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

Relationships between air temperature (Tair) and avian body temperature (Tb), 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 Tair setpoints for short periods (< 20-30 min), whereas a second seeks to achieve steady-state conditions by exposing birds to a single Tair for longer periods (> 1-2 h). To compare these two approaches, we measured Tb, RMR and EWL over Tair = 28 C to 44 C in the dark-capped bulbul (Pycnonotus tricolor). The two protocols yielded indistinguishable values of Tb, RMR and EWL and related variables at most Tair values, revealing that both are appropriate for quantifying avian thermal physiology during heat exposure over the range of Tair in the present study. The stepped protocol, however, has several ethical and practical advantages.Â急性热暴露期间，空气温度（air temperature, Tair）与鸟类体温（avian body temperature, Tb）、静息代谢率（resting metabolic rate, RMR）及蒸发失水（evaporative water loss, EWL）之间的关联，可通过多种呼吸测热法（respirometry）进行量化。其中一种方案为让鸟类在短时长（20~30分钟以内）内暴露于逐步升高的阶梯式Tair设定点序列；另一种方案则通过让鸟类在单一Tair下暴露更长时长（1~2小时以上）以达成稳态条件。为对比这两种实验方案，本研究以黑顶鹎（Pycnonotus tricolor）为受试对象，在28℃至44℃的Tair范围内测定了其Tb、RMR及EWL指标。在绝大多数Tair水平下，两种方案测得的Tb、RMR、EWL及相关变量均无显著差异，表明在本研究的Tair范围内，两种方法均适用于量化热暴露期间鸟类的热生理特征。不过，阶梯式实验方案在伦理与实操层面均具备多项优势。