Sanderling Life History

Habitat

Habitat ShorelinesSanderlings breed in the tundra of High Arctic Canadian islands and peninsulas, and rarely in Alaska. Their nesting habitat ranges from moist sites with lots of vegetation to well-drained clay or gravel slopes, to the tops of stony ridges; it often includes arctic willows, sedges, heathers, purple saxifrage, and mountain avens. While migrating along the North American coast, Sanderlings stop on hard-packed sand beaches, tidal mudflats, rocky coastlines, and inland bodies of water—including ponds, streams, reservoirs, and shallow prairie lakes. They spend the winter on sandy beaches all over the world; some stop as far north as southern Alaska, Nova Scotia, and Newfoundland while others go the length of South America. Less commonly, they may winter on mudflats, lakeshores, and riversides.Back to top

Food

Food Aquatic invertebratesSanderlings feed by running down the beach after a receding wave to pick up stranded invertebrates or probe for prey hidden in the wet sand. Its diet includes small crabs, amphipods and other small crustaceans, polychaete worms, mollusks, and horseshoe crab eggs. Sanderlings may also skim food from shallow pools while running, pick up moving prey on the ground, or—during the summertime—snap at flying insects. They eat crane flies, midges, mosquitoes, beetles, butterflies, and moths. When no animal prey is available, Sanderlings eat plant material, including saxifrage buds and shoots, roots, grass seeds, algae, and mosses.Back to top

Nesting

Nest Placement

Nest GroundThe female chooses a nest site near the shores of a freshwater lake or pond. The nest is placed on the ground in an exposed location with little or no vegetation, often at a pre-existing depression.

Nest Description

The nest is probably built by the female alone. She forms a shallow, cup-shaped hollow in the stony ground and lines it sparsely with willow leaves, saxifrage leaves, lichens, bits of moss, and occasionally dry willow twigs and pebbles. It measures about 3 inches across and 2.5 inches deep.

Nesting Facts
Clutch Size:3-4 eggs
Number of Broods:1 brood
Egg Length:1.3-1.5 in (3.3-3.8 cm)
Egg Width:0.9-1.0 in (2.4-2.6 cm)
Incubation Period:23-27 days
Egg Description:Dull green to olive-brown or greenish-blue), marked with brown spots and blackish streaks.
Condition at Hatching:Well-developed and downy, with dark legs and bill and black eyes.
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Behavior

Behavior ProbingOn beaches, Sanderlings are strong, fast runners as they perpetually scurry just ahead of arriving and retreating waves. On the nesting grounds males establish territories about 400 yards across, and both members of a breeding pair chase intruders from the territory. Sanderlings are mostly monogamous, but their mating system may differ from area to area and year to year. Males (and, less frequently, females) perform aerial displays before mating. The bird alternately flutters and glides in an erratic path in an area about 200 yards wide, dipping low to the ground and rising to 30 feet high or more while vocalizing; these displays can last 2 minutes. After pairing, the two birds accompany each other everywhere. Studies in Canada have found that females sometimes mate with multiple males in sequence when conditions are favorable. Both sexes incubate. When confronted with a predator, incubating parents freeze on the nest until the last second, when they creep away from the nest while feigning injury. Nest predators include Parasitic Jaegers, Long-tailed Jaegers, Glaucous Gulls, Snowy Owls, artic foxes, and wolves. During migration and winter Sanderlings may flock with other small shorebirds such as Dunlins, Red Knots, Black-bellied Plovers, Willets, Short-billed Dowitchers, Long-billed Dowitchers, Ruddy Turnstones, Semipalmated Sandpipers, and Western Sandpipers. They roost on beaches in closely packed flocks of up to several thousand birds, standing or squatting against the wind and jostling for the least exposed positions in the flock. When threatened by an avian predator such as a falcon, Sanderlings take flight and form a tight ball that careens erratically over the ocean. Back to top

Conservation

Conservation Low ConcernAlthough Sanderlings are one of our most common shorebirds, their populations are declining and they are listed as a species of high concern by the Western Hemisphere Shorebird Reserve Network. The world population is estimated at about 700,000 individuals, with about 300,000 occurring in the Americas. Sanderling is not on the 2014 State of the Birds Watch List. Shorebird population sizes are difficult to estimate because the birds cluster in large flocks scattered over large distances. However, surveys suggest that Sanderling populations are declining, sharply in places. According to Christmas Bird Counts, there was an overall decrease of 0.5% per year between 1959 and 1988, and California counts decreased by 3.7% per year. From 1974 to 1982, Sanderlings on the Atlantic Coast dropped by 13.7% per year. In that time, peak migration counts in Massachusetts dropped from 10,000-30,000 birds in the 1950s to an average of just 2,000 birds. Declines are probably caused by development or alteration of shoreline habitats—the sandy beaches Sanderlings live on are also prized by humans for recreation. Sanderlings are also vulnerable to pollution from pesticides and, especially, oil spills due to their close association with the ocean edge. In some areas, notably Chesapeake Bay where there has been a large fishery for horseshoe crab eggs, humans compete with Sanderlings and other shorebirds for food. Conservation of long-distance migrants like Sanderlings is always complicated because of the birds’ reliance on distantly separated staging areas, which have to provide enough food at the right time, and which are all subject to their own habitat pressures. Back to top

Credits

Andres, B. A., P. A. Smith, R. I. G. Morrison, C. L. Gratto-Trevor, S. C. Brown and C. A. Friis. 2012a. Population estimates of North American shorebirds, 2012. Wader Study Group Bulletin no. 119 (3):178-194.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2015.2. Patuxent Wildlife Research Center, Bird Banding Laboratory 2015.

Macwhirter, R. Bruce, Peter Austin-Smith Jr. and Donald E. Kroodsma. 2002. Sanderling (Calidris alba), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

North American Bird Conservation Initiative. 2014. The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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