“‘ ~ n o. N ‘ z 0" " ‘ ' ‘ -" nlt 0 “- Q ‘1. g I , ~ \ ' ‘ ',. ‘ . . of . x .. Us: \ - - . ..\....-a\ - .y,,.. .. . - h... .- ‘0 "‘ N . .' o . ‘ t I ‘ I. " I _ u 0-. t ~ ~<- rd 'v \:¢ v a r t ‘ I \- ‘ - O 5 o ‘ ' l lu- ‘ , . ‘ r - ~ - o g .' ‘S 3 r. " a . x ' .Z.‘ \ s ‘ .r n ' yoo‘S-o‘ '5'. Ov-‘r M ~;‘o~-u 59 00c. . . . f‘. 0 T ,~. 9 » O " :1 g :-:o. 'I- .c- . n n- F. ' I .5 L ' .,. - 7;} MN.- vn‘- \r " 3 d...~'...~l'“§.‘\v \ ~ " . .45 . - . ‘ ' ‘~ _~ , " o, , ‘ ‘ . - ‘ J... u .--a-- ~~ n‘x-‘n .. . M wan. .. -. I -g. n a ‘ ‘ “ ." ’ .o-\ ' (.7 5.9 THESIS This is to certifg that the thesis entitled Studies on Winter Activity of the Eastern Chipmunk presented ht] / Donald R. Breakey has been accepted towards fulfillment of the. requirements for M. 5. degree in z__°___EY_O]-° HR {314mb Major professor llfltf.‘ I'LL-1y 239 19520 ‘ . r ' O~169 PLACE ll RETURN BOX to remove thle checked from your record. TO AVOID FINES return on or before dete due. DATE DUE DATE DUE DATE DUE A a, .; a “ICE _ MSU le An Nflrmettve Action/EN Opportunity Inethwon Wane-9:1 Irv VI, n r Vlvln—i r . *7 {TR STUDIES ON WINTER ACTIVITY OF THE EASTERN CHIPMUNK by Donald Ray Ereaqu A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements ‘ for the degree 0! MASTER OF SCIENCE Department of Zoology Year 1952 ACKNOWLEDGMENTS The author wishes to express sincere thanks to Dr. Richard H. Heaville for his indispensible guidance and constructive criticism during the investigations and the preparation of this paper. To Mr. Earle Harrison, of the Michigan State College Animal House, the author is grateful for the assistance rendered with the captive animals. CONTENTS INTRODUCTION HISTORICAL REVIEW EXAMPLES OF HIBERNATORS TYPES AND EITENT OF HIBERNATION IN MAMMALS POSITIONS DURING HIBERNATIBN CHARACTERISTICS OF TYPICAL HIBERNATORS Temperature Respiration Heartbeat Irritability Loss of weight during hibernation METHODS OF AWAKENING FROM HIBERNATION PROBABLE CAUSES (F HIBERNATION Temperature Precooling Food Lack of available water Light Confined air Obesity Endocrine Glands Other possible causes "U m m 0 \O ‘O \O N -\‘| N O\ O\ UL U‘L U1 5‘ N N H KISS HIBERNATION IN THE EASTERN CHIPNUNK HISTORICAL REVIEW Fall disappearance and spring emergence dates BurrCW'constructicn and food storage Field observations of hibernation Experimental and captive animals Possible factors causing torpidity EXPERIMENTAL'WORK METHODS OF STUDY EXCAVATION OF BURRGWS First nest Second nest Third nest FOOD cbusmmxon EXPERIMENTS Introduction ‘Description of specimens First experiment Second experiment Third experiment SUMMARY OF EXPERIMENTS DISCUSSION LITERATURE CITED iv 15 15 15 17 17 18 19 22 22 LIST OF ILLUSTRATIONS TABLES PAGE Table I Average daily grain and apple-weight—loss for the 30 four specimens during the period of January 1h to February 3, 1952. Table II Daily apple-weight-loss, grain~weight-loss, daily 32 average temperature and daily hours and minutes of sunlight for the period of February h to February 15, 1952. Table III Appledweight-loss for the four specimens plus the 37 average daily temperature reading and total amount of hours and minutes of sunlight from February'lé to Nbrch.20, 1952. FIGURES Figure 1. Diagramatic cross-sectional sketch of the burrow 28 system Figure 2. Diagramatic horizontal sketch of the burrow 28 system Figure 3. Specimen No. l, sunlight and appledweight-loss 39 Figure h. Specimen No. 1, average temperature and apple- 39 weight-loss Figure 5, Specimen No. 2, sunlight and apple-weight-loss .hO Figure 6. Specimen No. 2, average temperature and apple- ho weight-loss PLATES Plate I Double cage used for outdoor specimens h6 Plate II h? A. Area where the excavations were made B. Closer view of area, showing thick ground cover of fallen leaves v Plate III A. Burrow Opening with refuse and dirt heap appearing in front. B. Nest material of oak leaf pieces and acorns taken from.the third nest. h8 STUDIES ON WINTER ACTIVITY OF THE EASTERN CHIPMUNK INTRODUCTION The purpose of this study was to observe the extent of winter activ- ity of the eastern chipmunk (Tami§2_striatus rufescens Bole and moulthrop) and to determine the extent of torpidity of this animal during the winter months. RNch speculation and experimental work have been carried on in an attempt to determine the causes of hibernation among homoiothermal animals but the picture, as concerns the eastern chipmunk, still remains rather vague. HISTORICAL REVIEII Hibernation stems from the Latin word 'hibernae' which means ti'to go to winter quarters" (Hahn, 1911;). However, at the present timethe term has a more restricted meaning. Hahn (1911;) describes the process as 'a protracted condition of letharg, during which vital organs of the animal are more or less completely suspended.‘ Hamilton (1939) explains it further as "an inactive state in which the metabolism is greatly lowered, resulting. in a bow temperature slightly higher than that of the surroundings." Iyman and Chatfield (1950) extend the definition to include a reduction of the heart rate and of respiration and e drop in the function of some vital organs concurrently with the lowering of the general metabolism and body temperature. EXAMPLES OF HIBERNATORS lost common and familiar among hibernators are the poikilothermal animals which, having no regulatory system, are inactive in the tem- perate zones during the colder months of the year. Common among inver- tebrate hibernators are snails and most arthrOpods. Amphibians and terrestial reptiles in the temperate region are also known to become torpid (hiring the colder time of year (Johnson, 1931). . Among the homoiothermal animals there are examples which, as far as can be determined, act much the same as the poikilothermal individ- uals during the colder period of the year, in that the body temperatures of these animals remain only slightly higher than in the surrounding environment and consequently there is a marked reduction of all how functions. 1‘his is probably due, in these species, to an imperfectly developed heat regulatory system; this trait may be retained to enable the individuals to become poikilothermal during a season when no food is available (JOhnson, 1929 ). Nevertheless, there seems to be a great deal of variation in extent or hibernation and the length or time, each season, which the individuals of these species spend in the actual hibernating state (Abbott, 1881; ). Among the homoiothermal animals, the best known hibernators and those used for much of the experimental work are the rodents hrmota (nrmots) and Citellns (ground squirrels). Much work has been carried on, using representatives of these two genera, aimed at determining the extent and causes of hibernation in general, as well as the body function reactions of these two forms in hibernation. . Other rodents which are known to hibernate are the hamsters (Cricetus ), dormice (miscardinus), prairie dogs (Cyngfls), and some of the juming mice (_z_ap_u_s_ and Napaeozapus) and pocket mice (Peroathus ), although most of these do not hibernate as deeply as Citellus and lsrmota. Among the more primitive mammals, hibernation is carried on by the llonotremes, some ' insectivores (e.g. European hedgehog) and the insect-eating bats (Johnson, 1931)e Io animal larger than the woodchuck has been definitely proved to be in a true hibernating state. Observations of the bear show cause for belief that this animal is not a true hibernator (Benedict and Lee. 1938). Among the birds, the only known example of hibernation occurs in the family Caprimulgidae. Jaeger (l9h9) has made observations on the hibernation o: the poor-will (Phalaenoptilus nuttalii) in California. TYPES AND EXTENT OF HIBERNATION IN MAMMILS