Comparative Accuracy of Aerial and Ground Telemetry Locations of Foraging Raptors

Widely ranging raptors are difficult to radio-track from fixed locations on the ground; therefore, we investigated the feasibility of tracking Prarie Falcons (Falco mexicanus) from a Cessna 182 airplane outfitted with a belly-mounted, rotary, H-antenna. Lo-cations were estimated by flying directly over the signal’s source, and recorded with an on-board global positioning system. Location estimates of stationary and mobile beacons derived from aerial tracking were more accurate than locations derived from triangulation by 4-6 ground-based trackers (x̄ 95% confidence ellipses: aerial = 112 ha, ground = 875 ha). Aerial accuracy was not influenced by mobility of a beacon and was similar for two observers. However, because falcons spend a majority of their time in proximity of their aerie, most aerial fixes were close to the nest site. This resulted in significant underestimates of falcon foraging ranges, especially for breeding males.