You fire a bullet that kills a wild pig while out hunting. That’s the last of that bullet, right? Wrong. The lead in the bullet has lingering effects on carrion-eating birds. This exposure means that birds like turkey vultures and golden eagles can suffer from neurological problems such as blindness if they eat lead-contaminated meat.
Christine Kreuder Johnson, associate professor of ecosystem health and epidemiology at UC Davis, and her colleagues captured free-flying birds in ecosystems near Monterey, Mendocino and Orange County. They targeted areas with deer and pig hunting, so as to test the variance in lead exposure in the birds before and after hunting seasons.
“Our studies add significantly to the growing body of evidence that indicate hunting with lead ammunition poses a risk of lead exposure in scavenging wildlife,” Johnson said.
She said that in her study with UC Davis Professor Terra Kelly, they were able to analyze the effects of the ban on lead ammunition that began in 2008. The regulation stated that lead projectiles could not be used in the range of the California condor, but Johnson and Kelly wanted to see lead’s effect on turkey vultures and golden eagles.
“When looking at the effects of the lead ammunition ban, the prevalence of lead exposure for turkey vultures decreased from 61 percent to 9 percent after the ban was instituted,” Johnson said.
Johnson said the reduction was even greater for golden eagles than turkey vultures after the ban.
“The prevalence of lead exposure in golden eagles, that were local to our study area, decreased from 83 percent to 0 percent – a 100 percent reduction in prevalence,” she said.
Johnson said that during hunting season, they were able to detect a noticeable surge in lead exposure.
“During deer hunting season the lead exposure in turkey vultures increased to 76 percent, in comparison to 36 percent before deer hunting season,” Johnson said.
When asked why turkey vultures were selected for the study, Johnson responded by saying that they serve as one of the best indicators for lead exposure in birds.
“Turkey vultures are good sentinels for understanding whether lead is contaminating hunted animals because vultures are highly dependent on carrion as a food source, and they also seem to be fairly resistant to the toxic effects of lead,” she said.
Johnson believes that their results indicate that hunters have done a good job in altering their ammunition selections to meet the regulations set forth by California’s Department of Fish and Game. Nevertheless, she said that birds affected by lead exposure can suffer some extreme effects.
“Birds can become emaciated and debilitated from lead poisoning. The most common signs are neurological problems, such as blindness and weakness,” Johnson said.
Steve Torres, wildlife investigations lab supervisor for California’s Department of Fish and Game, said he was surprised by the results. The Department of Fish and Game partly funded the study.
“I was surprised with the patterns and associations with lead levels in these raptors,” Torres said.
He said that the group might not have fully appreciated how much lead disperses when it hits an animal. Many bullets are designed to split in fragments on impact. Torres said that the extent of the effect lead has on these birds is unknown.
“We don’t know what kind of effect [lead] is having on them, for all we know, it could be neutral,” Torres said.
He said that the research done serves as a starting point and that no inferences or conclusions can be made as result of the research – since it was not designed that way.
“We’re concerned about anything negatively impacting wildlife populations, but we try to take an objective view, and be careful with all our regulations,” Torres said.
As for rehabilitation of the affected birds, Brett Stedman, manager of the UC Davis Raptor Rehabilitation Center, said that the treatment of the birds varies. He said that birds come in with different levels of exposure, and they are treated accordingly.
“They are given Calcium EDTA, an agent that will bind with lead to prevent it from binding with anything else,” said Stedman. “If lead can be taken out, physical rehabilitation takes place and then they are released back into the wild.”
Even with this lead exposure, hunting remains a pivotal tool for controlling wildlife populations.
“Hunting is very important to our wildlife management, and now with nontoxic ammunition becoming increasingly available, there’s a good solution for hunters to be able to eliminate toxic levels of lead exposure in scavenging wildlife,” Johnson said.
ERIC C. LIPSKY can be reached at science@theaggie.org.
