Potential negative effects of collisions with transmission lines on a Bonelli's Eagle population

The Bonelli's Eagle (Hieraaetus fasciatus) population decline in Europe has mainly been attributed to high levels of anthropogenic mortality. We evalu ated the potential negative effects of collisions with transmission lines o n a breeding population of Bonelli's Eagles in Catalonia, Spain. Between 19 90-97, two of the 12 recorded deaths of breeding Bonelli's Eagles were caus ed by collisions with transmission lines. All transmission lines within a 5 -km radius of 47 eagle nests were classified into two collision risk catego ries (low or high), depending on their locations and habitats. Pairs having high risk lines within I kin of nesting territories had turnover rates twi ce as high as pairs with no such lines (0.16 +/-0.11 [+/- SD] vs. 0.08 +/-0 .10). Greatest turnover rates were observed when high-risk lines occurred w ithin 100 m of nesting territories. Our results suggest that transmission l ines near Bonelli's Eagle nesting territories constitute a risk for eagles due to the danger of collisions. New transmission lines should avoid crossi ng areas near nesting territories and, as a precaution, those that are <1 k m from eagle nests should be marked in some way.