Juvenile ospreys (Pandion haliaetus) have been observed in other osprey nests from 0 – 23 days after fledging, remaining there for up to 21 days. In some, but not all cases, the switchers received alloparental care at the recipient nest. To assess the variation in switching events and identify factors that may be driving nest switching in ospreys, I marked all juveniles and manipulated brood size to control for differences in nestling milieu. Marking methods were analyzed in laboratory and field experiments.
Switches arose from all multiple-fledgling broods and two single-young broods. Although dominant brood members did not switch, the difference in food intake between checks that switched nests and those that did not was not statistically significant. Single chicks that switched nests received poor parental provisioning prior to fledging. Fledgling ospreys exhibited switching as a behavioral tactic in response to parental provisioning and their dominance status among siblings. Switching events that occurred early in the post-fledging period resulted in alloparental feeding and tolerance at the recipient nest overnight; events that occurred later involved no alloparental care and little or no tolerance. Early switchers appear to be motivated by hunger and relegated by dominance status, whereas late switchers appear to be exhibiting exploratory movement prior to dispersal.