Factors influencing the present distribution of the spanish imperial eagle Aquila adalberti

Abstract

In this paper we analyse the status of the Spanish imperial eagle Aquila adalberti in relation to its historic range in Spain, and try to determine geographic, climatic and land-use factors which may favour or limit its distribution. Fourteen of the 32 variables studied showed statistical differences between the grid squares where the eagle breeds and those grid squares sampled at random where it does not breed. The eagle remains in more forested areas, with lower levels of human land use and with a higher density of rabbits, but no clear topographic differences were observed. The eagle is associated with areas having a typical mediterranean climate—relatively warm dry summers and temperate rainy winters. A stepwise discriminant function analysis showed that it was possible to classify correctly more than 80% of the squares. A low incidence or absence of irrigated farmlands was the best predictor of the eagle's presence. The rapid increase of people in areas previously depopulated, and human presence in fields where irrigated cultures have been developed, had a negative effect on the eagle's distribution.