[241] The Condor 106:241–251  The Cooper Ornithological Society 2004 TO WINTER EAST OR WEST? HETEROGENEITY IN WINTER PHILOPATRY IN A CENTRAL-ARCTIC POPULATION OF KING EIDERS KATHERINE R. MEHL 1,3 ,RAY T. ALISAUSKAS 1,2 ,KEITH A. HOBSON 1,2 AND DANA K. KELLETT 2 1 University of Saskatchewan, Department of Biology, 112 Science Place, Saskatoon, SK S7N 5E2, Canada 2 Prairie and Northern Wildlife Research Centre, Canadian Wildlife Service, 115 Perimeter Road, Saskatoon, SK S7N 0X4, Canada Abstract. 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 ( 13 C, 15 N) 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 condi- tions with overall demography and individual fitness of King Eiders. Key words: carbon-13, King Eider, nitrogen-15, Somateria spectabilis, stable isotopes, winter philopatry. ¿Pasar el Invierno en el Este o en el Oeste? Heterogeneidad en la Filopatrı ´a al Sitio de Invernada en una Poblacio ´n de Somateria spectabilis del A ´ rtico Central Resumen. Para conectar las a ´reas de invernada con las de reproduccio ´n en la especie Somateria spectabilis, utilizamos datos de aves anilladas durante 2001 y 2002 en Karrak Lake, Nunavut, Canada ´, junto con ana ´lisis de isoto ´pos estables que se encuentran en la naturaleza y en las plumas ( 13 C, 15 N). Tambie ´n investigamos la existencia de filopatrı ´a al sitio de invernada entre hembras nidificantes, y examinamos los efectos del a ´rea de inver- nada sobre la reproduccio ´n subsiguiente. Los datos isoto ´picos sugirieron que el 66–73% de los individuos de esta poblacio ´n que nidifica en el A ´ rtico central pasa el invierno al oeste (i.e., Mar de Bering, Pacı ´fico Norte) y que el 24–37% restante lo hace al este (i.e., oeste de Groenlandia, noroeste del Atla ´ntico). En contraste, los pocos anillos puestos en la misma localidad reproductiva que fueron recobrados por cazadores, mostraron que alrededor del 56% de los individuos fueron cazados en a ´reas de invernada ubicadas al este. Estas dife- rencias probablemente reflejan que las presiones de cacerı ´a son ma ´s fuertes a lo largo de la costa de Groenlandia, lo que conlleva a que se recobren ma ´s anillos en esta a ´rea. Nuestros resultados sugieren que las hembras de S. spectabilis no son fuertemente filopa ´tricas a sus sitios de invernada entre an ˜os. Los individuos que invernaron en los mares del oeste inicia- ron sus nidos 1.9 dı ´as ma ´s temprano y tuvieron nidadas ligeramente ma ´s grandes durante la etapa temprana de iniciacio ´n en comparacio ´n con las hembras que invernaron al este. El parasitismo de nidos parecio ´ estar sesgado hacia las aves que nidificaron temprano, muchas de las cuales invernaron en el oeste. La condicio ´n de las hembras durante la incubacio ´n no Manuscript received 12 May 2003; accepted 23 January 2004. 3 Present address: Ducks Unlimited, 562 Water Street, St. John’s, NL A1E 1B7, Canada. E-mail: kmehl@ducks.ca Downloaded from https://academic.oup.com/condor/article/106/2/241/5563496 by guest on 26 September 2022