Regulation of body temperature in the Budherygah, Melopsittacus undulatus

Abstract

The standard metabolic rate of budgerygahs, determined during October and November, was 30% lower at night (1.96 ml O2 g-1 h-1) than during the day (2.55 ml O2 g-1h-1 ). The zone of thermal neutrality extended from 29 to 41ºC. At ambient temperatures (Ta) below 29ºC, oxygen consumption [V(02)] increased with decreasing Ta according to the relation V(02) (ml O2 g-1 h-1) = 5.65 - 0.127Ta. At Ta's between 0 and 16ºC, body temperature (Tb) averaged 37.7ºC (which is low by avian standards) and was independent of Ta. Above 20ºC, Tb increased with increasing Ta, and within the zone of thermal neutrality Tb increased by approximately 4ºC. The relation between V(O2) and Tb within the zone of thermal neutrality is described by the equation V(O2 = 6.29 - 0.105 Tb. This ability to decrease metabolic heat production while Tb rises could contribute to the water economy of budgerygahs. At moderate Ta's the rate of evaporative water loss of budgerygahs is only 60% that predicted for a 31 g bird. At Ta's below 14ºC budgerygahs can balance evaporative water loss with metabolic water production. At 45ºC Tb was between 1.0 and 5.0ºC below Ta, and evaporative cooling accounted for up to 156% of metabolic heat production. At high Ta's budgerygahs appear to augment evaporation by lingual flutter.