Migration

Long-distant complete migrant (i.e., no resident populations), both oceanic and transequatorial between northern breeding areas and wintering grounds. World breeding range divisible into 5 populations, 3 in North America (Cramp and Simmons 1983): (1) high-arctic ne. Canadian birds, A. i. interpres, from Axel Heiberg and Ellesmere Is. (and possibly n. Devon I.), and Greenland move to w. Europe, mainly from coastal Irish and North Seas to Iberia, with vagrants south to Mauritania; (2) interpres birds from w. Alaska (and e. Siberia) migrate to se. Asia, Australia, w. Pacific, and west coast of North America from Washington to Mexico; and (3) low-arctic morinella, breeding ne. Alaska to Baffin I., winters from Massachusetts and Gulf of Mexico south along both coasts of Middle and South America to central Argentina and Chile, with small numbers farther south along both coasts of South America. Most immatures remain at winter quarters during their first full summer and molt early, apparently related to their fat condition in spring (McNeil 1970, Thompson 1973, Cramp and Simmons 1983, Klaassen et al. 1990).

High-arctic Nearctic interpres on breeding grounds late May and early Jun to early Aug (adults) and late Aug–early Sep (mostly juveniles; Manniche 1910; Salomonsen 1950; Parmelee and MacDonald 1960; Nettleship 1967, 1973; Salomonsen 1967; Meltofte 1975, 1979; Morrison 1975, 1976), migrating to wintering grounds (for details, see above) either by a direct trans-Atlantic crossing or with stopover in Iceland or sw. Norway (Gudmundsson et al. 1991); return northward passage occurs between early and late May, with Canadian and w. Greenland birds moving earliest with lower fat deposition due to stopover in Iceland en route, and those destined for a direct flight to e. Greenland departing later at higher body mass (Morrison 1975, 1976; Clapham 1979; Wilson 1981).

Low-arctic interpres breeders from w. Alaska and e. Siberia display a circular migratory movement comprising 2 parts (summarized by Thompson 1973): Arrive on breeding grounds in late May and early Jun following a northward migration from winter areas (central and s. Pacific from Hawaiian Is. to Australia) in spring (Mar–May) via e. Asian coasts, reaching Japan and e. Siberia in May. Postbreeding exodus late Jul (adults) to early Sep south through the Pribilof Is., Aleutians, and central Pacific to Hawaiian Is. and Marshall Is. (main winter concentration), with some arriving e. and w. Australia between Aug and Nov (Thompson 1973).

Race morinella migrates south along both Atlantic and Pacific Coasts of North America to Central and South American wintering grounds from late Jul through Oct. Chief migration along East Coast, with smaller numbers in interior (rare to common east from Alberta, but some concentrations on Great Lakes) and West Coast (Godfrey 1986). Largest winter concentration found in n. Brazil (between Belém and Sao Luís, where >76% of South American total occurs; moderate numbers in Suriname and French Guiana, and smaller numbers on Pacific coast, most in Peru and Ecuador; in small numbers, on both coasts, south to Tierra del Fuego (Morrison and Ross 1989). Spring movement northward begins in Mar, staging in very large numbers in Delaware Bay from late Apr to early Jun (peak 20–31 May) before moving north-northwest to arctic breeding grounds, with most immatures remaining on their wintering grounds or south of breeding areas (Bent 1929; Loftin 1962; McNeil 1970; Johnson 1973, 1977, 1979; Thompson 1973; Harrington and Flowers 1996, van Gils and Wiersma 1996).

Behavior on wintering areas poorly known. Onset of migratory movements in spring relatively synchronous, except for immatures, which normally depart after adults. Usually in small groups of 10–20 individuals, sometimes in the 100s, in mixed flocks comprising mainly Red Knots (Calidris canutus), Semipalmated Sandpipers (C. pusilla), and Sanderlings (C. alba) along the Atlantic Coast (Stout et al. 1967, Harrington and Flowers 1996). On the west coast, seen regularly with Black Turnstones and Surfbirds along rocky shores, and Sanderlings, Dunlins (C. alpina), Red Knots on beaches and mudflats, occasionally with Pectoral Sandpipers (C. melanotos) in marshy areas (Paulson 1993). Long-distance migrants capable of moving across inland areas to and from breeding grounds. Concentrate at large estuaries, rocky coasts, and mixed pebble and sand beaches, where they feed rapidly, usually in tight groups, flying in unison from 1 patch to another, often running through and displacing the slower-foraging, probing sandpipers. Spring movements likely regulated by day length, with weather conditions determining actual departure and rate of movement to northern staging areas (Lank 1989). After breeding, birds move rapidly southward, displaying differential timing in migration of the sexes. Failed breeders leave first, followed by females midway through chick-rearing period, with most males departing once chicks have fledged; fledglings depart last, usually in small flocks accompanied by 1 or 2 adult males (Nettleship 1967, 1973). Movement to winter quarters by all Ruddy Turnstones usually rapid from Aug through most of Sep (Bent 1929, Morrison 1984, Godfrey 1986, Paulson 1993). See Sanger 1969 for a popular (and entertaining) account of spring and fall migratory movements.

Initiation of migration likely controlled by time of year (day length) and physiological condition. Spring departure and rate of northward movement influenced by fat deposition (see McNeil 1970 and others). Adults with low fat reserves usually depart wintering grounds late, sometimes remaining south of breeding range during summer. Fat content may regulate rate of movement to breeding location and time spent at staging areas while en route, but association complex and only partly documented (for details, see McNeil 1969; McNeil and Cadieux 1972; McNeil and Burton 1973, 1977; Morrison 1984). Southward movements and determinants of rate and length of stay at stopover foraging sites also complex, though likely related to food and fat accumulation, with some evidence of juveniles less capable of long nonstop movements than adults (see Morrison 1984).