Nombre en español: Vuelvepiedras oscuro

Nombre en inglés: Black Turnstone

Nombre científico: Arenaria melanocephala

Familia: Scolopacidae

Categorías: Hipotéticas

El vuelvepiedras oscuro, (Arenaria melanocephala) es una de las dos especies que componen el género de aves Arenaria, de la familia Scolopacidae. Esta monotípica especie habita en playas marinas del oeste de América del Norte, aunque nidifica solo en tundras árticas, en Alaska.​

Descripción

Mide entre 22 y 25 cm de largo, y tiene un peso de entre 100 y 170 g. Posee un cuerpo compacto, con sus patas, y cuello cortos, este último también grueso. Su pico, de 20 a 27 mm de longitud, tiene una forma específicamente evolucionada para facilitar al ave la búsqueda de alimento.

Su coloración varía con las estaciones, siendo, más viva, contrastada, o colorida en la temporada reproductiva (el verano boreal). Su aspecto es también llamativo en vuelo, al mostrar manchas blancas en el dorso, las alas y la cola.

Costumbres

Es un ave estrictamente costera, prefiriendo las playas rocosas o arenosas, en donde comparte el hábitat con otras especies de limícolas. Tal como indica su nombre vulgar, posee un pico especialmente adaptado para que pueda fácilmente dar vuelta a las piedras o algas que en las costas marinas encuentra, y de este modo queden expuestos los invertebrados que bajo esos restos se ocultan y que constituyen el alimento de esta ave, dieta que complementa con pescado en descomposición.

Al alimentarse, puede hacerlo de manera aislada, en grupos pequeños, o incluso en grandes bandadas; esta última es la manera en que realiza sus migraciones.

Construye nidos solitarios cerca de la costa. Esconde su nido entre la vegetación. La hembra pone huevos verdosos con manchas parduzcas, que son empollados por ambos progenitores. Los huevos eclosionan luego de 22 a 24 días.

Distribución

Esta especie nidifica entre mayo y principios de agosto en tundras árticas del oeste Alaska. En el invierno migra hacia el sur en busca de climas más amenos, en la costa pacífica de Estados Unidos, llegando por el sur hasta el noroeste de México.

Taxonomía

Esta especie monotípica fue descrita originalmente por Nicholas Aylward Vigors en el año 1829, bajo el nombre científico de: Strepsilas melanocephalus. Su localidad tipo es: «costa noroeste de América del Norte».

​Black turnstone

The black turnstone (Arenaria melanocephala) is a species of small wading bird. It is one of two species of turnstone in the genus Arenaria the ruddy turnstone (A. interpres) being the other. It is now classified in the sandpiper family, Scolopacidae, but was formerly sometimes placed in the plover family, Charadriidae. It is native to the west coast of North America and breeds only in Alaska.

Description

It is 22–25 centimeters long and weighs 100–170 grams. The black bill is 20–27 millimeters long and slightly upturned. The legs and feet are blackish-brown with a reddish tinge. The bird is largely black and white in appearance. Breeding-plumaged adults have a black head and breast apart from a white spot between the eye and bill, a white stripe over the eye and white flecks on the sides of the breast. The upperparts are blackish-brown with pale fringes to the wing-coverts and scapular feathers. The belly and vent are white. In flight it shows a white wingbar, white shoulder patch and white tail with a broad black band across it. There is white from the lower back to the uppertail-coverts apart from a dark bar across the rump.

In winter the head and breast become largely dark brown with little white. Juveniles are similar to winter adults but browner with buff fringes to the wing-coverts and scapulars and a grey-brown tip to the tail.

The ruddy turnstone is similar but has rufous-brown markings on the upperparts and more white on the head and breast, particularly in breeding plumage. It has narrower wings and a narrower white wingbar. Its legs are orange and brighter than those of the black turnstone though there can be some overlap.

The black turnstone has a variety of calls, especially a rattling trill which can be heard throughout the year. This call is higher and less harsh than the similar call of the ruddy turnstone. Other calls include a loud, screeching alarm call and a soft, purring call uttered to young chicks. Displaying males produce a long series of staccato notes in flight as well as chirruping trills on the ground.

Distribution

It breeds in western Alaska from the Alaska Peninsula in the south to Point Hope in the north. The bulk of the population nests in the Yukon-Kuskokwim Delta. It usually nests near the coast but in some areas it occurs further inland along the shores of rivers and lakes. There are a handful of records from north-east Siberia but there has been no sign of breeding there. The world population is estimated at 95,000 birds with about 80,000 of these in the Yukon-Kuskokwim Delta.

It winters on rocky shores along the Pacific coast of North America from southern Alaska southwards as far as north-west Mexico where it occurs in Baja California and Sonora with a single record from Nayarit. It is very occasionally seen inland during spring and fall migration; there are a number of records from the Salton Sea in southern California and scattered sightings from inland US states including Montana, Wisconsin, Nevada and Arizona. Vagrant birds have been recorded from Yukon and the Northwest Territories and there is one record from San Cristóbal Island in the Galápagos Islands.

Ecology

It feeds mainly on invertebrates, particularly crustaceans and mollusks in winter and insects during the breeding season. Seeds, eggs and carrion are also taken. At the breeding grounds it mainly feeds in wet meadows with sedges. In winter, its typical habitat is rocky coasts but it also feeds on beaches, mudflats and man-made structures such as jetties and breakwaters. It uses its bill to turn over stones, algal mats and other objects to get at prey hidden beneath.

It arrives on its breeding ground from early May to early June with the males arriving first. The birds often return to the same territory and pair with the same mate as previous years. The nest is a scrape dug mainly by the male. It is usually located amongst sedges or grasses or under willows. Four eggs are usually laid; they are olive or pale greenish with darker spots. The eggs are incubated for 21–24 days by both parents. The young birds are precocial and are able to leave the nest and feed themselves soon after hatching. They are able to fly well after 25–34 days.

Fuentes: Wikipedia/eBird/xeno-canto