Bar-tailed godwit

The bar-tailed godwit is a large and strongly migratory wader in the family Scolopacidae, which feeds on bristle-worms and shellfish on coastal mudflats and estuaries. It has distinctive red breeding plumage, long legs, and a long upturned bill. Bar-tailed godwits breed on Arctic coasts and tundra from Scandinavia to Alaska, and overwinter on coasts in temperate and tropical regions of Australia and New Zealand. The migration of the subspecies Limosa lapponica baueri across the Pacific Ocean from Alaska to New Zealand is the longest known non-stop flight of any bird, and also the longest journey without pausing to feed by any animal. The round-trip migration for this subspecies is over.

Taxonomy

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.
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.
Five subspecies are currently recognised, listed from west to east:

L. l. lapponica – breeds from northern Scandinavia east to the Yamal Peninsula; winters western coasts of Europe and Africa from the British Isles and the Netherlands south to South Africa, and also around the Persian Gulf. Smallest subspecies, males up to, females to. Population recently revised down to below 30,000 individuals; earlier citations of 150,000–180,000 individuals from winter counts being overestimates due to previously overlooked intermingling with L. l. taymyrensis in winter.
L. l. yamalensis Bom et al. 2022 – breeds in northwest Siberia including the Yamal Peninsula and the lower Ob River valley; winters in Oman east to west India, and probably the coast of east Africa, perhaps south to South Africa. Doubtfully distinct from L. l. taymyrensis, not distinguishable genetically.
L. l. taymyrensis Engelmoer & Roselaar, 1998 – breeds in central north Siberia from the lower Yenisei River valley east to the lower Anabar River valley; winters on the coasts of western Europe south to western Africa, overlapping extensively with L. l. lapponica.
L. l. menzbieri – Portenko, 1936 – breeds northeastern Asia from the Anabar River east to the Kolyma River delta; winters in southeast Asia and northwest Australia
L. l. baueri – Naumann, 1836 – breeds in Chukotka to north and west Alaska; winters in Australasia. Largest subspecies; includes L. l. anadyrensis. Population is less than 150,000 birds, with 75,000 of them wintering in New Zealand.
Description

The bar-tailed godwit is a relatively short-legged species of godwit. The bill-to-tail length is, with a wingspan of. Males average smaller than females but with much overlap; males weigh, while females weigh ; there is also some regional variation in size. The adult has blue-grey legs and a long, tapering, slightly upturned bi-coloured 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.
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.
The bar-tailed godwit is distinguished from the black-tailed godwit by its black-and-white horizontally-barred tail, and lack of white wing bars. The most similar species is the Asian dowitcher.

Distribution and migration

It was evident for some time that the migrating birds can fly distances up to 5000 km non stop. 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 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.
L. l. baueri 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 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 ; the actual track flown by one bird was, 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.
One specific female of the flock, flagged '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. This L. l. baueri female made a 174-day round-trip journey of 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 flight from Alaska, USA to New South Wales, Australia. The same individual held a previous record in 2020. In 2022, a juvenile godwit flagged 'B6' 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 in 11 days 1 hour, a record non-stop distance.
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 to. 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 in their northern migration. L. l. baueri birds rested for about 41 days before continuing approximately on to Alaska. L. l. menzbieri'' spent on average 38 days in the Yellow Sea region and flew an additional to high Arctic Russia.
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.

Behaviour and ecology

Breeding

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 two to five, averaging four. Both sexes share incubation of the eggs for 20 to 21 days, the male during the day and the female at night. The young fledge when they are around 28 days old. They first breed when aged two years. The earliest clutch may start by mid-May on coastal Yukon-Kuskokwim Delta. There are never 2 broods at once but it may replace the first clutch. The nest site is variable in selection where there is a slightly elevated ridge drier than surrounding vegetation. The site is frequently well concealed by standing vegetation and placed near or between tussocks. The construction of the nest is conducted by both parents which lining is added to the nest during egg laying. The eggs shape are pointed oval to pyriform and subpyriform to ovate pyriform and usually the latter eggs are elongate ovate.

Food and feeding

Their main source of food in wetlands is bristle-worms, 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. The sexual dimorphism also leads to differences in foraging behaviour which enables more effective exploitation.
Male bar-tailed godwits are smaller than females and have shorter bills. In a study at the Manawatū Estuary, New Zealand, shorter-billed birds 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.
They are known to forage actively in the day and night. They will pick items on the surface while walking or probes for items in matted vegetation by inserting and twisting bills. In Europe, the females tend to feed in deeper water than males. Males that feed in deeper water are less successful than males that feed in the tide line. Meanwhile, females are successful at both locations. Birds that prey in flocks have higher prey capture than birds that prey alone. The individuals also capture fewer prey when there is drop in ambient temperature that slows the activity of prey. The degree of feeding activity depends on the tide, weather, season and the behaviour exhibited by the prey. In New Zealand, female L. l. baueri have a probe rate of 26.5 probes per 4 minutes period which is 1.6 times higher than that of males but the feeding success is observed to be similar in both sexes. The tapping technique is seen to be more useful in males than the females.