Semipalmated Sandpipers moult, or shed, their body feathers twice a year. The change to the greyish-brown fall-winter plumage usually starts on the breeding grounds and is completed after arrival on the non-breeding area. The moult that takes place on the non-breeding area prior to spring migration gives them a slightly brighter (more brown) breeding plumage. Adults moult their flight feathers (wings and tail) gradually-retaining the ability to fly at all times-and only once per year, usually in the non-breeding area.
Some juveniles do not replace any flight feathers in their first winter, as these are quite new. Others, however, moult some of the outermost primaries (outer wing feathers), which are important for flight and wear most rapidly.
Listen to the sound of Semipalmated Sandpiper
Copyright remark: Most sounds derived from xeno-canto
|wingspan min.:||29||cm||wingspan max.:||30||cm|
|size min.:||13||cm||size max.:||15||cm|
|incubation min.:||18||days||incubation max.:||22||days|
|fledging min.:||18||days||fledging max.:||22||days|
Stages (stopover) during migration in areas of shallow fresh or salt water and little vegetation, muddy intertidal zones, or along edges of lakes, usually on soft silt/clay mudflats, or at junction of short-grass marsh and tidal flats. During winter
generally areas of shallow lagoons with dead mangroves; also low tidal zone of mudflats on wet or dry mud.
Once the pair is formed on the breeding grounds, the male makes small depressions, or scrapes, in the ground. The female chooses one of the scrapes and lays eggs in it when she has obtained enough food to produce them. Most birds lay their eggs in mid- to late June, very few as late as early July.
The female almost always lays four eggs, usually one per day. These eggs are very large, together weighing almost as much as the female. They are “pyriform” in shape, or quite pointed at the small end. This allows them to fit together tightly in the nest cup, which keeps the eggs warm longer, an important factor in an arctic environment. The eggs are well camouflaged, being speckled and splashed with dark brown and olive colours against a light green or brown background.
Once the clutch, or set of eggs, is complete, the parent birds share the task of incubating, or keeping the eggs warm until they hatch. This takes about 19 days. Many eggs are lost to predators, such as gulls, hawks, and foxes. Semipalmated Sandpipers are too small and defenceless to attack predators and instead rely on distraction displays to decoy them away from the nest area. Egg predation is higher in years when mice and voles are rare (every three or four years in the Arctic), because predators that normally exist on small rodents switch to other prey, such as shorebird eggs and young.
Weather may also be a problem for breeding Semipalmated Sandpipers. If the insects and tiny water animals that they feed upon are unavailable because of high water levels or extremely low temperatures, incubating birds may be forced to desert their nests to survive. In some years, many females are unable to lay eggs at all, probably because they cannot obtain enough food.
Because the eggs are not incubated until the clutch is completed, all four young normally hatch within 24 hours of one another. Chicks are extremely independent right from birth. They are born with open eyes and almost adult-sized legs. As soon as they are dry, they begin to stumble about, pecking for insects. Chicks are not fed by their parents at all but are periodically brooded, or kept warm by a parent, during their first week. They begin to fly weakly at about 14 days of age and can fly fairly well at about 18 days.
Females normally desert their broods within 10 days after they hatch, leaving them to the care of the male. The later in the year the nest hatches, the earlier the female leaves. This is thought to result in a higher survival of females, which may still be stressed from egg laying. Males usually desert the chicks at about the time the chicks fledge, or take their first flight.
The migration south begins in early July, when failed breeders and nonbreeders start out, followed quickly by adult females and then males that have left their young. Peak migration of adult Semipalmated Sandpipers in populated areas of Canada occurs around the end of July or beginning of August. Juveniles peak several weeks later; some travel with late adult migrants, but many apparently find their way to the wintering areas by instinct.
Most Semipalmated Sandpipers from the western Arctic migrate south through the interior of North America. Many of those that nested in the central or eastern Arctic stage in southern James Bay, the St. Lawrence estuary, and the Bay of Fundy in Canada, as well as on the northeastern coast of the United States. Instead of following the eastern coast of North America, most birds fly nonstop to South America over the Atlantic, a distance of more than 3 000 km.