Fig. 8. Predicted effects of increasing the temperature difference between air (T_AIR) and artificial sky (T_ASK) on the thermal budget at the external surface of the insulation plumage in pigeons exposed to a T_AIR of 25°C and a wind speed U_WIN=10 m s^-1. The line show the increase (%) in transplumage heat gain by this surface. Black bars, fractions of the heat loss attributed to radiation (F_RP); grey bars, fractions attributed to convection (F_CP), expressed relative to the transplumage gain (solid line; taken as 100%). At very low values of T_ASK (T_AIR-T_ASK>42°C), F_RP exceeds 100% because radiation also accounts for the dissipation of the heat gained by the plumage surface from the air through convection.