Yearly Temperature Fluctuations and Survey Speed Influence Road Counts of Wintering Raptors

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Researchers examined data from 2,155 road surveys of raptors conducted from 2001–2018 by community scientists while participating in the Pennsylvania Winter Raptor Survey.

Scientists estimated abundance and population growth rates in four raptors—American Kestrels, Northern Harriers, Red-tailed Hawks, and Rough-legged Hawks—while accounting for observation error by using dynamic Bayesian state-space models. Counts of wintering Bald Eagles, Red-shouldered Hawks, and Black Vultures increased over the course of the study. Warmer winter temperatures were associated with increased counts of partially migratory American Kestrels and Red-tailed Hawks, and with lower counts of long-distance arctic migrant Rough-legged Hawks. Generally, the number of individuals counted declined as survey speed increased, indicating that a ‘slower is better’ approach during road counts. This study highlights the utility of road surveys and advances analytical approaches to monitor raptors.

McClure, C.J., Rolek, B.W., Grove, G.W., Katzner, T.E., 2020, Yearly temperature fluctuations and survey speed influence road counts of wintering raptors: Ibis, v. 163, no. 2, p. 593-606,

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