Thermoregulatory Physiology of Australian Birds

Birds live an energetically-expensive lifestyle as they are mostly small, diurnal and use flight. However they are long-lived, dominate most Australian environments and survive successfully in harsh and highly-variable conditions. Despite these contradictions little is known about the mechanisms Australian birds use to cope with these constraints, particularly thermoregulatory adaptations. By comparison, strategies of co-occurring mammals are reasonably well-known; they utilise a variety of behavioural and physiological strategies to buffer energy requirements. To better understand how birds meet their energetic and thermoregulatory demands, we examined body temperature (Tb), metabolic rate (MR) and evaporative water loss (EWL) of three species of Australian bird. Standard open flow-through respirometry was used to gather continuous metabolic data at a range of ambient temperatures (Ta; 10 –– 32.5°C) for three species; Spotted Dove Streptopelia chinensis, Red Wattlebird Anthocaera carunculata and Rufous Whistler Pachycephala rufiventris. Continuous core Tb was logged using Passive Implantable Transponders. Despite differences in taxonomy, size and diet all three species showed similar Tb responses over the range of Tas tested. They maintained a constant Tb at and below thermoneutrality, achieved via a typical endothermic increase in MR. Similarly, wet thermal conductance (Cwet) and EWL remained constant at and below thermoneutrality and increased sharply at high Ta for all three species. The implications of these physiological responses for maintaining homeothermy will be considered in relation to the strategies of similar-sized sympatric mammals