TO WINTER EAST OR WEST? HETEROGENEITY IN WINTER PHILOPATRY IN A CENTRAL-ARCTIC POPULATION OF KING EIDERS

We used banding data from King Eiders (Somateria spectabilis) at Karrak Lake, Nunavut, Canada, during 2001 and 2002 in conjunction with analysis of naturally occurring stable isotopes (13C, 15N) from feathers to connect winter and breeding areas of individuals. We also investigated the occurrence of winter philopatry among nesting females, and examined cross-seasonal effects of wintering area on subsequent breeding. Isotopic data suggested that 66–73% of this central-arctic breeding population wintered to the west (i.e., Bering Sea and North Pacific) and the remaining 24–37% wintered to the east (i.e., west Greenland, northwest Atlantic). In contrast, limited band recoveries from hunter-killed King Eiders marked at the same breeding location suggested that about 56% of individuals were shot in eastern wintering areas. These differences likely reflect stronger hunting pressures along the coast of Greenland, which result in more band recoveries for this area. Our results suggest that female King Eiders were not strongly philopatric to wintering areas among years. Individuals that wintered in western seas initiated nests 1.9 days earlier and had slightly larger clutches during early initiation relative to females that wintered in the east. Nest parasitism appeared to be biased toward earlier nesters, many of which wintered in the west. Female condition during incubation did not vary by wintering area. Our results have important implications for gene flow and for potentially associating wintering-area conditions with overall demography and individual fitness of King Eiders. ¿Pasar el Invierno en el Este o en el Oeste? Heterogeneidad en la Filopatría al Sitio de Invernada en una Población de Somateria spectabilis del Ártico Central Resumen. Para conectar las áreas de invernada con las de reproducción en la especie Somateria spectabilis, utilizamos datos de aves anilladas durante 2001 y 2002 en Karrak Lake, Nunavut, Canadá, junto con análisis de isotópos estables que se encuentran en la naturaleza y en las plumas (13C, 15N). También investigamos la existencia de filopatría al sitio de invernada entre hembras nidificantes, y examinamos los efectos del área de invernada sobre la reproducción subsiguiente. Los datos isotópicos sugirieron que el 66–73% de los individuos de esta población que nidifica en el Ártico central pasa el invierno al oeste (i.e., Mar de Bering, Pacífico Norte) y que el 24–37% restante lo hace al este (i.e., oeste de Groenlandia, noroeste del