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Identificazione

The bar-tailed godwit is a relatively short-legged species of godwit. The bill-to-tail length is 37–41 cm (15–16 in), with a wingspan of 70–80 cm (28–31 in). Males average smaller than females but with much overlap; males weigh 190–400 g (6.7–14.1 oz), while females weigh 260–630 g (9.2–22.2 oz); there is also some regional variation in size (see subspecies, below). The adult has blue-grey legs and a long, tapering, slightly upturned bi-colored bill: pink at the base and black towards the tip. The neck, breast and belly are unbroken brick red in breeding plumage, and dark brown above. Females breeding plumage is much duller than males, with a chestnut to cinnamon belly. Breeding plumage is not fully apparent until the third year, and there are three distinguishable age classes; during their first migration north immature males are noticeably paler in colour than more mature males. Non-breeding birds seen in the Southern Hemisphere are plain grey-brown with darker feather centres, giving them a striped look, and are whitish underneath. Juveniles are similar to non-breeding adults but more buff overall with streaked plumages on flanks and breast.<p>Alaska-breeding bar-tailed godwits show an increase in body size from north to south, but this trend is not apparent in their non-breeding grounds in New Zealand; birds of different sizes mix freely.<p>Limosa lapponica is distinguished from the black-tailed godwit (Limosa limosa) by its black-and-white horizontally-barred (rather than wholly black) tail, and lack of white wing bars. The most similar species is the Asiatic dowitcher (Limnodromus semipalmatus).

Tassonomia

The bar-tailed godwit was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Scolopax limosa. It is now placed with three other godwits in the genus Limosa that was introduced by the French zoologist Mathurin Jacques Brisson in 1760. The genus name Limosa is from Latin and means "muddy", from limus, "mud", referring to its preferred habitat. The specific name lapponica refers to Lapland.<p>The English term "godwit" was first recorded in about 1416–17 and may be an imitation of the bird's call, or be derived from the Old English "god whit", meaning "good creature", perhaps referring to its eating qualities. Its English name is taken from the black-and-white barred tail and upper tail coverts in this species. In French it is known as barge rousse, Russian maliy veretennik, Inuit chiuchiuchiak, Yup'ik tevatevaaq, and Māori kūaka.<p>Four subspecies are recognised:

Nome scientifico

Limosa lapponica

Autorità

(Linnaeus, 1758)

Ordine

Caradriformi

Famiglia

Scolopacidi

Genere

Limosa

Areale e habitat

All bar-tailed godwits spend the Northern Hemisphere summer in the Arctic, where they breed, and make a long-distance migration south in winter to more temperate areas. L. l. lapponica make the shortest migration, some only as far as the North Sea, while others travel as far as India. Bar-tailed godwits nesting in Alaska (L. l. baueri) travel all the way to Australia and New Zealand. They undertake the longest non-stop migrations of any bird, and to fuel they carry the greatest fat loads of any migratory bird so far studied, reducing the size of their digestive organs to do so.<p>L. l. bauri breeds in Alaska and spends the non-breeding season in eastern Australia and New Zealand. L. l. menzbieri breeds in Siberia and migrates to northern and western Australia. Birds breeding in Siberia follow the coast of Asia northwards and southwards, but those breeding in Alaska migrate directly across the Pacific to Australasia 11,000 km (6,835 mi) away. To track the return journey, seven birds in New Zealand were tagged with surgically-implanted transmitters and tracked by satellite to the Yellow Sea in China, a distance of 9,575 km (5,950 mi); the actual track flown by one bird was 11,026 km (6,851 mi), taking nine days. At least three other bar-tailed godwits also appear to have reached the Yellow Sea after non-stop flights from New Zealand.<p>One specific female of the flock, nicknamed "E7", flew onward from China to Alaska and stayed there for the breeding season. Then in August 2007 she departed on an eight-day non-stop flight from western Alaska to the Piako River near Thames, New Zealand, setting a new known flight record of 11,680 km (7,258 mi). This L. l. bauri female made a 174 day round-trip journey of 29,280 km (18,194 mi) with 20 days of flying. In 2021, a male bar-tailed godwit, 4BBRW, set a new record for non-stop migratory flight with an 8,100 mile (approximately 13035 km) flight from Alaska, USA to New South Wales, Australia. The same individual held a previous record in 2020. In 2022, a godwit numbered 234684 left Alaska on 13 October and flew non-stop to Tasmania, the first time a tagged bird has flown this route. It flew a minimum of 13,560 km (8,430 mi) in 11 days 1 hour: a record non-stop distance.<p>To fuel such long journeys, L. l. baueri birds in New Zealand deposit much more fat for their body size than other subspecies, allowing them to fly 6,000 km (3,728 mi) to 8,600 km (5,344 mi). Both Australasian subspecies head north to their breeding grounds along the coast of Asia to the Yalu Jiang coastal wetland in the north Yellow Sea, the most important staging grounds for godwits and great knots (Calidris tenuirostris) in their northern migration. Baueri birds rested for about 41 days before continuing approximately 7,000 km (4,350 mi) on to Alaska. Menzbieri spent on average 38 days in the Yellow Sea region and flew an additional 4,100 km (2,548 mi) to high Arctic Russia.<p>Birds will often depart early from New Zealand if there are favourable winds; they seem to be able to predict weather patterns that will assist them on the entire migration route. Birds that had nested in southern Alaska were larger and departed New Zealand earliest; this pattern was repeated six months later, with birds departing Alaska in the same order they arrived, and over the same span of days. Birds in southern New Zealand departed on average 9–11 days earlier than birds in more northern sites. Godwits arrive at the Yukon-Kuskokwim Delta in Alaska in two waves; local breeders in early May, and larger flocks in the third week of May en route to breeding grounds further north.

Areale riproduttivo

PAL : patchily in low Arctic tundra of n Palearctic: far n Scandinavia to Chukotskiy and Anadyr pens. (ne Russia) and n, w Alaska

Areale non riproduttivo

AF, OR, AU : mainly temperate to tropical coasts: British Is., s Europe, w Mediterranean, Africa, Malagasy region through Middle East, Indian subcontinent, se Asia, Indonesian Arch.; Ryukyu Is. (s Japan), se China, Taiwan, Philippines, Australasia from New Guinea region to Melanesia and New Zealand, and Fiji (sw Polynesia)

Migrazione

Complete migrants

Comportamento

The bar-tailed godwit is a non-breeding migrant in Australia and New Zealand. Birds first depart for their northern hemisphere breeding sites at age 2–4. Breeding take place each year in Scandinavia, northern Asia, and Alaska. The nest is a shallow cup in moss sometimes lined with vegetation. Clutch size is from 2 to 5, averaging four. Both sexes share incubation of the eggs for 20 to 21 days, the female during the day and the male at night.<p>The birds' main source of food in wetlands is bristle-worms (up to 70%), supplemented by small bivalves and crustaceans. In wet pastures, bar-tailed godwits eat invertebrates. In a major staging site in the northern Yellow Sea, they continue to hunt polychaetes, but most of their food intake is the bivalve mollusc Potamocorbula laevis, which they generally swallow whole.<p>Male bar-tailed godwits are smaller than females and have shorter bills. In a study at the Manawatū Estuary, shorter-billed birds (males) fed mostly on small surface prey like Potamopyrgus snails, half being snail specialists, whereas females consumed more deeply-buried prey such as worms; the birds also displayed some individual food preferences.

Conservazione

Tendenza della popolazione

declining