Rock Sandpiper Life History

Habitat

Rock Sandpipers breed in tundra from coastal areas into higher areas, but usually below 1,000 feet elevation. They use both dry heath and wet tundra habitats, with abundant lichens, mosses, dwarf shrubs, and flowering plants. Nesting Rock Sandpipers are most numerous in lower hummocks and sedge meadows, usually near both freshwater bodies and coastal areas; places especially rich in insect life. The dominant plant species include dwarf birch, dwarf willows, four-angle mountain-heather, bog blueberry, crowberry, cloudberry, lingonberry, alpine azalea, wild celery, fireweed, arctic yarrow, Tilesius wormwood, Nootka lupine, boreal sagebrush, beach pea, Labrador tea, marsh marigold, buttercup, sorrel, horsetail, cottongrass, and grasses, such as circumpolar reed grass, lyme grass, red fescue, and various bluegrasses. Sedges, such as looseflower alpine sedge and Ramensk’s sedge, are important plants in wet areas, where adults forage near the nest. Like its close relative, Purple Sandpiper, Rock Sandpiper spends the entire nonbreeding season in tidal habitats. Both species are well adapted to feeding on small invertebrates that live among algae on rocky shorelines, including jetties and breakwaters. However, unlike Purple Sandpipers, Rock Sandpipers also make extensive use of muddy and sandy flats, especially near rivermouths, by probing into soft substrates for invertebrates, similar to Dunlin. At high tide, they roost on riverbanks, gravel bars, beaches, breakwaters, reefs, or even blocks of ice, and sometimes move a short distance inland to bathe in freshwater. Back to top

Food

Rock Sandpipers eat mostly insects (during the breeding season) and aquatic invertebrates (nonbreeding season). They pick small prey from rocks, using the bill tip like a tweezer. For prey hidden in mats of algae on rocks or in wrack, they insert the bill and forage by touch, sometimes probing from a low angle, with head held sideways, and sometimes walking forward with bill partly open, slicing through the algae until they detect prey. They sometimes hammer into barnacles or mussels. They also probe into sand and mud in search of small clams or worms. On breeding grounds, Rock Sandpipers feed near the nest in wet areas of the tundra, where they eat fly and beetle larvae, along with other insects, worms, and spiders. They sometimes chase flying insects to capture them in the air. Some also commute to coastal flats to forage in small flocks when nesting. Like many other shorebird species, Rock Sandpipers occasionally eat beached carcasses of marine animals, not for carrion but for fly larvae. Their prey items include midges, craneflies, stoneflies, flies, beetles, spiders, earthworms, polychaete worms, snails, barnacles, mussels, Baltic clam, tiny crustaceans (amphipods), jellyfish, and fish eggs (Pacific herring).

Nesting

Nest Placement

Nests are set on the ground or in patches of mossy hummocks; areas of relatively dry tundra vegetation that are slightly more elevated than surrounding sedge meadows. In dry heath away from wetlands, nests are set in areas with extensive dwarf shrubs.

Nest Description

Males and females visit many potential nest scrapes over a week and may begin several nests before selecting one. Males construct the nest, a deep cup made of willow leaves, sedges, grasses, and lichen, along with many other plants found nearby. Nests measure on average 3.7 inches across, with an interior cup 2.9 inches across and 1.8 inches deep.

Nesting Facts

Behavior

When Rock Sandpipers arrive at breeding areas, their nesting sites are often locked in snow and ice. They may pick small prey from the snow’s surface, as other newly arrived shorebirds do, but usually they gather in flocks and feed on mudflats, beaches, wrack, rocky shorelines, or snow-free areas of tundra until their nesting areas thaw. Males move into the nesting areas first and set up breeding territories that average about 13 acres. On their territories, which may be reused for several seasons, males sing and fly around the boundaries, chasing away other males as well as similar-sized shorebirds such as Dunlin. Males display both on the ground and in the air, advertising to prospective mates and warning off rivals. Most flight displays involve singing and hovering (on fluttering wingbeats) high above the territory, then descending to land with wings held upward, in a V-shape. In other displays, the male may fly for long distances on trembling wings or in an undulating flight pattern while vocalizing. Often, after landing, the male raises one wing toward the sky, showing the whitish underwing pattern (even if no other birds are nearby). Males also stand in a prominent area, neck stretched upward, and give a cricketlike call. Females attracted to a displaying male often land nearby to observe, sometimes raising one wing. Once paired, the male leads the female around the territory and performs a “scraping” display, in which he crouches and turns, as if preparing a nest site; he then leans forward and “points” to the site with the bill, drooping wings and calling. Females indicate acceptance of a nest site by walking into it.

Rock Sandpipers are socially monogamous, and in some places, pairs reunite in successive nesting seasons. Males chase females before mating and guard them carefully through egg-laying. If a rival male enters the territory, the territorial male usually gives a warning display and call. If these are unsuccessful, he chases the rival on the ground, in the air (often in a zigzag flight pattern), or engages in combat. Unlike the Purple Sandpiper, both sexes incubate the eggs and remain in the territory to defend the young. Young birds and adults forage in wet depressions in meadows near the nest, on slough banks, and sometimes in creeks or drainage areas. In the nonbreeding season, Rock Sandpipers gather in flocks and are not territorial.

Conservation

Partners in Flight estimates a global breeding population of 140,000 individuals and rates the species 13 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. Rock Sandpipers spend most of their lives in tidal zones, which makes them vulnerable to oil spills. Other potential conservation threats include pesticides and other pollutants and loss or degradation of habitats, particularly from global climate change.

Credits

Andres, B. A., P. A. Smith, R. I. G. Morrison, C. L. Gratto-Trevor, S. C. Brown, and C. A. Friis (2012). Population estimates of North American shorebirds, 2012. Wader Study Group Bulletin 119:178–194.

Gill, Robert E., Pavel S. Tomkovich and Brian J. McCaffery. (2002). Rock Sandpiper (Calidris ptilocnemis), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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