Factors influencing the post-fledging period and timing of dispersal in Bobelli's eagles Hieratus fasciatus in southwestern Spain

Abstract

We studied factors influencing the length of the post-fledging period (from fledging to the start of dispersal) of Bonelli’s Eagle (Hieraaetusfasciatus) nestlings in soutlswestern Spain, using 13 nestlings equipped with radiotransmitters. The age at fledging was negatively correlated with hatching date, but the duration of the post-fledging period was directly related to hatching date. This pattern could be explained by seasonal changes in prey abundance, especially that of wild rabbits (Oryctolagus cuniculus). Young in­ creased their mobility throughout the post-fledging period, with a significant increase in the middle of the period. Dispersal began suddenly. The direction of dispersal was random, but most of the areas first used were located <25 km away and at lower altitudes than the nesting area