LARGE-SCALE MAPPING OF PURPLE MARTIN PREMIGRATORY ROOSTS USING WSR-88D WEATHER SURVEILLANCE RADAR

Recent advances in remote sensing technologies allow researchers to in ventory and study bird populations at large spatial scales. We used Na tional Weather Service WSR-88D weather surveillance radar images, acqu ired from the Internet, to detect and map the locations of Purple Mart in (Progne subis) pre-migratory roosts across the eastern United State s. Purple Martins form a distinctive ring or annulus on radar during p re-dawn departures from roosts, allowing mapping of roost sites based on this signature. Overall, we identified 33 roost sites from 13 state s. Although most roosts were confined to the southeastern United State s, sites as far north as Missouri and Kentucky and as far west as cent ral Texas and Oklahoma were detected. Seventy-three percent (24/33) of roosts were clearly associated with large bodies of water such as lak es and rivers. We found that using Internet-acquired radar images for bird studies had limitations when compared with direct acquisition of images from WSR-88D radar stations or through contracts with WSR-88D p roduct providers. However, the increased expertise and financial inves tment associated with these methods make Internet-acquired radar data an attractive alternative for rapid assessment of roost locations and dynamics over large geographical areas.