As scavengers, vultures rely on leftovers that hunters, both animal and human, leave behind. And when they feed on carcasses or gut-piles of animals that were killed with lead bullets, they’re potentially being exposed to high concentrations of lead. An analysis of the bones of turkey and black vultures, culled at random from flocks around Richmond, Virginia, found chronically high lead levels that indicated long-term and repeated exposure. The consistency of the result surprised the scientists.
“I’ve never, in 20 years of research, been able to make a statement that 100 percent of my study subjects did anything,” said wildlife biologist Todd Katzner, who supervised the work published in the scientific journal Environment International. Lead exposure, he stated, “is clearly a fact of life for birds that spend a lot of time scavenging.”
Lead mimics aspects of calcium in its chemical structure, so it’s incorporated, like calcium, into the nervous system and bones of birds as well as humans. The lead that found its way into the vultures Katzner’s team looked at had a chemical signature consistent with the lead used to make bullets and shotgun pellets, though the researchers couldn’t rule out other factors.
Other studies put a finer point on things. A review of three decades of research recently published in the The Condor, an ornithology journal, concluded that ingesting lead ammunition and fishing tackle is directly linked to illness and death in more than 120 different bird species. Among some species, like turkeys and black vultures, most individual animals appear to survive the exposure. For others – such as eagles, California condors, and loons – a significant percentage do not.
The findings have led to renewed calls to ban lead ammunition. Mark Pokras, a veterinarian and researcher from Tufts University, testified during a hearing held by the Vermont state legislature in May 2015. “I can categorically state that lead toxicosis from ingestion of hunting ammunition is a serious problem for wildlife in Vermont and the rest of New England,” he told the House Fish, Wildlife and Water Resources Committee, which was considering a bill that would ban the use of lead bullets for hunting.
Opponents argue that such a ban is unnecessary. “Traditional ammunition has never been proven to have a species population-level impact on wildlife,” wrote Jake McGuigan, director of state affairs for the Connecticut-based National Shooting Sports Foundation, in his testimony to Vermont lawmakers. In short, members of the group agree that individual birds are sometimes poisoned by swallowing lead shot or fragments of bullets left behind in piles of offal and other remains, but they don’t see evidence that lead is hampering bird populations as a whole, particularly in the context of other threats, including predation from domestic cats and the loss of habitat from development. Currently, the Vermont bill and a similar one under review at the Rhode Island statehouse are being held back from floor votes pending further study.
In Connecticut, New Hampshire, and New York, fish and wildlife departments have taken an educational rather than legislative approach, providing information on their websites about alternatives to lead bullets. Copper and copper-alloy bullets are now available in many popular ammunition sizes, particularly those used to hunt large game. They tend to be more expensive than lead bullets, but the performance of copper bullets has been favorably reviewed by those who use them. In educating the public, these agencies go beyond the effect that lead has on animals to emphasize the toll that ingesting lead can have on human health. In particular, many studies have tied high blood lead levels in young children to developmental delays.
New Hampshire’s Fish and Game Department warns that even the most carefully dressed meat from animals shot with lead bullets may contain fragments too small to notice. “Lead particles in game meat are a concern,” it says. Pregnant or nursing women and children younger than six “should minimize or avoid consumption of venison harvested with lead ammunition.” That said, adults who eat venison infrequently are unlikely to be at risk.
Many wildlife managers and researchers believe that tapping into hunters’ long-standing concern with wildlife conservation and animal welfare may be the best way to encourage a voluntary switch to non-lead ammunition.