A new view of territoriality in large eagles: the territory pre-exists regardless of its occupants

Knowledge of vertebrate territoriality and spatial use is a topic of great interest in the study of animal behaviour and conservation biology. Investigating the plasticity of territory boundaries, the shape of territories and how territories can be modified depending on their owners is important to deepen our knowledge of the behaviour of territorial species. We analysed the variation and tested the similarity of the distribution area of individuals from the same territory between 2015 and 2021, using data from 51 Bonelli's eagles (Aquila fasciata) from 22 different territories, tagged with GPS/GSM transmitters in eastern Spain. We calculated the percentage of overlap between the territories of the same individual in different years using the 95% kernel density estimator. We also analysed the changes in territory size and shape following the replacement of territory owners either by a single individual or by the whole pair. Our results show that territories retain the same shape and extent regardless of the occupying members, and that their boundaries change little over time. Identifying and maintaining large eagle territories, regardless of their owners, is therefore key to ensuring the long-term recovery of these threatened species.