Cape Town – When scientists attached tracking devices to 21 endangered bearded vultures in the Drakensberg, they did not expect that almost half the birds would be killed by poison and power lines during their study.
Of the 10 dead birds, one was killed by an electric power line and the other nine by eating carcasses laced with poison.
Sonja Krüger, lead author of the study, which was published in the ornithological journal Condor this month, said the poisons were mainly pesticides that farmers had purposely put on animal carcasses to kill livestock predators such as jackal.
“Farmers do have a predator problem, but there are other ways of dealing with it. Poison is unfortunately the quick and easy way. The birds were feeding on the same carcasses left to kill jackal.”
The other killer is power lines. All new lines have to be “raptor-friendly” with insulators on top of poles where birds may land, and with “flappers” on the lines to make them more visible. However, most of the old lines are not raptor-friendly, and there is an urgent need to make them so.
The bearded vulture, or lammergeier, was once widespread throughout southern Africa, but is now categorised as critically endangered and restricted to the Drakensberg region. There has been an almost 50 percent reduction in bearded vulture nesting sites on the sub-continent since the 1960s.
Krüger said the high death rate of the tracked birds had come as a surprise. Some of them did not even make it to adulthood. She believes if action is not taken soon – and if wind farms are built in the birds’ range – they may become extinct.
Krüger, from EKZN Wildlife, and Arjun Amar, of UCT’s Percy FitzPatrick Institute of African Ornithology, tracked the birds between 2007 and 2014 to explore their movements, their range and to better understand why some nesting sites had been abandoned.
They found that the biggest difference between the bearded vultures’ abandoned and occupied territories was human-related factors: settlement density and power lines. These were more than twice as high in the areas where vultures had abandoned territories compared to those which were still occupied.
Their results also suggested food abundance may influence the birds’ overall distribution, and that supplementary vulture feeding schemes may help the plight of the endangered vultures. More than 95 percent of the bearded vulture’s diet is bone, which they drop from heights to crack open to get at the marrow.
The satellite trackers revealed that the young non-breeding birds travelled significantly farther than the adult breeding birds, and so were more vulnerable to human impact. The non-breeding birds had a home range of about 286km² – about the size of Denmark. The range for breeding birds was 95km².
Krüger said there were proposals to build wind farms in Lesotho and in the northern Eastern Cape, both within the range of the critically endangered birds.
“In Lesotho the proposal is to put them right on the cliff top. If wind farms are built in their area, that will be the end for them.”