Power line casualties are considered one of the main causes of mortality in the endangered Bonelli’s Eagle Hieraaetus fasciatus, although little is known about factors involved in collisions with wires and their consequences at population level. We studied 18 radio-tracked individuals to determine the risk of collision with power lines at two spatial scales (flight height and span crossings). Through logistic regression modelling we found that the risk of collision was mainly determined by eagles’ home range use, being reduced in kernel 80%, kernel 95% and MCP respectively to 0.421, 0.114 and 0.032 times in comparison to risk associated to the 50% kernel area. In addition, the risk of collision increased in open habitats (around 1.5 times higher than in forested habitats) far from urban areas (2.345 times higher than near urban areas) that were good for hunting, and in cliff areas used for breeding and roosting, where eagles fly at a lower height (the probability of eagles flying at a low height was 1.470 times higher than in forested habitats). A significant positive correlation was found between territorial turnover rates and the risk ascribed to transmission lines with earth wires in 15 breeding territories. Moreover, this correlation had a higher significance for the 50% kernel area when transmission without earth wires and double circuit distribution lines were added, although no correlations were encountered for distribution lines. These results suggested that power line collisions might be more important than previously reported as a cause of mortality for the species and thus conservation actions should be applied in order to minimise their effects on population dynamics. Predictive models may be a useful tool in careful planning of new power line routes and the wire-marking of the existing ones. Kernel areas should be used rather than fixed radii given that distances from nests may not adequately match the risk of collision.
(Received June 15 2009)
(Accepted November 10 2009)
(Online publication April 26 2010)