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Call-Response Surveys for Monitoring Breeding Waterbirds

James P. Gibbs and Scott M. Melvin
The Journal of Wildlife Management
Vol. 57, No. 1 (Jan., 1993), pp. 27-34
Published by: Wiley on behalf of the Wildlife Society
DOI: 10.2307/3808996
Stable URL: http://www.jstor.org/stable/3808996
Page Count: 8
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Call-Response Surveys for Monitoring Breeding Waterbirds
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Abstract

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. Least bitterns, soras, and Virginia rails were detected primarily within 50 m of observers; pied-billed grebes and American bitterns were detected up to 500 m distant. Most responses were aural. Responsiveness of each species varied nonsystematically in relation to seasonal chronology, time of day, wind, precipitation, and cloud cover. Single, annual surveys at a stratified random sample of wetlands (i.e., waterbird "miniroutes") can generate sufficient encounter rates for these species to monitor population trends.

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