Avian thermoregulation in the heat: resting metabolism, evaporative cooling and heat tolerance in Sonoran Desert doves and quail

Birds in subtropical deserts face significant thermoregulatory challenges because environmental temperatures regularly exceed avian body temperature. To understand the differing susceptibility of desert birds to increasing temperatures, we examined thermoregulatory performance and estimated heat tolerance limits (HTLs) for three Sonoran Desert nesting bird species - Gambel's quail, mourning doves and white-winged doves. Using flow-through respirometry we measured daytime resting metabolism, evaporative water loss and real-time body temperature at air temperatures (T-air) from 30 degrees C to 66 degrees C. We found marked increases in resting metabolism at the upper critical temperature (T-uc), which was significantly lower in the quail (T-air=41.1 degrees C) than in both dove species (T-air=45.9-46.5 degrees C). Gambel's quail maintained low resting metabolic rates and low rates of evaporative water loss at their T-uc (0.71 W and 1.20 g H2O h(-1), respectively), but were more sensitive to increasing air temperature, reaching their HTL at T-air of 52 degrees C. Mourning doves and white-winged doves maintained low resting metabolic rates (0.66 and 0.94 W), but higher rates of evaporative water loss (1.91 and 2.99 g H2O h(-1)) at their T-uc and reached their HTL at T-air of 58-60 degrees C. Mass-specific evaporative water loss in white-winged doves (147 g) and mourning doves (104 g) was 45% and 30% greater, respectively, than the rate observed in Gambel's quail (161 g) at T-air of 48 degrees C. Higher rates of evaporation and higher T-uc made the doves exceptionally heat tolerant, allowing them to maintain body temperatures at least 14 degrees C below air temperatures as high as 60 degrees C (140 degrees F).