Corriere tridattilo

Identificazione

The sanderling is a small plump sandpiper, 18–20 cm (7.1–7.9 in) in length. Its weight ranges from 40–100 g (1.4–3.5 oz). The winter bird is very pale, almost white apart from a dark shoulder patch. This is the source of the specific name, alba, which is the Latin for "white". Later in the summer, the face and throat become brick-red. The juvenile bird is spangled black and white, and shows much more contrast than the adult.<p>If its size is misjudged, a sanderling in breeding plumage can be mistaken for some varieties of stint, or a sanderling in winter plumage can be mistaken for a dunlin or red knot. It can be told from other small wading birds, given good views, by its lack of a hind toe. Its behavior is also distinctive.

Tassonomia

Nome scientifico

Calidris alba

Autorità

(Pallas, 1764)

Ordine

Caradriformi

Famiglia

Scolopacidi

Genere

Calidris

Areale e habitat

Areale riproduttivo

NA, PAL : high Arctic tundra wetlands of Holarctic: nw, se Greenland, Svalbard (n of Norway), n Taymyr Pen. and Severnaya Zemlya (to n), Lena Delta and New Siberian Is. (nc Siberia), Alaskan North Slope (rare), Canadian Arctic islands from Banks to Ellesmere and s to Southampton

Areale non riproduttivo

Worldwide : sandy coastal beaches from temperate to tropical zone: British Is. and Macaronesia (nw of n Africa) through Africa, Malagasy region, Middle East, s, se Asia through Indonesian Arch. to Australia, Melanesia, Philippines and s, c Japan (but rare New Guinea and New Zealand); sw, se Canada and Caribbean s to Tierra del Fuego and including remote islands through e Polynesia

Migrazione

Complete migrants

Comportamento

Sanderlings feed on invertebrate prey buried in the sand in the upper intertidal zone. In North America, this diet largely consists of the isopods Excirolana linguifrons, Excirolana kincaidii, and the mole crab, Emerita analoga. When the tide is out, these crustaceans live in burrows some way beneath the surface. When the tide comes in, they move into the upper layers of sand and feed on the plankton and detritus that washes over them with each wave. They then burrow rapidly down again as the water retreats. They leave no marks on the surface, so the sanderlings hunt for them by plunging their beaks into the sand at random, consuming whatever they find. Their bills can penetrate only 2 or 3 cm (0.79 or 1.18 in) and as the water swirls around and retreats, the sand is softer; this makes it easier for the birds' beaks to penetrate further. In the spring, when much breeding activity is taking place in the benthic community, there may be as many as 4000 invertebrates per square metre, but their average size is smaller than later in the year. The birds appear to rush madly around at the edge of the surf, but in reality they are maximising their chances of catching as many prey animals as possible when they are at their most vulnerable near the surface.<p>At breeding time sanderlings are territorial, with the male aggressively defending its territory. They may either form monogamous pairs or polyandrous (one female and two male) pairings.

Conservazione

Tendenza della popolazione

unknown