Coupling Delayed Breeding with Short-distance Dispersal in Cooperatively Breeding Birds


Department of Biology, 105 OML, Yale University, New Haven, CT 06511, U.S.A.


Short-distance dispersal in cooperatively breeding birds is demonstrated and a new model describes how it could be causally related to delayed breeding. Nonbreeders are hypothesized to wait for specific, adjacent territories of high quality. Strong, predictable differences in territory quality select for extended natal philopatry in comparison with species whose young disperse upon maturity. A nonbreeder's ability to discriminate territory quality, and competitive advantages of age and proximity in obtaining nearby breeding positions, are necessary conditions of this model. Direct benefits to both males (potential for inheritance of a breeding position on the natal territory) and females (priority to nearby territories of high quality) result from philopatry. This model differs from most others by emphasizing potential direct benefits of delayed dispersal, rather than assuming constraints, such as habitat saturation. Short-distance dispersal is widespread in other bird and mammal social systems characterized by natal philopatry and delayed breeding, suggesting a general application of this model.