Landscape alteration affects the demography of an endangered avian predator by reducing the habitat quality

Abstract

Habitat transformation is identified as major threat to biodiversity loss globally, affecting threatened raptors. Changes in land use can alter the abundance and distribution of birds of prey by affecting habitat availability and quality. In this study, we used multivariate analyses to investigate the effect of habitat alteration on the demography of a declining Eastern Imperial Eagle (Aquila heliaca), making assumptions for future population trajectories. We used the Generalized Linear Mixed Models with Poisson distribution and Log link function, searching a relationship between the demographic parameters and the landscape structure and possible effects of fragmentation. In our study area, habitat change affected dramatically permanent grasslands, shrinking their availability. As we expected, the share of grasslands in eagles’ territories significantly affected occupancy rate, but not productivity and breeding frequency. We found that occupancy rate decreased significantly, while productivity and breeding frequency showed no trend. Modeling the effect of habitat alteration on Eastern Imperial Eagle demography, we found out that territory quality was a more powerful factor driving the response of a top predator to the alteration of favorite foraging habitats. Only the habitat quality in source territories had a significant positive effect on eagle productivity. We found that simple rules to predict adverse agricultural impact on territory abandonment or breeding productivity of a top predator were not reliable. Our results could be used for planning conservation of other large territorial raptors, facing the same type of threat.