The Timing of Endothermy in the Development of Altrical Birds

Nestlings of altricial birds are unable to mainties were measured only at temperatures other than tain homeothermic body temperatures at 20°C; these are noted in table 1.For birds which hatching, and their abilities to thermoregulate were studied over a wide range of ambient temperaimprove gradually during growth.Numerous tures, age of endothermy calculated as 75% of adult regulation at ambient temperatures from 15" to 25°C studies have indicated the ages at which varidid not differ by more than O-l day from that calous species become essentially homeothermic culated at 20°C (Dawson and Evans 1957, 1960, (the "age of endothermy," e.g.