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9 December 2015 Fall migratory patterns of the Blackpoll Warbler at a continental scale
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Abstract

Blackpoll Warblers (Setophaga striata) breed across Canada and the northern United States and fly across the Atlantic Ocean to South America in fall. Studies of fall migration in this species have centered on the extensive overwater flights but have ignored other aspects of this migration, including potential geographic variation. We used Blackpoll Warbler banding records from 3 coastal (Atlantic seaboard) sites and 9 inland sites to study the fall migration. The sites covered a wide range of the species' geographic distribution during breeding and fall migration in North America. The data spanned the years 1967–2013, though the particular years sampled varied considerably among the stations. We found that the Blackpoll Warbler's fall migration is occurring later by ~1 day decade−1. Young birds generally moved through western sites before adults, whereas at eastern sites the reverse was generally true, which suggests that young birds are taking longer on migration. We also found that young birds were in poorer condition than adults, which may lead to an overall decreased rate of migration due to shorter flights and/or longer stops. Wing chords differed between western birds (longer wings) and eastern birds (shorter wings), and wing chords from the 2 more southerly coastal sites may reflect mixing of these groups. Birds were captured at coastal sites >10 days later than at inland sites, even when at similar latitudes. The heaviest individuals and those with the most fat were found at the 2 more southerly coastal sites from late September to mid-October. These results suggest that Blackpoll Warblers from the west move toward the east, where they develop the energy stores needed for their extensive overwater flights.

Sara R. Morris, Kristen M. Covino, Jason D. Jacobs, and Philip D. Taylor "Fall migratory patterns of the Blackpoll Warbler at a continental scale," The Auk 133(1), (9 December 2015). https://doi.org/10.1642/AUK-15-133.1
Received: 20 July 2015; Accepted: 1 September 2015; Published: 9 December 2015
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