Landscape features and sea ice influence nesting common eider abundance and dispersion

Factors that influence individual and colony spacing are still not well understood in many organisms. Common eiders ( Somateria mollissima (L. 1758)) nest on coastal islands and forage in intertidal and shallow subtidal waters. We considered several biotic and abiotic factors, their interactions, and how these might influence the distribution of eider colonies at several spatial scales in Labrador, Canada. At the island level, nest abundance was not related to intertidal prey density. At the 104 km2grid scale, eider nest abundance and the coefficient of dispersion (CD; the variance to mean ratio of colony size or grid cell, where CD indicates population dispersion) were negatively related to the number of islands. Spring ice cover was positively related to the number of islands but was negatively related to eider nest abundance and to CD. Ice cover – abundance and ice cover – CD were significant at two spatial scales (104 and 455 km2, respectively), but other relationships were weaker at the larger spatial scale. We hypothesize that during the spring, archipelagos with many islands trap ice, providing terrestrial predators access to nesting islands by acting as bridges and that increased predation reduces habitat quality causing nesting eiders to disperse. Our findings suggest that eiders respond to landscape features, including ice cover, a feature that is being influenced by climate change.