Differential migration by age and sex in central European Ospreys Pandion haliaetus

摘要

Differential migration reflects various constraints and selective forces on different individuals in a population, and has been explained by several hypotheses. Most previous studies about differential migration focused on only one aspect (e.g. spring timing, autumn timing or wintering area), which could not give a full picture of differential migration of the study population and carry out an overall investigation into the hypotheses. In this study, we analyse the migration patterns of European Ospreys Pandion haliaetus ringed in Germany based on the ring recovery database between 1980 and 2008. The migration routes of the study population form a broad front between south and southwest of the ringing area, and the wintering sites are in West Africa south of the Sahara and around the western Mediterranean. We demonstrate differential migration of the population in both spring and autumn timings as well as in the use of wintering grounds. Adult (third year and older) males return earliest to the breeding area in spring, followed by adult females and then two-year-old birds. In autumn, the adult females leave the breeding area earlier than adult males, while the migration of first-year Ospreys takes place over a wide time-span. Adult males were discovered mainly around the western Mediterranean in winter, closer to the ringing area than adult females and younger birds. We suggest that the selection for prior access to breeding resources on males shapes the patterns of differential migration in Ospreys.