Slow development of foraging skills and parental costs of family-living in a semi-precocial, non-cooperatively breeding bird

摘要

Family-living has been recognized as a first step in the evolution of cooperative breeding. Although delayed juvenile dispersal occurs in non-cooperative breeders, studies investigating family formation in these species are rare. Juveniles delay natal dispersal in response to ecological constraints of dispersal and/or benefits of philopatry, with parents predicted to adjust their tolerance towards independent offspring according to their direct fitness benefits. Consequently, precocial chick development is often associated with low parental care and short family association. White-breasted mesites (Mesitornis variegata) are group-living but non-cooperatively breeding birds that live in saturated habitats, whose semi-precocial young exhibit large variation in the timing of natal dispersal. We investigated whether the development of foraging skills of nutritionally independent juvenile mesites affects their dispersal decisions. Additionally, because parents show aggression towards older offspring particularly around the subsequent breeding season, we studied whether family-living is costly for parents. Our results indicate that juveniles develop their foraging skills slowly, that juveniles with poorer foraging skills tend to disperse later, and that adults experience foraging and reproductive costs from extended juvenile association. Therefore, it may be beneficial for less skilled juveniles to remain longer in the safety of the family when breeding vacancies are scarce. Furthermore, parental costs of family-living may trigger parental aggression towards juveniles, resulting in the dissolution of families and the lack of cooperative breeding in this species. This study highlights the importance of cost-benefit analyses from both the parents’ and offspring’s perspective to understand family stability and, hence, evolutionary routes towards cooperative breeding.