Calidris alba
sanderling

Sanderlings have one of the widest winter ranges of any shorebird. They are found along the coastlines of all oceans and seas from about 50 degrees north to about 50 degrees south in winter, including both temperate and tropical coastal areas. Their winter range in the Americas includes Pacific coastal areas as far north as British Columbia to northern Chile in the south, and Atlantic coastal areas as far north as southern Maine and southwards to Brazil. They are found throughout the coastlines of the Great Lakes, Gulf of Mexico, and Antillean Islands as well. Winter range outside of the Americas is from the British Isles to the Mediterranean Sea, Caspian Sea and throughout southeast Asia to South Africa, Australia, and many South Pacific islands. In the breeding season they are found in high arctic areas of Greenland, Scandinavia, Russia, Siberia, and Canada. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings are found in distinct habitats in the breeding and winter seasons. In winter they are mainly found along sandy beaches, where they probe for food ahead of and behind waves in the active surf zone. They may also forage in mudflats, lagoons, and rocky intertidal areas. They are most common along ocean coasts, but are also found on sandy beaches of inland lakes, prairie potholes, and saline or alkaline flats. In the breeding season, sanderlings are found in the high arctic tundra, where they nest in a variety of habitats, but mainly rocky ridges or slopes near moist tundra or ponds. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings are small sandpipers with black legs and feet and a stout, short, black beak. They are from 18 to 20 cm in length and 40 to 100 g. In their non-breeding plumage these sandpipers have a very pale, whitish head, with pale gray upperparts and white underparts. In all plumages they have a dark shoulder patch that extends onto the throat and breast. In flight they have a white wing stripe that is bordered by black. In their breeding plumage the upperparts take on a reddish brown color and the head becomes more deeply colored. Juveniles are similar to adults, but have darker plumage on the upperparts. Females and males are similar, although males tend to be slightly more colorful. They are easily confused with other, similarly-sized sandpipers, but their black bill, pale head, and their sandy, coastal habits help to differentiate them. Birds in breeding plumage may be confused with red-necked stints (Calidris ruficollis), except that these birds lack any dark markings that extend on the neck and chest. Sanderlings also lack a hind toe, helping to distinguish them from other sandpipers, but this is difficult to discern in the field. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Despite their exceptionally large geographic range, there are no described subspecies or regional variants. Some variation in plumage brightness and size has been described. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

The longest recorded lifespan in a sanderling was 13 years. Adult survival is estimated at 83% yearly. Most natural mortality can be attributed to predation and cold stress on young. Sanderling populations are also impacted by human habitat degradation, especially in their beach habitats. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings are found in tightly packed flocks during most of the year. Flocks can be just a handful of individuals to over 80. They flock with other shorebirds during winter and migration. They roost together on the ground and in the open, individuals are packed relatively tightly together when roosting. They can run very quickly, something that is especially noticeable when they are following crashing waves up and down the surf zone. Flocks take flight when disturbed and fly quickly to a nearby area of shore to continue foraging. Sanderlings spend much of their time foraging, from 40 to 85% of their daily budget. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings migrate northwards from March to June and southwards from July to October. Adults and juveniles are not segregated on wintering grounds and don't migrate separately. Populations do not seem to have established migration routes and there seems to be much mixing among populations over large distances. However, most migration occurs along coastlines and similar suitable habitats. The average migration distance is 77 degrees of latitude. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Home Range

