Abstract
1. 1. Standard metabolic rate of three Giant Hummingbirds (mean weight, 19·1 g) was 2·7 cm 3 O 2/g/hr, and thermal conductance was 0·17 cm 3 O 2/g/hr/°C. 2. 2. Torpid metabolism increased exponentially with ambient temperature ( Q 10 = 3·7). 3. 3. Thermal conductance in birds is inversely related to body weight, described by: log C = log 0·848–0·508 log W, where C is thermal conductance in cm 3 O 2/g/hr/°C, and W is body weight in grams. 4. 4. Rates of entry into and arousal from torpor are inversely related to body weight. 5. 5. Evaporative water loss is inversely related to ambient water vapor pressure at ambient temperature of 25°C. 6. 6. Homeothermic heart rates ranged from 300–1020/min, and minimum breathing rate was 106/min. Wing beat frequency during hovering flight was 15/sec.
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