The effects of temperature on the metabolic rate and evaporative water loss of the sage sparrow Amphispiza belli nevadensis

Abstract

1. 1. The thermoneutral zone of the sage sparrow, Amphispiza belli nevadensis, extended from ca. 28 to 37°C. The standard metabolic rate at 35°C was 7·41 kcal/day (mean body wt. = 18·6 g 2. 2. The temperature coefficient (5·8 per cent) and thermal conductance (3·96 kcal/m 2 per hr per °C) were relatively high, indicating poor insulation which is adaptive for desert existence. 3. 3. Between 10 and 35°C the rate of evaporative water loss was constant and averaged 6·7 mg H 2O/g per hr. Evaporative cooling began above 35°C. 4. 4. At high temperatures (43°C) and low humidities (25 per cent) sage sparrows dissipate up to 110 per cent of their metabolic heat production by evaporative cooling. 5. 5. The heat dissipating characteristics and evaporative cooling efficiency of the sage sparrow are somewhat less than in other desert birds.