Nature Of Migration
Long distances (often transoceanic) between breeding areas in low arctic North America and wintering range in northern South America.
Most yearlings summer in South America and do not migrate north until their second year.
Timing And Routes Of Migration
Most western breeders migrate south through the prairies, along with some birds from central arctic populations. Remaining central arctic and eastern breeders return to South America primarily via the North Atlantic coast of North America.
From breeding grounds in Churchill, Manitoba, many/most juveniles and adults appear to migrate to s. James Bay and, from there, to staging areas on the Bay of Fundy (New Brunswick -- Nova Scotia), as confirmed by sightings of color-marked birds and banding recoveries. From there, most individuals fly directly over ocean (powered by extensive fat reserves; see Control and Physiology of Migration, below) to make landfall along the northeast coast of South America in Surinam and French Guiana. One adult banded in the Bay of Fundy on 29 July 1987 was captured in Corentyne, Guiana, on 4 September the same year), and 16 adults also banded and marked in the Bay of Fundy were captured in French Guiana. Two birds shot by hunters in French Guiana had been banded as juveniles in James Bay, Ontario, confirming southward movement between James Bay and the Guianas.
Along the coastlines of Mana and Kourou in French Guiana, numbers of roosting Semipalmated Sandpipers increase quickly through August and September, followed by sharp declines in September-October, inclusive, suggesting a short stopover and rapid passage through the Guianas towards more southern regions in Brazil. This initial movement to Brazil is followed by increasing numbers in Suriname and French Guiana in November-December, with relatively high and stable numbers remaining in both countries through winter. However, throughout the period December-April, inclusive, a secondary movement of wintering birds continues migrating through the Guianas and across the Gulf of Maranhão into the north-central coast of Brazil. These data and observations suggest that the earlier-migrating eastern breeding birds may overwinter further south (Brazil) than the more western breeding populations and, to a large extent, may consist primarily of larger female birds (see below), followed by juveniles in December.
One Semipalmated Sandpiper banded in the Bay of Fundy was captured in Maranhão, Brazil and two sandpipers banded in Brazil were captured in the Bay of Fundy, suggesting that the same populations migrating through the Bay of Fundy wintered in Suriname and Brazil.
Adults migrate earlier than juveniles in fall, leading to two distinct migration peaks between age classes. Adults start southward in mid-July, reaching maxima in late July to mid-August; juveniles (young of the year) migrate from mid-July to late October, peaking (normally at lower numbers than adults) late August to mid-September.
Adults and juveniles banded in the Bay of Fundy have been seen and/or captured in Caribbean countries (Guadaloupe) as well as regions further south and east. Earliest migrating adults are probably non-breeders; flocks contain a proportionately high number of yearlings, although most yearlings appear to remain on wintering grounds over the summer months; e.g., ca. 15% of shorebirds seen in the Gulf of Maranhão, Brazil, June - August are Semipalmated Sandpipers.
During the main wave of adult migration, females normally precede males by about 5 days, since females usually desert broods earlier than males do. Migration may be timed in relation to a decrease in prey availability at staging areas -- birds leaving when food is depleted. These observations suggest some segregation in wintering sites used by adult males and females.
Western arctic breeders appear to winter farther west in South America than eastern breeders, possibly mixed with Western Sandpipers in Central and South American countries such as Panama and others.
Highest concentrations of this species in central North America are found at Cheyenne Bottoms, Kansasand at Quill Lakes, Saskatchewan, but large flocks appear also in the upper Bay of Fundy;e.g., up to 350,000 at Mary's Point, New Brunswick. recorded in mid-August, 2006 .In the Bay of Fundy, these constitute about 95% of all shorebirds inthe area during fall migration and represent 40-74% of the world population of this species.
Spring migration along the Atlantic coast and interior continental US and s. Canada lasts from April to June, normally peaking early May, to early June. Highest concentrations are found along the northeast Atlantic coast at Delaware Bay, New Jersey in the last week of May (with average peak numbers of approximately 115,000; mid-continentally at Cheyenne Bottoms, Kansas, in late April-early May (up to 200,000; and at Quill Lakes, Saskatchewan, on the fourth week of May to the first week of June (up to 150,000). Peak of northward migration is less protracted than fall (southward) peak, even excluding juveniles. Since males arrive on breeding grounds a few days earlier than females, males probably precede females by several days during spring migration.
