November 8, 2005
Seals, Sea Lions Can Be Condor Food
WASHINGTON -- The growing populations of harbor seals and sea lions along the West Coast may be good news for California condors.
While condors are now best known for eating dead deer, cattle and other animals, new research shows that carcasses of marine animals once formed a large part of their diet. Some condors are already finding food in sea lion and seal rookeries that have been growing along the coast, reports Stanford University researcher Page Chamberlain.A large part of the condor's current diet is dead animals provided by conservationists, said Chamberlain, a professor of environmental science.
"We need to find a natural food source," he said, and the marine mammals could be it.
Condors will eat whatever they can find, he explained, and once they find a source of food they will continue to fly over the area looking for more.
To help reintroduce them to the seals and sea lions some young condors are being raised in pens near the marine mammals breeding ground. When these are released they know of this source of food and others will follow them there, Chamberlain said.
Chamberlain's research team has studied what condors were eating over the last 10,000 years. They determined the diet by comparing the amounts of carbon and nitrogen in feather and bone fragments over time. Their findings are reported in Tuesday's issue of Proceedings of the National Academy of Sciences.
At one time California condors ranged across the nation from the West Coast across the southern states and even north to western New York.
The researchers found that 10,000 years ago marine mammals were an important component of condor diets along the West Coast, while the birds living inland focused on the abundant large mammals. With the extinction of many large mammals, condor range was reduced to the West Coast and the food source from the ocean.
Indeed, Lewis and Clark reported seeing the giant condors feeding on whale carcasses in 1806 in the mouth of the Columbia River.
In the following years the seal and sea lion population was reduced by trapping, and condors turned to land animals, particularly cattle which were then being introduced into California.
Over time, however, condor numbers declined with only a few remaining, mostly in captivity. With efforts underway to re-establish populations of wild condors the growing availability of marine mammals along the coast should enhance their chance of surviving.
The research was funded by the Lucille and David Packard Foundation, the National Science Foundation, U.S. Fish and Wildlife Service and Bodega Bay Institute.
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Proceedings of the National Academy of Sciences: http://www.pnas.org