Migration

Intermediate- to short-distance migrant between breeding areas in coastal, low arctic and subarctic North America and wintering range in coastal, temperate North America and Central America and East Asia. Generally, one of the last shorebird species to leave the breeding grounds, with most adults and juveniles migrating together (REG), although juvenile C. a. pacifica generally arrive on California wintering grounds earlier than returning adult birds (Warnock 1994). North American races delay southward migration until completion of Prebasic molt (Holmes 1971, Cramp and Simmons 1983, Greenwood 1986).

Spring

Northward movement Jan–May.

Western. Migration of C. a. arcticola from coastal wintering areas in South and East Asia begins in Mar in Japan, peaks mid-May (Brazil 1991); route from wintering grounds to breeding grounds unknown, but presumed coastal over Sea of Okhotsk and w. Bering Sea. Arrival on Alaska breeding grounds: Chuckchi Sea coast, 26 May, peak 2–6 Jun (Lehnhausen and Quinlan 1982); Barrow, late May but variable depending on snow cover (Holmes 1971); Prudhoe Bay and Canning River Delta, last week of May (Martin 1983, TERA 1993, R. Lanctot pers. comm.).

C. a. pacifica, in part, migrate through interior of Central Valley of California and w. Great Basin (w. Great Basin birds probably C. a. pacifica, but data are lacking), others up coast. Possible route from Mexico through Colorado River Delta into Salton Sea and then up through Central Valley or w. Great Basin (NDW); part of coastal California birds move to interior Central Valley before moving northward (see also Distribution) (Page 1974, Warnock et al. 1995); approximately 50,000 counted in Central Valley in Apr 1994 (Shuford et al. 1994); common in Willamette Valley, OR; rare in e. Oregon, e. Washington, Idaho, Montana, interior British Columbia (Paulson 1993). Migration appears to be largely coastal from Washington/British Columbia to Copper River Delta, AK, then direct to breeding areas; movement begins Jan with peak Apr–early May. Major coastal stopover sites at San Francisco Bay, CA; Willapa Bay-Grays Harbor, WA; Fraser River Delta, British Columbia; and Stikine and Copper River deltas, AK (Page 1974, Butler and Campbell 1987, Senner et al. 1989, Campbell et al. 1990, Paulson 1993). Peak passage at the Copper River Delta usually 5–10 May. The degree to which specific cohorts of birds depend on 1 or more of the sites during migration is unknown; most appear to use the Copper River Delta before moving to breeding areas. Mean first arrival (1973–1993) on Yukon-Kuskokwim Delta 7–8 May (range 1–15 May) (C. Ely pers. comm.).

Interior. Only C. a. hudsonia migrate through interior east of Rocky Mtns.; more in spring than in fall, but relatively few compared to numbers using Atlantic Coast route. Extent to which birds wintering in Gulf of Mexico, mostly Texas, migrate through interior of continent needs attention (Reid et al. 1983, B. Harrington [International Shorebird Survey data] pers. comm., S. Skagen pers. comm.). Limited numbers recorded in midwestern plains states, except North Dakota (e.g., 25,000 at Devils Lake, Ramsey Co., 23 May 1993), suggests that birds migrating through interior may fly directly from Gulf Coast wintering sites to e. North Dakota (S. Skagen pers. comm.) and possibly Winnipeg, Manitoba, where mean occurrence is 25 May, (1980–1990; Steeves and Holohan 1995), before final flight to breeding grounds (see following).

Eastern. Movement (C. a. hudsonia) coastal beginning mid-Mar along Gulf of Mexico (but see above) and north to New England (not Canadian Maritimes), becoming overland through Great Lakes region to Hudson Bay and north (Bent 1927, Oberholser 1974, Holohan 1983, Rappole and Blacklock 1985, Hicklin 1987). Peak numbers along Texas and Florida coasts during Apr with abrupt departure first week May; fewer along coast of Mid-Atlantic states and New England with peaks late Apr to mid-May (e.g., Delaware Bay second–third week May; Montreal 17 May and 2 Jun = median arrival and departure) (Bent 1927, Holohan 1983, Rappole and Blacklock 1985, Hicklin 1987, B. Harrington [International Shorebird Survey data] pers. comm.). Overall chronology about 7–10 d later compared to C. a. pacifica . Arrive on breeding grounds (Churchill, Manitoba) last week of May, resident first week of Jun; first arrival at Mackenzie District, Northwest Territories, 27 May (Jehl and Smith 1970, Salter et al. 1980).

Fall

Following nesting, pronounced movement by all races to coast of breeding grounds where length of stay is a function of latitude and molt schedule (Holmes 1971), usually Jul–Oct, but into Nov.

Western. C. a. arcticola in Alaska: in ne. Alaska at Colville River, birds move to littoral areas early Jul–early Sep, peak usually 10–25 Aug (Andres 1989). Andres (1989) reported 67% of migrants moving west, but 22% to east toward Canada—this needs further study (compare Johnson and Herter 1989). Along Beaufort Sea coast, littoral zone use from early Jul–early Sep, peak mid-Aug (Connors 1984). Along Chukchi Sea coast at Kasegaluk Lagoon, peak passage 14–16 Aug, few birds after first week Sep (Lehnhausen and Quinlin 1982, Johnson et al. 1993). Some birds may leave n. Alaska directly for wintering areas in East Asia (Norton 1971); most thought to continue south to Yukon-Kuskokwim Delta to mix with C. a. pacifica before moving to Asia in Sep or Oct (REG). Return to wintering grounds presumably via same route as spring, but may be weather aided as with C. a. pacifica (see below). Arrival in Japan late Jul, peak mid-Sep to late Oct (Brazil 1991).

