Turkey Vultures (Cathartes aura) and Black Vultures (Coragyps atratus) were observed at a day perch in south-central Pennsylvania during winter of 1984–85 to determine whether there were species-specific differences in behavior that could be correlated with microclimatic variables. Multiple linear regression analysis was used to relate behavior at the day perch to wind speed, solar radiation, and air temperature. Turkey Vultures arrived earlier at the day perch and moved more predictably than did Black Vultures from high branches to a fence or to the ground as solar radiation and wind speed rose. Although neither species made adjustments in solar orientation to changing conditions, the Turkey Vulture predictably demonstrated wing-spreading behavior in conjunction with high solar radiation.