The Food That Once Saved Condors May Now Be Poisoning Them

A new study finds that condors that dine on the bodies of marine mammals consume worrying levels of toxic chemicals such as DDT.

Nathan Rupert

Life must have been pretty cushy for condors back in the Pleistocene. As connoisseurs of rotting flesh, these ancient buzzards would have had their pick of giant sloths, giant tortoises, giant armadillos, and the “giant” versions of myriad other hulking beasts. We’re talking about a time when even beavers were six feet long, a time when an animal dropping dead would feed a condor for weeks. Yes, it must have been quite a flesh feast.

But nothing lasts forever, and around 10,000 years ago, the megafauna buffet bubble finally burst in what’s known as the Quaternary extinction event.

The Pleistocene extinction did a number on biodiversity, claiming 72 percent of the mammalian megafauna across North America. As species after species went extinct, the scavengers that depended on them started to blink out, too. These included great and terrible birds like the teratorn, some of which may have had wingspans up to 20 feet! (That would be like stacking three Andre the Giants on top of each other.) And almost every subpopulation of condors disappeared, too—all except those that lived along the California coast.

The bird wasn’t a “California” condor back then. It was just a condor, soaring over a range that stretched from coast to coast. A paper published in 2006 has a pretty good theory explaining why only the ones living on the West Coast survived: They evolved to eat seafood.

You see, the mammals in the ocean did not experience the mass extinctions that wrecked their fellow lactaters on land. So there were still plenty of sea lions and dolphins to die and wash up on the beach to be picked clean by hungry scavengers. For condors on the coast, the megafauna buffet never really stopped.

Fast-forward to many millennia later, and this sea-based diet has allowed the coastal condor to dodge another bullet—literally. Lead bullets are the number one threat to the critically endangered California condor. The ammunition poisons the flesh of the animals it strikes, but these lead-laden meals are largely avoided by the seafood lovers on the coast.

Unfortunately, something else is now contaminating the meat of sea mammals. A new study published in July in Environmental Science & Technology has found that marine-mammal meat is rife with toxic chemicals, including mercury, pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs).

The good news is that this cocktail of pollutants doesn’t appear to affect the birds immediately. That is, a condor won’t drop over dead after eating flesh from a body laced with heavy metals, as it might from one sprayed with shotgun lead. The bad news is that these sorts of toxic chemicals tend to build up in an animal, causing problems over time that could ultimately threaten the species’ recovery—something that’s come a long way in the past three decades. In 1982, there were just 23 California condors left on earth. Today there are 435.

“PCBs are known carcinogens, endocrine disrupters, and neurotoxins. PBDEs are known hormone disrupters and neurotoxins, and mercury is a known neurotoxin,” says the study’s lead author, Carolyn Kurle, an ecologist at the University of California, San Diego. “So, while we don’t know the long-term risks to condors of ingesting these contaminants, it can't be good.”

One pollutant in particular will ring a bell: DDT, the pesticide that contributed to declines in many bird species, most famously bald eagles, until it was banned in 1972. The researchers found that around 95 percent of the pesticides present in coastal condor blood was DDE, which is what DDT turns into after it spends some time inside a marine mammal.

With so few California condors remaining, no scientist wants to test what will happen if you pump one full of DDE, but the evidence collected so far does not bode well for the bird. DDE’s impact can vary by species, but at least one study conducted by the U.S. Geological Survey suggests that condors might actually be more sensitive to the pesticide than bald eagles. And that’s troubling, because Kurle’s research found that coastal condors had DDE levels just as high as those that thinned the eggshells of eagles, causing population-wide reproductive failure. And a 2013 study found that the eggshells of condors on the coast were 34 percent thinner than those of condors inland.

“You can never ‘prove’ anything in science, but you can certainly amass enough data to strongly support a hypothesis,” Kurle says. “And this is what we have done.”

Much of the DDE found in California’s marine mammals probably came from Montrose Chemical in Los Angeles, which dumped more than 2,000 tons of DDT into the ocean between the 1947 and 1971. Montrose closed its doors in 1982 (its grounds remain a Superfund site), but the company’s pollution is still swirling out there in the Pacific. DDT does not biodegrade. Instead, it becomes stored in the fatty tissues of animals, where it accumulates as it moves up the food chain. So a bird that evolved to eat big things gets a big dose—so much so that it would be better for condors to lay off dead dolphin for a while.

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