Migration

Migrates between subarctic breeding grounds and wintering sites from s. U.S. to s. Chile. Flight range estimates and active molt on migrating birds in fall implies that migration consists of short hops of up to several hundred kilometers each (McNeil and Cadieux 1972). One of first shorebirds to arrive on breeding grounds in spring. Long fall migration period; failed birds leave breeding grounds as early as midsummer, while others linger into late fall. Nonbreeders regularly occur throughout winter range during breeding season. Migrates earlier than Lesser Yellowlegs in spring. In fall, migration period begins before Lesser Yellowlegs but extends later.

Spring Migration

Migrates earlier than most other shorebirds, and occurs across much of the Americas; numbers generally highest at coastal sites (International Shorebird Surveys, Manomet Observatory, unpubl.). Begins to leave South American wintering sites by late Feb–Mar (Myers and Myers 1979, Thomas 1987); peaks Mar–early Apr in Suriname and Venezuela (McNeil 1970, Spaans 1978) and Apr–May in Costa Rica and Bermuda (Stiles and Skutch 1989, Amos 1991). Farther north, migration begins in Feb in North America, peaking between mid-Mar and mid-May, and ending early Jun (see Fig. 4). Usually later at interior sites. Selected dates for coastal sites: South Carolina, early Feb–late Apr (Weber and Haig 1996); Delaware, Mar–May (Hess et al. in press); New Jersey, late Feb–mid-Jun (Urner and Storer 1949); California, Mar–early May (Shuford et al. 1989); Washington State, mid-Feb–late Apr (Buchanan 1988); British Columbia, late Feb–late May (Campbell et al. 1990). Inland sites: Central Valley, CA, mid-Feb–Apr (CSE); Utah, early Mar–early May (Paton et al. 1992); Oklahoma, late Mar–late Apr (Oring and Davis 1966); Missouri, early Apr (Robbins and Easterla 1992); British Columbia and Alberta, early Apr–late May (Campbell et al. 1990, Pinel et al. 1991). Migration timing for U.S., east of Rockies, is summarized in Table 1 . Some suggestion that spring migration in Washington State now occurs earlier than it did in first half of twentieth century (Buchanan 1988); this observation coincident with expanding winter range on Pacific Coast. First birds arrive in s. Alaska mid-Apr (Isleib and Kessel 1973, R. MacIntosh, S. Savage, and G. West pers. comm.), and w. Alaska by 25 Apr (range 21–28 Apr, n = 6 yr; B. McCaffery pers. comm.).

No information on routes of specific populations. Spring migration takes place across North America (Bent 1927). Flight range estimates suggest direct flights across Caribbean, from main wintering areas on northern coast of South America to se. U.S. (McNeil 1970).

On migration, casual north of breeding range: Bering Sea islands, n. Alaska, s. Mackenzie and Keewatin, Southampton, and Baffin Is., n. Quebec, Greenland.

Fall Migration

Prolonged, and timing seems more variable than in spring (see Fig. 4, Table 1). Adults begin to leave breeding grounds in late Jun (Cannings et al. 1987, Pinel et al. 1991) and are seen throughout North America by early Jul. Females leave breeding grounds before males (McNeil and Cadieux 1972). Juveniles first seen south of breeding grounds mid-Jul in s. British Columbia (Cannings et al. 1987), late Jul in Washington State (Paulson 1993), early Aug in New Jersey (Sibley 1993), and mid-Aug in California (Page et al. 1979), and usually are responsible for a second peak in abundance after most adults have moved through an area.

