STABLE ISOTOPE ANALYSIS

RESULTS OF FEATHER ANALYSES

Since 2005 we have collected feathers from >200 individuals. Since the molt phenology of King Eiders is poorly known, we also collected claw tips from birds starting in 2006. Generally, King Eiders molt their primaries in August and September, and head feathers from late October through January. Claw tips that we collect in June are presumably grown between January and April when birds are on wintering grounds. By using birds equipped with satellite transmitters we were able to delineate the isotopic ranges of the wintering regions in the Bering Sea.

The map below shows the three wintering regions in the Bering Sea, circled by a colored line. King Eiders do not move between those regions between late December and April. The range of feather and claw isotope ratios from birds wintering in these regions are shown in the graph next to the map, with single feathers shown in the same color as the region where the bird wintered in.

By analysing the feathers and claws of 60 King Eiders captured on breeding grounds we found that equal proportions of birds winter in the three regions. This is essentially the same result we found by tracking 80 different birds with satellite transmitters. We therefore believe that stable isotope analysis of feathers and claws provides a reliable and affordable alternative to explore the winter distribution of King Eiders in the Bering Sea.

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