Concerns Rise Over Known and Potential Impacts of Lead on Wildlife
Mallard on right with characteristic drooping
wing, a symptom of lead poisoning
Photo by James Runningen
Seventeen years after nontoxic shot requirements were established for hunting waterfowl, attention has shifted to lead poisoning in other species. These include upland game birds, scavengers (such as vultures, hawks and eagles) and other waterbirds that are exposed to lead through the ingestion of spent lead shot, bullet fragments and fishing sinkers.
Lead is a metal with no known biologically beneficial role, and its use in gasoline, paint, pesticides and solder in food cans has nearly been eliminated. Although lead shot was banned for waterfowl hunting in 1991, its use in ammunition for upland hunting, shooting sports and in fishing tackle remains widespread.
The most significant hazard to wildlife is through direct ingestion of spent lead shot and bullets, lost fishing sinkers, tackle and related fragments, or through consumption of wounded or dead prey containing lead shot, bullets or fragments.
Dr. Barnett Rattner, USGS contaminant expert comments, "The magnitude of poisoning in some species such as waterfowl, eagles, California condors, swans and loons, is daunting. For this reason, on July 1, 2008, the state of California put restrictions on the use of lead ammunition in parts of the range of the endangered California condor because the element poses such a threat to this endangered species." Lead poisoning causes behavioral, physiological, biochemical effects and often death. While fish ingest sinkers, jigs and hooks, mortality in fish seems to be related to injury, blood loss, exposure to air and exhaustion rather than the lead toxicity that affects warm-blooded species.
Although lead from spent ammunition and lost fishing tackle is not readily released into aquatic and terrestrial systems, under some environmental conditions it can slowly dissolve and enter groundwater, making it potentially hazardous for plants, animals and perhaps even people if it enters water bodies or is taken up in plant roots. For example, said Rattner, dissolved lead can result in lead contamination in groundwater near some shooting ranges and at heavily hunted sites, particularly those hunted year after year.
Research on lead poisoning has been focused on bird species, with at least two studies indicating that the ban on the use of lead shot for hunting waterfowl in North America has been successful in reducing lead exposure in waterfowl. The authors found that upland game, like doves and quail, and scavenging birds, such as vultures and eagles, continue to be exposed to lead shot, putting some populations (condors in particular) at risk of lead poisoning.
Some states have limited the use of lead shot in upland areas to minimize such effects, and others are considering such restrictions. Environmentally safe alternatives to lead shot and sinkers exist and are available in North America and elsewhere, but use of these alternatives is not widespread.
To obtain a copy of The Wildlife Society technical review report, "Sources and Implications of Lead-Based Ammunition and Fishing Tackle on Natural Resources," visit www.wildlife.org. Also, the American Fisheries Society published an article on the known and potential impacts of lead in shooting and fishing.
Early Lead Poisoning Studies and Subsequent Ban on Lead Shot for Hunting Waterfowl
From 1983 through 1985, the U.S. Fish and Wildlife Service conducted a nationwide monitoring program for lead exposure in waterfowl. Samples from more than 8,000 waterfowl were collected on National Wildlife Refuges and analyzed at the National Wildlife Health Center. During the first two years of monitoring, the prevalence of ingested lead shot was highest in diving ducks at nearly 10%, with lower frequencies in dabbling ducks, geese, and swans. The study provided data that addressed phase-in criteria for nontoxic shot zones, but the impetus for the implementation of the nationwide ban on lead shot for waterfowl hunting was lead poisoning of bald eagles. In addition, of more than 2,000 bald eagles examined by The Fish and Wildlife Service from 1963 to 1986, 119 were diagnosed as having died of lead poisoning.
As early as the 1930s, the U.S. Fish and Wildlife Service had made efforts to understand the complex relationships between lead poisoning and the use of lead shot for hunting. Lead poisoning is a slow-acting and debilitating disease that renders birds more susceptible to natural predators, and is often mistaken for crippling. Therefore, lead poisoning in wildlife and specifically waterfowl may not immediately be identified.
Lead Poisoning Effects on Birds
Lead poisoning is a toxicosis caused by the absorption of hazardous levels of lead in body tissues. Ingested lead pellets from shotgun shells have been a common source of lead poisoning in birds. Other sources include lead fishing sinkers, mine wastes, paint chips, bullets and other swallowed lead objects.
Lead poisoning is considered a chronic disease in wild birds. Sick and dead birds are usually observed in low numbers, if at all. Large scale mortality due to lead poisoning occurs rarely. Birds are often mistaken for cripples during or after the hunting season. Signs include: lethargy, progressive weakness, green-stained feces and vent (cloaca) due to bile staining, reluctance to fly or inability to sustain flight, and weight loss leading to emaciation. Severely affected birds often do not have an escape response but will usually seek isolation and cover, making them difficult to find. Green-colored feces can be seen in areas used by lead-poisoned waterfowl.
Waterfowl are often emaciated with severe wasting of breast muscles, impaction of the esophagus and/or proventriculus with food material, and an enlarged gallbladder containing thick, dark green bile. Green bile staining may be seen in the gizzard and/or around the vent. The gizzard may or may not contain lead fragments. The diagnosis is confirmed by detecting toxic levels of lead in tissues, including liver, kidney, and blood.
For more information on this or any other wildlife health issue, please contact the National Wildlife Health Center at 608-270-2400.
For a map of lead poisoning in wild birds:
- Go to the National Atlas
- Click on the yellow 'Map Maker' button in the menu
- Select: 'Biology' > 'Wildlife Mortality' >
- Click on the blinking 'Redraw map' button above the side menu