some members of the family Vespertilionidae (insectneating bats) are, of the known examples, probably the nearest approach to the poiki- lothermal animal among the mammals and are said to ”take to hibernation with the greatest of ease." (Lyman and Chatfield, (1950). Reeder (1939) found that the body temperature °f.HZ23$E californicus pallidus in California had 'an interesting relationship to that of the environment.” It is known that, in bats the body temperature and metabolic rate drop markedly every time these mammals go to sleep (Lyman and Chatfield, 1950). There seem to be two separate groups of hibernators among the rodents, each showing basic differences in the extent of, and.preparation for, hibernation. The first group is represented by the woodchucks (or mammots) and the ground squirrels which accumulate a great deal of fat during the summer and fall, entering into a deep and continuous torpor either after sufficient fat has been accumulated or at the advent of colder weather (Iyman and Chatfield, 1950). There seems to be some question as to whether the woodchuck actually hibernates over the entire period of cold weather without awakening to feed or stir. Some authors actually say that there are awakenings during the hibernating period. The second group of hibernators is represented by the hamsters (Gricetus) and the jumping mice (_Z_ap_u_§ and Napaempu) and are those which do not accumulate excess fat, but instead store grain or other food.materials in the dens. This store of food is drawn upon throughout the winter as the animals awaken frequently (nyman and Chatfield, 1950). The eastern chipmunk could very easily be classified in this category, if the data presented.by most authors are true. POSITIONS DURING HIBERNATION The position assumed.hy mammals during the hibernation period is said to vary with species and individuals (Abbott, 188h), but it seems to he basically the same in all fossorial hibernators. One thing is clear, namely, that the most efficient position is taken for retaining the greatest amount of heat within the body during hibernation (Johnson, 1931). The usual position for hibernators is to curl into a tight ball, the nose touching the pelvic region or the chest region, the feet on each side brought close together, and the limbs rigid while the , tail is laid to one side, over the head and down the spine. The eyes and lips are usually closed tightly (Hamilton, 1939; Johnson, 1931). CHARACTERISTICS OF TYPICAL HIBERNATORS Typical hibernation possesses certain characteristics which dis- tinguish the process from sleep or other subenormal metabolic processes. The most apparent of these are as follows: Temperature. Body temperature during hibernation is typically much lower than the near constant body temperature of the normally active animals. It has been found that the temperature of hibernas tors, even when active, is usually lower than that of non-hibernators (Bea ilton, 1939 ). and this may be due to the inadequately developed hypothalamus or heat-regulatory'system.in these animals (nyman and Chatfield, 1950). The body temperature of most hibernators is found to flncuate with that of the surrounding medium.and, as reportsd.in ground squirrels by Johnson (1928), the body temperature will remain I‘ I. f. at approximately BhQF. If an animal remains dormant when there is a drop in atmospheric temperature to freezing or lower, it will freeze to death, but, as is usually the case, the animal awakens when a temperature' drop to freezing occurs (Hamilton, 1939; Lyman and Chatfield, 1950). Svihla (19hl) found that daily underground temperatures in the vicinity of Kenniwick,'fiashington, remained essentially constant as compared to the great deal of daily fluctuation in air temperatures. Caves, in which bats hibernate, usually have a fairly constant tempera- ture (50° to 609?.) and often possess a high degree of humidity (Ml-“n: 1939 )e Respiration. The rate of respiration in hibernating mammals varies in species and individuals, but is usually extremely low. Rates of respiration may vary from.seven or eight inspirations per minute in the marmot to four or five in certain bats. Periods of several minutes have been known to occur when there is no inspiration at all (Johnson, 1931) and in some bats (Eatesicus) these periods are followed hy several minutes of relatively rapid breathing of 50 to 80 inspirations per minute (Hamilton, 1939). Heartbeat. Very slow circulation is characteristic during hiber- nation and the heartbeat may be as low as three to four beats per minute during profound torpidity in marmots (Johnson, 1931). Johnson (1928) recorded the lowest heartbeat in hibernating ground squirrels at five beats per minute. Because of the extremely slow rate of circulation, the effect of toxic substances was found to be greatly decreased in hibernating mammals (Johnson, 1931). Irritability. Response to stimuli decreases with the decrease in body temperature. It has been shown that ground squirrels which have bow temperatures of 68° to 86°F. move in a dazed manner, while a drop to 50°F. will bring only a raised head or other weak response. If the bow temperature approaches that of freezing, there is no response what- soever to stimuli (Hamilton, 1939). It was found that the peripheral nerves in woodchucks and hamsters do not function below 36.5%. and the cortex of the brain is incapable of electrical activity below tempera- tures of 68°F. Only the peripheral nerves, and those more basic for heat production, function during profound hibernation and during a period of hibernation the animals are completely deaf as the auditory nerves cannot transmit sound (Isman and Chatfield, 1950). Loss of weight during hibernation. It has been shown that there is a very definite loss of weight in manuals ,during hibernation, especially in those which accumulate body fat. This loss was found to be, on the average, about 115 per cent of the total body weight in hibernating ground squirrels after 156 days of torpidity; during this time the animals spent 83 per cent of the time in a typically hibernating state (Johnson, 1931). This would indicate that an extreme prolonged period of hibernation would probably be fatal to most hibernating mammals. METHOD OF AWAKENING FROM HIBERNATIOH Awakening from hibernation, as described by Johnson (1929 )3 seems to be of two general types. Both types include a raising of body tempera- ture and general metabolism to near normal for the species so that the hibernator is transformed from an inert state to an active state by muscular activity; both types seem to be caused by some stimulus or series of stimli which initiate one or the other type of awakening. The first type of awakening is a rapid one, accompanied by spas- mdic tremblings and intense shaking of the body and head. This type usually follows an abnormal stimulus such as a disturbance of the animal by removing it from the nest and transfering it to another location. The breathing increases markedly; the body shows slight movement at first followed by convulsive movements as the body is straightened. The hair, especially on the back, seems to stand upright during this process. The convulsive movements are evidently a rapid method by which to increase the metabolism and therefore raise the body temperature. The second type of awakening is a much slower process than the one previously described and usually occurs without trembling and shaking. This process includes a slow, steady increase in the breathing rate 1 slow movements of the head, until the head is worked out from under the W. After a time the body is straightened, slowly, to the normal position. This in time leads to the standing