The interactions of behavioral and autonomic thermoregulation in pigeons during ambient heat load were studied by simultaneous measurements of instrumental response rate for cold air reinforcement and respiratory rate. When providing sufficient reinforcement-magnitudes, deep body temperatures were stabilized, due to a linear increase of response rate with ambient loads from 40-60 degrees C, without involving an increase in respiratory heat dissipation. This was effected by maintaining the temporal mean of air temperature and consequently of all skin temperatures at a level independent from load temperature (Fig. 3). When the efficiency of instrumental thermoregulation was limited by reducing the reinforcement-magnitude, not only the instrumental response rate increased, but in addition body temperatures and subsequently respiratory rate rose with the thermal load. Thus a positive correlation between body temperatures and response rate and a simultaneous increase of autonomic heat defence activities characterize incomplete behavioral thermoregulation. The instrumental response rate rapidly followed changes of external load temperature without preceding changes of core temperatures or skin temperatures at well feathered areas (Fig. 6). These findings suggest that the input signal controlling instrumental thermoregulatory behavior is related to the rate of change of temperatures at exposed areas of the body shell, whereas the autonomic heat defence response follows the steady displacements of body temperatures. This points to an important difference between the input signals controlling behavioral and autonomic heat defence in the pigeon.