Hypothermia of Tits in the Arctic Winter

Air temperature was compared with body temperature, weight, breathing rate, depth of sleep, and frequency of shivering in 25 Willow Tits Parus montanus, 8 Siberian Tits P. cinctus, and 1 Great Tit P. major kept overnight in special roosting boxes outdoors at Skoganvarre, Finnmark (690 50'N) in Jan.-Feb. 1960. Body temperature was measured in proventriculus in the evening, night, and morning. In both cinctus and montanus, temperature at sleep was on the average 50 C lower than standard deep body temperature in the day, but only in cinctus correlated with air temperature (r = +0.84; P(0.02). Weight loss, frequency of shivering, and breathing rate varied inversely with air temperature in both species. Shivering probably stabilizes body temperature at a level preventing dangerous physiological development. It is suggested that hypothermia is an important adaptation to the winter cold and restricted food supply.