Sanderling space use and degree of territoriality varies substantially throughout their range. In winter, non-breeding season, most individuals are found in flocks, although some individuals will defend foraging territories. Both sexes and all ages may be territorial and the strength of the territorial response to an intruder varies as well. In some areas, territoriality seems to be a characteristic of migrating individuals and not over-wintering individuals. The degree of territoriality in a local population may also depend on the availability and abundance of prey and the presence or absence of avian predators. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings use visual displays and calls during courtship and breeding. Outside of the breeding season they are relatively quiet. It is not thought that they learn calls. Chicks give a chirp when startled that will cause their nestmates to run away, this chirp is similar to the sound used by adults to alert others of a predator ("chidik"). Adults also use a call to tell their hatchlings that the danger has passed. Various other calls are used when departing from the nest, in aggressive interactions, and during displays and copulation. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings eat aquatic and terrestrial invertebrates that are found in their preferred, sandy or tundra open habitats. In the breeding season, along pond or stream edges in tundra, insects are the primary prey, including especially craneflies, midges, and mosquitoes. During winter and migration, when most sanderlings are found along coastlines, they eat mainly small crustaceans, bivalves, polychaete worms, insects, and talitrid amphipods. Examples of important winter and migratory prey are sand crabs, isopods, and horseshoe crab eggs along the Atlantic coast. They will occasionally take plant seeds, buds, roots, and shoots when animal prey is not available. Sanderlings feed by probing with their bills or picking things off the ground. They run just ahead of and behind waves on beaches, probing the soft sand for prey as they go. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

When threatened by predators, sanderlings that are on a nest may crouch on the nest, flattened out, or run a short distance and then crouch on the ground, as if protecting a nest. They may also pretend to be injured or mob jaegers in groups. When young are hatched, parents alert young of danger with a sharp call, which causes them to freeze. The cryptic coloration of sanderlings helps to protect them against predation. In their arctic breeding areas, most predation is on eggs and young. Parasitic jaegers (Stercorarius parasiticus) and long-tailed jaegers (Stercorarius longicaudus) have been seen eating eggs and young and glaucous gulls (Larus hyperboreus), snowy owls (Nyctea scandiaca), wolves (Canis lupus), and arctic foxes (Vulpes lagopus) may also take eggs and young. In winter and migration, adults have been preyed on by merlins (Falco columbarius), peregrine falcons (Falco peregrinus), cinereous harriers (Circus cinerea), burowing owls (Athene cunicularia), short-eared owls (Asio flammeus), Sechuran foxes (Lycalopex sechurae), house rats (Rattus rattus), laughing gulls (Larus atricilla), and domestic cats (Felis catus). (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings are important predators of marine crustaceans in the intertidal zone. They are found in association with a wide variety of other shorebirds in foraging flocks in winter and migration, including dunlins (Calidris alpina), red knots (Calidris canutus), black-bellied plovers (Pluvialis squatarola), willets (Catoptrophorus semipalmatus), dowitchers (Limnodromus), ruddy turnstones (Arenaria interpres), semipalmated sandpipers (Calidris pusilla), western sandpipers (Calidris mauri), two-banded plovers (Charadrius falklandicus), and white-rumped sandpipers. There is competition among these birds for food items, and larger shorebirds, such as Franklin's gulls (Larus pipixcan) and gray gulls (Larus modestus), will steal prey from sanderlings. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings are parasitized by several nematode species that they get by eating aquatic crustaceans.

There are no adverse effects of sanderlings on humans.

Sanderlings are interesting members of arctic, temperate, and tropical coastal habitats. Historically they were considered a game species and were hunted for market. Arctic natives collected eggs to eat. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)

Sanderlings have a large range and large population sizes, so they are not considered threatened currently. They are protected as a migratory bird by the U.S. Migratory Bird Act. Their breeding habitats in the arctic tundra are threatened by global climate changes, resulting in increased temperatures in the arctic. Their migratory and wintering habitats are threatened by oil spills, beach and wetland development, and other kinds of habitat degradation and contamination. Sanderling populations rely on the timing of seasonally abundant prey at migratory stopovers, such as the breeding of horseshoe crabs on the Atlantic coast of North America. Sanderlings feed on horseshoe crab eggs at a critical point in their migration and the loss of this resource may impact survival during migration and breeding success. Sanderlings will leave areas with heavy human or vehicle use of beaches, further reducing their available habitat. (Macwhirter, Austin-Smith Jr., and Kroodsma, 2002)