Thermal properties of hibernacula and sequences of arousals have been studied in four adult hedgehogs for seven months starting in October. Departures and entries to the nesting chamber were continuously monitored together with ambient temperature and the temperature in the hibernacula.During the two first months of the experimental period nest departures were intermittently recorded, predominantly in the two females which also occasionally foraged. The longest periods spent continuously in the hibernaculum ranged from 129 to 178 days. The natural hibernation season for Danish hedgehogs was found to comprise the six months from October onwards when there is little shelter where hedgehogs normally roam.Ambient temperatures recorded were -11 to +13° C being subzero for half the total time measured. The nest temperatures generally were higher, and above 0° C during 78-99% of total time, most commonly ranging from 0° to 4° C and thus reflecting deep hibernation.Between December and May spontaneous increases in nest temperatures amounting to 7-26° C (average 18° C) and bringing these temperatures to 10-29.5° C were recorded in 58 cases. Fiftyfour arousals did not involve departure from the hibernaculum (partial arousals). In the remaining cases (full arousals) the preceding rewarming lasted 4 1/2-6 1/2 h and nest departures amounted to 10,2 and 5 min in one female hedgehog and 90 min in another.The hedgehogs showed 12-18 arousals, the mean duration of which was 34-44 h. The high energy expenditure associated with arousals however, was found to last on average 21 h during each arousal. It is hypothesized that the body temperature during arousals chiefly was below 35-37° C.The time between arousals was 3-15 days. Periods in hibernation averaged 7-8 days in the females and 9-10 days in the heavier males, being generally longest in January-February. Neither arousals nor re-entries into deep hibernation occurred at any particular time of the day. It is suggested that for undisturbed hedgehogs arousals are induced and controlled by endogenous factors. In conclusion it is stressed that future studies on hibernation should recognize the importance of individual variability in the response pattern and focus interest on the endogenous factors which govern this important process.

A dormouse found in hibernation in its winter nest on January 26 was studied continously from February 5 until May 11 by recording ambient temperature, temperatures inside the nest ball and 5 cm from it, and by recording any possible motor activity. The first emergence from hibernaculum occurred on April 3 after which the animal was active each day with the exception of April 11, 13 and 14. Activity mainly occurred during evening and night hours and lasted on average 4 hrs (2-8 hrs) per day. Outside periods of activity the winter nest was consistently used as a place of shelter and for sleep.The ambient temperature ranged from-0.5° to 21.0°C being chiefly 1°C less the nestbox temperature. The difference between the nest-box and nest temperature was also about 1°C when the animal was inactive, thus clearly indicating torpidity. Steep increases in nest temperature, amounting to 14-18°C and raising nest temperature up to 30°C, were recorded on four occasions. This is interpreted as shallow torpor, since no activity occurred on these days.The spontaneous warming up from deep hypothermia to shallow torpor lasted on average 40 min (30-70 min), while the duration of passive cooling when returning to the hypothermic condition amounted to 5 hrs. In the weeks following continuous hibernation the dormouse alternated between activity, shallow torpor, and relatively deep torpor each day. The species should be considered as a true aestivator.

A pair of common dormice discovered while torpid in their natural hibernaculum on December 5, was studied continously outdoors, exposed to natural fluctuations in temperature and rainfall. Temperature inside and outside the nest ball and motor activity were recorded. The first emergence from hibernaculum occurred on March 4, after which the dormice were daily active, chiefly during evening and night hours. Nest departures lasted on average 10.5 h (6.5-14 h) per day.During the 88 days while the animals remained in the hibernaculum ambient temperature ranged from -5° to 8.5° C. Nest temperature never fell below zero, being chiefly 1.0°C above ambient temperature during 68 of these days and thus reflecting deep hibernation in both animals. However, on 19 occasions nest temperature was raised steeply from average 5.6°C (2.0-8.0°C) to average 23.0°C (17.5-32.5°C). These increases of nest temperature, lasting roughly 4 h (3-8 h) are interpreted as partial arousals. The total duration of partial arousals was 76 h, i.e. 3.6% of the time during which the animals remained consistently in the nest.The interarousal time varied, being 16 days at the most and 12 h at the least. The frequency of arousals increased with rising maximum values of ambient temperature, and partial arousals never were recorded on days when temperature remained below 2°C. It is believed that partial arousals correspond to the periodic or spontaneous arousals previously recorded in laboratory experiments of some other hibernating mammals. However, the energetic expenditure seems to be smaller during periodic arousals because of their shorter duration and the fact that no departure from the hibernaculum occurs.Possible mechanisms governing partial arousals are discussed. As these events chiefly occurred during night they may partly be controlled by an inherent time sense.

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M arek GĘBCZYŃSKI G ębczyński M., 1981: Body te m p e ra tu re and resistan ce to cooling in grow ing pin e voles. A cta theriol., 26, 34: 495-499 [W ith 1 T able].Body te m p e ra tu re in the pine vole Pitymys subterraneus (de S elys-L ongcham ps, 1836) is about 33°C a t b irth , b u t reach es 38° b y th e fo u rth w eek of life. Increase in body te m p e ra tu re is m ost rap id d u rin g the firs t w eek of life. Its value does n o t v ary b etw een th e 7th and 12th day of life. R eaction to cooling is form ed d u rin g the firs t nine days a fte r birth .[M am m als Res. Inst., P olish Acad. Sci., 17-230 Białow ieża]. INTRODUCTIONPine voles, Pitymys subterraneus (de Selys-Longchamps, 1835) are not capable after birth, like m any other mammal species, of m aintaining constant body tem perature. This does not mean, however, th at the body tem perature (TB) during the postnatal development period of young pine voles still living in the nest is subject to considerable and random fluctuations. Data on poikilothermy during the postnatal period do not in any way contradict the above statem ent, but each of these conclusions applies to a different situation. The opinion as to relatively constant body tem perature refers to individuals under natural conditions, in the nest, under m aternal (parental) care. The second opinion as to complete poikilothermy of newborn mammals is based on m easurem ents made under laboratory conditions, frequently on anim al's k ep t singly and outside the nest. Such research makes it possible to supplem ent our knowledge on the development of therm oregulation during the postnatal period, b u t does not state the tem perature of the growing rodents. Only measurements made on individuals in the nest can provide inform ation as to the value and range of variations in this index. Collection of data in the field is, however, limited with the present technical facilities available. Another solution is to use animals kept under sem i-natural conditions (enclosures) (Gębczyński, 1975). Meas urements made under laboratory conditions at different am bient tem peratures nevertheless give some guide as to the body tem perature of growing animals.The rate at which poikilothermy is formed can be evaluated by means of the capacity for maintaining constant body tem perature under conditions of physiological cold. In this way it is possible to estimate the anim al's resistance to cooling, which may be expressed by an index estimating the rate of changes in body tem perature in a unit of time. I[495]