Conservation in a Changing World: Assessing the Conservation Status of an Agriculturally Adapted Species, the Blue Crane. Chapter 3: Powerlines

<p dir="ltr">Chapter 3 from: Craig CA. 2024. Conservation in a Changing World: Assessing the Conservation Status of an Agriculturally Adapted Species, the Blue Crane. PhD. University of Cape Town.</p><p dir="ltr">Overhead powerlines pose a significant risk to birds. Blue Cranes <i>Anthropoides paradiseus </i>(IUCN Red List: Vulnerable) are particularly prone to colliding with powerlines. Between 2019 and 2022, I conducted powerline surveys in three Blue Crane strongholds, the Swartland, Overberg and Karoo. In the Overberg I repeated a previous powerline survey conducted in 2008. The Overberg and Swartland are intensively farmed and could only be surveyed once per year, in summer after crops have been harvested, whereas Karoo lines were surveyed quarterly. Between March 2019 and January 2022, I surveyed 1994 km of powerlines, recording 556 carcasses of 40 bird and two mammal species across all regions. Ten of the bird species are globally threatened. The Blue Crane was the most frequently recorded species in all three regions, with collision rates of 0.18 (95% CI 0.13–0.24) cranes/km/year in the Karoo, 0.08 (0.02–0.17) in the Swartland and 0.05 (0.02–0.08) in the Overberg. With scavenger, observer and crippling bias, these collision rates may be up to 6 times higher in the Karoo, and 7 and 8 times higher in the Swartland and Overberg respectively. Overberg collision rates were almost half those recorded in 2008, possibly due in part to lower Blue Crane abundance (Chapter 2). A greater proportion of the lines were marked in my study compared to 2008 but I did not find a correlation between proportion line marked and mortality rate per line (<i>r = </i>–0.19, 95% CI = –0.49 to 0.14, p = 0.26). Using a binomial Generalized Linear Mixed Model, I found that proximity to seasonal water was the strongest predictor of Blue Crane collisions; mortality probability reduced to nearly zero for powerlines > 2.5 km from a seasonal water body. This finding could guide placement of new powerlines, and proactive retro-marking of existing powerlines close to water bodies. A previous study on transmission lines in the Karoo found that line marking reduced Blue Crane collision rate by over 90%. Further research is needed to thoroughly test line marker effectiveness on distribution lines, especially near roost sites where many collisions occur at dawn and dusk, when markers may be less effective in low light conditions.</p>