Call-Response Surveys for Monitoring Breeding Waterbirds

We broadcast vocalizations of pied-billed grebe (Podilymbus podiceps), American bittern (Botaurus lentiginosus), least bittern (Ixobrychus exilis), Virginia rail (Rallus limicola), and sora (Porzana carolina) to derive a standardized method to monitor breeding populations of these secretive waterbirds. Broadcast of tape-recorded calls at 60 wetlands in Maine improved species detectability by 93-1, 320% over passive observation. Detection rates at wetlands where target species were known to occur ranged between 0.56 (least bittern) and 0.86 (pied-billed grebe) per survey visit. Three visits to a wetland were adequate to determine the presence or absence of all species with 90% certainty