The effect of short-time fasting on metabolism and nocturnal hypothermia in the Willow TitParus montanus

Abstract

1. The effect of body weight on O2-consumption rate and nocturnal hypothermia was studied in winter acclimatized Willow TitsParus montanus. 2. During the fasting experiments, the birds were kept at a constant ambient temperature of 0°C, and a photoperiod of 8L: 16D. O2-consumption rate and deep body temperature were recorded continuously throughout the night. The O2-consumption rate during the night was positively correlated to the body weight of the birds. Consequently, the depth of hypothermia achieved at thermal homeostasis was inversely correlated to the body weight. 3. The results obtained indicate that depending on season, ambient temperature and energy reserves, the Willow Tit regulates its metabolic rate so as to keep it at a level which corresponds fairly well to the maximum affordable energy expenditure.