posture. This type of awakening is probably the one most typical in nature, but the first stated is the one usually described by most authors (Johnson, 1929 ). Ghatfield and Lyman (1950) found evidences which ”correlate with the Impothesis that the process of arousal is essentially a mass activation of the centers of the hypothalmus which govern heat pro- duction and conservation and which give rise to the maximal functional activity of the mathetico-adrenal and adrenal motor nervous sys tem ." (he theory as to the time of emergence from the burrows in the spring, in ground squirrels, has been proposed by Wade (1950 ), who found that this was determined by soil temperatures. He observed that frozen soil presents a barrier to the ground squirrels and makes it impossible for these animals to ”dig out" until the ground has thawed. PROBABLE CAUSES (F HIBERNATION Causes of the process of hibernation have been investigated by a great number of authors for several hundred years and it has been said that writings concerning this subject can be traced back to Aristotle. Ramssen (1916) very neatly summarized all experimental work and theories up to that time and the experiments concerning possible causa- tive factors of hibernation still continue. Temperature. Early works laid much stress on the necessity for cool to cold temperatures (Rasmussen, 1916), but it has since been concluded that this external condition plays a secondary role, if any, among the causative factors. Benedict and Lee (1938) concluded that "cold 35 2 is, in general, a contributory factor, but not of itself sufficient to cause hibernation.” It was observed, further, that wood- chucks begin to awaken from the hibernating state at a time when the surrounding temperatures have reached the lowest point (Simpson, 1913). loderate cold seems to be more favorable, however, than severe cold which may cause death in the animal or result in an awakening and a consequent exhilarated activity by the animal (Hamilton, 1939). Precoeling. Some workers have concluded that hibernation cannot be artificially brought about in the summer and therefore a period of precooling is necessary before hibernation can take place. However, it has been shown that hibernation can be induced in the laboratory at 10 any time of the year, but there seems to be a higher mortality during spring and summer, probably due to internal factors (Britten, 1928; Johnson, 1931; Stuckey and Coco, 19m; woodward and Condrin, 1916). Some workers have found it possible to induce a state of torpidity by a combination of insulin and cold in cats and dogs (Cassidy 22 21., 1925); a combination of cold.with the introduction of a high percentage of carbon dioxide has a similar effect in the marmot (Henedict and Lee, 1938). Johnson (1931) concluded that precooling "should not perhaps be considered a necessary cause in nature", but 'intermittent or gradual cooling of the ground in the fall doubtless aids somewhat in preparing the animal for hibernation.” £229. Lack of food is another causative factor which has been stressed by many authors (Abbott, 188k; Simpson, 1912). Johnson (1931) found that starvation increased the incidence of induced hibernation among ground squirrels. It certainly is a possible cause among the insect-eating bats (Hamilton, 1939), and the amount’of available food decreases or is entirely lacking during the period of natural hibernae tion. Hesse, tiles, and Schimidt (1951) state that 'the scarcity of food is a greater peril to homoiothermal animals than is cold.” However, the lack of food as a cause for the inducement of marmot hibernation has been questioned as woodchucks are said to retire into their winter dens at the time of a rejuvination of their natural food, due to fall rains (Hamilton, 1939) and.at least have food available in their dens as they use hay and other vegetation for bedding material (Benedict and Lee, 1938). Johnson (1931) found that ground squirrels readily took food when available and the inducement to a state of hibernation was extremely low in animals which had food available. Lack of available water. The lack of available water has been little stressed as a major cause of hibernation. Some experimental work has been carried on along this line, however, to determine the effect of water in the general metabolism of the animals during the period of hibernation. In woodohucks, it was found that the percentage of water by volume, in the blood, was lowest Just before hibernation occurred; at that time the percentage of water in the blood increased.progressively through the hibernation period until it reached a peak near the termina- tion of hibernation (Rasmussen, a. 1'. and G. 13., 1917). Experiments carried on with hibernating ground squirrels (Citellus townsendii) and Jumping mice (£3223 trinotus) showed that the peritoneal injection of water or a mixture of hydrochloric acid, salt and water caused these animals to awaken for periods up to eight days before reentering hibernation (Svihla, l9hl). Inst of the stress for the lack of water as a causative factor has been placed on the process of aestivation and the role dry food.p1ays in causing this process. JOhnson (1931) found that ground squirrels fed on dry oats would go into hibernation several days sooner, on the average, than those animals fed on water-soaked oats and concluded that dry food, as compared to moist, may serve as a partial cause of torpor. A.further clue relating to the habits of ground squirrels was the observation of Bvihla (19h1) that captive animals at no time drink, even when water is available. It was therefore concluded (by Svihla) that body moisture was gained by the animals from succulent vegetation and metabolically. 12 we Lack of light does not seem to cause hibernation and the presence of light does not seem to have a profound effect on preventing hibernation (Johnson, 1931). is is usually the case, however, no animal would naturally be found hibernating in direct sunlight (Benedict and Lee, 1938) and the position of the animal while hibernating would tend to shut out light from the eyes if light were present (Johnson, 1931). Johnson and Gun (1933) concluded that light showed little effect on hibernation or on the sexual cycle. Confined air. Dubois (1895 ) extended the autonarcosis theory which stated, briefly, that hibernation was caused by an excess of carbon dioxide in the blood; as a primary cause of hibernation, this theory has not stood the test of time (lumen and Chatfield, 1950). Johnson (1931) showed that ground squirrels hibernated Just as soon when placed in a refrigerator in a half-gallon can which was generously perforated with air holes, as did those in which the can was almost air-tight. In woodchucks, it was found that a high percentage of carbon dioxide in the blood would cause the animals to become torpid, but if this high per- centage were continued over longer periods, the animals would die within 80 hours (Benedict and Lee, 1938 ). Obesifz. Among the profoundly hibernating mammals, storage of fat is believed to be one of the primary causes of hibernation. Those which fail to accumulate sufficient fat are said to remain active well into the winter. Fatty tissue is said to make up one-third of the weight in bats and one-seventh of the weight in woodchucks. 