Seal Meat May Help Save California Condor

November 8, 2005

The California condor began eating seals and whales after the Ice Age, when its regular meals of land animals were wiped off the menu, according to a new study.

If the birds—among North America's biggest and rarest—return to eating sea-mammal meat, the flying scavenger's range could expand northward along the Pacific Coast as far as Canada, the study authors say. This would bring the condor's range closer to what it was hundreds of years ago.

Writing this week in the journal Proceedings of the National Academy of Sciences, researchers say they were able to tell whether condors historically ate remains of land or marine mammals. The scientists did so by comparing carbon and nitrogen traces in the birds' feathers and bones.

"It is possible to use both carbon and nitrogen isotopes for 'paleo-diet' studies, because essentially you are what you eat," said lead author Page Chamberlain, professor of geological and environmental sciences at Stanford University in California.

Higher carbon levels in dead condor specimens were linked to a diet of plant-eaters such as cattle and deer. Higher nitrogen levels suggested a diet of predatory marine mammals.

The analysis of modern, historic (1800 to 1965), and prehistoric (up to 36,000 years ago) condor remains revealed major shifts in the bird's diet since the last ice age, which ended around 8,000 years ago.

Pre-Ice Age condor specimens recovered from the Rancho La Brea tar pits in Los Angeles, California, showed that these populations targeted solely land mammals.

North America cooled around 11,000 years ago. Subsequent ice age conditions appear to have frozen big land animals out of the continent and confined condors to the West Coast. There, "stranded marine mammals offered the only remaining, abundant source of large animal carcasses," the authors say.

But specimens suggest California condors (Gymnogyps californianus) switched back to land-based food in the 18th and early 19th centuries. The likely cause: the rise of cattle ranching in the state, which yielded "a large bounty of carcasses."

Whale Hunting

At the same time, the researchers say, industrial-scale hunting of seals and whales severely depleted the bird's marine food supply.

The study team now recommends reacquainting California condors with marine-mammal meat as part of efforts to establish viable condor populations in the U.S.

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