C. a. pacifica: mostly resident on littoral areas from late Jun to late Sep–early Oct, with gradual movement south from northern range; in Alaska, peak use throughout staging area from mid-Aug in north (Seward Peninsula) to early Oct in south (Alaska Peninsula), some as late as early Nov (Gill and Jorgensen 1979, Shields and Payton 1979, Connors 1984, Gill and Handel 1990). Majority of birds depart Alaska Peninsula estuaries en masse in early Oct (mean = 13 Oct, range 6–26 Oct, n = 13 yr between 1976 and 1995; REG). Migration from Alaska Peninsula and probably Yukon-Kuskokwim Delta transoceanic in association with predictable weather systems, bypassing Copper River Delta (REG). Small flocks arrive along Pacific Coast (s. British Columbia-central California) late Sep, most beginning mid-Oct (Page 1974, Butler and Campbell 1987, Campbell et al. 1990, Paulson 1993). From Alaska, Yukon-Kuskokwim Delta birds winter in Pacific Northwest, Alaska Peninsula birds mostly in n. California; some drift of birds from northern areas south through winter (REG).

Interior. C. a. hudsonia rare in Alberta; uncommon in Saskatchewan; locally common in Manitoba and Quebec, but no major use areas in Prairie Provinces identified to date (Morrison et al. 1995). Migration through Great Plains of lesser magnitude and more irregular than in spring; needs study (S. Skagen pers. comm.).

Eastern. Postbreeding birds (C. a. hudsonia) move to Hudson and James bays to complete Prebasic molt (Jul–Aug), then move rapidly down Atlantic Coast. Route from breeding grounds swings more easterly than in spring. In Maritime Provinces, peak Oct–early Nov; Lake Ontario, peak 25 Oct; Montreal, Quebec, area median arrival and departure 30 Aug and 15 Nov, respectively; New England arrival first week Sep, peak late Oct and beyond; New Jersey coast peak mid-Dec; arrive Gulf of Mexico beginning late Sep–early Oct (Urner and Storer 1949, Oberholser 1974, Weir and Cooke 1976, Morrison and Harrington 1979, Rappole and Blacklock 1985, Hicklin 1987, Morrison et al. 1994, B. Harrington [International Shorebird Survey data] pers. comm.). Major use areas Delaware Bay (Cape May, Bombay Hook National Wildlife Refuge [NWR], Oceanville), Virginia (Chincoteague NWR, Cape Charles), several sites along coasts of Louisiana and Texas, e.g., Creole, Cameron Parrish, Port Aransas, and Freeport (B. Harrington [International Shorebird Survey data] pers. comm.).

Winter Movements

C. a. pacifica thought to move gradually inland into Central Valley of California for rest of winter prior to northward migration (Page 1974); movements of up to 150 km appear to be stimulated by rainfall (Warnock et al. 1995).

Commonly seen in large flocks away from breeding grounds; multiple flocks of >1,000 birds each seen departing on fall migration from Alaska. Recorded departures from Alaska Peninsula staging sites between 1976 and 1995 occurred both after sunset (n = 11 yr) and during daylight (n = 3 yr); all departures associated with weather systems favorable for migration across Gulf of Alaska (REG). Week prior to departure, birds very active and vocal (compare Handel and Gill 1992 for Yukon-Kuskokwim Delta); on departure give repeated treep calls (REG); see also Sounds: vocalizations.

C. a. pacifica and C. a. arcticola in Alaska dependent on lipid-rich intertidal invertebrates (principally bivalves; see Food Habits) for molt and migration. Rate of lipid deposition at fall staging sites estimated at 0.38 g/d for both adults and juvenile C. a. pacifica and C. a. arcticola (Yukon-Kuskokwim Delta) and 0.29 and 0.36 g/d for juvenile and adult C. a. pacifica, respectively, at Nelson Lagoon, Alaska Peninsula (REG). Holmgren et al. (1993a) found that average gain in body mass (mostly lipids) of C. a. alpina in fall in Sweden was 1.8–2.7 g/d. Length of stay at Swedish site usually < 2 d compared to average 40-d period at Alaska sites. Mass during week of departure from Yukon-Kuskokwim Delta averaged 74.6 ± 1.1 SD g for adults (n = 114) and 70.8 ± 4.3 g for juveniles (n = 10); from Alaska Peninsula, 71.7 ± 0.6 g for adults (n = 157) and 68.0 ± 1.4 g for juveniles (n = 41) (REG). Cohorts of birds remaining after major departures mostly juveniles with significantly less mass, suggesting they have insufficient fuel reserves to complete the nonstop flight to California, a great-circle distance of 3,500 km. Individually marked birds sighted in California <72 h after departing Alaska (REG). In early May, average mass (n, range) of C. a. pacifica at the Copper River Delta, the last known staging area before dispersing to breeding areas, a maximum 1,200 km distance: 59.7 ± 7.1 SD g (52, 49.0–77.0) for males and 63.6 ± 7.7 g (58, 51.0–81.0) for females (S. Senner unpubl. data).