INTERSPECIFIC COMPETITION BETWEEN VULTURES FOR PREFERRED ROOST POSITIONS

I recorded the spatial distribution of Black Vultures (Corogyps atratu s) and Turkey Vultures (Carhartes aura) roosting on electricity pylons in south Texas on 14 evenings. Both species clearly preferred to roos t on the upper level of the pylons, and when there was little competit ion for space most vultures used the upper middle section. However as densities of vultures increased, Black Vultures monopolized the upper level and Turkey Vultures became Increasingly concentrated on the lowe r level. Although there were many potential roosting sites available o n other pylons, Turkey Vultures chose to roost on the lower level of o ccupied pylons rather than move. Their decision to stay suggests that there is a potential cost to moving, perhaps an increased risk of pred ation.