How Is This Banned Poison Still Killing America's Rarest and Biggest Bird?
Researchers have found that an alarmingly large number of critically endangered California condors—with a 10-foot wingspan, they're North America’s largest bird—still suffer from lead poisoning, six years after the state banned the use of lead ammunition in the animal’s habitat.
Condors feed on carrion, and ingesting lead from the bullet-ridden carcasses of deer, pigs, and other targets of hunters contributed to the birds' near extinction 30 years ago. By 1987 only 22 survived in the wild, and all were captured in a last-ditch captive breeding program.
Today there are some 400 condors, with about half flying free in the wild. But when scientists ran blood tests on 150 condors between 2009 and 2011—after the 2008 lead bullet ban went into effect—they discovered that a median 81 percent of birds contained elevated lead levels, according to a new study published in the journal Conservation Biology. In contrast, a median 75 percent of condors had elevated blood levels between 1997 and 2011—lead bullets were permitted in all but three of those years.
How could that be?
It turns out that condors are victims of their own success. When biologists first began releasing hand-raised condors back into the wild in 1992, they provided lead-free carcasses for the birds to eat as they became acclimated to their new home. The condors tended to stick close to their release sites, but over the years as the birds matured and increased in number, they expanded their range and began eating dead pigs and deer they found on their own. Many of those animals had been shot with lead bullets.
“A recovering self-sustaining condor population requires natural foraging; however, lead ammunition in the condor’s natural food sources will select against this strategy and could preclude recovery,” the study’s authors wrote.
So why hasn’t the bullet ban worked?
“These regulations that were implemented in 2008 left some exemptions for when lead ammunition could be used to shoot wildlife,” Terra Kelly, an epidemiologist at University of California, Davis, and the study’s lead author, said in an email. “During that [2009 to 2011] period, blood lead levels were lower during certain years in some, but not all sites within the condor range. So the regulations appear to have helped reduce but not eliminate their exposure to lead.”
“Lead poisoning is a major cause of death in the population and a significant challenge for recovering self-sustaining populations in the wild,” she added.
The threat is exacerbated by the fact that condors eat communally, arranging themselves around a carcass like it’s a supper table. That means one lead-riddled pig, for instance, can contaminate several birds. Making matters worse, the alpha male of the group gets first dibs on dinner and thus often consumes more lead than the others, especially since the dominant bird tends to start eating at the bullet wound, the scientists said.
That’s especially problematic as the death of an alpha male can disrupt condor breeding patterns and the avian hierarchy, according to biologists.
The condors with the highest lead levels were found in Pinnacles National Park in Northern California, where the researchers said the birds foraged over long distances and were least reliant on food supplied by humans. Pinnacles is also encircled by private land where feral pigs and other “nuisance wildlife” are permitted to be shot with lead bullets.
“There was no evidence of reduced exposure during the post-ban period,” the study concluded about Pinnacles, noting that lead poisoning in condors spiked during hunting season across their range.
The healthiest condors soar above coastal Big Sur, where they mainly find sustenance in seals and other lead-free marine mammals that wash ashore.
So how to solve the condor conundrum?
Help is on the way. California Gov. Jerry Brown last year signed legislation that will phase out lead bullets statewide by 2019. The question is whether condors can hang on until then.
“We’re hopeful that more comprehensive statewide legislation and outreach efforts by the condor program (encouraging hunters and ranchers to use non-lead ammunition) will further reduce the risk of lead exposure for condors,” said Kelly. “Until we can ensure natural food sources are free from lead ammunition for the population, condors will continue to be threatened by lead poisoning.”