Further Evidence for Hibernation of Bears

Abstract

Abstract : In the previous symposia on the Biology of Bears, we presented the argument that three species of bears undergo a form of dormancy which is in several senses more profound than in the typical or classical hibernators, such as woodchucks(Marmota monax) (Folk et al. 1967, 1968, 1972, 1977). In essence, frequently these three species of bears (grizzly, black, polar) are independent of food and water, and do not defecate or urinate for three to five months, and probably as long as seven months in northern Alaska. These observations have been confirmed by Nelson et al. (1973) and Craighead, J.J. et al. (1974). Bears do not drop their body temperature in hibernation to the same extent as observed in small hibernators, such as woodchucks. This would be a biological disadvantage to bears because it would take them several days to warm up spontaneously at a time of emergency. However, Craighead et al. (1974) has shown a drop from the usual core temperature of 37 deg C to 31.8 deg C; Rausch (1961) found a drop to 33.0 deg C. There is other physiological depression, however: all three species of bears slowly alter their cardiovascular function over a period of approximately one month in the fall; their summer sleeping heart rate ranges from 40 to 50 bpm; yet in the state of dormancy in extreme winter weather, they frequently have a heart beat as low as 8 to 10 bpm.