Thermoregulatory physiology of the Crested Pigeon<Emphasis Type="Italic"> Ocyphaps lophotes</Emphasis> and the Brush Bronzewing<Emphasis Type="Italic"> Phaps elegans</Emphasis>

The metabolic physiology of the Crested Pigeon (Ocyphaps lophotes) and the Brush Bronzewing (Phaps elegans) is generally similar to that expected for birds of their size, but the Crested Pigeon has a number of characteristics which would aid survival in hot and dry regions. Body temperature increased similarly for the Crested Pigeon (from 38.8 degrees C to 41.5 degrees C) and the Brush Bronzewing (39.3 degrees C to 41.4 degrees C) over ambient temperatures (T(a)s) from 10 degrees C to 35 degrees C. Both species became hyperthermic (body temperature, T(b)>42 degrees C) at T(a)=45 degrees C. Basal metabolic rate of the Crested Pigeon (0.65 ml O(2) g(-1) h(-1) at 40 degrees C) was approximately 71% of that predicted for a columbid bird, while BMR of the Brush Bronzewing (0.87 ml O(2) g(-1) h(-1) at 20 degrees C to 40 degrees C) was approximately 102% of predicted. Total evaporative water loss increased exponentially with T(a) for both species, from <1 mg H(2)O g(-1) h(-1) at 10 degrees C to >12 mg H(2)O g(-1) h(-1) at 45 degrees C. It was similar and low for both species at T(a)<30 degrees C, but was higher for the Brush Bronzewing than the Crested Pigeon at T(a)>30 degrees C. Ventilatory minute volume matched oxygen consumption, such that oxygen extraction efficiency did not change with T(a) and was similar for both species (approximately 20%). Expired air temperature was considerably lower than T(b) for both species at T(a)<35 degrees C, potentially reducing respiratory water loss by approximately 65% at T(a)=10 degrees C to approximately 30% at T(a)=35 degrees C. Cutaneous evaporative cooling was significant for both species, with skin resistance decreasing as T(a) increased. The Crested Pigeon had a lower skin resistance than the Brush Bronzewing at T(a)=45 degrees C. The Brush Bronzewing had apparently reached its maximum cutaneous water loss at 30 degrees C and relied on panting to cool at higher T(a).