Migration ecology and morphometrics of two Bar-tailed Godwit populations in Australia

Bar-tailed Godwits (Limosa lapponica) are long-distance migratory shorebirds. About a third of the global population migrate to Australia during the non-breeding season where they occur mainly in the north-west and east. Using measurements of bill, wing, tarsus and total-head ( head and bill), we show that birds from the two main Australian non-breeding regions belong to separate populations. Individuals in north-western Australia are subspecies L. l. menzbieri, which breeds in north-eastern Russia, whereas those in south-eastern Australia are subspecies L. l. baueri, which breeds in northern and western Alaska. Resightings and recoveries of marked birds showed that there is little exchange between the two populations on the non-breeding grounds. They also take different routes during northward migration: L. l. menzbieri was more frequent on staging areas in the western Yellow Sea and largely absent from Japan, whereas L. l. baueri was more numerous in the eastern Yellow Sea and was often recorded in Japan. L. l. baueri left on northward migration 1-2 weeks earlier than L. l. menzbieri and gained more body mass before departure, presumably in preparation for a longer migratory leg. Our data suggest that on northward migration, L. l. menzbieri and L. l. baueri make direct flights of 5400-6200 km and 8200-8500 km, respectively, to reach staging areas in East Asia. The route of Limosa l. menzbieri on its southern passage is similar to that of northward migration, with stop-overs in East Asia. Limosa l. baueri, however, make an similar to 10400-km nonstop flight across the Pacific Ocean from Alaska to eastern Australia, one of the longest non-stop migratory flights known amongst birds.