Are inbred offspring less fit? Survival in a natural population of Mexican jays

The importance of inbreeding avoidance for the fitness of individuals is currently undergoing reevaluation. Especially when the frequency of inbreeding is low, it may be difficult to accumulate sufficient information. In a long-term study of the Mexican jay (Aphelocoma ultramarina) in Arizona, we found inbreeding, as determined by pedigree, to be rare even though this species exhibits strong natal philopatry and commonly lives in social groups of close relatives. Brood sizes of inbred pairs were significantly lower than those of outbred pairs, suggesting hatching failure; but there uas no difference in the probability that one or more young would fledge from a nest. Survival of inbred nestlings to the next year was significantly lower than that of outbred nestlings.