Nature Of Migration In The Species
Harrington et al. (1991) summarize as follows: "…migrate between Canadian Arctic breeding areas and 'wintering' areas in Patagonia-one of the longest migrations of any animal in the Western Hemisphere…Employ both long-distance, nonstop and short-distance, multiple-stop flights. Southbound migrants fly over the Atlantic ocean from ne. North America to South America…then gradually move southeast along northeastern coasts before turning inland in trans-Amazon travel requiring about one month. Northward migration routes from Patagonia evidently are similar but are traversed in a rapid series of long non-stop flights. Staging zones (flocking/feeding areas used prior to migratory flights) are unknown in northern South America during northward migration, in the Caribbean basin, or on the Atlantic coastal plain of the U.S. A major staging area is identified in the Great Plains (Cheyenne Bottoms, Kansas), where birds evidently prepare for a last remaining flight to the Arctic. The migration system of this small sandpiper makes the species vulnerable to loss of strategic habitats."
Timing And Routes Of Migration
Details, especially staging areas, still not well known for much of the route. Coastal build-up in Argentina starts as early as late March; by mid-April local (and perhaps other) migrants are gone. In s. Brazil, numbers fall gradually in February, sharply in March, earlier if feeding conditions are poor. Migrants peak in Venezuela and Surinam late April to mid-May. Flight north thought to pass primarily over Greater Antilles and through Central America, e. Mexico, and interior North America from Rockies east to Mississippi and Ohio valleys; major staging area in Great Plains (Cheyenne Bottoms, Kansas). Species rare in spring on Atlantic seaboard north to Maritime Provinces. At Cheyenne Bottoms, extreme dates of spring migration 29 April and 19 June, peak numbers last 10 days of May, about 10 days after the peak in Venzuela.
First arrivals at Canadian breeding grounds as early as 28 May (Victoria Island and as late as 19 June (Bylot Island). Arrival dates vary considerably among localities, and may vary year-to-year at a given locality. Both sexes may arrive at the same time, but not known to be paired on arrival.
Males abandon breeding grounds following egg laying; their numbers decline noticeably from mid-June. Exceptionally late nestings (based on 7-11 August specimens of small downy young in National Museum of Canada), however, suggest unusual late residency of at least some males on breeding grounds. Others form loose, premigratory flocks at coastal areas nearby, not necessarily at beaches. Attending females with young depart later, but appear to leave singly without premigratory flocking inland, although individuals will leave young temporarily to join flocking males. Females eventually flock at beaches with males and unattended juveniles), and commonly with other shorebirds, especially migrating Semipalmated Sandpipers (Calidris pusilla;). Individuals of any age and sex are largely gone from their breeding grounds and adjacent coastal areas by early August, although some remain at the beaches into September, even as late as 10 October, frequenting streams and marshy spots inland rather than the beaches.
For details, see Harrington et al. (1991); data in this section are from that study, plus those noted. Arrive east coast of Canada (e.g., Magdalen Is. in Gulf of St. Lawrence, Quebec) August and early September; few after mid-September. In Bay of Fundy, peak numbers mid-August, generally later than Semipalmated and Least (Calidris minutilla) sandpipers. Less common in New Brunswick and Novembera Scotia than farther north and east.
Banding studies and flight range estimates (see below: physiology of migration) show this species capable of flying directly over the Atlantic Ocean from east Canada to northeast. South America; arrives principally in the coastal Guianas late August, remains there through mid-September. Then employs low altitude, "short-hop" flights along coasts of Guyana and Surinam; few birds have fat reserves for flights of more than a few hundred kilometers. Coastwise migration thought to continue along nw. Brazil to areas east of Amazon River mouth; birds probably head inland from there, with short flights and frequent stops on river bars and banks during September-November when water levels are low. Sharp peak in arrivals s. coastal Brazil and mid-Atlantic coast of Argentina mid-November to December. Some capable of further southward migration.
Control And Physiology Of Migration
Energetics, in the context of an annual migration strategy, covered in detail by Harrington et al. (1991). Flight range estimates, calculated from mass of bird, size (wing length), and potential flight speed, suggest that fat White-rumps, such as those netted in southeast Canada in late summer, can fly at least 4,000 km in one hop (i.e., sustained flight for 40 to 45 hours-Canada to Surinam). Such dramatic energy expenditure depends on stops at food-rich staging areas (wetlands, mudflats), where migrants can accumulate enough lipids quickly to fuel long flights. Weight gain potentially impressive, e.g., 35 g to almost 50 g in 20-30 days in south Brazil just prior to northward migration; similar gains in se. Canada in August and at Cheyenne Bottoms, KS in May. Less fattening and lower weights in regions where migratory flights are shorter, e.g., Venezuela and Surinam coasts in May and September.
Thanks to Parmelee, David F. 1992. White-rumped Sandpiper (Calidris fuscicollis), The Birds of North America Online (A. Poole, Ed.).: species no. 029