In recent months, the Animal Survival International (formerly Political Animal Lobby) has publicised the plight of African vultures whose numbers have declined so rapidly that most species are now endangered or critically endangered.
Now, a study conducted by researchers from the University of Cape Town (UCT) has demonstrated that the birds face a new threat: lead poisoning from ammunition used by game hunters.
The birds eat fragments of lead bullets in the carcasses of animals that have been shot. Lead is highly toxic to all animals. It can cause death and even sub-lethal levels can negatively affect survival and reproductive rates.
This threat has until now received very little attention, but the UCT study, which was published in the journal Science of the Total Environment, suggests it should be taken seriously to increase the chance of saving vultures from extinction across their African range.
Researchers tested the blood of nearly 600 critically endangered white-backed vultures (Gyps africanus) in Botswana over four years. The birds were caught inside and outside the hunting season, and inside and outside hunting areas. Thirty percent had elevated blood lead levels. Most importantly, lead levels were highest during the hunting season and in hunting areas. This finding points toward lead ammunition used in hunting being the most likely source.
When an animal is shot, a lead bullet fragments widely throughout the carcass. The carcass or the guts of these animals are often left out in the open. Vultures then ingest fragments while they are feeding. The study suggested that this is what was happening in Botswana.
Concern over the threat to scavenging raptors is increasing. Recent research has shown that lead poisoning can have negative effects even if it doesn’t kill the birds. For example it can alter their movement patterns and reduce their breeding performance. For some birds, even moderately elevated lead levels could increase the likelihood of collisons with power lines.
There are alternatives to lead ammunition. Copper or copper alloy bullets are the most obvious. But hunters are reluctant to use them because of their comparatively high cost.
“Poisoning from lead bullets may not be the only reason that vulture numbers are falling across Africa, but the cumulative effects of habitat loss, poisoning by poachers and farmers and the fact that vulture body parts are sometimes used in traditional medicine is that vultures are fast disappearing from the African bush,” said Animal Survival International (formerly Political Animal Lobby) spokesman, David Barritt.
“ASI calls on the government of Botswana and those of neighbouring countries where hunting takes plce legally, to regulate the use of lead ammunition and eventually phase it out.