Nature Of Migration In The Species
Medium-distance continental migrant from s. Canada to Mexico. Patterns poorly known and variable among years. In w. U.S., migration has both north-south component and inland-coastal component. Stops for prolonged periods at intermediate sites throughout migratory period. In w. U.S., greatest fall and spring migration concentrations through southeast. Oregon; central California; San Francisco Bay; Lahontan Valley, Nevada; and Great Salt Lake, Utah. In central U.S., migration pattern more dispersed and opportunistic. Migration in Mexico unstudied. Individuals breeding in central California, central Mexico, and Gulf Coast of Texas could be either nonmigratory or replaced by other migrants. Migrants occur regularly on East Coast particularly from Delaware south to Florida and priMarchily during fall.
Sex ratios of banded American Avocets at stopover sites do not differ from 1:1, suggesting similar migration path for both sexes. However, first-year individuals significantly more likely to be seen along coastal sites of California, and adults more likely to be seen inland. Some sibling groups might migrate together: pair of avocet siblings seen together at stopover site early in migration. Some nonbreeding 1-yr-olds return to breeding grounds; others do not.
Timing And Routes Of Migration
Northbound movement protracted from March to May, as early as February and as late as June.
Pacific Coast. Departs lower Colorado River valley (California and Arizona) mid-March-early May; peak migration in April. Depart Baja California as late as May. At Humboldt Bay, California (a wintering area north of breeding range), all wintering birds depart by late April or early May. Transients in British Columbia arrive during first 2 weeks of May and as early as mid-April. Early arrival along Washington coast on 31 March; peaks in late April and early May.
Inland Western. In inland California (Klamath, Modoc, and Lassen Counties), arrives mid-March-mid-April). At Honey Lake Valley (Lassen County California), no discrete flux of spring migrants is distinguishable from arriving breeding birds. First arrivals mid-March; transient migrants present primarily late April-mid-May; by end of May, most birds present are breeders. In Oregon, migrants arrive mid-March, as early as late February, with most movement in early-mid-April.
Inland Central. In Missouri, seen only as migrant from mid-April through late May (as early as late March, peak in late April. Arrives mid-April in New Mexico, early April and as early as mid-March in Kansas, late March in Utah, last week of April to mid-May and as early as mid-March in South Dakota, and mid-April-mid-May in Minnesota. Dates for areas where occurrence during migration is rare: mid-April-early June in Ohio (Peterjohn 1989), mid-April-mid-May in Iowa (Dinsmore et al. 1984).
Atlantic and Gulf Coasts. On Atlantic Coast, spring migrants much less common than fall migrants. Departs Mexican coast by April (Howell and Webb 1995). In Texas, departs late March-late May (as early as early March, as late as late June. In south Florida, birds that migrate have usually departed by mid-June, but peak numbers observed at Tampa Bay in mid-June suggest later departure. Spring arrival dates in Delaware (mid-February-early March, peak in late April are early relative to other migration dates. Arrival in Massachusetts late April-early May.
Southward movement protracted July-October. As early as June and as late as November.
Pacific Coast. Departs British Columbia in early September and as late as early December. At Humboldt Bay, California (a wintering area north of breeding range), arrives in August; other fall migrants seen sporadically farther north along Washington and Oregon coasts July through December. Arrives in lower Colorado River valley (California and Arizona) late July-mid-October; peak migration in October. Arrives in Baja California as early as July.
Inland Western. In Oregon, migration begins in early July, peaks in August, continues through September and October, and is finished by mid-November. High counts in southeast. Oregon can occur from July through September in some years; in 1984, peak was in early November. Migratory peaks in southeast Idaho in August).
Migratory movements through Honey Lake valley (Lassen County, California) begin in June, with steady flux of migrants through July and early August; a few local breeders and young-of-the-year still present in September; latest departure by end of October. Beginning in June, breeding birds from Honey Lake valley sometimes migrate immediately if nest is depredated, arriving at stopover sites in central California several days later.
Inland Central. Departs Minnesota July-mid-October, and as late as November 1. Departs South Dakota primarily mid-September, and as late as early November. In Colorado, peak migration mid-August; in Kansas, most migrants depart by mid-October, and as late as end of December. However, last departures earlier in New Mexico (early September. In Utah, departs August through September and as early as late June, as late as end of October (Cache County, Utah;. Passes through Missouri mid-August through early November; peak in October. Dates for areas where occurrence during migration is rare: early July-early November in Iowa, early July-mid-August in Ohio.
Atlantic and Gulf Coasts. Most migrants recorded on Atlantic Coast occur during fall migration, and numbers of fall migrants appear to have been increasing since 1970s. Fall departure in Delaware mid-July-late November; most birds gone by early December. In Massachusetts, most migrants sighted August-September, but as late as mid-November. Recent records for Virginia were June through August; at Cape May, New Jersey, June through September
In Tampa Bay, Florida, arriving migrants produce peak numbers in November. Migrants arrive at Texas Gulf Coast mid-July-mid-November, as early as early July and as late as early January. Arrives on Mexican Gulf Coast in November.
Accidental Records. In West Indies, in August and September; in Panama, September-October; in Costa Rica, December-May. Accidental in Bermuda in fall only (early September-early October.
No systematic data available. Pacific Coast individuals presumably move along coast. Avocets from inland western breeding areas move west and south. Avocets banded at Honey Lake, Lassen County, northeast California, were resighted at migration stopovers at Mono Lake, California, inland central California, and San Francisco Bay. These birds eventually wintered along California coast from Arcata southward, and along western coast of Mexico. One avocet male breeding at Honey Lake migrated south 480 km to Tulare Basin in September, but eventually wintered at Arcata, 700 km to the north.
Avocets from inland central breeding areas probably move south to Mexico and to Atlantic and Gulf Coasts. Although they banded an approximately equal number of avocet chicks at Great Salt Lake as in n. California, Robinson and Oring (1996) resighted only 1 Utah bird wintering in Sinaloa, Mexico. Some birds from east and west sides of Great Basin might mix on wintering grounds in Sinaloa, but most birds breeding in Utah probably winter at other locations.
Postbreeding individuals join in small flocks, which may depart immediately (as do birds from northeast California or band together in groups of thousands before migrating (as in southeast Oregon. Adults sometimes depart immediately after failed breeding attempt, without flocking. Juveniles tend to depart later than adults.
Thanks to Robinson, Julie A., Lewis W. Oring, Joseph P. Skorupa and Ruth Boettcher. 1997. American Avocet (Recurvirostra americana), The Birds of North America Online (A. Poole, Ed.). species no.275.