Genetic composition of communal roosts of the eurasian magpie (pica pica) inferred from non-invasive samples

Many animal species form communal roosts in which they aggregate and sleep together. Several benefits of communal roost have been suggested, but due to lack of data on relatedness among group members, it is unknown whether these benefits can be amplified by the formation of kin-based communal roosts. We investigate the genetic composition of two winter roosts of Eurasian Magpies (Pica pica), using microsatellite markers on non-invasive samples. Using permutation tests by reshuffling the alleles presented in the roosts, we determined that individuals in the communal roosts of magpies were not more related than expected by chance, suggesting that kinship may not be a driving force for the formation of communal roosts in magpies. However, the pairwise relatedness and estimated relationship based on a maximum likelihood approach revealed that the roosts involve both kin and non-kin. Relatedness coefficients varied widely within a roost, indicating that family subgroups form a small proportion of the total number of birds in a roost. Our results suggest that ecological benefits of communal roost in animals are sufficient for the evolution of communal roosts without any involvement of kinship.