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

Using modern comparative methods, we found that both time toindependence and time with parents were significantly longerin southern hemisphere and tropical birds than in northern hemisphereones. These differences held even after removing Australianpasserines or cooperatively breeding species, and they do notdepend on habitat, diet, or migration pattern. In southern hemisphereand tropical regions, both cooperative breeding and non-cooperativeparents continue to feed their young for a similar length oftime, but cooperative breeders allow them to stay longer intheir natal territory after they become nutritionally independent.Nevertheless, the young of non-cooperative species stay longerwith their parents than do the young of non-cooperative speciesin the temperate northern hemisphere. The fact that extendedperiods of post-fledging parental care are widespread amongpasserines provides further empirical support for the view thatlife 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 supportrecent theoretical models that predict that high adult survivaland low turnover of territory owners generally favor natal philopatry.We suggest that the reasons why some species (with or withoutcooperative breeding) exhibit natal philopatry and others donot lie in the balance between productivity and survival ofadults and of retained or dispersing offspring.