Data from: Extreme genetic structure in a social bird species despite high dispersal capacity

Social barriers have been shown to reduce gene flow and contribute to
genetic structure among populations in species with high cognitive
capacity and complex societies, such as cetaceans, apes and humans. In
birds, high dispersal capacity is thought to prevent population divergence
unless major geographic or habitat barriers induce isolation patterns by
dispersal, colonization or adaptation limitation. We report that Iberian
populations of the red-billed chough, a social, gregarious corvid with
high dispersal capacity, show a striking degree of genetic structure
composed of at least 15 distinct genetic units. Monitoring of marked
individuals over 30 years revealed that long-distance movements over
hundreds of kilometres are common, yet recruitment into breeding
populations is infrequent and highly philopatric. Genetic differentiation
is weakly related to geographic distance and habitat types used are
overall qualitatively similar among regions and regularly shared by
individuals of different populations, so that genetic structure is
unlikely to be due solely to isolation by distance or isolation by
adaptation. Moreover, most population nuclei showed relatively high levels
of genetic diversity, suggesting a limited role for genetic drift in
significantly differentiating populations. We propose that social
mechanisms may underlie this unprecedented level of genetic structure in
birds through a pattern of isolation by social barriers not yet described,
which may have driven this remarkable population divergence in the absence
of geographic and environmental barriers.