West Coast wind farm a new threat to vulnerable pelicans
Ornithologists reckon 2,000 birds are at risk every year
A wind farm planned for the Cape west coast is expected to kill about 22 great white pelicans annually.
But ornithologists who studied the area on behalf of the would-be developers said the predicted annual collision rate could be as high as 2,230.
Even at 22 fatalities a year, they said the 35-turbine wind farm would hit population numbers at the only pelican breeding site in the region, on Dassen Island, 8km off Yzerfontein.
But the ornithologists said their predictions were inherently unreliable because of the number of variables for which they had been forced to make assumptions.
“In reality, the effect of the wind farm on the Dassen Island pelican population could be negligible or it could result in rapid regional extinction,” said Andrew Jenkins, writing in the journal PLOS One.Jenkins’s company, Avisense, was engaged by Moyeng Energy to assess the pelican collision risk at the proposed 105MW wind farm, which will cover 80km² between Darling and Yzerfontein.
The company used human observers and radar to monitor the flight paths of pelicans between Dassen Island and their main feeding ground, Vissershok landfill site 50km away.
In six sampling periods spread over eight months, totalling 180 hours, the observers counted 4,539 pelicans flying through the wind farm area. Radar counted 28,783 individual pelican flights.
High-risk flights — those most likely to result in collisions with turbine blades — were most likely in spring, when the wind was blowing from the north-west, between 9am and 3pm and with higher wind speeds.
Said Jenkins: “Allowing for various bird vs rotor speed combinations, and a range of possible avoidance rates, the predicted [annual] pelican collision rate for the proposed wind farm layout ranges from five to 2,230, with about 22 ... casualties annually perhaps the most likely outcome.”In the absence of the turbines, the Dassen Island population was “thought to be approximately stable”, he said. “However, even low levels of collision mortality resulting from the construction of the wind farm could possibly tip the population into decline.
“If aggregate collision rates for the population are higher than the tested scenarios, then the population could go into rapid decline.”
The research showed that 10 of the turbines — with hubs 120m high and a rotor diameter of up to 126m — would be responsible for 94% of high-risk flights.
“Even removal of the five highest-risk turbines reduced the predicted collision rate by more than 80%, and seasonal and temporal curtailment of the same suite of machines [for six hours of the day, every day, for three months of the year] lowered collision risk by more than 70%.”
Jenkins, also a research associate at the Percy FitzPatrick Institute of African Ornithology at the University of Cape Town, said pelicans had recently been declared vulnerable in South Africa.
“The Dassen Island pelicans should be considered as a conservation priority, and any potentially unsustainable impacts on this population should be viewed in a very serious light,” he said.