Diurnal body temperature variations and hibernation in the birchmouse, Sicista betulina

Abstract

Body temperatures, oxygen consumption and electrocardiograms were recorded in the birchmouse. The diurnal body temperature cycle ranged from 5° to 18°C during a regular 24-hour sequence. The highest body temperatures (37–38°C) are present around midnight, coinciding with the time of maximal activity. Body temperatures and oxygen consumption were studied at various ambient temperatures. With decreasing temperature the oxygen consumption commonly followed two successive patterns: first, a period of compensatory increase after which body temperature and oxygen consumption decreased; the compensation lasted from 5 minutes to 4 hours. At low ambient temperatures the animals went into a state of dormancy similar to seasonal hibernation in other mammals. The reduction in heart and respiratory rate as well as in oxygen consumption and body temperature confirmed those values reported earlier. Arousal from hibernation in the birchmouse is unique in the great speed of reaction with which the awakening takes place. Body temperature may increase as much as 1°C/min. and, within a period of 30 minutes, the oxygen consumption may increase 25 times.