BROOD REDUCTION AND BEGGING BEHAVIOR IN THE SWIFT APUS-APUS - NO EVIDENCE THAT LARGE NESTLINGS RESTRICT PARENTAL CHOICE

Brood reduction in birds is generally viewed as an adaptive process by which parents can maximize reproductive success in the face of an unp redictable environment, However, brood reduction may not be adaptive f or the parents if the reduction is instead caused by large nestlings t hat block the nest entrance, thereby restricting parental choice, To d etermine the degree of difficulty faced by the parents in obtaining ac cess to their smallest nestlings, a simple experiment was conducted in the Swift Apus apus. By inserting a human hand blindly into Swift nes ting holes, nestlings were stimulated to beg and to grasp the approach ing fingers. The results show that the smallest nestlings in the nest were the first to encounter the approaching fingers. Small nestlings w ere also just as likely to be found with at least some food in their c rops as were medium and large nestlings, but gained mass at a signific antly slower rate. I suggest that parent Swifts can easily access smal l nestlings, but prefer either to allocate more food to larger nestlin gs or to allow sibling competition in order to facilitate brood reduct ion.