Author: Shiloh Schulte (SS), NC Cooperative Fish and Wildlife Research Unit , Dept. Biology, NC State University, Raleigh, NC. and Manomet Center for Conservation Science, Manomet, MA.
Migration patterns are known from mark-recapture studies on the Atlantic and Gulf Coasts (American Oystercatcher Working Group in prep). 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will leave breeding territories to join local roosting flocks during non-breeding season (Sanders et al. 2004; B. Winn, unpublished). Movement patterns for Gulf Coast poorly known. Approximately half the birds breeding from NC to NJ do not migrate, while the remainder move south into wintering areas from South Carolina to Florida (Schulte et al. in prep). Oystercatchers breeding in Massachusetts are fully migratory, though a few birds are regularly found on Christmas bird counts on Nantucket Island (Stewart and Robbins 1958; Palmer 1967; Veit and Petersen 1993; Schulte et al. in prep). Northern populations use ‘leapfrog” migration, often bypassing Atlantic coast sites to overwinter on Florida’s Northwest coast. This region holds 10% to 15% of the total United States 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 Southeast Atlantic coast and Florida Gulf coast wintering sites.
Oystercatchers form pre-migration flocks during July, and August. Southbound migration occurs August through mid-November, peak mid-September (RH, Zaradusky 1985, Veit and Petersen 1993; Schulte et al. in prep). Longest known migration is 2047km from Monomoy Island, MA to the 10,000 islands region of Everglades National Park. 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). Oystercatchers may follow coastal or oceanic routes depending on distance of migration but apparently not over land except in FL: Atlantic Coast birds cross FL peninsula to 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 the southern Atlantic coast states actively defend territories in February (Sanders et al. 2004; B. Winn unpublished). Texas residents defend territories in January and begin nesting in early February (Heath, unpublished). The first spring migrants arrive in North Carolina and Virginia during the last week in February and the 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. in prep). 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. in prep).
Oystercatchers exhibit highly individual migratory behavior and typically do not migrate or overwinter in family groups (e.g., one chick from Ocracoke, NC, flew 220km north to Virginia, spent winter near Cape Charles, a second chick from same family group flew 75km south to a wintering flock near Beaufort, SC. Paired adults also appear to exhibit different migratory behavior. For example, one adult from a NC pair stayed on territory throughout winter, the other flew nearly 800km south to overwinter in Northeast Florida (Schulte et al. in prep). First year birds oversummer 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. in prep).