Preliminary effects of UAS angle of approach on escape responses of a large-bodied raptor

Animal responses to unoccupied aircraft systems (UAS) can be exploited to reduce human-wildlife conflicts. We investigated how same-level UAS approaches (0°) would be perceived by Turkey Vultures ( Cathartes aura; “vultures”) compared to stoop approaches (20° descent 50 m away) given the directness of the approach. We measured the % of animals that escaped, escape time, flight-initiation distance horizontally and diagonally, vulture remaining index (index of the number of vultures remaining after treatment by the number present before), and latency to return by vultures at a landfill in response to UAS approaches. All vultures exposed to same-level approaches escaped on the first approach, whereas escape occurred in 73% of stoop approaches. When vultures escaped, they did so 1.69 s faster and over 11 and 15 m greater horizontal and diagonal escape distances when exposed to stoop approaches. Vultures exposed to stoop approaches showed over 31 min longer latencies. Our results, though limited by sample size, indicate that stoop approaches might pose greater perceived risk to vultures.