Bird of the Month: Sanderling
By Andy McCormick
Scientific Name: Calidris alba
Length 8 in
Wingspan 17 in
Weight 2.1 oz (60 g)
AOU Band code SAND
The Sanderling is the most widespread maritime shorebird wintering in North America. It is the common sandpiper of sandy beaches and is familiar to beach goers as it runs with whirring legs after waves and then retreats just as fast from the oncoming waves. It forages primarily for sand crabs which inhabit the intertidal zone (Kaufman). Marine worms, crustaceans, insects and small mollusks complete its diet (Bell & Kennedy).
The Sanderling is one of 18 North American shorebirds in the genus Calidris, from the Greek kalidris, used by Aristotle to describe a speckled waterbird (Holloway). Alba, Latin for white refers to its white under parts or its reputation as the palest of all shorebirds in winter (Alderfer).
It is larger than the “peeps” (other small Calidris sandpipers) and has a plumper profile. It has a short, black bill and black legs. In nonbreeding (Basic) plumage the Sanderling looks nearly white-headed with very pale gray upperparts and white below. In breeding (Alternative) plumage its head, breast and upperparts are coarsely mottled reddish brown. The Sanderling does not breed in Washington and is therefore difficult to see in breeding plumage since it spends little time here in Spring. Fall migration begins in late July and can extend through October.
Breeding is exclusive to the high arctic tundra. In North America the Sanderling’s territory includes the islands from Banks and Victoria Islands in the west to the Province of Nunavit and northern Hudson Bay in the east. The nest is a shallow scrape in the gravel lined with some grass and a few leaves. Typically four lightly spotted olive-green to pale brown eggs are deposited. Both sexes incubate the eggs for about four weeks. Sanderlings are known for serial polyandry and females sometimes have two clutches simultaneously, incubating one while a male incubates the other, or having two mates each tending a nest while the female departs (Kaufman). Young birds leave the nest soon after hatching and feed themselves. First flight occurs about 17 days after birth.
Sanderlings generally spread out along the beach when foraging and can be aggressive when defending a feeding area from other Sanderlings. They will however join in close flight formation when alarmed. They roost in a tight flock fairly close to the water’s edge and will be found sleeping while standing on one leg. They may also hop away on one leg from intruders.
The actual global population of Sanderlings is unknown but the North American population is thought to be around 300,000. There have been lower totals for Sanderlings on Christmas Bird Counts in California and Delaware Bay through the 1990s.
Ongoing degradation of salt marsh and beach habitat may be the cause of some of the decline. Sanderlings are more vulnerable to oil spills than many species because they spend much more time in marine environments. Warming global temperatures could also affect Sanderlings adversely by making the water too warm for development of its invertebrate prey.