Peak numbers of adults and juveniles occur in the Gulf of Maranhão, Brazil, in September-November and December, respectively, suggesting that some birds depart the coast of Suriname and continue to Brazil, presumably to wintering areas south of Maranhão, while others fly from North American staging areas, such as the Bay of Fundy, directly to the Gulf of Maranhão in a single migratory flight. Fewer birds cross the Gulf of Maranhão in spring (see below), although summering birds are present in the area over the period June-August.
Wintering Semipalmated Sandpipers depart the northeast coast of Brazil to Suriname and French Guyana in March and April. In April and May, some sandpipers migrate from the northeast coast of South America along the north Atlantic coast to Delaware Bay, although large numbers follow a continental route northward and stop over in Cheyenne Bottoms, Kansas, prior to reaching sub-arctic breeding grounds; some birds appear to fly directly from the coast of Maranhão to North America.
Experimentally, this sandpiper shows strong orientation under clear skies but not under overcast skies, so it appears to use stellar cues in orientation. It probably also uses magnetic cues; experimental orientation behavior under translucent covers changes with rotation of a magnetic field.
Weather conditions determine departure from staging areas. Birds normally depart southward from fall staging areas in noisy flocks, orienting south or southeast near sunset. Larger flocks orient better. In coastal areas, flocks normally depart near high tide (when foraging areas are inundated) and when winds favor southeastern flight. Flocks usually migrate at night, but also diurnally during long nonstop flights.
Control And Physiology Of Migration
In late summer and fall, Semipalmated Sandpipers appear to undertake nonstop transoceanic flights of more than 3,200 km from the northeast coast of North America to wintering areas in South America, powered by extensive fat reserves. Individuals store larger fat reserves before migrating southward from northeast Canada than they do before northward flight from Venezuela.
According to the flight range formula of McNeil and Cadieux (1972b), using average flight speed of 90 km/hr, the birds must acquire fat reserves equaling 40% of their fat-free dry weight to make this flight. Many in the Bay of Fundy do acquire sufficient reserves. This formula, however, may overestimate necessary reserves; one bird flew from Maine to South America with only 23% fat within the 40-60 hours necessary for the flight.
During stopover in the Bay of Fundy in late summer and fall, by ingesting large quantities of n-3 polyunsaturated fatty acids when foraging on the burrowing amphipod Corophium volutator, the lipid composition of flight tissues is modified in order to improve their capacity for endurance exercise. The consequent improved oxidative capacity of the flight muscles allows Semipalmated Sandpipers to successfully complete the demanding non-stop transoceanic flight between eastern Canada and the northeast coast of South America each year.
In fall, migratory restlessness increases with the approach of a cold front. During fall migration, rate of weight gain and departure weight may depend upon the density of invertebrate prey available, and the length of the subsequent nonstop flight. Rate of fat deposition at James Bay, Ontario, was estimated at 0.4 g per day, and in Bay of Fundy at 1.0 - 2.0 g per day, depending on a bird's fresh weight and time of arrival (rate declines as birds gain weight. Invertebrate densities are much greater in the Bay of Fundy than in James Bay, as are average body masses of individuals (see Measurements). Average length of nonstop flight from s. James Bay was estimated at 1,100-1,500 km (to east coast of Canada, and from Bay of Fundy 4,300 km (to n. South America).
Fat content of individuals is apparently a poor predictor of their subsequent length of stay at stopovers, even before long nonstop flights. Estimated arrival and departure weights are much lower for juveniles than adults at James Bay and coastal Maine; juveniles arrive in northern South America with very low fat stores, or none. More juveniles than adults marked at James Bay, Ontario, were later reported from the Caribbean, suggesting that juveniles cannot fly as far nonstop.
Thanks to Hicklin, Peter and Cheri L. Gratto-Trevor. 2010. Semipalmated Sandpiper (Calidris pusilla), The Birds of North America Online (A. Poole, Ed.).Species no. 006