13 Those animals which do enter hibernation without a sufficient accumu- lation of fat usually die during torpor, so it cannot be said that this is a natural hibernating state (Johnson, 1931). Endocrine glands. Mamy*workers have tried to show that all or cer- tain endocrine glands cause hibernation, but removal of any one endocrine gland does not induce a hibernating state (Lyman and Chatfield, 1950). It is thought that the process of arousal from hibernation is pro- duced by increased activity of the sympatico—adrenal system, and, con- versely, the entrance into hibernation is caused by a decrease in activ- ity of this system (Britten, 1928; Chatfield and Lyman, 1950; Johnson, 1931; Lyman and Chatfield, 1950). .Further, adrenal weights were found to increase from.a January low to a peak in midsummer (Woodward and Condrin, 19145 ). Cushing and Goetsch (1915) concluded that deprivation of the pitu- itary gland (of the entire ductless gland series) produces a group of symptoms comparable to that of hibernation, but Hahn (1916) found that demonstrable changes in the pituitary gland and other ductless glands of a large number of ground squirrels (Citellus tridecemlineatus) were absent or so inoonstant that the assumption of a lack of function of all or one of the ductless glands is not Justified. Johnson (1931) concludes that there has been no definite evidence produced showing that the poste- rior*pituitary has any influence on hibernation and injections of pitui- trin show that this substance is neither an inhibitor nor a cause of hibernation. 1h Gonadal enlargements in hibernating forms in the spring have been observed by marw workers, and it has been found that castrated ground squirrels hibernated to a greater extent during the breeding season than did normal individuals (Johnson, 1931). I Other possible causes. A combined action of cold and injected in- sulin has been reported to produce a hibernating-like state in cats and dogs (Cassidy 33'. 2., 1925 ). The absence of external stimuli was found to be a. contributory cause of hibernation in marmots, but it was observed that natural hibernation occurred by the middle of December, even in captivity (Benedict and Lee, 1938 ). HIBERNATION IN THE EASTERN CHIPMUNK HISTORICAL REVIEW Fall disappearance and spring emergence dates. Fall disappearance and spring emergence dates probably depend upon the latitude and geo- graphical location of the animals under observation and also upon the climatic conditions of the area for each particular year (Howell, 1929 ). Fall disappearance over a three-year period was found to be of the average date of October 214, in the vicinity of Wells River, Vermont (Smith, 1931). In New Hampshire, two chipmunks were seen as late as December 1, 1931; (Preble, 1936) and Manville (191.19) reported the latest date of a chipmunk being seen in the Huron Mountain region of northern Iichigan as October 16, 1939. Linduska (1950) found two chipmunks in traps in late December, 19140, and another in a trap in mid-January of 1952, in the vicinity of East Lansing, Echigan. It is thought that the fall disappearance of Eagiag corresponds to the time of the first heavy frost in the northern states (Allen, 1918 3 Blun, 19503 Dickenson, 1907 3 Seton, 1929 )9 but many authors have reported activity by these animals in warm spells of mid-winter (Cahalane, 191:7; Cory, 1912; Hahn, 1908; Hamilton, 1939; Howell, 1929). Anthony (1928) stated that a good average date of fall disappearance for the northern states would be from September through October. The last chipmunk seen by this author in the East Lansing area was on November 20, 1951, and it seemed to be quite active. The animal it- self uas observed in the shade, but there was sunlight present in the 16 immediate vicinity. The temperature at the time of the observation was approximme 25°F. and the temperature had been below freezing for a continuous period of at least eigxt days preceeding the observation. Spring emergence from the burrows is, likewise, dependent upon the general weather conditions. In the vicinity of Fort Beige, Ohio, it was found that the average date of emergence fell within the last two weeks of February and the first two weeks of March (Condrin, 1936) and Preble (1936) reported an observation of a chipmunk seen on March 17, 1935 which he believed was the average date of emergence in New Hampshire. Smith (1931) reported an average date of spring emergence to be larch 21, over a three-year period in the vicinity of Wells River, Vermont. Ianville (191:9) reported the first spring appearance to be on March 30, 191:0 in the Enron Mountain region of northern llichigan. It has been observed that the males emerge first, followed by the females at a later date (Burt, 191463 Hamilton, 1913; Ianville, 191:9) and Burt (191:6) reported the average time of mating in Washtensw County, mchigan, as the first week of April. Two chipmunks were seen by this author as early as February 21;, 1952 on the mohigan State College campus during a warm spell and another was seen on February 27, 1952. Even though there was periodic snow, from this date on, chipmunks were seen regularly during the warmer and sunnier days. (11 March 13, 1952, a chipmunk was seen abroad even though the temerature was near freezing and the slq overcast. No animals were seen between November 20, 1951 and February 21;, 1952, but a check of burrow Openings on January 21, 1952, showed fresh acorn shells and bits of meat as well as chipmunk-like droppings in front of three of the 1? burrows in this vicinity. The temperature had reached a high of 59°F. on January 17, 1952, but there were highs of 32°, hZO, 37°, and 25°F. on January 18, 19, 20, and 21, 1952 respectively (U.S. Weather Bureau, Lansing, Jan., 1952). Burrow construction and food stoxggg. Burrows are constructed by the eastern chipmunk in which it spends much of its life. It is unknown if all chipmunks will construct a new burrow or burrow system every summer, but.Allen (1938) thinks they do not. iIOst of the burrows are found to be quite complicated (Hamilton, 1939) and usually no dirt is found in the vicinity of the burrow opening, although there may be a small, freshly excavated pile of earth at the "back door“ opening which may or may not be plugged, eventually (Allen, 1938). Storage of food in underground dens is the common practice with this animal and Seton (1929) reported finding as may as 150 hickory nuts, :1 pint of cats, and a pint of basswood seeds within an excavated den. much of the food stored in the East Lansing area, on the basis of first-hand observations by this author, consisted of acorns. Field observations of hibernation. Field observations have been node on various degrees of torpidity in chipmunks found in excavated burrows. Most authors feel that the eastern chipmunk, in the northern states, is not a deep hibernator, but must be classed as a hibernating form (Brownell, 1923; Cahalane, 19W; Condrin, 1936; Lyon, 1936; Seton, 1929 ). Howell (1929) summarizes marry reports in which chipmunks have 18 been found in a torpid condition within the dens. A notable account of a torpid chipmunk found in an excavated den is reported by Robinson (1923). Probably the eastern chipmunk should be classed in the second group of hibernators, as reported by Lyman and Chatfield (1950), which includes those animals which store food, do not accumulate fat, and interrupt the short periods of torpidity by frequent awakenings in order to feed. water relationships during the winter are little known.. It has been reported that the animals went without water for two weeks during the winter while eating dry food, though the animal cannot be deprived of water during the summer months (Dickenson, 1907). Cahalane (19h?) stated that the animals emerge from the burrows to lick snow during the winter months, but no other visual records could be found to support this theory of behavior. Experimental and captive animals. Several workers have made obser— vations on captive animals or have carried on experimental work regarding hibernation in the eastern