Editing Common eider (section)

==Social behaviour==
Eiders are colonial breeders. They nest on coastal islands in colonies ranging in size of less than 100 to upwards of 15,000 individuals.<ref name=Chapdelaine1986a/> Female eiders frequently exhibit a high degree of natal [[philopatry]], where they return to breed on the same island where they were hatched. This can lead to a high degree of relatedness between individuals nesting on the same island, as well as the development of [[kinship|kin]]-based female social structures.<ref name=McKinnon2006/> This relatedness has likely played a role in the evolution of co-operative breeding behaviours amongst eiders. Examples of these behaviours include laying eggs in the nests of related individuals<ref name=Andersson2007/> and [[Crèche (zoology)|crèching]], where female eiders team up and share the work of rearing ducklings.<ref name=Amnat/>