Body Mass, Food Habits, and the Use of Torpor in Birds
The sensitivity of birds to cold temperatures varies greatly. Some cannot tolerate temperatures below 0°C, while others can tolerate temperatures between -20 and -40°C (see Steen, 1958), even at high wind velocities. Various factors, including body size, rate of metabolism, and insulation, directly influence this sensitivity. Response to low temperatures, however, also includes their evasion by migration and by entrance into torpor. The selection of a response, itself, is influenced by many factors, including body size, food habits, and rate of metabolism. The object of this paper is to examine the physiological and ecological conditions that determine which response to cold is used by birds.
KeywordsBasal Rate Boundary Curve Food Habit Standard Metabolic Rate Evaporative Water Loss
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