chipmmnk. Certain phases of the work includes simulated hibernation and physiological studies (woodward and Condrin, l9h5); observations of captive animals under various conditions of tempera- ture, confinement, light, humidity, etc. (Allen, 1938); and observations of captive animals under near-field conditions in the South (Engels, 1951). Shnfeldt (1919) reported finding a captive chipmunk in a state of case plate torpor and in the typical hibernating position. Cahalane (19h?) reported that the eastern chipmunk probably hibernates in the North, but does not do so in the South. However, the degree of hibernation in relation to latitude is still rather questionable and Engels (1951) 19 reported lack of activity above ground for extended periods in the vicinity of Chapel Hill, North Carolina, during the winter months. Possible factors causingwtorpidiby. Engels (1951) found the animals to have prolonged periods of inactivity above ground, even though the temperature failed to go below LSQF. for the winter period. In simu- lated hibernation studies,‘woodward and Condrin (l9h5) reported that when the rectal temperature dropped from a normal of 93.50 to between 62.2° and 8h°F., torpidity ensued. If the rectal temperatures remained high, even though the surrounding temperatures were low, the animals would remain active, and if the rectal temperatures dropped much below 62.29F., the animals would not survive. A high percentage of mortality was reported in the experiment, but this may have been due to the fact that these experiments were carried on under artificial conditions and during most months of the year. Allen (1938) carried on observations of animals under various con- ditions of confinement. Several animals which passed the winter months in a large Opensair room, at outdoor temperatures, were found not to hibernate while another animal which was in a large cage, exPosed to outdoor temperatures, was found to enter periods of torpidity. The greatest torpidiby was recorded at h0°, and the animal was awake and active at ~8°F. An animal in a small cage, exposed to outdoor tempera- tures, was also found to enter torpidity several times during the winter months. Animals kept in a dark, damp cellar which was above freezing did not normally become torpid, but one animal did enter a period of com? plete lethargy for two days or so. Correspondingly, those kept in 20 small cages at room temperatures did not normally hibernate, but one animal did enter a state of semi-torpidity for a short period. The conclusion may be drawn that temperature alone is not the most important predisposing factor for hibernation in the eastern chipmunk (Condrin, 1936), but that other factors are also concerned. Allen (1938) concluded that temperatures below 50°F. are necessary before a condition of torpidity is normally induced. The eastern chipmunk does not normally accumulate excessive fat before the winter season and is definitely known to store large quantities of food within its burrow during the fall of the year (Hamilton, 1939 3 Seton, 1928 ). Allen (1938) found that animals which were deprived of food would become very active andchmand it, and if) sufficient food were made available, the animals would either enter short periods of torpidity or continue to remain active. It was therefore suggested that food was not a controlling factor for hibernation and sufficient food at the disposal of the animals was required for the animals to pass the winter. During the colder months of the year, the chipmunk does not seem to require drinking water, but may obtain sufficient amounts metabolically (Dickenson, . 1907) or possibly by occassionally licking snow or frozen water (Cabalane, 19h? ). Drinking water is not usually available, in the liquid state, on the surface during the winter months, but the state and amounts of drinking water available in the burrow system itself is not well understood. It has been stated that light does not have much effect on hiberna- tion in general (Benedict and Lee, 1938 ), but strong light is probably not conducive to hibernation (Allen, 1938). No theory of phototropism 21 has been advanced but during the normal sequence of events, the eastern chipmunk spends much of the time throughout the year, and nearly all the time during the winter months, within the burrow system where light does not normally penetrate. Allen (1938) found that confinement in small cages, either at room temperature or outdoor temperatures, failed to induce hibernation in the eastern chipmunk. ‘Weights of adrenal glands were found to increase from a minimum.in January to a maximum plateau during July. August, and September (woodward and Condrin, 19h5). Blood sugar was found to increase 80 per cent from.January to July in animals kept at 68°F. all year around and most animals were found to have a marked drop in blood sugar, even in the summer, if thevaere kept 2b to h8 hours at from 39.2° to h2.8°F. Further, it was found that if the blood sugar fell below 100mg/ 100 c.c. the animals became torpid (loodward and Condrin, l9h5). In this same study it was found that the erythrocyte count was higher in the summer than in the winter, but there was no indication of a seasonal change in leucoqyte counts. EXPERIMENTAL'WORK METHODS OF STUDY Two methods were employed to collect data on the extent of activity of chipmunks during the winter months; one of these methods was to exca- vate previously marked burrows, or burrow systems, and to observe con- dition, extent and size of the burrows excavated; condition, size and relative amount and kinds of material within the dens; and presence of any animals within these dens or indications that animals had previously been there. The other method of study was concerned with animals which had been captured the previous fall and placed in similar cages. The object of this study was to determine the amount of food eaten by the animals ex~ posed to conditions similar to those found in the field, as cOmpared to animals kept in an area where the temperatures were constant and rela- tively high for the winter months. EXCAVATION OF BURROWS Burrows to be excavated were marked during the time of chipmunk activity in the fall; a later check of the diameter of six burrow Openings showed them to be from.2.25 to 3.0 inches in diameter. The actual excavations were carried on during the months of January and February while the ground.uas frozen to a depth of from.5 to 8 inches. Air temperatures varied from 21.20 to 37.89F. during the actual time of excavation. 23 Before excavation was started, a green, barked twig was pushed into the burrow as far as the length of the twig or the curvature of the burrow would allow. In this way, during the course of digging, the burrow would not be "lost” by a cave-in and it could be easily followed at intervals of a foot or two at a time. .At times, it was necessary to discontinue excavations before a burrow was completely exposed, and when this occurred, a twig was placed as a marker. The freshly excavated.portion was either filled or covered first with large slabs of bark or wood, before filling. This protected the uncompleted excavation from.sdverse weather conditions which might have made the excavation hard to work, or exceptionally wet, with danger of a cave-in. Due to the frozen soil and clay-type under-soil, two or three days were usually required to complete an excavation. All burrows excavated were found on a relatively steep bank over- looking the Red.pedar River on the Michigan State College campus. There ‘was very little ground vegetation of the bushesize (or smaller), but the bank contained a number of trees, mostly oaks. A thick ground cover of leaves which had fallen the previous fall was present, but very little humus was found under this layer. Directly under the layer of leaves the soil was frozen during the time of the excavations. This soil contained an extremely high percent- age of clay to a vertical depth of approximately 25 to 32 inches from. the surface, where sand was encountered. There were three separate nests observed during these excavations. First Nest. 