June 26th, 2012 by James Ayre
New research from environmental toxicologists at the University of California, Santa Cruz, shows that California condors are exposed to harmful levels of lead regularly. The main source of this being from ingesting lead ammunition. This continual exposure to lead is preventing the condor’s recovery — if it wasn’t for condor recovery programs, this issue would have already led to the bird’s extinction.
The new findings are reported in a paper to be published in the Proceedings of the National Academy of Sciences. Study author Myra Finkelstein, a research toxicologist at UC Santa Cruz, said that the research makes it clear that without a permanent solution to the problem of lead poisoning, “the condor population can only be sustained through intensive and costly management efforts.”
“We will never have a self-sustaining wild condor population if we don’t solve this problem,” she said. “Currently, California condors are tagged and monitored, trapped twice a year for blood tests, and when necessary treated for lead poisoning in veterinary hospitals, and they still die from lead poisoning on a regular basis.”
In 1982, the California condor was on the brink of extinction (primarily because of humans) — there were only 22 individual birds left. But a captive breeding program was created, and allowed the eventual reintroduction of condors into the wild; in California, Arizona, and Baja California. The population had rebounded to nearly 400 birds by the end of 2010.
But the population in California is still on the verge of collapse, only being sustained because of ongoing human intervention.
“Since 1997, about half of all free-flying condors in California have required treatment for lead poisoning, and each year about one in five birds needs treatment. This usually involves capturing the birds and transporting them to a zoo where they can receive chelation therapy to remove lead from their blood and supportive care until they are healthy enough to return to the wild.”
“Condors are opportunistic scavengers, feeding primarily on the carcasses of large mammals such as deer. They can ingest fragments of lead bullets from feeding on carcasses or gut piles of animals shot by hunters. Lead poisoning was probably one of several factors that led to the near extinction of the species.”
The new research was done by bringing together several different lines of evidence to understand the impact that lead is having on the condor population. A previous study from the same research team had already “identified ammunition as the principal source of lead poisoning in condors.”
“The UCSC researchers are able to identify the source of the lead in a condor blood sample using a ‘fingerprinting’ technique based on the isotope ratios found in different sources of lead. Condors raised in captivity that have not yet been released into the wild have low blood lead levels, with lead isotope ratios that fall within the range of background environmental lead in California. Most free-flying condors, however, have lead isotope ratios consistent with those found in ammunition, and the higher a bird’s blood lead level, the more likely that its lead isotope ratio matches the lead in ammunition.”
The researchers also analyzed lead levels in the condors’ feathers. Because feathers take a couple of months to grow, “sampling sequentially along the length of the feather gives a record of the bird’s history of lead exposure.”
“The results not only show that condors are chronically lead poisoned, but also suggest that the magnitude of lead exposure is likely much higher than indicated by periodic blood monitoring,” Finkelstein said.
“The study also found that even when blood lead levels are below the threshold that would prompt treatment for lead poisoning, condors experience sublethal health effects from lead exposure. The researchers used a biochemical test that is a well-established biomarker for lead toxicity in humans and wildlife. The results showed that condors are as sensitive to lead as other species, and about 30 percent of condors every year are exposed to levels that cause sublethal health effects.”
The analysis of condor population demographics was particularly discouraging for the researchers. Without the continual release of captive-bred birds and regular interventions to treat lead-poisoning, the condor population would again rapidly head towards extinction. “How long this would take depends on assumptions about the mortality rate from lead-poisoning, but demographic projections indicated that, within the next few decades, the wild condor population in California would be reduced once again to just 22 birds. The free-flying condor population does appear to be roughly stable under current levels of intensive management, the study found.”
“Coauthor Jesse Grantham, who recently retired as head of the condor recovery program for the U.S. Fish and Wildlife Service, estimated the current cost of the condor program to be about $5 million per year, including the contributions of all the agencies and organizations involved in the effort. This level of management would have to continue in perpetuity to keep the population from again declining toward extinction.”
There have been efforts to solve the problem of lead exposure in California — state regulations now ban the use of lead ammunition in condor habitat. There was a partial ban that began in July 2008 and was then expanded. So far, researchers haven’t found any evidence that the ban has resulted in a the blood lead levels of condors being reduced.
“Unfortunately, even if only a few people are still using lead ammunition, there will be enough contaminated carcasses to cause lead poisoning in a significant number of condors,” Finkelstein said. “We found that over the course of 10 years, if just one half of one percent of carcasses have lead in them, the probability that each free-flying condor will be exposed is 85 to 98 percent, and one exposure event could kill a condor.”
This means that greater regulation of lead-based ammunition will be necessary to protect condors. Alternatives to lead ammunition are widely available, but regulations to limit the use of lead ammunition are opposed by most hunting organizations and ‘gun-rights’ groups.
It’s interesting to note that the ‘Californian’ condor was widespread throughout North America only 10,000 years ago, and throughout all of the Americas before that.
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