by Frank Keim
The Rock sandpiper is a tough shorebird. Not only does it nest in the Arctic on Alaska’s Bering Sea coasts and islands as far north as the Seward Peninsula, but it also winters farther north than most other shorebirds, from frost-rimed rocky seashores and mudflats on Alaska’s south coast all the way down to the craggy northern coast of Oregon and California.
Its Yup’ik names that I have run across are: Cenaqiiq and Cenarpak, both referring to a large shorebird that feeds and nests along coastlines. Its scientific name is from three Ancient Greek words: calidris, meaning gray waterbird; ptilon, for feather; and knēmē, leg. Together, they mean feathery-legged gray waterbird. Their common English name, Rock sandpiper, derives from its habit of foraging along rocky coastlines during most of the year.
When Cenarpak returns to its summer breeding ground in early May, it heads for dry mossy to wet tundra regions of the Y-K Delta and Bering Sea islands such as the Pribilofs, St. Matthew, Nunivak, St. Lawrence Island and the Aleutians. There they are guaranteed a nutritious diet to prepare them for nesting. This includes insects and spiders, but also small invertebrates like mollusks, crustaceans and marine worms which they find along the rocky, muddy or sandy shorelines of those habitats. Herring eggs may be a part of their menu as well. Unlike most other sandpipers, they will also eat berries, seeds, moss and algae. They will sometimes chase flying insects and capture them in the air, and will often commute to coastal flats to hunt in small flocks when nesting. While feeding, they probe, pick, or slash back and forth in a zigzag motion, depending upon their food choice.
When their nesting areas in the tundra are finally free from snow, the males are the first to move into them to claim breeding territories that average about 13 acres. These territories may already have been used for several seasons, and to defend them the proprietors sing and fly around the boundaries, chasing away competitors.
Males also display in the air above them or on the ground, advertising to possible mates and warning off rivals. The courting displays include singing and hovering on fluttering wingbeats above the territory, then slow descent to the land with wings held upward in a V-shape.
In other displays, the male might fly in a widening circle on trembling wings or in an undulating pattern while giving trilled calls. After landing, the male often raises just one wing, showing the whitish underwing pattern. He may also stand on higher ground, neck stretched to the sky, giving a cricket-like call.
Females attracted to his displays may land nearby and observe him, sometimes also raising one wing. Once paired, the male leads the female around his domain and performs a scraping display in which he crouches and turns, as if preparing a nest site. He then leans forward and points at the site with his bill, drooping his wings and calling. The female indicates her acceptance of the nest site by walking into it. The nest sites are located both in low dry sedge meadows and in higher places below 1000 feet elevation, usually not far from both freshwater and coastal areas that are especially rich in insect life.
Cenarpak is a monogamous sandpiper, and often pairs reunite over multiple nesting seasons. Males chase females before mating, and guard them aggressively through egg-laying. Nests are set directly on the ground, or on patches of mossy hummocks slightly elevated above the surrounding sedge meadows, or in dry heather surrounded by dwarf shrubs.
Mated pairs visit many possible nest scrapes over about a week before deciding which one to use. Males construct the nest, which is a deep cup made of willow leaves, sedges, grasses, mosses and lichens. Four brown-splotched, grayish-olive eggs are laid, and incubation is by both parents for about 20 days. If a predator, such as a jaeger, threatens the nest, the adult may do a fluttering broken-wing act as a distraction.
The young hatch fully clothed in downy feathers and ready to leave the nest within only hours after hatching. They are tended by the father bird, rarely by their mother or both parents. Young birds actively search for their own food in wet depressions in meadows near the nest, on slough banks, in creeks or around pothole ponds. Their age at first flight is about three weeks.
After fattening up for another two months or so, both young and old birds gather in large flocks and begin slowly migrating southward along Alaska’s west coast. They are in no hurry, since they don’t have far to go to their wintering grounds. Those that winter in the Pacific Northwest spend much of their time foraging cooperatively with other sandpipers like turnstones, sanderlings and surfbirds. The species’ different sizes and bill shapes allow them to focus on different kinds of prey without competing with each other.
Their global breeding population is still fairly stable, but since they spend most of their lives in tidal zones, they are constantly vulnerable to oil spills. Other conservation threats in today’s increasingly polluted world include pesticides and other toxic pollutants. Loss and degradation of their habitats everywhere, especially from the looming reality of climate change, is also a serious concern. Only modifications in human behavior could change this.