Respirometry protocols for avian thermoregulation at high air temperatures: stepped and steady-state profiles yield similar results

Relationships between air temperature (T-air) and avian body temperature (T-b), resting metabolic rate (RMR) and evaporative water loss (EWL) during acute heat exposure can be quantified through respirometry using several approaches. One involves birds exposed to a stepped series of progressively increasing T-air setpoints for short periods (<20-30 min), whereas a second seeks to achieve steady-state conditions by exposing birds to a single T-air for longer periods (>1-2 h). To compare these two approaches, we measured T-b, RMR and EWL over T-air=28 degrees C to 44 degrees C in the dark-capped bulbul (Pycnonotus tricolor). The two protocols yielded indistinguishable values of T-b, RMR and EWL and related variables at most T-air values, revealing that both are appropriate for quantifying avian thermal physiology during heat exposure over the range of T-air in the present study. The stepped protocol, however, has several ethical and practical advantages.

Automated summary

The relationship between air temperature and avian physiology can be studied using respirometry, and both the stepped and steady-state protocols are suitable for quantifying avian thermal physiology during heat exposure. However, the stepped protocol has ethical and practical advantages.