Nature Of Migration In The Species
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. 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.
Timing And Routes Of Migration
Migrates earlier than most other shorebirds, and occurs across much of the Americas; numbers generally highest at coastal sites. Begins to leave April-May in Costa Rica and Bermuda. Farther north, migration begins in February in North America, peaking between mid-March and mid-May, and ending early June. Usually later at interior sites. Selected dates for coastal sites: South Carolina, early February-late April; Delaware, March-May; New Jersey, late February-mid-June; California, March-early May; Washington State, mid-February-late April; British Columbia, late February-late May . Inland sites: Central Valley, California, mid-February-April; Utah, early March-early May; Oklahoma, late March-late April; Missouri, early April; British Columbia and Alberta, early April-late May.
Some suggestion that spring migration in Washington State now occurs earlier than it did in first half of twentieth century; this observation coincident with expanding winter range on Pacific Coast. First birds arrive in s. Alaska mid-April, and w. Alaska by 25 April (range 21-28 Apr, n = 6 yr).
No information on routes of specific populations. Spring migration takes place across North America. Flight range estimates suggest direct flights across Caribbean, from main wintering areas on northern coast of South America to se. U.S..
On migration, casual north of breeding range: Bering Sea islands, n. Alaska, s. Mackenzie and Keewatin, Southampton, and Baffin Is., n. Quebec, Greenland.
Prolonged, and timing seems more variable than in spring. Adults begin to leave breeding grounds in late June and are seen throughout North America by early July. Females leave breeding grounds before males. Juveniles first seen south of breeding grounds mid-July in south British Columbia, late July in Washington State, early August in New Jersey, and mid-August in California, 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 July in south-central Alaska. On Alaska Peninsula, a peak, of mostly juveniles, occurs in mid-October. In Canada, fall passage peaks mid-August-September in coastal British Columbia, slightly earlier inland, August in Alberta, and early August in east Quebec. Selected dates for peak in contiguous U.S.: Washington State, California, and Utah-September; Missouri late August-early September; Oklahoma July-early September; Massachusetts late August-late September; New Jersey August-October; Delaware late July-September
In Bermuda, adults begin to arrive mid-July and peak in August; most juveniles do not arrive until October. Migrants pass through Costa Rica August-October. First adults arrive in Venezuela mid-July; juveniles in October. In Surinam, peak arrival later than in Venezuela. Birds reach Argentina by late August.
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 and greater in east Canada. Records from Atlantic and Caribbean islands more numerous in fall, and offshore observations of migrating birds further suggest slight easterly shift in fall, with some birds traveling over sea from northeast 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.
Information limited. In fall, females peak earlier than males and adults earlier than juveniles. Fall migrating adults that were observed departing staging areas in south-central Alaska flew in compact flocks of 14-130 birds at altitude of 150-200 m and vocalized constantly. 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. Nocturnal migration of small flocks (10-15 birds) seen 80-130 km off Atlantic Coast of North America during fall. 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. 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. 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.
Control And Physiology
In north Venezuela, fat content increased from winter levels of less than 30% to more than 50% (maximum 114) lean dry mass between mid-February and April, giving flight range estimate of less than 1,600 km (maximum 3,032. 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.
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. Spring trematode infestations are negatively correlated with fat scores and are greater in second-year birds; may determine whether or not birds migrate.
Thanks to Elphick, Chris S. and T. Lee Tibbitts. 1998. Greater Yellowlegs (Tringa melanoleuca), The Birds of North America Online (A. Poole, Ed.). species no.355