...) and evaporative water loss (EWL) at T a between 25°C and ∼58°C in birds exposed to successive increments in T a . Normothermic T b averaged 39.0°C, lower than typical avian values. At T a >34.5°C, T b increased linearly to a maximum of 43.6°C at T a =56°C. The upper critical limit of thermoneutrality ( T uc...

... Upper critical limit of thermoneutrality The ability to maintain body temperature ( T b ) below lethal levels when exposed to environmental temperatures that exceed T b is a prerequisite for the occupancy of hot, arid habitats by diurnal animals. Daytime air temperatures ( T a ) in many...