There’s a dark side to renewable energy: wind turbine blades kill birds and bats. Birds of prey such as eagles, buzzards and vultures are particularly vulnerable because they use the same wind resources that the turbines need to operate.
Last year, one study found that more than 800 birds had died between 2014 and 2018 after being struck at 20 wind farms in South Africa. Birds of prey comprised 36% of the carcasses. Between 2015 and 2019, 14 adult and five juvenile Verreaux’s eagles were reported killed by wind turbines.
Now a team from the University of Cape Town, the FitzPatrick Institute of African Ornithology, HawkWatch International, and the University of Amsterdam have pioneered a new tool — the Verreaux’s Eagle Risk Assessment (Vera) — that enables developers to identify the best locations to build wind farms and reduce the risk of the eagles being killed.
Found in mountainous areas, the Verreaux’s eagle, previously called the black eagle or witkruisarend because of its colour and a V on its back, is particularly vulnerable to collisions with wind turbines, whose outer blade tips spin at speeds of up to 290km an hour.
As birds of prey have long lifespans, and produce relatively few young each year, even a small increase in deaths can lead to population decline, the researchers say.
The researchers say it’s not clear if birds don’t see the moving blades or don’t perceive them as a threat.
With the rapid growth of wind energy developments worldwide, “it is critical that the negative impacts on wildlife are considered and mitigated”, write the authors in their study, which was published earlier this month in the Journal of Applied Ecology.
To minimise collisions, developers usually try to build wind turbines away from areas in “high use” by birds of prey, or they create simple buffers around a nest. But these exclusion buffers are not working.
Lead author Megan Murgatroyd, of HawkWatch International, says that by using the predictive model to account for how these eagles use their habitats a greater area of land can be made available for wind energy development without increased mortality risk for raptors.
“Circular exclusion buffers have been ineffective compared to our models, firstly because they have been variable in size, with some developers applying buffers as small as 800m radius; to work, they need to be much larger than that,” says avian conservation biologist Arjun Amar, an associate professor at the FitzPatrick Institute and co-author of the study. “They also assume that the eagles will use the space around their nest sites in a uniform and circular manner, which is obviously not going to be the case.”
Vera’s models use data from GPS tracking devices attached to 15 Verreaux’s eagles across South Africa that was gathered by Murgatroyd over the past eight years.
The tracking devices, developed at the University of Amsterdam, provide a record of where and how high a bird is flying every three seconds.
“When we started this project, most tags available collected a location once per hour; while we were collecting track up to every three seconds,” she explains. “Tracking technology has since improved a lot, but this is still probably the highest resolution data set for any African eagle.”
Sam Ralston-Paton, the birds and renewable energy project manager at BirdLife South Africa, explains that the 2019 Integrated Resource Plan makes provision for 17 700 megawatts for wind energy by 2030.
By then, about 22% of installed capacity should come from wind energy and this could mean more than 35 000 birds will be killed each year, including about 1 500 raptors.
As well as the Verreaux’s eagle, other threatened species affected by wind farms in South Africa include vultures, martial eagles and black harriers.
“These risks can be avoided, or at least minimised, with the considered location of wind turbines. Location is the most effective and cost-effective mitigation strategy. Fortunately, much of South Africa has excellent wind resources, and we have many alternative locations for wind energy available for consideration,” says Ralston-Paton.