unreasonable assumption can survive deep hypothermia and arouse. since the animal is curled up inside a well-insulated The kind of winter inactivity shown by captive nest (Broadbooks 1958). chipmunks, which become sluggish in behavior but The average daily expenditure of energy might which permit their body temperatures to drop no be about 6 kcal, or a total of 720 kcal during lower than 300 C, is reminiscent of the kind of a period of 120 days of hibernation. If one as- hibernation reported by Hock (1957, 1960) for sumes further that the chipmunk is about 70% the black bear ( Ursus americanus). Hock ( 1958) efficient in using the total energy available in its has used the term "carnivorean lethargy" to desig- food (see Brody 1945), then its total energy re- nate the condition found in bears and some other quirement for a season of hibernation is equivalent carnivores. For the similar condition found in to about 294 g of graminecous seeds (see Spector Eutamias such a term is obviously inappropriate, 1956, for caloric values of various grains) or about and a more general term such as "shallow hiberna- 208 g of sunflower seeds or other highly fatty seed tion," which contrasts nicely in meaning with the such as pine nuts. It is also equivalent to 78 g flow well-recognized term "deep hibernation" of animal fat. made popular by Lyman and Chatfield (1955), is Quite obviously no chipmunk can accumulate preferable. enough body fat to survive a winter in a state of In short, then, as their main adaptation for sur- shallow hibernation without supplemental food vival during the winter, species of Eutamias seem stores, as a bear can (Hock 1960; Morrison 1960). more dependent upon storing food sufficient for the In his field studies of E. amoenus, Broadbooks winter season in the hibernaculum than on drasti- (1958) unearthed 3 November nests which con- cally reducing metabolic rate and energy require- tained, respectively, 70.0, 170.0, and 190.1 g of ments by means of deep hibernation, although that food, mostly seeds. The latter 2 values are close may be an alternative possibility for some species. enough to the calculated need to permit the con- By greatly reducing their activity in the winter, clusion that a western chipmunk can pass the however, these chipmunks achieve a kind of adap- winter in a state of shallow hibernation on the tive compromise between the minimum energy energy available to it in 10 to 20 g of body fat requirements of a deep hibernator and the high plus a single store of seeds placed in the lining energy requirements of a rodent that remains of its nest. active all winter. Thus they gain the advantage of SUMMARY a relatively low energy expenditure during a period when the food supply is short without The ecological distribution of species in the losing all the advantages of an active life, such as genus Eutamias suggests adaptive differences escape from predators and from flooding of among these closely related populations with re- burrows. spect to periods of activity and torpidity. Seven captive chipmunks representing 3 sympatric spe- BIOENERGETICS AND SHALLOW HIBERNATION cies, E. amoenus, E. quadrimaculatus, and E. spe- If this hypothesis is true, then it is worthwhile ciosus, were studied from this point of view from to consider the energy requirements of a chipmunk October, 1958, to February, 1959, in California. spending the winter in a state of shallow hiberna- The chipmunks were kept together in an outdoor tion. How much food must such a chipmunk cage and were individually marked. store for the winter, and is this amount consistent All chipmunks had labile body temperatures, and with the known capabilities of hoarding chip- one amoenus entered a state of deep hibernation munks? Unfortunately, metabolic rates of chip- in a refrigerator at 30 to 40C without food and Spring 1963 ECOLOGY OF SOIL ARACHNIDS 261 subsequently aroused at a room temperature of tures of active and "hibernating" black bears. Fed. 20'C. One quadrimacuzlatusand one amoenus in Proc. 16:440. the outdoor cage became progressively less active . 1958. Hibernation. In: Cold Injury. Trans. 5th Conf. Josiah as winter advanced, but neither entered deep Macy Found., pp. 61-133. . 1960. Seasonal variations in physiologic func- hibernation. Evidence from the field and from tions of arctic ground squirrels and black bears. captives indicates that species of Eutacmiasdo not Bull. Musc. Comp. 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STUDIES ON THE ECOLOGY OF SOIL ARACHNIDS EDGAR C. GASDORF' AND CLARENCE J. GOODNIGHT Department of Biological Sciences, Purdue University, Lafayette, Indiana

INTRODUCTION abundant forms encountered, and spiders, pseudo- In nearly every type of soil environment the scorpions, opilionids, and other forms are found arachnids are well represented. In many soils, in lesser numbers. In spite of the abundance of they are the most numerous of the smaller animals arachnids in the soil, they have not been intensively present. Of the arachnids, the mites are the most studied. 1 Present address: Biology Department, Bradley Uni- A number of investigators (Elliot 1930; Riha versity, Peoria, Illinois. 1951; and Becker 1951) have found that soil