Populations of the Bar-tailed Godwit (Limosa lapponica; Scolopacidae) embark on some of the longest migrations known among birds. The baueri race breeds in western Alaska and spends the nonbreeding season a hemisphere away in New Zealand and eastern Australia; the menzbieri race breeds in Siberia and migrates to western and northern Australia. Although the Siberian birds are known to follow the coast of Asia during both migrations, the southern pathway followed by the Alaska breeders has remained unknown. Two questions have particular ecological importance: (1) do Alaska godwits migrate directly across the Pacific, a distance of 11 000 km? and (2) are they capable of doing this in a single flight without stopping to rest or refuel? We explored six lines of evidence to answer these questions. The distribution of resightings of marked birds of the baueri and menzbieri races was significantly different between northward and southward flights with virtually no marked baueri resighted along the Asian mainland during southward migration. The timing of southward migration of the two races further indicates the absence of a coastal Asia route by baueri with peak passage of godwits in general occurring there a month prior to the departure of most birds from Alaska. The use of a direct route across the Pacific is also supported by significantly more records of godwits reported from within a direct migration corridor than elsewhere in Oceania, and during the September to November period than at other times of the year. The annual but rare occurrence of Hudsonian Godwits (L. haemastica) in New Zealand and the absence of their records along the Asian mainland also support a direct flight and are best explained by Hudsonian Godwits accompanying Bar-tailed Godwits from known communal staging areas in Alaska. Flight simulation models, extreme fat loads, and the apparent evolution of a wind-selected migration from Alaska further support a direct, nonstop flight.

Atravesando la Barrera Ecológica Final: Evidencia de un Vuelo sin Escala de 11 000 km de Longitud desde Alaska a Nueva Zelanda y el Este de Australia por Limosa lapponica

Resumen. Las poblaciones de Limosa lapponica (Scolopacidae) se embarcan en una de las migraciones más largas conocidas para aves. La raza baueri cría en el oeste de Alaska y pasa la estación no reproductiva a un hemisferio de distancia en Nueva Zelanda y el este de Australia; la raza menzbieri cría en Siberia y migra hacia el oeste y el norte de Australia. Aunque se sabe que las aves de Siberia siguen la costa de Asia durante ambas migraciones, la ruta meridional que siguen las aves reproductivas de Alaska ha permanecido desconocida. Dos preguntas tienen particular importancia ecológica: (1) ¿las aves de Alaska migran directamente a través de Pacífico, a lo largo de 11 000 km? y (2) ¿son capaces de hacerlo en un único vuelo sin parar a descansar y reabastecerse? Exploramos seis líneas de evidencia para responder a estas preguntas. La distribución de avistamientos de aves marcadas de las razas baueri y menzbieri fue significativamente diferente entre vuelos hacia el norte y el sur, sin que hubiera prácticamente un solo avistamiento de individuos marcados de baueri a lo largo del continente asiático durante la migración hacia el sur. El período de la migración hacia el sur de ambas razas indica la ausencia de una ruta costera asiátic