Brood reduction and begging behaviour in the Swift Apus apus; no evidence that large nestlings restrict parental choice

• Published in: Ibis
• Main Author: LOTEM, ARNON
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1998
• Subjects: Apus apus
• Online Access: http://dx.doi.org/10.1111/j.1474-919x.1998.tb04612.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1474-919X.1998.tb04612.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1474-919X.1998.tb04612.x

Brood reduction in birds is generally viewed as an adaptive process by which parents can maximize reproductive success in the face of an unpredictable environment. However, brood reduction may not be adaptive for the parents if the reduction is instead caused by large nestlings that block the nest entrance, thereby restricting parental choice. To determine the degree of difficulty faced by the parents in obtaining access to their smallest nestlings, a simple experiment was conducted in the Swift Apus apus. By inserting a human hand blindly into Swift nesting holes, nestlings were stimulated to beg and to grasp the approaching fingers. The results show that the smallest nestlings in the nest were the first to encounter the approaching fingers. Small nestlings were also just as likely to be found with at least some food in their crops as were medium and large nestlings, but gained mass at a significantly slower rate. I suggest that parent Swifts can easily access small nestlings, but prefer either to allocate more food to larger nestlings or to allow sibling competition in order to facilitate brood reduction.