Spread-Winged Posture of Turkey Vultures: Single or Multiple Function?

The behavior and spread-winged postures of Turkey Vultures (Cathartes aura) were examined at a communal roost near Superior, Arizona, from April-June, 1979. The temporal occurrence of wing-spreading during the morning pre-departure period was positively correlated with the intensity of the sun's rays, but was independent of the ambient low overnight temperature. Wing-spreading was more common when vultures were wet than when they were dry. Turkey Vultures appear to spread their wings for at least two reasons: (1) to dry feathers, and (2) to ameliorate the thermal gradient between themselves and their environment, although the two functions are not mutually exclusive. Spreading the wings to realign feathers or to increase the mobility of ectoparasites seems unlikely.