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Nature Of Migration In The Species
Migration patterns are known from mark-recapture studies on the Atlantic and Gulf coasts (American Oystercatcher Working Group, unpubl.). Degree of migration varies with latitude. Breeding birds from South Carolina to Florida are generally non-migratory, but will leave breeding territories to join local roosting flocks during the non-breeding season (Sanders et al. 2004; B. Winn, unpubl.). Movement patterns for the Gulf Coast remain poorly known. Approximately half the birds breeding from N. Carolina to New Jersey do not migrate, while the remainder move south into wintering areas from South Carolina to Florida (Schulte et al. unpubl.). Oystercatchers breeding in Massachusetts are fully migratory, though a few birds are regularly found on Christmas bird counts on Nantucket I. (Stewart and Robbins 1958; Palmer 1967; Veit and Petersen 1993; Schulte et al. unpubl.).
Northern populations use "leapfrog” migration, often bypassing Atlantic coastal sites to overwinter on Florida’s northwest coast. This region holds 10% to 15% of the total US population of American Oystercatchers during the winter months (Brown et al. 2005), but hosts up to 40% of the breeding population from the Northeast. In contrast, Oystercatchers migrating from Virginia and North Carolina are distributed fairly evenly between se. Atlantic coast and Florida Gulf coast wintering sites.
Timing And Routes Of Migration
Forms pre-migration flocks during July and August. Migrates south August through mid-November, peak mid-September (RH, Zaradusky 1985, Veit and Petersen 1993; Schulte et al. unpubl.). Longest known migration is 2047 km from Monomoy I., MA to the 10,000 islands region of Everglades National Park, FL.
Important migration staging and stopover sites include Monomoy NWR and Tern Island flats in Chatham, MA (Humphrey 1990, Schulte and Brown 2003); Stone Harbor, NJ (Brown et al. 2005); the Eastern Shore of Virginia (Brown et al., 2005); Cape Romain Region, SC (Sanders et al. 2004, Marsh and Wilkinson 1991); and the Altamaha River delta in Georgia (Brown et al. 2005, Wilke 2009).
May follow coastal or oceanic routes, depending on distance of migration, but individuals apparently do not over fly land except in Florida; Atlantic Coast birds cross the Florida peninsula to the Gulf Coast. Wintering concentrations in New Jersey, Virginia, South Carolina, Georgia, and Florida begin to break up in late February and early March. Resident birds on southern Atlantic coast states actively defend territories in February (Sanders et al. 2004, B. Winn unpubl.). Texas residents defend territories in January and begin nesting in early February (Heath, unpubl.).
First spring migrants arrive in North Carolina and Virginia during the last week in February and first week in March and reach New York and New England by the last week in March and the first week in April (Baker and Cadman 1980; Schulte et al. unpubl.). Northbound migrants continue to arrive through early May. A second wave of northbound migration occurs in late May and June as 2nd and 3rd year birds arrive on breeding grounds to search for future breeding territories. These birds often range widely along the coastline either alone or in small groups (McGowan et al. 2005a; Schulte et al. unpubl.).
Oystercatchers exhibit highly individual migratory behavior and typically do not migrate or overwinter in family groups (e.g., one chick from Ocracoke, NC, flew 220 km north to Virginia, and spent winter near Cape Charles; a second chick from the same family group flew 75 km south to a wintering flock near Beaufort, SC). Paired adults also appear to exhibit different migratory behavior. For example, one adult from a N. Carolina pair stayed on territory throughout the winter, the other flew nearly 800 km south to overwinter in ne. Florida (Schulte et al. unpubl.). First year birds over-summer for at least one year before returning to the breeding grounds in the second, third, or fourth year (McGowan et al. 2005a; Schulte et al. unpubl.).
American Oystercatcher Working Group,, Erica Nol and Robert C. Humphrey. 2012. American Oystercatcher (Haematopus palliatus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/082