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. 

Body temperatures, resting metabolic rates and rates of evaporative water loss in Dark-capped bulbuls (Pycnonotus tricolor) were measured using two different protocols (stepped and steady-state) of flow-through respirometry at high air temperatures. These data were collected to determine whether conclusions regarding avian thermoregulation during acute heat exposure depend on the type of respirometry protocol used.

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