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Scientists aim to solve mystery of sea eagle's early life

The San Diego Zoo is teaming up with a pair of ornithologists on a project that is expected to shed light on the dark ages in the life of Steller’s sea eagle, a large east Asian cousin of the bald eagle.

Mike McGrady, an ornithologist with Scotland-based Natural Research who is leading the effort, said the body of scientific knowledge about one of the world’s largest eagles is largely confined to the nest. That is, the 80 days fledglings spend there before being booted out, and the time adults spend breeding once they reach maturity at age 4.

“Almost nothing is known about what eagles do for the first four years of their lives,” McGrady said, in a recent lecture at the San Diego Zoo’s Wild Animal Park near Escondido.

The San Diego Zoo houses one of six pairs of Steller’s sea eagles being bred in captivity in the United States. The other five pairs are housed at zoos in Los Angeles; Denver; Louisville, Ky.; Cincinnati; and Pittsburgh, and all of them are owned by the San Diego Zoo, said David Rimlinger, zoo curator of ornithology.

The birds on display at U.S. zoos are employed to educate Americans about the plight of the sea eagles, said Yadira Galindo, a San Diego Zoo spokeswoman.

In the wild, there are about 3,500 breeding pairs and they live around the coastal rim of Asia, spread from Kamchatka Island in Russia to Hokkaido Island in Japan, the bird’s primary wintering ground.

Adults are known for their distinct dark-brown-and-white feathers and their 10-foot wing spans. Females weigh about 20 pounds and males about 15 pounds.

“They are ridiculously big birds,” McGrady said. “They are a lot like bald eagles. They build these gigantic nests. And the nests can be on trees or on cliffs.”

Scientists know that when fledglings leave the nest, they tend to be a tad on the plump side, McGrady said.

“They’re a lot like humans, in that they’re a little bit overweight,” he said. “They haven’t been working out much. Then they start exercising and slimming down as they fend for themselves.”

But almost nothing is known about what happens to them next.

That’s beginning to change, however, thanks to McGrady, who lives in Australia, and his scientist teammate Eugene Potapov, a professor at Bryn Athyn College in Philadelphia. The two have taken several trips to Asia to study the birds and are preparing to return in July. Joining them will be Rimlinger of the San Diego Zoo.

Last year, McGrady and Potapov scaled towering evergreens and vertical rock faces in order to place long-lasting satellite transmitters on the backs of five young Steller’s sea eagles getting ready to leave the nest.

Accompanied by Rimlinger, the scientists plan to climb up into nests again this summer and tag five more birds.

“This is a pretty wild place in Russia,” Potapov said. “There are no roads. Sometimes we have to scare bears out of nests.”

Designed to continue sending signals for up to four years, the transmitters will allow ornithologists to map the young eagles’ travels, as they stake out less desirable habitat adult birds left unclaimed.

Not only are the transmitters designed to stand the test of time, they can pinpoint the birds’ whereabouts within a few meters, McGrady said. That should help scientists figure out the type of habitat the young eagles are selecting.

Over the last two years, Galindo said, the zoo has financed $60,000 of the cost of the research project. She said the zoo plans to unveil this week a page on its Web site (www.sandiegozoo.org) that charts the eagles’ travel patterns.

The transmitters are roughly 1 1/2 inches by 1 1/2 inches in size, with 10-inch-long antennas. Mike Wallace, leader of the California Condor recovery team at the Wild Animal Park, said the devices weigh about 50 grams, or about one-tenth of a pound.

McGrady said the breeding pairs generally select nesting sites along the shore, and along lakes and rivers close to the ocean. Pairs breed in February and March, and raise one or two chicks a year, sometimes three.

The big birds’ diet is composed primarily of fish, smaller sea birds, small mammals and carrion.

McGrady said the Steller’s sea eagle is not in danger of going extinct. But the population is in decline and faces significant pressures from fishermen who pursue the salmon the birds feast on, oil and timber development, and the giant blades of wind turbines that generate electricity, he said.

“The sea eagles have shown themselves to be particularly vulnerable to collisions with wind farms” in Japan, McGrady said.

He said the scientists’ work is expected to identify sites that need to be preserved in addition to nesting areas, to guarantee the birds’ long-term welfare.

Contact staff writer Dave Downey at (760) 740-5442 or ddowney@nctimes.com.

North County Times

Saturday, February 3, 2007