Home range requirements in Bonelli’s eagle (Aquila fasciata): prey abundance or trophic stability?

Abstract

Prey abundance is one of the limiting factors for establishment a home range. In particular, biomass abundance could act as a key element for generalist top predators, with wide prey type spectrum, for establishing their home ranges. We studied if biomass abundance may act as a limiting factor for the establishment of home range in a generalist top predator, Bonelli’s eagle (Aquila fasciata). We used GPS satellite data on breeding individuals over a 10-year period to deepen into home range behaviour. To quantify biomass abundance, we performed surveys at different periods of the year cycle for potential prey inside the home ranges and outside them. We checked if differences in biomass were identified between home ranges and potential adjacent areas. Also, annual and seasonal variation in biomass abundance may be recorded. Variations in biomass abundance among home range were detected but no annual or seasonal variation within home range was identified. Differences in biomass abundance were identified between each of the home range and their potential adjacent areas. Although biomass abundance is lower inside the home range, it remains stable throughout the year while strong fluctuations in biomass abundance were detected outside them. Our results show that Bonelli’s eagle may establish their home range based on permanent biomass stability (Trophic Stability Hypothesis) rather than great seasonal but unpredictable abundances. This approach may have strong implications for management conservation programs of territorial top generalist predators.