Nature Of Migration In The Species
Large variation in annual densities in staging areas and on breeding grounds may coincide with changes in local food abundance and conditions on the migratory route. Sightings of birds in Saskatchewan throughout summer (1 May-5 October and at Beaverhills Lake, Alberta, into mid-June, suggest some birds "short-stop" migration and fail to reach the breeding grounds. Information on these individuals is needed.
Timing And Routes Of Migration
Most birds depart Buenos Aires Province in Argentina by early February, although some birds, primarily females, remain into late March Northward migration is via central Amazonia /Pantanal flyway, through Brazil in March, and through Venezuela, Guyana, and Surinam in April. Birds arrive in Texas and Louisiana late April-early May after flying over the Gulf of Mexico. Migration in North America follows a narrow corridor (94-100°W) through states and provinces such as Oklahoma (9-12 May, s. Kansas, e. Nebraska (8 May, Iowa, Missouri, Saskatchewan and Alberta (12 Ma)y. Birds arrive at southern edge of breeding grounds by late May and at remote sites by the second week in June. Males precede females from wintering grounds and through Oklahoma and Alberta, but both sexes arrive simultaneously on breeding grounds. Virtually unseen on Atlantic or Pacific coasts during the spring.
Males and non- and failed-breeding females leave breeding grounds after nest initiation during mid-June to early July. Females that breed successfully, and their broods, depart late July to early September. Birds generally follow the same route south (as their northerly route in spring) but travel over a wider corridor: from British Columbia (25 July-8 October to Nova Scotia (22 July-22 September. Small numbers move east before flying south along the w. side of Hudson Bay (14 July-17 August, across the Great Lakes, and through the New England states (1 August-1 November. Migration in South America retraces the Central Amazonia/Pantanal flyway but covers a broader front than northward migration. Birds reported in every South American country except from Chile. Birds arrive on wintering grounds in Argentina during second week of September; numbers grow through mid-October and remain constant through January.
Based on collection location and age of museum specimens, adults thought to migrate south via Central Flyway, whereas juveniles may use east and west coasts of North America more frequently. Adults also thought to precede juveniles through prairie provinces (last 3 weeks of August vs. September.
Highest concentrations of this species in North America found (March-April) east of Houston, Texas (flocks of 500); York County, Nebraska (100s and 1,000s each year); and Beaverhills Lake near Edmonton, Alberta (flocks of 300-2,000. A flock of 222 near Saskatoon, Saskatchewan, May 1985 indicated this may be an important staging area. Migration distance from U.S. indicates a staging area should exist in n. South America. Besides one 500 bird flock near Meta, Colombia, in March 1977, no large concentrations have been observed. Myers estimated as many as 2,000 birds wintered on the 11,000 ha Estancia Medaland ranch in Buenos Aires Province, Argentina, in 1973.
Birds commonly observed as singles or pairs, occasionally in flocks of ? 5; suspected of being nocturnal migrants Species uses the same fields from year to year. Given suitable environmental conditions, birds may concentrate at particular locations, but often in only one field despite the availability of others; feed in small, evenly distributed territories.
Control And Physiology Of Migration
Birds shot in Nebraska and Alberta were extremely fat. No information available on rate of weight gain prior to or during migration. Post- and failed-breeders spend the majority of time feeding.
Thanks to Lanctot, R. B. and C. D. Laredo. 1994. Buff-breasted Sandpiper (Calidris subruficollis), The Birds of North America Online (A. Poole, Ed.).Species no.91