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Endangered California condors eating contaminated carrion

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California condors are making a comeback. But now conservationists worry the endangered species’ diet is putting the birds are risk.

Marine mammals are an abundant food source, but they’re also a repository for contaminants accumulating in the ocean. New research shows coastal condors in Central California have higher levels of pesticides and other toxins than their peers living farther inland.

Condors are equal opportunity consumers, feeding on animal carcasses of all kinds. On the coast, marine mammal carcasses are plentiful.

Initially, scientists were encouraged by the dietary trend. Condors can get lead poisoning from feeding on land mammals killed by lead-tipped bullets.

The new research, published in the journal Environmental Science and Technology, suggests marine mammal consumption isn’t any safer.

“The problem with condors eating marine mammals is that they contain significant amounts of contaminants that have been shown to harm reproduction in other birds and are therefore a potential threat to the ongoing recovery of California condors,” Carolyn Kurle, an assistant professor of biology at University of California, San Diego, said in a news release.

Kurle and her colleagues found both marine mammals and coastal condors in Central California possessed significant levels of DDE, a derivative of the now-banned pesticide DDT. Forty percent of the tested breeding-age coastal condors possessed DDE concentrations on par with levels that caused eggshell thinning in studies involving bald eagles. Roughly 20 percent had DDE levels associated with bald eagle nest failure.

“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. “Our results indicate that ongoing marine foraging elevates DDE levels in condors, even for birds just entering the population today.”