NONADAPTIVE ADOPTIONS OF NESTLINGS IN THE COLONIAL LESSER KESTREL - PROXIMATE CAUSES AND FITNESS CONSEQUENCES

We examined the causes, costs and benefits of adoption in the altricia l lesser kestrel Falco naumanni. Specifically, we tested the intergene rational conflict hypothesis, proposed to explain adoption in some bir ds. Adoptions involved 76% of the nests and 51% of the nestlings at a mean age of 25 days (12 days before fledging). Nest-switching nestling s were not in poorer body condition, more parasitized or younger than their siblings, and body condition and prey delivery rates of their pa rents did not differ from those of other parents. In the foster nest, adopted nestlings did not benefit from higher feeding rates or a prolo ngation of the nestling period. They did not have fewer nest-mates or achieve higher rank within the new brood. Thus, adopted nestlings did not improve their body condition and survival. Adult lesser kestrels s eemed unable to finely discriminate beween their own and alien chicks. Foster parents bore the cost of an increase of prey delivery rates, a lthough it did not affect their survival or subsequent reproductive pe rformance. Therefore, our results do not support the intergenerational conflict hypothesis, and suggest that adoption in this species is non -adaptive. Traditionally, the lesser kestrel bred in cliffs where move ment among nest-sites was restricted. Nowadays, about half of the colo nies are in tiled roofs which facilitate nest-switching by nestlings. The high rate of adoptions may thus be explained as reproductive error s associated with the recent occupation of a new breeding habitat.