Critically Endangered California Condors Have a Toxic Diet

The poisonous carcasses of marine mammals may hamper the recovery of the iconic California condor.

For thousands of years, the majestic California condor has been dining on the carcasses of washed up marine mammals. Though historically, dead whales and sea lions have been an important dietary supplement for the massive birds, the nutrition they provide is now being offset by the toxins in their tissues, which may be putting already critically endangered condors at an even greater risk, according to a study published in Environmental Science and Technology.

The ocean is swimming with contaminants, including the pesticide DDT, which was banned in the US in 1972, but only after large quantities were dumped into the Pacific. Being top ocean predators, sea lions get exposed to high levels of these contaminants by constantly consuming toxin-laden fish.

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The researchers wanted to know just how much of these contaminants the condors were ingesting, so they measured the levels of DDE (what DDT becomes after it’s been metabolized) in their blood. They found that the condors living on the coast, where marine mammals’ carcasses were widely available, had substantially higher levels of the toxin than the inland condors.

"DDE is highly persistent and can accumulate in apex predators such as California sea lions and California condors," said Victoria Bakker of Montana State University, in a press release. "Our results indicate that ongoing marine foraging elevates DDE levels in condors, even for birds just entering the population today."

California condors were on the brink of extinction 30 years ago. Though the California Condor Recovery Program has helped to bring the population up to more than 400 birds, their recovery has been hampered by a number of factors, the most significant of which is lead poisoning acquired from feeding on land animal carcasses that are contaminated with lead-based ammunition.

"We already know that lead contamination of land-based foods has a huge effect on condor population growth,” says Makker. “We have more work to do to understand the relative importance of DDE in marine foods for the recovery of this iconic species."

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