Extended parental care and delayed dispersal: northern, tropical, and southern passerines compared

Using modern comparative methods, we found that both time to independence and time with parents were significantly longer in southern hemisphere and tropical birds than in northern hemisphere ones. These differences held even after removing Australian passerines or cooperatively breeding species, and they do not depend on habitat, diet, or migration pattern. In southern hemisphere and tropical regions, both cooperative breeding and non-cooperative parents continue to feed their young for a similar length of time, but cooperative breeders allow them to stay longer in their natal territory after they become nutritionally independent. Nevertheless, the young of non-cooperative species stay longer with their parents than do the young of non-cooperative species in the temperate northern hemisphere. The fact that extended periods of post-fledging parental care are widespread among passerines provides further empirical support for the view that life histories of southern and tropical birds are 'slow,' with small clutches, extended parental care, and long lifespan; parents take care of fewer young for longer. These results support recent theoretical models that predict that high adult survival and low turnover of territory owners generally favor natal philopatry. We suggest that the reasons why some species (with or without cooperative breeding) exhibit natal philopatry and others do not lie in the balance between productivity and survival of adults and of retained or dispersing offspring.