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 (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. 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. 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). Distribution and migration 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. 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 away. To track the