Floaters are sexually mature individuals that are not able to reproduce in a given population. Floaters coexist with breeders and interact with them mainly through nest prospections, probably used to gather public information or to compete for a breeding site. We tested the hypothesis that floaters preferentially prospect nests in which they have a better chance of taking over, and that this information is obtained by observing nest owners and assessing their resource holding potential. We conducted a handicap experiment in a spotless starling (Sturnus unicolor) population, where individuals are marked with radiofrequency identification (RFID) tags. Since floaters of both sexes are abundant in this population, we manipulated male and female owners and predicted sex-specific responses. We manipulated the flight capacity of male and female breeders (only one sex manipulated by pair) by clipping two central primary feathers of each wing one month before egg laying, and registered the identity and number of visits by floaters during the peak of chick rearing period, when the prospective activity of floaters is maximal. By reducing flight capacity, we expected physical condition to decline and predicted that nests owned by handicapped individuals would be visited by a higher number of same-sex floaters than controls. The results show that nests owned by handicapped males were indeed visited by a greater number of different male floaters than the nests of control males. This effect was absent in the case of the visits of female floaters to nests of experimental females. This study shows that male floaters preferentially visit nests in which the owner shows a reduced resource holding potential. This strategy likely allows floater males to evict weak owners and take over their nests for future reproductive attempts.

Resumen del trabajo presentado al XVIII Congreso Nacional y XV Iberoamericano de Etología y Ecología Evolutiva, celebrados en Badajoz (España) del 31 de octubre al 3 de noviembre de 2023.

Peer reviewed