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Rock Sandpiper | Calidris ptilocnemis

Beringstrandloper | Correlimos roquero

The Rock Sandpiper is the Pacific counterpart of the Purple Sandpiper: just as plump, just as attached to weed and stone, but with a black belly patch in breeding plumage. Almost the whole of the largest subspecies winters at the head of Cook Inlet in Alaska, the coldest non-breeding range known for any wader.

Rock Sandpiper (Calidris ptilocnemis) — Photo: Credit USFWS — Public domain · Wikimedia Commons

Voice

The male sings in a display flight on quivering wings above his patch of tundra: a long series of trills in short, paired phrases, per-deerrr per-deerrr, beri beri, rita rita. Standing on a tussock he adds a cricket-like chirp. The usual call is a short quit, in flight a grating cheerrt. Alarm brings a descending rattle of staccato notes; in the winter flock there is little more than soft chatter.

No freely licensed recording has been found for this species yet; what to listen for is described below.

Identification

A very plump sandpiper with a short neck and short legs and a fairly long, slightly curved bill. In breeding plumage it has a chestnut crown and ear patch, a pale face, a back mixed of grey, rust and gold, and — in the birds of the Bering Sea islands — a large black belly patch. In winter plumage it is deep slate grey with pale, grey-spotted underparts, an orange bill base and greenish-yellow legs. Juveniles are dark brown with golden feather edges and a buff, faintly streaked breast. The four subspecies differ mainly in size and in the extent of the belly patch; the Pribilof birds are the largest and palest.

Confusion species

Purple Sandpiper (Calidris maritima) is its double in winter plumage, but belongs on the Atlantic side; the two never occur together. Dunlin (C. alpina) also has a black belly patch when breeding, but is slimmer, browner-backed, and has black legs and a longer, evenly curved bill. Surfbird (C. virgata) shares the same rocky shore, but is bigger, much thicker in the bill, and shows a white tail base with a black terminal band in flight. Among Dunlin on a mudflat the Rock Sandpiper gives itself away by its heavier build and its orange bill base.

Habitat

Outside the breeding season on weed-covered rocky shores, reefs and breakwaters, but unlike Purple Sandpiper also freely on mud and sand flats at river mouths and in estuaries. At high water it rests on banks, gravel bars and harbour walls. It breeds on wet or dry coastal tundra below about three hundred metres, with low hummocks and small sedge meadows, usually close to both fresh water and the sea. In winter the quality of the food decides everything: at the head of Cook Inlet it lives almost entirely on small bivalves that carry strikingly much flesh in little shell.

Where the bird is most often found, arranged by the USNVC — the vegetation classification of the United States and Canada — and CMECS for sea and coast.

Range and movements

Breeds on the coasts of western Alaska, on the islands of the Bering Sea and along the Aleutians, and on the Russian side on Chukotka and Kamchatka. It winters on ice-free rocky coasts of the Pacific from the Aleutians and Cook Inlet south to British Columbia, Washington and Oregon; farther south it becomes scarce quickly. The subspecies leapfrog one another: the birds of the Pribilofs and St Matthew stay closest to home, those of Chukotka and western Alaska travel furthest. Some twenty thousand birds spend the winter at the head of Cook Inlet, where midwinter brings only five hours of light.

Resident
Breeding (summer)
Winter
Passage
dark = core range, pale = thinly spread

The map is a density field, not a drawn range boundary: it is built from the records themselves and therefore does not follow state or national borders. Both the seasonal colour and the depth of colour come, cell by cell, from the records of GBIF (2006–2026), counted per 0,7° cell and divided by all bird records in that same cell, so that the density of birdwatchers does not count. Every cell is counted separately for June–July, December–January and the migration months, and takes the colour of the season that wins there; a cell is only called summer or winter where the other season is nearly empty. Country outlines: Natural Earth (public domain).

Where and when to look

On the coast of Washington and Oregon look for it from November to April on basalt points, jetties and breakwaters, among Surfbirds and Black Turnstones — scan the party for the bird with the orange bill base. In Alaska it is the other way round: there it stands on the mudflats in winter. Around high water the groups bunch together on a rocky point and are far easier to count than at low tide.

Conservation

The world population is put at about 140,000 birds; the Pribilof form accounts for only a few tens of thousands of those. More than half the birds disappeared over fifty years, although recent years appear stable. Oil is the heaviest threat, because virtually the whole population lives in a narrow tidal band and gathers in a handful of bays in winter.

Scientific name

Calidris ptilocnemis | (Coues, 1873)

Coues described the species in 1873 as Tringa ptilocnemis; because it was later moved to another genus, author and year stand in parentheses. The genus Calidris goes back to Greek kalidris, in Aristotle the name of a grey bird of the waterside. ptilocnemis is built from Greek ptilon, 'feather', and knēmē, 'lower leg', after the feathering that in this species runs far down the shin. The described specimen came from St George in the Pribilof Islands, exactly where the largest and palest form breeds.