'Excavation on this burrow commenced on January 30, 1952. The air temperature at the time was 21.29F. Excavation was carried on 2h until the burrow was lost in the sandy soil, or just before this point, at a depth of 28 inches from the surface. A horizontal connecting bur- row was encountered at 114 inches from the surface, which connected with another vertical burrow 8 inches west and slightly up the bank from the first vertical burrow. This second vertical burrow, also, had an outside Opening and the first foot or two of this burrow was lined with black, humic-like soil. This burrow ran diagonally down and along the bank for 12 inches before it turned directly to the bank, and after a distance of 6 to 8 inches, a nest was encountered. The nest (or den) was an excavation 12 inches long, 6 inches wide, and 7 inches deep, dug down to, but not into, the sandy portion of the soil which was found under the clay. -There was a large tree root (2 inches in diameter) extending over the back portion of the nest, and the nest was dug under, and slightly up and behind this tree root. The nest itself was filled to capacity (i.e. no appreciable air space between the filling and roof of the nest) with small pieces' of oak leases and, underlying this, a store of acorns. Some whole leaves were encount- ered, but most of the leaves were in pieces of 2 or 3 inches in diameter, having either been torn or cut. Host of the acorns were under the leaf mass and were resting directly upon the bare, sandy soil- under the leaves. The nest contained about forty whole acorns, as well as a few empty acorn shells, bits of meat, and partially shelled acorns. No animal was encountered. Second nest. A second excavation commenced on February 8, 1952, with an air temperature of 29.8%} at the time. This burrow opening was 15 feet to the west and slighty down the bank from the first burrow system excavated. This second burrow'proceeded lb inches diagonally, into the bank, changing direction only slightly before a sharp turn parallel to the bank was encountered. After h inches, a nest was encountered in back of a large tree root (2.5 inches in diameter) which vertically sectioned the entrance of the nest into two parts. This nest, similarly, was filled to near capacity with oak leaf pieces overlying a store of acorns. The floor of the nest, also, rested on the sandy portion of the soil, but did not go into this portion. The nest was 12 inches long, 12 inches wide and 8 inches deep. A slight musty odor was found to be present in this nest and investi- gation revealed the skin of a chipmunk among the pieces of leaves. This skin was turned completely inside out and was dry and clean, containing only the bones of the lower leg. No flesh remained on the skin. Predation was evidently the cause of death. Two possible predators might have been a weasel, which is said to be the chipmunk's worst enemy (Hamilton, 19h3; Seton, 1928), or another of the same (eastern chipmunk) species. Allen (1938) reported cases of cannibalism among captive animals and this possibility certainly cannot be disregarded. Third nest. The third excavation immediately revealed a more exten- sive burrow system than the other two. Investigation of an opening under a tree root (exposed by erosion) revealed a burrow running into and up the bank. Concurrently with investigation of'this particular burrow, another opening farther up the bank was noticed and since it was a more inconspicous opening, which is usually more to the liking of a chipmunk 26 as a doorway, it was decided to investigate the burrow system.from this new angle. Previous to the actual excavation of this second opening, a barked, green twig, as previously described, as inserted into the opening to mark the entrance. A.preliminary investigation revealed the fact that the twig had been cut and gnawed into small pieces after being pulled farther into the burrow. This burrow proceeded for 26 inches parallel to the bank, after a drop to a depth of 20 inches. At this point, it changed direction slightly extending downhill, and increasing slightly in depth for a length of h inches, and then it made an abrupt change of direction directly into the bank for 8 inches. After this it made a slight turn in the direction of (parallel to) the bank for 6 inches before turning again, directly into the bank. The sides of the burrow at the last point of direction change were wider than the usual 3 to h inches, being up to 7 inches in width. During excavation of this section of the burrow, another burrow was encountered running parallel to the bank and Just 10 inches under the surface, passing over the lower burrow. This burrow contained a plug of acorn shells and clay on one end and connected to the burrow system several feet in the Opposite direction of the burrow then being followed. After the last turn of the lower burrow, it continued into the bank for several inches until an entrance to a nest was encountered. This nest appeared to contain more material than the two nests previously described and was 18 inches long, 7 inches wide, and 6 inches deep. It contained over eighty acorns, most still in the shell, but some recently shelled and eaten, partially or entirely. 27 The nest material was similar to the other two, consisting of small cut or torn pieces of oak leaves. The floor of this nest was, also, resting on the sandy portion of the soil and was, like the others, in the vicinity of a large tree root of about 3 inches in diameter. This large root extended diagonally across the Opening to the nest. The nest itself was found to be 30 inches from the ground surface on the up-bank side and 2h inches on the down-bank side. The nest, therefore, was parallel to the horizontal plane. No animals were encountered. FOOD CONSUMPTION EXPERIMENTS Introduction. For this series of experiments, four animals captured during the previous fall were placed in cages. One cage, partitioned so as to contain one animal in each half, was placed outdoors. A sloping roof was constructed of tar paper which protected the inside of each cage from excessive moisture. The animals were provided with a small cardboard carton (approximately 1h inches long, 9 inches deep and 12 inches wide), and these in turn were filled with excelsior and shredded paper. The remaining cage, containing the other two animals, was placed in the Animal House on the Michigan State College campus where the tempera- ture and other environmental conditions were fairly constant throughout the extent of the experiment. The temperature remained at approximately 75°F. in the Animal House. These animals did not have a nest box in the cage, but the cage contained a mass of shredded paper. 28 Diagramatic views of a burrow system based on the third excavation. 5537 ) Figure 1. Diagrammatic cross-sectional sketch of the burrow system. if; p “’5' GED END NEST OPE {ClOPENING Figure 2. Diagramsti‘c horizontal sketch of the burrow system. 