June 26, 2012
California Condor Population Still Under Threat From Lead Poisoning
Brett Smith for redOrbit.com
Despite efforts to protect them, California condors are being decimated more than previously thought from lead poisoning caused by ingesting hunters´ bullets, according to a new study published in the Proceedings of the National Academy of Sciences.
Being opportunistic scavengers, condors feed primarily on the carcasses or organs of large mammals such as deer, many of which have been shot and left behind by hunters who might only take cuts of meat. Lead bullets used by these hunters have been targeted for restriction by environmental activists looking to prevent lead poisoning in California and other states for the past few years.
The rare birds have slowly come back from a miniscule population of just 22 in 1982, and have since recovered to number about 400. Around $5 million dollars are spent per year on programs to boost the birds' population through captive breeding and release programs, but if those programs ended, the birds would likely die off again from lead poisoning and other factors, according to the study.
"We will never have a self-sustaining wild condor population if we don't solve this problem," said the study´s first author Myra Finkelstein, a research toxicologist at the University of California at Santa Cruz.
"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."
The study reviewed more than 1,154 blood samples taken from wild California condors and tested between 1997 and 2010. Researchers found that 48 percent of the birds had lead levels so high that they would have died without intervention.
While previous research by co-author and UC Santa Cruz professor Donald Smith showed that ammunition was the principal source of lead poisoning for the condors, the latest study includes five times as many cases and expands on Smith´s previous findings.
By measuring the different isotope ratios found in various kinds of lead, researchers showed that condors are often poisoned by the type that comes from bullets.
Because feathers grow over a period of several months, the scientists also took sequential samples along the length of the condor feathers, giving them record of the sample bird's history of lead exposure.
The results from testing the feathers showed not only that condors are constantly exposed to lead, but they also indicate that the extent of lead exposure is likely much higher than indicated by blood sampling alone, Finkelstein said.
Steps have already been taken to mitigate the impact lead bullets are having on the giant birds. In 2007, then Governor Arnold Schwarzenegger signed a California law into effect that banned the use of hunting with lead bullets in the condors' range, which extends from Los Angeles to San Jose. Sadly, the study showed that the law has had little effect-- with birds analyzed before the law took effect having the same lead levels as those analyzed afterward.
"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 ten 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."
In addition to Finkelstein, Smith, Dan Doak, and Grantham, the coauthors of the PNAS paper include Daniel George, condor program manager at Pinnacles National Monument; Joe Burnett of the Ventana Wildlife Society; Joseph Brandt of the U.S. Fish and Wildlife Service; and Molly Church of the San Diego Zoo's Wildlife Disease Laboratories. This research was supported by the National Park Service, Western National Park Association, and the U.S. Fish and Wildlife Service.