The spatial distribution of avian relatives: do obligate army-ant-following birds roost and feed near family members?

The ocellated antbird (Phaenostictus mcleannani) feeds in groups and therefore is an informative species in which to study the biological factors that modulate avian group living. These birds congregate at swarms of army ants to capture fleeing prey, and previous observations suggest that males may be philopatric, feed with close relatives, and defend communal feeding ranges. We assessed whether kin selection could be an important factor maintaining group formation in a population of ocellated antbirds inhabiting continuous forest at La Selva Biological Station, Costa Rica, using radiotelemetry and 15 novel microsatellite markers. We predicted that the roosting areas of closely related adult males should overlap and that adult males feeding simultaneously at the same swarm should be highly related. We banded and genotyped 65 individuals (>or= 88% of the population) and radiotagged 30 of them. The results generally did not conform to our predictions. Little overlap occurred among the roosting areas of same-sex individuals, and nearest roosting neighbours (either same or opposite sex) were generally unrelated. A small proportion of male dyads suggested short-distance dispersal, but in general the distribution of genotypes within the study area approached randomness. We found little evidence of natal philopatry in either sex. Less than half of the feeding groups sampled included highly related males; most consisted of unrelated individuals. Hence, we found limited potential for kin selection to favour group living and suggest that other factors, particularly direct benefits (e.g. food intake), are probably more important than indirect effects (nepotism).