29 The designations used for the animals are as follows: Nos. 1 and 2 refer to the two animals outdoors and Nos. 3 and h to the two animals indoors. Description of specimens. Unfortunately, only two specimens were weighed before the third experiment commenced, so an accurate picture of weight gain or weight loss was possible only for the two specimens indoors. These weighings were made on January 25-26 which was during the second experiment and twentyhone (or twenty) days before the commencement of the third experiment. Therefore, these weights cannot be accurately attrib- uted to the third experiment, but are only relative weights for that experiment. Both animals were males and both weighed 112 grams at the time of the first weighing. After the termination of the third experiment, on lurch 20, 1952, all specimens were weighed and the specimens outdoors were sexed as well. Specimen No. 3 weighed 93.2 grams at this time which was a weight loss of 8.8 grams. Specimen No. h weighed 115oh grams, a weight gain of 3.h grams. 0f the two specimens outdoors, Specimen No. 1 was the only female of the four and weighed 97 grams, while Specimen No. 3, a male, weighed 110.h grams at the termination of the third experiment. First experiment. The experiment was conducted as three separate, consecutive units. The first experiment was started on January 1h, 1952, and terminated on February 3, 1952. It consisted of placing a provi- ously weighed amount of grain in each cage at periodic intervals and reweighing the grain remaining within each cage after an interval of 30 several days. All animals had drinking water available in the cages at all times, although in the cages outdoors the water was frozen most of the time. Occasionally, a portion of previously weighed apple was placed in the cages, and if any remained after a few days, it was also reweighed. The results of this experiment, including the average daily appledweight- loss and the grain consumed, is summarized in Table I.1 TABLE I AVERAGE DAILY GRAIN AND APPLE-RFIGHT—Loss FOR THE FOUR smcnmns DURING THE PERIOD (x JANUARY 11: TO FEBRUARY 3, 1952. W Specimen No. Graindweight-loss Appledweight-loss ‘ (grams) (game) 1 23 .9 h.272 2 7.9 3.866 3 9.5 3.h16 h 11.5 3.989 fir, 1 The temperature and hours and minutes of sunlight data were taken from the records of the Capital City Airport (U.S. Dept. of Commerce, 1952; January, February and march), and therefore are.not accurate for the experimental area; the airport weather station is approximately ten miles from the experimental area. In view of this, the data should be considered as only approximating the actual condition found in the experimental area. Some adjustment of average daily temperatures, and hours and minutes of sunlight had to be made from.the Capital City Airport-records so that this data would correspond with the readings from the three experiments. Food checks, especially daily food checks, were made at approximately noon of the date listed on the tables and graphs. Since this would be twelve hours later than the dates listed on the weather bureau records, the adjustment was necessary. 31 Second experiment. During the first experiment, it was realized that a more adequate day by day check of food consumption should be car- ried on. Therefore, on February 1;, 1952 the second experiment (or unit) was begun, and this experiment was terminated on February 15, 1952. Unfortunately, the daily check of grain did not commence until February 9, 1952, which leaves a gap of five days from the termination of the first experiment, until the above date. However, a comparison can be mde between the food consumed (1.9. both apple and grain) for each day and the average temperatures or hours and minutes of sunlight from February 9, 1952 to the termination on February 15, 1952. It will be noticed from data on average grain taken in Table II. that less grain was taken by Specimen No. 1 than by any of the others. There was no grain taken on several of the days, but at no time did this specimen fail to take some food on any of the days listed (i.e. from the beginning of the grain check on February 9, 1952). However, the apple-weight-loss in the cage of this specimen was nearly twice as much as that in the cage of Specimen No. 2, so the apple-weight- loss probably compensates for the low, daily average of grain taken by Specimen No. 1. There seems to be a fair comparison, on most days, with the average daily temperatures. The most notable correlation can be seen on Feb- ruary 12, where the total amount of both grain and appledweight-loss was more than on arv other day, from February 9, 1952 to the termination. ~- At the same time, the average temperature was extremely high, in contrast to other average temperatures during the time from February 9 to the termination. 32 m5.m ~.0H ;.~. mm.m m.~ 5m.m mm.a mm.0 ometme< 5H”; aw 0.mH m.m 0.0 3.5 0.0 ~.H 0.0 «.5 ma .nmm mmuo m.0m 0.0 «.ma 0.; 4.Ha 0.5 5.H 0.m 0.m 4H .nmm Hahn mm 0.0 0.m 0.5. m.m 0.0 m.: 0.0 0.m ma .nmm 5:»5 m.5~ 0.0 0.3 0.0a 4.0 0.0 0.0 0.0 3.5 NH .pom omen :m 0.0 0.0 0.0 H.m 0.: a.m 0.0 m.0a ea .hom mm.m mm 0.0: e.m 0.; a.aa 0.0 0.0 0.0 0.0 0H .nom «mud mm 0.0a m.HN 0.0m m.aa 0.0m ~.~ 0.mm :.m m .noe 00”0 m.5~ m.ma m.e m.a m.a m .noa 5d0 mam «A «.0 m5 4.: 5 :2 85 5 e .99.“ 005 mm med 113 we do m .nmm 00.0 mam mé 0.m ; .hom memem madam memnm madam madam mesh» madam «seam 5 fl 5 5 5 5 5 5 .mo 530 3&4 555 3&4. See 334 fish 3&4 unwaamsm oases oohd : comma : tomam m .oemm n ocean N .oeam N ocean H ocean H .oQO .ome «mmH amH HMdbmmmm OH 4 Hmdbxmmm ho COHmmm mus mom HmoHAZDm mo mMBDZHE 024 mmbom MHHdQ Q24 ambadmmmfime mo< muQT Fdwmuy ho Specimen No. 2 Figure 5 madam ca neoqleemeRTeHamd A? 1 94» 1 4| [H \4 ||||||| .MV I WIII I F’/ I IHHI III I r II V T \\ I (I. IN“ \I\\ e: 777777777 n a: III/HI a, 7777777 I 9 hr\\ \\\\\ a? 7 8K llllll 4 lllllllllllllll 5 4 e' 11 a: IIIII : A: \I .I d: I n llllll ar IIV )T \\\ \\ w 1 IIIIIII T IIIIII . _: l t. r, , 1 .II/ t / hr II IIIII i \IIIII 1 WI T rl S p a l e r WI/L] r a r F m mm m n~ m m nu D 8 no 4 2 nopscfia new meson ea vnmaandm Specimen No. 2 ane6 February Fi tunes e e 40- IIfiI . macaw ea eeonlpawweuwodaad 0 0 0 hi ._.1 a q E m .m.moonmoo ea snowshoes.» omeuo>< mud: Fdrmuy hl of these specimens, as the cages of the specimens were not in direct line with any windows. A.good comparison can be made, on some days, of the appledweight-loss with the average temperature, but again it is doubtful that there was any relationship between these two. It is noticed (Table III) that Specimen No. 3 had an average daily appledweight-loss second lowest only to Specimen No. 1 and Specimen No. h had the highest appledweight-loss of all four. The difference in average daily appledweight-loss was not as great for the specimens in- doors as it was in the cages of the specimens outdoors. Nevertheless, the same relationship existed for the average appledweight-losses for the specimens indoors as that between those outdoors. That is, a greater appleeweight-loss was recorded from the cages which had drinking water available. On March 3, 1952 a zero reading for apple-weight-loss was recorded for Specimen No. 3 and at the same time, Specimen No. b had the lowest (with the exception of the first day) appledweight-loss recorded for the experimental period. There may have been a common inhibiting factor present which caused this correlation of low appledweight-loss for these two specimens. The zero reading recorded for Specimen No. 3, on this date, may indicate a short period of torpidity, but no positive proof other than this one point was noted for either of the specimens indoors entering a state of torpidity. The appledweighteloss of both specimens indoors varied correspondingly which may indicate that they were both affected by common environmental conditions to which they reacted 81M”. smamRT 0F EXPERIMENTS No positive evidence of actual torpidity was found from the excava- tion study as no live animals were encountered. Acorn shells, bits of acorn meats, and acorns