Habitat used by common and king eiders in spring in the southeast Beaufort Sea and overlap with resource exploration

The southeast Beaufort Sea is a critical spring staging area for common and king eiders (Somateria mollissima v-nigrum, S. spectabilis), and is for many the final stop before they reach their breeding grounds throughout the western Canadian Arctic. The region also has significant oil and gas potential, and the recent approval of a pipeline through the Mackenzie Valley may make development of these resources economically viable. We used satellite telemetry to determine the distribution and habitat use of eiders staging in the southeast Beaufort Sea in spring, and the overlap of eiders with oil and gas exploration. From 2004 to 2009, we monitored 51 eiders equipped with platform terminal transmitters (PTTs) throughout spring migration (MayJune). We compared the marine habitats used by each species, and evaluated habitat preferences using resource selection functions. The location and extent of the flaw lead (open water along the interface between mobile pack ice and stationary landfast ice) at the time when eiders were staging varied among years, but both species showed a strong preference for use of flaw lead habitats. This preference was stronger for common eiders than for king eiders, which also used pack ice extensively. Common eiders generally occurred near the landfast ice edge, whereas king eiders were just as often nearer to the pack ice edge of the flaw lead. Average water depth (+/- SE) for common eiders was 22 +/- 2m compared to 30 +/- 1m for king eiders. Kernel density estimators showed that eiders generally occurred in lower densities in areas of otherwise suitable habitat off the Mackenzie River delta. We suggest that this is a result of the highly turbid water discharged by the Mackenzie River, which limits visibility. Oil and gas exploration overlapped significantly with the areas used by eiders. The high density of birds using the restricted and ice-rich flaw lead habitats indicates that an accidental spill in the region could be catastrophic for Canada's western Arctic eider populations. (c) 2013 The Wildlife Society.