This small North American shorebird breeds near water in low and sub-arctic tundra and winters along the northern and central coasts of South America. Despite numerous studies of this species during migration, comparatively little is known of its wintering biology, distribution, and abundance -- except for recent work in the Dominican Republic, Puerto Rico (Collazo et al. Collazo et al. 1995 ), and along the northeast coast of Brazil ( Rodrigues 2000 ). Its breeding biology has been examined in only two areas: Alaska and northern Manitoba.
Where its food (small aquatic and marine invertebrates) is abundant, flocks of up to 300,000 Semipalmated Sandpipers may gather in key migration staging areas and on wintering grounds. Individuals from eastern populations undertake nonstop transoceanic flights of 3,000-4,000 km from New England and southern Canada to South America, powered by extensive fat reserves. In spring, eastern breeders follow an Atlantic route from northeastern South America to staging areas along the northeast coast of North America, the interior U.S., and northern Canada, gathering the energy resources to complete migration to sub-arctic breeding grounds -- and for egg-production. These annual spring and fall migrations create an elliptical migration route across the Western Hemisphere.
Although sometimes considered a colonial breeder, this sandpiper is generally not social on its breeding grounds. It is monogamous and territorial, raising up to four young in just a few weeks of arctic summer. No geographic variation in plumage has been described for this bird, although size, particularly bill length, declines from the eastern part of the breeding range to the west. No subspecies has been named.
Over the past few decades, significant population declines at migration staging areas (Morrison et al. Morrison et al. 1994b ; Morrison et al., Morrison et al. 2000 ; Morrison 2001b ; Morrison et al., Morrison et al. 2001a ; Morrison and Hicklin 2001 ) and on breeding grounds ( Hitchcock and GrattoTrevor 1997 ; Gratto-Trevor et al., Gratto-Trevor et al. 1998 ; Jehl and Lin 2001 ; Jehl, Jehl 2004a , Jehl 2007 ) have been recognized, raising concerns about the fate of this species. Other recent studies have documented the residency periods and fat dynamics of Semipalmated Sandpipers at spring staging areas ( Skagen and Knopf 1994b ) and on breeding grounds (Krapu et al., Krapu et al. 2006 ), as well as the foraging behaviors of migrants ( Wilson and Vogel 1997 ; Beauchamp, Beauchamp 2005 , Beauchamp 2007 ; Maillet and Weber 2006 ).