Seal Meat May Help Save California Condor

James Owen
for National Geographic News

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.

Chamberlain says big mammals such as deer are likely to become increasingly scarce in southwestern California, where the condor is being reintroduced.

"This is now all agricultural land, and it is being developed," he said. "Loss of habitat for large mammals in the Central Valley and southern California would most certainly reduce the possible food sources for wild condors."

Sea lions, meanwhile, are recovering along the Pacific Coast. The California sea lion population is increasing by 5 to 6 percent a year, with total numbers up to around 240,000, according to the U.S. National Oceanic and Atmospheric Administration.

Likewise, harbor seal numbers in California have recovered markedly since the 1970s. The current population is put at 28,000.

If condors can tap into this food source, Chamberlain says, the prospects of the birds spreading across their former West Coast range are "excellent."

"As the seal and sea lion rookeries become reestablished northward, the condors could follow," he added.

Conservationists working on condor captive-breeding and release programs aim to encourage the birds to eat seal carcasses by setting up holding and release sites near these rookeries.

One such site has already been established at Big Sur, California, by the Ventana Wildlife Society (VWS) as part of the California Condor Recovery Program.

This scheme is proving a success, according to VWS executive director Kelly Sorenson.

Sea Lion Meals

"The condors in Big Sur are primarily eating dead sea lions of all ages," he said. "To a lesser extent harbor seals are eaten, and we suspect on at least one occasion the birds found and fed upon a dead elephant seal."

Washed-up whales may also reappear on the condors' menu, Sorenson said.

Although authorities often dispose of whale carcasses before condors get a chance to feed on the mammals, "I believe [whale eating] will eventually happen," he added.

There are a few historical accounts of condors feeding on whale meat. For instance in 1806 the explorers Meriwether Lewis and William Clark saw the birds feeding on dead whales at the mouth of the Columbia River, which empties into the Pacific Ocean at the Oregon-Washington border.

"This bird [flies] very clumsily, nor do I know whether it ever seizes its prey alive, but I am induced to believe it does not," Clark wrote.

The explorer was correct. California condors are "obligate" scavengers, meaning they never kill, eating only the remains of dead animals.

In pre-Ice Age times the condor was found in western North America from what is now Mexico to Canada and in the east from Florida to New York. The bird, which has a 9.5-foot (2.9-meter) wingspan, had retreated to North America's West Coast by the time the first European settlers arrived.

Subsequent pressures—including habitat loss, hunting, poisoning by pesticides and lead, and egg collecting—eventually restricted the bird to California.

By 1982 just 22 individuals survived.

Since then a captive-breeding program and subsequent releases into the wild have returned the condor to areas of California and Arizona in the United States and Baja California in Mexico.

With its total wild population currently standing at 130, the species remains one of the world's most endangered birds.

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