Nest-site materials affect nest-bowl use by Common Eiders (Somateria mollissima)

Nest-site characteristics influence reproductive success in birds. Most studies of nest-site selection evaluate nest characteristics following the commencement of egg-laying, possibly overlooking the importance of pre-existing nest-site features that may be altered during the nesting process. Because Common Eiders (Somateria mollissima (L.,1758)) often lay their eggs in nest bowls created in previous years, we were able to experimentally place moss or feather down in nest bowls prior to nesting. We then quantified whether these materials increased nest establishment or advanced laying dates relative to control nests and nests where material was removed prior to arrival of nesting females. We found no difference in the likelihood of successful nest establishment between groups. However, the onset of incubation occurred 2-3 days earlier in nest bowls that contained feather down versus nest bowls with little or no nesting material. Nest bowls containing feathers or vegetation may be selected first if they increase nest survival, perhaps by enhancing egg concealment during the critical early-laying period. The presence of material for egg concealment may be particularly important in nesting environments where tall or dense vegetation is not available to provide nest cover.