(CN) – A third of the vultures caught and tested in the African nation of Botswana for a new study had elevated levels of lead in their blood, likely the result of them eating the flesh of animals shot by hunters using lead bullets.
“We were all shocked by how widespread lead poisoning was for this population and just how clearly these elevated levels were associated with recreational hunting activity,” said Arjun Amar, who supervised the research published Wednesday in the journal Science of the Total Environment.
Hunters’ bullets shatter inside their prey, which when eaten by vultures can lead to the absorption of lead into their bloodstream. Lead is highly toxic to birds and humans alike.
“The findings are important for a number of reasons,” Amar told Courthouse News in an email. “Firstly, they show that a high percentage (30 percent) of a critically endangered bird species has elevated levels of lead, and secondly that the most likely source of this is from spent ammunition. This is the first time that this link has been explicitly made in Africa.
“Conservationists have suggested we are facing an ‘African vulture crisis’ and therefore these findings are significant in that they expose yet another key threat to these species.”
After testing nearly 600 critically endangered Africa white-backed vultures, the team found higher lead levels in the birds’ blood during hunting season and in hunting areas. This suggests that lead bullets are the source of these elevated lead levels.
“The only logical explanation for the patterns of lead poisoning we observed is if lead bullets were the source of this contamination,” said lead author Beckie Garbett, who conducted the research as part of her doctorate at the University of Cape Town in South Africa.
The four-year study was conducted in partnership with Raptors Botswana, a conservation nonprofit. The findings have sparked a call for a national ban on lead bullets in order to minimize the negative impacts on vulture populations, which are dwindling throughout Africa.
“Alternatives for lead ammunition are available, and there is increasing recognition by more conservation-minded hunters that they need to move away from toxic lead ammunition for a whole host of reasons,” said Amar, who is an associate professor at the University of Cape Town’s FitzPatrick Institute of African Ornithology.
“Our findings are therefore another reason to promote the use of alternatives and for policymakers to think seriously about banning these types of bullets.”
Previous research has linked declines in several vulture species across Africa to mass poisoning, typically by farmers try to kill other predators, or poachers intentionally attempting to kill vultures for fear they might announce their location.
Scientists believe alternative non-lead ammunition, which have already been adopted in some nations, could help vulture populations.
“Whilst lead poisoning may not be the main driver for the declines in vultures across Africa, it is something that can be tackled more easily through simple legislation, as compared to stopping the illegal actions of livestock owners or poachers,” Amar said.
Lead poisoning was one of the causes of the near extinction of the California condor and is known to hinder breeding performance in and heighten mortality of birds. As such, lead in the carcasses of big game animals in Africa could also be precipitating the decline of vultures.
The findings also suggest the 2014 ban on hunting on government-owned land in Botswana has not impacted lead levels in vultures. In fact, vultures actually showed higher levels of lead after the ban. The team believes the vultures might have veered their foraging to private game farms where hunting is still allowed.
“Hunting may have become more concentrated after the ban and this might explain the increase in lead levels in vultures following the ban, since the vultures may have tapped more into this food supply,” said Garbett.
“We also need to consider that because vultures range so widely, they are exposed to lead use throughout the region, therefore mitigation of this issue needs to be addressed at a regional level.”
The researchers have called for greater appreciation among policymakers of the threat that lead bullets may pose to vultures.
The Convention for Migratory Species has also urged all party nations to phase out lead ammunition. Though Botswana is one of the few nations yet to sign the convention, the team encourages policymakers in the nation to heed this call.
“To do so is particularly important for species like vultures that range widely across international borders,” the authors write.
The research was funded by the Denver Zoological Foundation; the Rufford Small Grants Foundation; the Leslie Brown Memorial Fund; the Wilderness Wildlife Trust; Mohammed bin Zayed, the Crown Prince of Abu Dhabi; the National Research Foundation of South Africa, and the DST-NRF Center of Excellence grant to the FitzPatrick Institute of African Ornithology.