The Role of Breeding Habitat Loss in the Decline of Eastern Whip-Poor-Will (Antrostomus Vociferus) Populations in Canada
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Populations of birds that feed on flying insects (i.e., aerial insectivores) have been declining for several decades in North America, yet the cause of these declines is poorly understood. Among aerial insectivores, Eastern Whip-poor-will (Antrostomus vociferus; “Whip-poor-will”) populations have declined across their breeding range since at least the late 1960s, and breeding habitat loss is thought to be a primary cause. Here we test this hypothesis using data from the North American Breeding Bird Survey — the same data that were used to document long-term Whip-poor-will population declines in Canada. If breeding habitat loss contributed to the observed Whip-poor-will population declines, then we predicted that changes in breeding habitat cover would, in part, explain changes in Whip-poor-will occurrence at precise survey locations. We used aerial photographs and satellite imagery to measure changes in land cover at Breeding Bird Survey stops in Canada that have lost or gained Whip-poor-wills over time. We found support for our hypothesis: the loss of useable open habitat (e.g., forest clear-cuts, old fields) within 1140 m of Breeding Bird Survey stops predicted the declines in Whip-poor-wills at the same stops. The loss of useable open habitat at stops was primarily caused by forest succession of clear-cuts and old fields; any gains in useable open habitat were primarily a result of forest clear-cutting and initial succession of abandoned farmland. Overall, declines in useable open habitat explained approximately 40-57% of the variation in Whip-poor-will occurrence, suggesting that breeding habitat loss was an important contributor to the declines in Whip-poor-wills at Breeding Bird Survey stops in Canada. The results also suggest that breeding habitat loss cannot fully explain the reductions of Whip-poor-will populations, and that other unidentified factors, such as habitat loss on the wintering grounds or declines in available insect prey, have also contributed to the population declines of this species in Canada.