Bar-tailed godwit

The bar-tailed godwit (Limosa lapponica) 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.

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

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. Females breeding plumage is much duller than males, with a chestnut to cinnamon belly. 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.

The bar-tailed godwit 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 Asian dowitcher (Limnodromus semipalmatus).

Distribution and migration

thumb|Banding L. l. baueri at [[Miranda Naturalists' Trust|Miranda Shorebird Centre, New Zealand]]

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. 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. In 2021, a male bar-tailed godwit, 4BBRW, set a new record for non-stop migratory flight with an , flight from Alaska to New South Wales. 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 . 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. 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 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.

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. 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. 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, 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.

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. The most common song-flight they have done is the ceremonial flights. ceremonial flights are performed disproportionately by the males and the function is mainly heterosexual. The flight was not found to induce ceremonial flight in neighbouring males. There are 4 stages in ceremonial flights; (1) ascent, (2) limping flight, (3) gliding, and (4) descent to attract the females.

There are 3 categories in ceremonial flights; (A) a straight line, (B) performing 1 or more circles, (C) wide circles. The ceremonial flight is also known to be similar to Black-tailed godwit. They lack the flight that corresponds to the tumbling flight and the limping flight is not so erratic as in Black-tailed Godwit. The main purpose of this flight is to announce to the females that they are not mated yet. Their territorial defence behaviour is most likely limited to male-to-male aggression on the ground and other Limosa species also do not show high level territoriality. The bar-tailed godwit does not exhibit the "tumbling flight" that the Black-tailed Godwit shows after its ascending phase, and its limping flight is much more ordered and less chaotic than that of the Black-tailed Godwit. The sexual dimorphism is also thought to contribute to them having different fuel deposition. The typical shorebird fat loads are 35%-40% of their body mass. Juvenile males migrating from South Alaska have the highest fat load, but we cannot conclude that for all godwits migrating from the same breeding ground since juveniles are still growing and have smaller body sizes than adults. The female godwits are found to be the heaviest due to their body size being larger than males, and the fat content was also found to be high, from 197-280g.

Sometimes during Southward migration, they will make some stopovers in different staging sites if their destinations are likely to be father north than Australia or Papua New Guinea and Irian Jaya. These massive flights might involve extensive fuelling periods before and during migration. This calls for the utilization of a flight's network of locations. They will rest, moult and refuel themselves for the remaining distance. L. l. baueri are highly conservative in their use of staging sites to refuel and most of them just stopped in one or two countries when migrating northwards. During southwards migration, some of them will stop in a few islands in the Southwest Pacific Ocean. These altered routes are suggested to be adaptive reactions to the risks of continuing to fly over open oceans when the wind is unfavourable. This migration strategy of Australasian bar-tailed godwits is exemplify by their exceptional travels, which cross hemispheres and encompass 10,000 km, and their reliance on a few number of refuelling sites. These extreme flights are also dependent on the presence and productivity of these staging sites.

Status

The status of the bar-tailed godwit is Near Threatened, and the population is declining. The construction of seawalls and the reclamation of mudflats have led to a critical reduction in food supplies for migrating birds, particularly subspecies like L. l. menzbieri that rely on the Yalu Jiang estuary on both their northward and southward migrations. Numbers of L. l. baueri have declined in New Zealand from over 100,000 in the late 1980s to 67,500 in 2018. Meanwhile, a wader census conducted Bird New Zealand in 1983 and they found that the number of bar-tailed godwits in New Zealand as well has declined over the last 35 years which drops from 101,000 in 1983–1993 to 78,000 in 2005–2019. The decline in numbers of bar-tailed godwits is probably associated with habitat loss and degradation near Yellow Sea. They are quite sensitive and easily spooked so it prevents them from disturbance at high tide roosts which leads to stress since they could not rest. In 2024, L. l. baueri and L. l. menzbieri were listed as Endangered under the Australian EPBC Act.

The bar-tailed godwit is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies. In New Zealand the species is protected under the 1953 Wildlife Act.

Gallery

File:Limosa lapponica MHNT.jpg|Egg

File:Limosa lapponica Landing - Orielton Lagoon.jpg|L. l. baueri in Tasmania, Australia (note the barring on the tail)

File:Bar Tailed Godwit in breeding plumage (8586327398).jpg|Breeding plumage at Sandbanks, Poole, Dorset

File:Bar-tailed Godwits (8592998386).jpg|In flight, Dorset

File:Limosa lapponica lapponica.jpg|L. l. lapponica, Spain

</gallery>

References

Identification

External links

Bar-tailed godwit species text in The Atlas of Southern African Birds
The kūaka discussed on RNZ Critter of the Week, 21 Feb 2020