In the early ’80s, the California condor almost scavenged its way to extinction. The grisly-looking birds survive off the remains of animals, often leftovers shot by hunters. But those hunters often used lead ammunition. Condors were dying of lead poisoning, their numbers dropping as low as 22.
In one of conservation’s greatest success stories, a frantic captive breeding program brought the huge, glorious scavenger roaring back; today, the condors number close to 450, over half of which are wild. While an outright ban on lead ammunition won’t kick in until 2019, aggressive public education has helped safeguard the species–inland at least. But scientists have found a new threat to the reestablished condors: extremely high levels of mercury and the pesticide DDT in the birds’ blood. This time, it’s an appetite for marine mammal flesh that may threaten the condor.
A new study out today in the journal Environmental Science and Technology highlights the problem’s source: the tainted waters near the Channel Islands in Southern California. Sea lions from up and down the West Coast gather to breed here, where several companies expelled astounding amounts of DDT from the ’40s to the ’70s. One charming little outfit called Montrose Chemical Corporation alone discharged 2,000 tons of the stuff.
That DDT is still making its way up the food chain. Sea lions eat contaminated fish, and their bodies start breaking down the DDT into a fat-soluble chemical called DDE. “So it basically lodges itself in the fat of the animal and just stays there,” says conservation ecologist Carolyn Kurle, an author of the study. The stuff will accumulate more and more over a sea lion’s life–until it mutters its last arf and becomes condor food.
All that DDE makes condor mothers lay thin-shelled eggs, which they’re more likely to crush. Thin shells also mess with the gas exchange that’s crucial for a developing chick. This is of particular concern for the condor flock that frequents the coast of central California, as opposed to another flock that sticks to inland Southern California. “If you’re a condor foraging up in Big Sur on the coast, your hatching success is 20 to 40 percent, versus if you’re foraging inland down south, your hatching success is 70 to 80 percent,” says Kurle.
Oddly enough, one scientist, Lloyd Kiff, warned of the dangers of DDE in a 1979 paper. He presented condor shell fragments that appeared abnormally thin–but because a normal shell changes in thickness depending on what part you’re looking at, other scientists questioned his link. “There was some question as to whether or not his data was reliable,” says supervisory wildlife biologist Joseph Brandt of the California Condor Recovery Program. “It turns out that it was probably on the mark, because what we’re seeing now is very, very comparable to what Lloyd saw back in the late ’70s.”
This goes to show just how difficult conservation can be. Scientists agreed that lead poisoning was what nearly drove the condor to extinction. “They thought, ‘Wow these birds are getting contaminated with lead inland, maybe it’s better if they’re foraging on marine mammals on the coast,'” says Kurle. It’s difficult to predict every peril that will face a newly reinstated population of endangered species, as Kiff did–and even harder to get the conservation community to listen.
Now that conservationists are investigating another threat to the condors, they may have to start considering new strategies to protect the birds. Problem is, this is now a wild population–a closely monitored population, yes, but not one that conservationists can just order to stop eating marine mammals. This study is just one part of a larger campaign to figure out how best to manage the still-precarious California condor population. Should conservationists really focus on the marine populations, for instance swapping out a contaminated condor’s thin eggs for ones raised in captivity? Further research on DDE and other contaminates will tell.