Study Shows High Lead Levels in Ravens During Hunting Season
23 January 2008Ravens in the Greater Yellowstone area have greatly elevated levels of lead in their blood during the hunting season, according to a report in the January edition of The Journal of Wildlife Management.
The ravens became poisoned with lead after scavenging on gut piles left in the field by hunters who shot deer, elk, and other big game with lead-based ammunition, said researcher and author Derek Craighead, executive director of Craighead Beringia South, a non-profit science and education organization in Kelly, Wyoming. The report is co-authored by Bryan Bedrosian, a biologist with Craighead Beringia South.
"The implications of our study are that lead contamination should be suspect in all species, including humans, that feed on hunter-killed animals," Craighead said. "Fortunately, using non-lead bullets is one relatively easy solution to curb this form of lead contamination."
Craighead has unpublished data showing an even worse problem with Bald Eagles and Golden Eagles, whose blood lead levels can reach fatal levels. Craighead will present this information at a conference sponsored by The Peregrine Fund in May.
Craighead serves on the board of directors of The Peregrine Fund, a Boise-based conservation group for birds of prey.
The conference, "Ingestion of Spent Lead Ammunition: Implications for Wildlife and Humans," will be held 12-15 May 2008, at Boise State University to promote a better understanding among biologists, scientists, health professionals, hunter groups, and sporting industries of lead bullets as a source of contamination.
The Peregrine Fund expects to release the results of its own continuing studies on lead in hunter-killed animals at the conference.
Research shows that lead bullets fragment into dozens or hundreds of tiny pieces that disperse through hunted animals when they are shot. These tiny particles can be ingested when the animal is consumed.
Craighead's team tested common raven blood lead levels during a four-year period during and after the elk-hunting seasons in Jackson Hole, Wyoming. The median blood lead level in ravens (10.2 micrograms per deciliter) was more than five times higher during the hunting season than during the non-hunting season, according to the report. The median blood lead level also was five times higher than what would be regarded as safe for humans (2 micrograms per deciliter), the authors said.
One microgram per deciliter equals 10 parts per billion.
The effect of lead poisoning in animals is well-documented, Craighead said. Animals that don't die of lead poisoning can experience a variety of mental and physical ailments, including an inability to compete well for food, more collisions with power lines and other obstructions, anemia, decreased weight and muscle mass, higher blood pressure, lower bone density, and paralysis of the nervous system.
The implications of lead poisoning in wildlife are evident in California Condors, an endangered species that The Peregrine Fund is helping to recover. Because condors eat only carrion, they often feed on game animals shot by hunters or the gut piles that remain after the animal's internal organs are removed and left behind. Currently every condor in the wild must be captured at least once a year and tested for blood lead levels. Many require treatment. In 2007 five condors in Arizona died, all but one attributed to lead poisoning.
In California, where a geographically separate population of condors is being established, a ban on lead bullets in condor territory was approved by the California Legislature and signed by the governor in October 2007. In December, the California Fish and Game Commission adopted hunting rules to further safeguard condors from the effects of exposure to lead.
Also in December, the New York State Department of Environmental Conservation announced that its officers and rangers would switch to "green ammo" from lead-based ammunition during training to reduce the environmental impact of lead at firing ranges.
In 1991 the federal Fish and Wildlife Service banned lead shot for waterfowl to address a die-off of ducks, geese, and other water-based game birds that ingested the toxin. Lead bullets are legal for hunting upland birds and mammals, such as deer and elk, and for target practice and trap shooting.
In Yellowstone Park, where hunting is prohibited, anglers cannot use lead sinkers and anchors when fishing within park boundaries.
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