Abstract :
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.
