Fig. 1. Time course of four temperatures measured on a pigeon's body during a typical experimental run at a constant air temperature (T_AIR=25°C): one of the body core (T_INT) and three of external surfaces of the wing, at level of the skin (T_SIW), insulation plumage (T_PIW) and flight plumage (T_PFW). Phase 1 corresponds to a period where T_INT is increased and phase 2 to a period where T_INT is stabilized, both by adjustment of the microwave load (P_MW). Phase 3 begins when the wind speed (U_WIN) is increased from 0 to 11 m s^-1 and the artificial sky temperature (T_ASK) is decreased from T_AIR to a nominal value of -78°C. Phase 4 began by switching the microwave source off. The increase in T_ASK during phase 3 and 4 was due to heating of the tunnel walls by the moving air. The regular oscillations of air and other temperatures were due to the room cooling system.