The sharp-tailed sandpiper (Calidris acuminata) (but see below) is a small-medium migratory wader or shorebird, found mostly in Siberia breeding over summer (June - August) and Australia for wintering (September - March).
A review of data has indicated that this bird should perhaps better be placed into the genus Philomachus – as P. acuminatus – which now contains only the ruff, but if the sharp-tailed sandpiper is merged into it, it would need to accommodate the broad-billed sandpiper.[2]
While the latter is a peculiar calidrid, the sharp-tailed sandpiper is much more similar to other Calidris/Erolia species such as the pectoral sandpiper. On the one hand, its larger size and long-legged stance, and the breast pattern which gradually fades away on the belly as in the ruff instead of having a fairly sharp border as in the Calidris/Erolia stints indicate that placement in Philomachus may be correct. Still, it is just as possible that – given the fairly common instances of hybridization in calidrines – mitochondrial DNA data has given a false picture of this species' true affinities. The curlew sandpiper, which is a proposed parent of the hybrid called "Cooper's sandpiper" ("Calidris" × cooperi) together with the sharp-tailed sandpiper, is another unusual calidrid that is hard to place systematically.
The genus name is from Ancient Greek kalidris or skalidris, a term used by Aristotle for some grey-coloured waterside birds. The specific acuminata is from Latin acuminatus, 'sharp, pointed'.[3]
A small-medium wader, the portly sandpiper has a pot belly, flat back and somewhat drawn-out rear end.[4] They have a mottled chestnut-brown upperbody with sharp looking feathers with a dark centre. Chestnut cap on their heads and brown stripe though the eye. Dark grey to black straight bills and olive to yellow coloured legs. The underparts are white or paler in colour with the similar mottling on the breast and sides of the belly.[5] The plumage is duller during winterting and more vivid during the breeding season.[6][7] The juveniles are more bright and sharp during wintering than adults. Having sharper feathers, brighter chestnut coloured crowns contrasting the white mantle stripes and bright buffy chests.[5]
This bird looks a lot like the pectoral sandpiper, within whose Asian range it breeds. It differs from that species in its breast pattern, stronger supercilium and more chestnut crown. It has some similarities to the long-toed stint, but is much larger than the stint.
Measurements:[8]
Sharp-tailed sandpipers are strongly migratory, breeding solely in eastern Siberia from the Taimyr Penninsula to Chaun Bay in Chukotka. They have a complex migration, with Adults departing Siberia in July and juveniles in August to head south, where the majority of the population winters in Australasia. They largely take two routes with the majority of post-breeding adults flying south in flocks of less than 1000, east of Lake Baikal, to the Pacific coast of Russia and the Yellow Sea coasts of China and Korea. They mostly all fly direct to Micronesia and New Guinea in late August, departing here with the onset of the wetseason to north-west Australia in mid September. They start moving towards south-east Australia with numbers peaking in December to February. The other route heads east, taking most juveniles but a few adults into Alaska across the Bering Strait. Staying here from mid August to late October to fatten, it is presumed they take a direct non-stop trans-Pacific flight of more than 10,000 km to reach Australia and New Zealand. Some will continue south along the Pacific coast of North America into Washington state, less frequently to California and possibly into Latin America but only two recent records occur in Panama and Bolivia.[9][5]
It occurs as a rare autumn migrant to North America, but in western Europe only as a very rare vagrant with records in 11 different countries, mostly in the United Kindgom between August and October. It has been recorded in the Middle East and Central Asia, six times in Kazakhstan, once in Yeman and Oman. Within the Indian Ocean they have been documented at Christmas Island four times, totalling 16 birds between October and December. Three recorded observations at Cocos Island in Novmeber and December. Five records at the Chagos archipelago from September to December. Five records at the Seychelles, one in July, two in September to February overwintering and two on passage in November. They have been recently documented in Mozambique southern Africa for the first time in 2018.[9]
In Siberia the breeding ground are mostly tundra made up of peat-hummock and lichen. On passage between breeding and wintering areas they favor the muddy edges of shallow freshwater or brackish wetlands with grass, emergent or inundated sedges, saltmarsh or other low vegetation. These include swamps, lakes, lagoons, and pools near coasts, waterholes, dams, saltpans and hypersaline salt lakes inland.[9] In Alaska they seem to prefer coastal moist graminoid meadows and riverine intertidally exposed mudbanks.[10] In Australia they are largely found around wetlands, preferring freshwater inland wetlands with grassy edges.[7] Once these epheneral terrestrial wetlands have dried out they tend to be on coastal mudflats, salt marsh and brackish lagoons and less often on similar wet fields of short grass.[9] Other areas they have been spotted in Australia include around sewage farms, flooded fields, mangroves, rocky shores and beaches.[7]
Little is known about the behavious of the Sharp-tailed sandpiper but its behavious and structure are most similar to the Pectoral Sandpiper.[5]
They breed from to June to August in the short Siberian summer, making shallow hollow lined nests with leave and grass that are hidden on the ground. The clutch size is usually four eggs, with the females incubating and raising the chicks.[6] The breeding plumage is more vivid, with breast feathers greater in chestnut colour and their chevron-shaped markings becoming more defined.[7]
These birds forage on the edge of wetlands, intertidal mudflats, either on sand or bare wet mud and in shallow water. They will also forage among inundated vegetation of grass, sedges or saltmarsh. After rain they can be found in paddocks of short grass, well away from water. At low tides they can be found on the intertidal mudflats, before moving inland to freshwater wetlands at the high tide. Occasionaly they forage on dry or wet mats of algae, among rotting seaweed or seagrass on beaches, edges of stony wetlands and exposed reefs.[4] Picking up food by sight or sometimes by probing, they mainly eat aquatic insects, molluscs, crustaceans, worms, occasionally seeds and other invertebrates.[7]
The sharp-tailed sandpiper (Calidris acuminata) (but see below) is a small-medium migratory wader or shorebird, found mostly in Siberia breeding over summer (June - August) and Australia for wintering (September - March).
