The transition from dependence to independence in birds
Avian parents initially provide their offspring with resources such as food and protection from predators but the offspring then undergo a period of transition from dependency to independence. That transition represents a crucial period of an individual’s life as their inexperience in simultaneously searching for food and avoiding predators’ means that the risks of mortality are higher than during other periods of their life. Unfortunately, our understanding of the transition to independence has lagged behind other life history stages due to the logistical challenges associated with tracking individuals after they have left the relatively safe confines of the nest. However, recent technological advances that have enabled individuals to be tracked remotely have dramatically increased our understanding of the process by which offspring acquire independence. First, interspecific studies of birds have demonstrated that the offspring of species that suffer both high levels of nest predation and ectoparasite-induced nestling mortality leave the nest comparatively sooner than the offspring of species that suffer lower levels of nest predation and ectoparasite-induced nestling mortality. Second, intraspecific studies have become much more prevalent in recent years as new technologies have been used to show that between-brood or litter variation in the timing of independence is influenced by predation risk, ectoparasite-induced nestling mortality and parent-offspring conflict over the provision of care. Further studies have shown that within-brood variation in the timing of independence also occurs as a result of both genetic effects such as parentage and offspring sex, and parental effects such as hatching asynchrony, that result in inequalities between siblings. In summary, there is considerable variation in the process by which avian offspring acquire independence at the interspecific and intraspecific levels. However, whilst we have a reasonable understanding of the causes of such variation, our understanding of the consequences of such variation is less developed and deserves further research.