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. 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. Females and males are similar.
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 latitude to about 50 degrees south latitude in winter, including both temperate and tropical coastal areas. Their winter range in the Americas includes the Pacific coast from British Columbia to northern Chile, Atlantic coast from southern Maine to Brazil, and coastlines of the Great Lakes, Gulf of Mexico, and Antillean Islands. In the breeding season they are found in high arctic areas of Greenland, Scandinavia, Russia, Siberia, and Canada.
Sanderlings are found in distinct habitats in the breeding and winter seasons. In winter they are mainly found along sandy coastlines, 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. In the breeding season, sanderlings are found in the high arctic tundra.
Mating systems in sanderlings are flexible. Males and females can form mated pairs, or males or females can have multiple mates. Mating systems vary regionally and from year to year, depending on conditions. Mating bonds are formed soon after sanderlings arrive on the breeding grounds, in Late May to mid June. These birds perform elaborate visual displays accompanied by songs. The display flight is described as a flight with the body parallel to the ground and the head held down. Birds move their heads from side to side as they fly and rapidly flutter their wings, followed by a brief glide. Once a pair bond is formed, the male uses a jerky walk and calls to the female, who calls back. Males and females are inseparable at this time. In some populations one or the other mate will abandon its partner soon after incubation starts.
Females choose an area for a nest, which is just a shallow depression on the ground lined with a few leaves. They lay 4 greenish, spotted eggs in late June or early July and incubate them for 23 to 32 days. One day after hatching a parent will lead the young away from he nest. Young can fly at 12 to 14 days old and become independent at 17 to 21 days old. Females lay 1 to 2 clutches, depending on how much prey is available. If a female lays 2 clutches, her male mate remains with the first set of young and the female rears the second set. Sanderlings breed in the second year after they hatch.
Both parents incubate and protect the young. When females lay a second, or even third, clutch, they will abandon their male mate with the first clutches and then care for the final clutch on their own. Young have downy feathers and can walk and feed themselves soon after hatching. They are kept warm and protected by the parents until a few days after they can fly, usually from 17 to 21 days after hatching.
The longest recorded lifespan in a sanderling was 13 years. Most natural deaths are from predation and exposure to the cold. Sanderling populations are also impacted by human habitat degradation, especially in their beach habitats.
Sanderlings are found in tightly packed flocks during most of the year. Flocks can be just a handful of individuals to over 80. 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.
Sanderling are sometimes territorial and sometimes not, depending on the region, the abundance of prey, and whether there are predators around.
Sanderlings use visual displays and calls during courtship and breeding. When they are not breeding, they are relatively quiet. 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.
Sanderlings eat aquatic and terrestrial invertebrates that are found in their preferred habitats. In the breeding season, along pond or stream edges in the arctic tundra, insects are the primary prey, 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 amphipods. They will occasionally take plant parts 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.
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 predators in groups. When young are hatched, parents use a sharp call to tell the young there is danger nearby, which causes them to freeze. Their brown colors help them to blend in to their surroundings. 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).
Sanderlings are important predators of marine crustaceans on beaches. They are found in flocks with a wide variety of other shorebirds in winter and migration, including dunlins, red knots, black-bellied plovers, willets, dowitchers, ruddy turnstones, semipalmated sandpipers, and western sandpipers. There is competition among these birds for food items, and larger shorebirds, such as gulls, will steal prey from sanderlings.
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, et al., 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 disturbance.
Tanya Dewey (author), Animal Diversity Web.
Macwhirter, B., P. Austin-Smith Jr., D. Kroodsma. 2002. Sanderling (Calidris alba). The Birds of North America Online, 653: 1-20. Accessed April 02, 2009 at http://bna.birds.cornell.edu/bna/species/653.