Nest clustering correlates with breeding phenology rather than female relatedness in Red-breasted Mergansers (Mergus serrator)

Fine-scale spatial and temporal genetic structuring of nests is possible in colonial birds that return to breed at their natal sites, and notably in waterfowl for which females are more philopatric than males. We genotyped female Red-breasted Mergansers Mergus serrator breeding colonially on a coastal archipelago in eastern New Brunswick, Canada, during 2015 and calculated pairwise kinship coefficients using 4270 single nucleotide polymorphisms to assess whether related hens nest near each other and initiate their nests around the same time. We found no spatial or temporal genetic structure across islands; however, nesting was relatively synchronous between hens nesting close together. Red-breasted Mergansers initiating their nests at the same time may select nearby nest-sites based on the availability of dense vegetation that conceals nests, limiting opportunities for kin to nest near one another in this population.