Collision

Bird interactions with power lines can also result in collision mortality when birds hit aerial cables. This is due to the bird’s difficulty in seeing and avoiding the cables, partly because of the lateral positioning of their eyes on the head, which reduces their frontal visual acuity. This risk varies between species depending on their morphology, flight behavior, phenology, and age. For example, larger and heavier species have reduced flight agility.

For the Great Bustard, collisions with power lines are the leading cause of unnatural mortality. In Portugal, there were 37 recorded collisions between 2003 and 2020, resulting in a mortality rate of 0.12 birds/km/year. The Little Bustard is also a bird highly susceptible to collisions and this is the main anthropogenic threat to the adult population of this species. It is estimated that 1.5% of the Portuguese population of Little Bustards dies due to this threat, with 63 collisions recorded and a mortality rate of 0.2 birds/km/year.