THE HEAT LOAD FROM SOLAR-RADIATION ON A LARGE, DIURNALLY ACTIVE BIRD,THE EMU (DROMAIUS-NOVAEHOLLANDIAE)

1. The emu (Dromaius novaehollandiae) is a large (40 kg) diurnal bird that inhabits the arid inland of Australia where solar radiation level s can exceed 1000 W/m(2) for many hours of the day. 2. We measured the solar heat load at skin level below plumage samples from wild emus. A t low wind speeds the heat load was less than 10% of the incident radi ation load. This fell to less than 1% at wind speeds above 6 m/s. 3. A pplication of a simple model shows that the radiation is absorbed clos e to the surface of the plumage. The resultant heat is prevented from flowing to the skin by the coats' insulation. 4. On an average summer day in the arid zone an emu will require less than 330 g of water to e vaporate the solar heat load.