Lead poisoning stymies condor recovery

Iconic species may not stand on its own without complete shift to nontoxic ammunition

The California condor’s return to flying free in the wild after a close brush with extinction may be an illusory recovery.

UNSAFE SCAVENGING The California condor, a species that survived near-extinction, isn’t establishing self-sustaining populations in the wild because of lead ammunition in carcasses the birds scavenge, researchers say. Courtesy of Daniel George

The hundred-plus condors soaring over California swallow so much lead shot as they scavenge carcasses that the population can’t sustain itself without steady medical care and continual resupply from captive populations, says toxicologist Myra Finkelstein of the University of California, Santa Cruz. She and colleagues describe analyses of lead in blood and feathers June 25 in Proceedings of the National Academy of Sciences.

About 30 percent of blood samples collected annually from free-flying condors in California show lead concentrations high enough to affect the birds’ physiology, Finkelstein and her colleagues report. Each year about 20 percent of the state’s monitored birds flunk their lead test badly enough to need detox.

This grim paper supplies the data to confirm the toll of lead ammunition on condors in the wild, which conservation biologists have warned about for years, says Jeff Walters of Virginia Tech in Blacksburg. Regional or species-specific regulations do restrict ammunition in California and Arizona, the two states where condors live. But those rules don’t seem to be solving the problem, Walters says.

Without a politically difficult nationwide ban on lead ammunition, he says, California condors “exist in the wild only due to costly, extensive human intervention, essentially in an outdoor-zoo state.”

The world population of free-flying California condors had dropped to 22 birds in 1982 when biologists stepped in with an ambitious plan to save them. Even though no one had bred this condor species in captivity, biologists eventually trapped all the remaining wild birds to try breeding them. The effort succeeded well enough for biologists to start releasing condors back into the wild, albeit with plenty of monitoring and help. The same threats that eroded the species to begin with are still a menace, however.

Making a wild landscape safe for condors requires strict reductions in lead exposure, Finkelstein warns. Even if only 0.5 percent of carcasses carry lead tidbits, a condor still has an 85 percent to 98 percent chance per decade of flapping down to eat one. That kind of risk matters for birds that, if healthy, live 60 to 70 years.

“I certainly would not want to see us let go of the condor — it’s an iconic species of tremendous cultural value — but it’s hard to justify a continued release effort until the lead issue is addressed,” says conservation biologist David Wilcove of Princeton University. “It might well be better to call off the releases until regulators develop the backbone to do something about lead.”

Walters predicts that a lead ban will eventually happen. “There is no doubt in my mind that use of lead ammunition is resulting in exposure of human children to harmful effects of lead,” he says. “We just haven’t documented the extent of this or its impact yet.  Eventually this will go the way of lead toys.” The condors may not be unusual in their reliance on people for apparent comebacks, says Mike Scott of the University of Idaho, who has written about what he calls “conservation-reliant species.” In 2010, he and his colleagues estimated that 84 percent of species listed for federal protection will need ongoing support to persist in the wild.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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