freshly shelled, either partially or entirely, found in the first and third nest excavated may indicate chipmunk activ- ity just previous to and during the actual excavation of these two nests. Acorn shells observed near the entrances of some of the burrows and the cutting and gnawing of a marker twig also points to this conclusion. The frozen ground was a disadvantage in that it hindered digging to the point where it took more than one day to complete an excavation and this may have enabled the animals to escape to another burrow or burrow system without being detected. No chipmunks were observed in this area, above ground, between November 20, 1951 and February 27, 1952. In the food consumption experiments, Specimen No. 2 seemed to be more active than Specimen No. 1, as reflected in the daily'appledweight- losses, and this may have been due to the drinking water which was avail- able in this cage. The appledweight-loss in the cage of this specimen seemed to correspond less with changes in average daily temperature and daily hours and minutes of total sunlight than did the appledweight-loss from.the cage of Specimen No. 1. This may be an indication of a relation- ship between available drinking water and the specimen's ability to main- tain activity despite extreme and sudden temperature changes by utiliza- tion of available food. £3 0! the two specimens indoors, the relative amounts of appledweight- loss from the cages of these two, correlated with each other on most of the days. These two specimens were subject to identical and constant environmental conditions which probably accounts for this correlation. At no time, during the entire period of captivity, did a gentle shaking of the nest box, or some similar, mild disturbance, fail to bring about a seemingly normal response from any of the specimens. The best visual evidence of torpidity was observed on March 2. On this date, both cages of the specimens outdoors were investigated and a period of ten minutes of periodic shaking of the nest boxes was necessary to bring about a seemingly normal response from the specimens (1.9., quick, fast movements from the nest box and within the cage). The series of three experiments show that there may be a correla- tion between the activity of the eastern chipmunk and the amount of heat present. It seems possible, also, that sunlight plays an important role in causing activation, but this cause may be, in turn, controlled by the temperature at the time. These two environmental factors certainly can- not be the only factors controlling the amount of activity in the eastern chipmunk, as evidenced by the low appleaweight-loss readings (including those which were read as zero) which occurred on days when the average temperature and/or the total hours and minutes of sunlight were neither extremely high nor extremely low. i ll 4.1 I]... '\ DISCUSSION From.the experimental work, the following tentative conclusions nmg'be formulated: The degree of heat and sunlight present may be determining factors responsible for the degree of activity in the eastern chipmunk, during the winter months. However, these two factors certainly cannot be the only determining factors. -The temperature fluctuation and daily sun- light fluctuation may be two of a large number of interacting factors which determine the degree of daily activity of the eastern chipmunk. The factor of available water and the utilization of water when it is frozen during the winter months cannot be determined from the litera- ture nor the experiments. ‘L supposition, based upon the experiments, is that the eastern chipmunk can utilize frozen water and that this ability to utilize water in the frozen state determines the amount of activity of the eastern chipmunk during the winter months. On the basis of the third experiment, it may be stated that avail- able drinking water, even though it may be frozen water, seems to be necessary for maintenance of weight at higher temperatures and a fairly high rate of activity at lower temperatures. Also, available drinking ‘water seems to be necessary, in order for the eastern chipmunk to remain relatively active during the periods of low temperature and low amounts of sunlight. Taking the literature and the experimental work into account, a general theory for the passage of winter by the eastern chipmunk can be formulated. ,1 LS In view of the fact that the eastern chipmunk does not accumulate fat, but instead stores food within the burrow system, it appears that this mammal is not a deep or profound hibernator, nor does it enter deep, prolonged periods of torpidity. It may, however, enter short periods of typical and true hibernation during the winter. These periods would probably last for only a few days before there is an awakening for an undetermined period in order to feed. The winter is probably passed in an active or semi-active state, the chipmunk utilizing the complete burrow system for all life activities during this period. PLATE I kWM~AN-wMA~ mm V ‘MA—\"\ \_ «(K‘ "'"\ \‘\, DOUBLE CAGE USED FOR OUTDOW SPECDENS PLATE II i\\ “ifi\\\.~\_.\—e\ _\ \“ ‘~\ g \" AREA IBERE THE EXCAVATIONS IERE MADE A. a. .I at .r... affl. .' DANA? . m!“ a... . ‘hr 9.0 (.p. . v. M . ogaxtw have“. i... .msmzl l -—""\~~ ‘\‘.\ \ x —\ \ _ \-\._ CLOSER VIEW (1“ AREA, SHOWING THICK GROUND COVER OF FALLEN IEAVES. B. PLATE III 4 ' l. "a ”“115 \ -\~m ‘Nxvm IM A- ~P\—WV\/.\AWMAAA‘~~—-\ "\, A. BURRW OPENING WITH MUSE AND DDT! REAP APPEARING IN FRONT \‘ \m~/‘\. M M A‘Atw ’—\-« ‘\4t—\ A x“ A ,m‘m ‘\x B. NESTlflTERIAI-OF OAKLEAF PIECEBAND ACORNS TAKEN FROM THE THIRD NEST. LITERATURE CITED Abbott Charles Co 1581;. Notes on hibernating mammals. Science 3:538-Sh1. Allen, Elsa GO ‘ 1918. The chipmunk. Nature Stucb' Review 114:301-302. 1938. The habits and life history of the eastern chipmunk (Tonnes striatus lysteri). N. I. State Mus. Bull. No. 311:. p' p"‘1"12. - 2. “than, H. E. I h A 1928. Field Book of North American Marshals. N. L: Putman, p. 2113. Benedict F. G. and R. C. Lee ‘ ‘ ' 193 . Hibernation and the marmot phy'siolog. Publ. Carnegie Inst. , Washington, D. 6. N0. 1497. pp. 1-297. Blun, Glam ' ‘ ’ ’ 1950. lb: friend ltr. Chipmunk. Audubon Mag. 52:2314-2373 2147 illus. Britt“, 80 '0 1928. Adrenin secretion on exposure to cold tOgether with possible explanation of hibernation. Amer. Jour. Physiol. 8h3119-131. Brownell, L. I. 1923. How squirrels pass the winter. Nature Mag. 2:289-2913 305. Burt, Iilliam s. ‘ ' ‘ 191:6. The Mammals of nichigan. Ann Arbor: Univ. of Mich. Press. 50 182'1850 Cabalane, Victor B. ' ' 19,47. Mammals of North America. N.I.8 Naomillian Co. Pp. 377.383. Cassidy, G. J., S. Dworkin and I. H. Finney ' ' 1925. Insulin and the mechanism of hibernation. Amer. Jour. PIVsiol. 73 811174380 Chatfield, Paul 0. and Charles P. Ignaz) 1950. CirculatOry changes during process of arousel in hibernating hamsters. Amer. JON-re Phy8101. 163 3566‘57he Condrin, J. I. . 1936. Observations on the seasonal and reproductive activities of the eastern chipmunk. Jour. Mann. 173231-231» 50 Cory, C. E. 1912. The Mammals of Illinois and Wisconsin. Field Mus. of Nat. Hist. Publ. No. 153, 2001. Series, 1131-505. Cushing, H. and E. Goetsch 1915. Hibernation and the pituitary body. Jour. Exper. Mbd. 22: 25‘h7e Dickenson, Mary C. 1907. When winter comes. Country Life. 13 257-60. Dubois, R. 1895. (Three short articles on autonarcosis) Comp. Rend. Soc. Biol. Paris 147311394513 8111-8153 830-831. Engels,'William L. 1951. “inter inactivity of some captive chipmunks (Tamias s. striatus) at Chapel Hill, North Carolina. EcoI. 32:3h9-555. Hahn, Falter L. 1908. The Mammals of Indiana. 33rd Ann. Rept. 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