Modelling power-line collision risk for the Blue Crane Anthropoides paradiseus in South Africa

The Overberg wheatbelt population of Blue Cranes Anthropoides paradiseus in the Western Cape of South Africa is approximately half the global population of this vulnerable species. Blue Cranes are highly susceptible to collisions with overhead power lines, and a spatial model was developed to identify high-risk lines in the Overberg for proactive mitigation. To ground-truth this model, we surveyed 199 km of power lines. Although Blue Cranes were the most commonly killed birds found (54% of all carcasses), the model was unable to predict lines with high collision risk for Blue Cranes. Further Geographic Information System (GIS) modelling was undertaken to test a wider range of landscape and power-line variables, but only the presence or absence of cultivated land could usefully identify lines posing a collision risk. Modelling was limited by a lack of detailed spatial habitat data and recent information on Crane numbers and distributions. We used recent carcass counts to estimate a Blue Crane collision rate, corrected for sample biases, of 0.31/km power line per year (95% CI 0.13-0.59/km/year), which means that approximately 12% (5-23%) of the total Blue Crane population within the Overberg study area is killed annually in power-line collisions. This represents a possibly unsustainable source of mortality. There is urgent need for further research into risk factors and for mitigation measures to be more widely implemented.