Demography and conservation of western European Bonelli's eagle Hieraaetus fasciatus populations

Abstract

The basic demographic parameters of six Bonelli's eagle Hieraaetus fasciatus populations in Spain and France were calculated from field data obtained in the last 15 years. Average annual productivity ranged from 0.36 to 1.24 young/pair and average annual adult survival from 84% to 96%. Preadult survival (from fledging to recruitment) was estimated at 10%. All the populations were declining at annual rates ranging from −7.3 to −1.1%. Although no statistically significant disagreement was observed between the predictions of a Leslie matrix model fitted to the population parameters and the real trends, some populations declined faster and others more slowly than expected. These differences were interpreted as a result of differential emigration, recruitment rates or preadult survival not accounted for by the model. Since the intrinsic population growth rate was about four times less sensitive to changes in preadult survival than to changes in adult survival, and about ten times less sensitive to changes in fecundity and predispersal survival, conservation efforts must be primarily directed towards increasing adult and preadult survival. Power line casualties and direct persecution must be eliminated in order to reduce mortality. Priorities on research should address dispersal, mortality and habitat relationships involving these two parameters. Monitoring should be extended to other populations.