Posted on behalf of Brendan Borrell
In the latest chapter of a long-running debate over lead bullets, researchers presented the strongest evidence to date that hunting ammo is poisoning endangered California Condors.
Myra Finkelstein, an environmental toxicologist at the University of California at Santa Cruz, and colleagues analyzed lead isotope ratios in 65 birds after their release into the environment and found they fell between 0.81 and 0.83 – within the range of that found in bullet samples, most of which were turned in by hunters in California. Pre-release birds had lower concentrations of lead in their blood, and their isotopic ratios were higher (0.83 to 0.85). In addition, Finkelstein found that sub-lethal concentrations of lead in blood (20 ug/dL), result in a 60% decrease in the levels of aminolevulinic acid dehydratase – an enzyme necessary for cellular energy and hemoglobin production. The results were presented yesterday at the Society for Conservation Biology meeting in Edmonton, Canada.
California condors used to soar across the western United States, but by 1982 only 22 remained in the wild. Their captive breeding programme is often cited as the most expensive species recovery effort in US history, costing up to US$2 million per year. Yet today, out of 304 birds released into the wild, 116 have died. Half of those deaths are due to lead poisoning, which, among other effects, damages the nervous system. Condors are scavengers and most scientists believe they are being poisoned by feeding on carcasses killed by hunters.
Steve Beissinger, a conservation biologist at the University of California at Berkeley who was not involved in the research said the results were another “smoking gun” that lead bullets are killing condors. “The California condor is a classic example of what happens when you try to return a species to an environment where the factor that caused its decline has not been reversed,” he said.
The new study, however, is already being contested by gun advocates. Don Saba, a cancer researcher with the private consulting firm Sierra Bioresearch in Tucson, Arizona, who challenged the group’s 2006 study in Environmental Science and Technology, says that the analysis is based on a “fallacy” that serves a “political agenda.” “You can’t say that lead in ammunition has a particular isotopic ratio,” he says, pointing out that every batch of ammunition is different.
“All the evidence to date suggest ammunition is the only plausible source,” Finkelstein counters. The matter may soon be settled once and for all: In July 2008, California restricted the use of lead ammunition within the range of condors. Birds sampled in 2009 still showed high levels of lead, but Finkelstein says it is still too early to know how well hunters are complying with the ban on public and private land.
Image: California condor / Don Smith, UCSC