A spatially explicit approach to assess the collision risk between birds and overhead power lines: A case study with the little bustard

Collisions between birds and overhead power lines are an important cause of human-induced mortality. Mapping collision risk is an important prerequisite to minimise the negative impact of these structures on bird populations, particularly for species of high conservation concern and that are prone to collision. We mapped and modelled power line collision risk of a threatened and collision-prone species, the little bustard (Tetrax tetrax), based on three types of information: (i) the average daily distance flown by an individual, calculated from a satellite-telemetry study; (ii) the average percentage of flight movements at phase-conductor or shield-wire height, based on field focal observations; and (iii) a habitat suitability map for three different seasons (breeding, post-breeding and winter), modelled from an independent dataset of a nationwide population survey. An overall spatially explicit collision risk map was generated and validated with an independent mortality dataset derived from monitoring bird casualties in a sample of power lines. Collision risk of little bustards varied significantly both spatially and temporally. Compared to post-breeding and winter, little bustards moved smaller distances and flew at lower risk height during the breeding season, therefore minimising collision risk. The overall collision risk map contributed with relevant information to predict the likelihood of mortality events in a set of sampled power line sections. The described approach can be extended to transmission power lines, as well as to other bird species.