Heat stress in tropical birds: behavioural thermoregulation during flight

Pacific Swallows and Blue‐throated Bee‐eaters in Malaysia commonly exposed their legs when flying. The habit was most frequent around midday and was interpreted as a mechanism to dissipate heat and thereby reduce stress. The main cause of heat stress was thought to be solar radiation combined with high endogenous heat production during flight. Stress was probably increased by high ambient temperature and humidity. The occurrence of leg exposure during flight in a total of 17 species showed the habit was widespread among open habitat species in Malaysia.