Semipalmated Sandpiper (Calidris pusilla) populations have undergone significant declines at core nonbreeding sites in northeastern South America. Breeding populations have also declined in the eastern North American Arctic, but appear to be stable or increasing in the central and western Arctic. To identify vulnerable populations and sites, we documented the migratory connectivity of Semipalmated Sandpipers using light-level geolocators, deploying 250 at 8 Arctic sites across the species’ breeding range from 2011 to 2015, plus 87 at a single wintering site in northeastern Brazil in 2013 and 2014.

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