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 col- onies at several spatial scales in Labrador, Canada. At the island level, nest abundance was not related to intertidal prey density. At the 104 km 2 grid 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 km 2 , 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. Resume ´ : Les facteurs qui influencent l'espacement des individus et des colonies restent encore mal connus chez de nom- breux organismes. Les eiders aduvet (Somateria mollissima (L. 1758)) nichent sur des oles cotieres et se nourrissent dans la region intertidale et les eaux peu profondes de la zone subtidale. Nous avons examineplusieurs facteurs biotiques et abiotiques et leurs interactions afin de voir comment ils peuvent influencer la repartition de colonies d'eiders adifferentes echelles spatiales au Labrador, Canada. Al'echelle des oles, la densitedes nids n'est pas relieeala densitedes proies de la zone intertidale. Al'echelle d'une grille de 104 km 2 , l'abondance des nids d'eiders et le coefficient de dispersion (CD,