Adult migration peaks during third week of Jul in s.-central Alaska (TLT). On Alaska Peninsula, a peak, of mostly juveniles, occurs in mid-Oct (R. Gill pers. comm.). In Canada, fall passage peaks mid-Aug–Sep in coastal British Columbia, slightly earlier inland (Cannings et al. 1987, Campbell et al. 1990), Aug in Alberta (Pinel et al. 1991), and early Aug in e. Quebec (McNeil and Cadieux 1972). Selected dates for peak in contiguous U.S.: Washington State, California, and Utah—Sep (Buchanan 1988, Shuford et al. 1989, Paton et al. 1992); Missouri—late Aug–early Sep (Robbins and Easterla 1992); Oklahoma—Jul–early Sep (Oring and Davis 1966); Massachusetts—late Aug–late Sep (Veit and Peterson 1993); New Jersey—Aug–Oct (Urner and Storer 1949, Sibley 1993); Delaware—late Jul–Sep (Hess et al. in press). See Table 1 for more details.

In Bermuda, adults begin to arrive mid-Jul and peak in Aug; most juveniles do not arrive until Oct (Amos 1991). Migrants pass through Costa Rica Aug–Oct (Stiles and Skutch 1989). First adults arrive in Venezuela mid-Jul; juveniles in Oct (McNeil 1970). In Suriname, peak arrival later than in Venezuela (Spaans 1978). Birds reach Argentina by late Aug (Myers and Myers 1979).

On basis of similar fat deposition patterns before spring and fall migration, McNeil and Cadieux (1972) inferred that, unlike most shorebirds, eastern birds follow similar route in both migrations. Compared to spring migration, however, fall numbers are reduced in interior North America (Bent 1927) and greater in e. Canada. Records from Atlantic and Caribbean islands more numerous in fall (Herklots 1961, McNeil and Cadieux 1972, Amos 1991; but see Collazo et al. 1995), and offshore observations of migrating birds (Brady 1990–1991, 1992–1993) further suggest slight easterly shift in fall, with some birds traveling over sea from ne. North America to West Indies.

It has been suggested that some birds staying on wintering grounds during breeding season undergo a partial migration to more northerly parts of wintering range (W. Hudson in Bent 1927, McNeil 1970).

Information limited. In fall, females peak earlier than males and adults earlier than juveniles. Fall migrating adults that were observed departing staging areas in s.-central Alaska flew in compact flocks of 14–130 birds at altitude of 150–200 m and vocalized constantly (TLT). A major movement of fall migrants across Alaska Peninsula on 16–17 Oct 1985 included several flocks of 200–400 (maximum about 700) birds, all flying 250–400 m high (R. Gill pers. comm.). Nocturnal migration of small flocks (10–15 birds) seen 80–130 km off Atlantic Coast of North America during fall (Brady 1990–1991, 1992–1993). These birds flew in tight groups and at low altitude, and were associated with larger flights of warblers, other shorebirds, and herons. At an Oklahoma wetland, most arrived in unmixed flocks at or after sunset (Oring and Davis 1966). In central California, flocks of 20–100 birds occasionally were seen moving through small wetlands in spring, suggesting diurnal movement consisting of very short hops (CSE). Flight speeds of 65–70 km/h reported by McNeil (1969). Brooks (1965) showed that fall shorebird (including Greater Yellowlegs) migration in central U.S. is associated with wind shifts to north, passage of cold fronts, and, later in season, falling minimum temperatures and decreased precipitation.

In n. Venezuela, fat content increased from winter levels of <30% to >50% (maximum 114) lean dry mass between mid-Feb and Apr, giving flight range estimate of >1,600 km (maximum 3,032; McNeil 1970). McNeil and Cadieux (1972) estimated mean flight range of fall migrants as 1,378 km (maximum 2,864), based on fat content of birds migrating south through e. Canada. Many fall migrants in Venezuela also had elevated fat content, corresponding to flight range estimates of up to 2,912 km, during period when birds depart for locations farther south (McNeil 1970).

Individuals that spend the breeding season in tropical areas (predominantly second-year birds, but also some adults) delay or fail to undergo premigratory molt and fattening (McNeil 1970). Spring trematode infestations are negatively correlated with fat scores and are greater in second-year birds; may determine whether or not birds migrate (McNeil et al. 1995, 1996).