Jackson Hole News & Guide, February 24, 2010
Lead in ravens drops with copper bullets
Researchers hope to distribute nonlead ammunition to more hunters next year
By Cory Hatch
Hunters who shot copper bullets instead of lead ones during hunts on the National Elk Refuge and in Grand Teton National Park likely helped reduce blood lead levels in Jackson Hole’s ravens, scientists say.
Last fall, researchers from Craighead Beringia South distributed 194 boxes of copper bullets to hunters with permits for the park and the refuge. Researchers then captured 46 ravens, birds that typically scavenge the discarded gut piles, during hunting season and tested their blood for lead.
Craighead Beringia South biologist Bryan Bedrosian said an estimated 24 percent of hunters used copper bullets this year, resulting in a 28 percent drop in blood lead levels in ravens compared with what would have been expected.
Previous studies have shown that the blood lead levels in ravens rise about two weeks after the start of hunting season and drop about two weeks after the season ends. Researchers think ravens eat the lead bullet fragments and the lead persists in the bloodstream for about two weeks before it’s deposited in the birds’ tissues.
The reason Bedrosian’s latest study works is that he’s documented a “clear and strong relationship” between the average lead level in ravens and the total number of elk and bison killed. In other words, the more carcasses, the more lead there is available in the environment for ravens to ingest. While some ravens eat more lead than others over the course of the hunting season, the average lead level among all the birds goes up with each elk or bison killed.
“Of the limited number of hunters who we handed out nonlead ammo to, it made a significant positive impact for the lead levels in the ravens,” Bedrosian said. “As you’d expect, the more animals that are harvested, the higher the lead levels in the ravens.”
This year, since some hunters used copper bullets, the lead levels in the ravens are much lower than they should be if everyone had used lead, he said.
“When you take only the number of animals harvested with lead ammunition, the average lead level of the ravens lines up perfectly,” Bedrosian continued. “It’s the best evidence we’ve seen for a direct cause-and-effect relationship between hunting with lead ammunition and lead toxicity in the birds.”
Bedrosian said the research is possible because the park and the refuge kept track of how many successful hunters used copper or lead ammunition. One unknown is how many hunters on the nearby forest opted to use nonlead ammunition this year.
“To us, it’s pretty amazing that even the small proportion of hunters that switched over to copper ammunition made a measurable impact on our wildlife populations,” he said.
One thing that’s not clear yet is the voluntary program’s effect on the eagles.
After 12 eagles were tested, researchers could not find a statistically significant drop in lead in their blood this past hunting season. Bedrosian said that while the small sample size, only 12 birds, could be one reason for the confounding results, eagles also seem to metabolize lead differently than ravens.
While blood lead levels in ravens typically range from zero to 60 micrograms per liter, lead in eagles can range from zero to 700 micrograms. Given such a wide variation in eagles, the small number of hunter-killed game shot with copper bullets might not show much of an impact.
“We saw a pretty clear relationship with the ravens, but not the eagles,” Bedrosian said. “There is something different. They’re eating the same food per volume of blood. Somehow more lead is getting into the bloodstream of an eagle verses the raven. That’s why condors die much more readily than other species with the same amount of lead.”
This past hunting season, researchers weren’t able to secure funding until the season started and therefore got a late start with the distribution of copper ammunition, said Derek Craighead, executive director and chairman of the board of Craighead Beringia South.
He hopes next year’s program is bigger; then the results could be published in a peer-reviewed journal.
“We were concerned during the period we were collecting data this past hunting season that we just hadn’t handed out enough copper bullets,” he said. “If you have the money and can do enough [public education] and make it easy enough for the hunter to exchange the bullets, there’s a lot of them out there that are more than willing to do it. Fifty percent of the hunters is the goal; in our wildest dreams it would be 90 percent.”
Eventually, Craighead said he hopes the idea of nonlead bullets catches on.
“My personal goal would be to see lead bullets disappear from sport hunting across the country, and that’s ultimately what I hope does happen,” he said. “There’s an argument to be made that it probably won’t happen unless there is some legislation passed. We want this to be a voluntary, grassroots movement really coming from the sportsmen who would drive a change in national policy.
“We’re not campaigning against hunting; we’re campaigning for responsible hunting,” Craighead said. “By that I mean we’re not leaving toxic waste out there for ravens and eagles and potentially people who are eating the game meat. It’s kind of a no-brainer. It’s not often that you’re faced with a problem that has such a simple solution.”
Jack Dennis Sports, Cabela’s Inc., the 1 Percent for the Tetons Foundation, Grand Teton, the refuge and various private individuals helped pay for and distribute the copper bullets.
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