THERMOREGULATION IN A LARGE BIRD, THE EMU (DROMAIUS-NOVAEHOLLANDIAE)

The emu is a large, flightless bird native to Australia. Its habitats range from the high snow country to the arid interior of the continent. Our experiments show that the emu maintains a constant body temperature within the ambient temperature range -5 to 45 degrees C. The males regulate their body temperature about 0.5 degrees C lower than the females. With falling ambient temperature the emu regulates its body temperature initially by reducing conductance and then by increasing heat production. At -5 degrees C the cost of maintaining thermal balance is 2.6 times basal metabolic rate. By sitting down and reducing heat loss from the legs the cost of homeothermy at -5 degrees C is reduced to 1.5 times basal metabolic rate. At high ambient temperatures the emu utilises cutaneous evaporative water loss in addition to panting. At 45 degrees C evaporation is equal to 160% of heat production. Panting accounts for 70% of total evaporation at 45 degrees C, The cost of utilising cutaneous evaporation for the other 30% appears to be an increase in dry conductance.