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CORVALLIS - Bald eagles nesting in Oregon and along the lower Columbia River in Washington are steadily increasing, according to a 25-year study by biologists from Oregon Cooperative Fish and Wildlife Research Unit at Oregon State University.

With help from more than 275 volunteer observers and biologists, OSU wildlife researchers documented 441 nesting pairs of bald eagles in Oregon and the lower Columbia in Washington in 2002. There were only 57 breeding pairs known in the same area when the research began in 1978.

"Basically, our data shows that the number of bald eagle breeding pairs in Oregon has doubled every 10 years since the mid-70s," said Frank Isaacs, OSU wildlife biologist. Since 1978, Isaacs has worked along with OSU professor of wildlife biology Bob Anth ony and other researchers to study bald eagles in Oregon and the lower Columbia River.

Contributors to these studies include the U.S. Forest Service, the Bureau of Land Management, Oregon Department of Fish and Wildlife, the U.S. Fish and Wildlife Service, the U.S. Geological Survey and more than 15 other groups, including private industry.

The biologists survey each nest by helicopter or from the ground in late winter and early spring, then return in late spring and early summer to see how many eaglets each breeding pair has raised. They have observed nesting bald eagles in every county of Oregon except Sherman, Gilliam, Morrow and Malheur. The eagles nest in a wide variety of habitats, from mountain lakes to coastal estuaries.

Pairs of bald eagles tend to use the same nest year after year, explained Isaacs. Many are year-round residents and some have been known to travel out of the state during the non-breeding part of the year. They usually come back to the same nesting territ ory for the breeding season.

"Their nesting territory is their home," said Isaacs. "If they lose a mate, they will attract a new one to their breeding area."

In 2002, they found 62 previously unknown nests. Nesting pairs produce on average just less than one eaglet per year. Nesting success was 66 percent in Oregon and 63 percent in the lower Columbia region of Washington this year, said Isaacs.

The net increase in the nesting population of bald eagles in 2002 was the lowest since the beginning of the project, though Isaacs thinks this might be due to survey techniques, rather than a real decrease in the rate of population increase.

Change in human behavior is one of the factors helping Oregon's bald eagle populations to increase over the past few decades, according to Isaacs.

"Eagles were trapped, poisoned and shot indiscriminately and their habitat was altered during the 1800s and much of the 1900s," he said. "The Bald Eagle Protection Act of 1940 was the first attempt to protect the bird. Bald eagles had become uncommon year s before DDT was used."

Another factor was DDT, a pesticide that was used extensively in Oregon and other parts of North America from the late 1940s until the early 1970s. It contaminated the food chain and kept bald eagle populations from increasing even after the Endangered Sp ecies Act protected them, said Isaacs.

"DDT made bald eagle and other predatory birds' eggshells so thin that they would break when an adult bird would try and incubate them," he said.

By the 1960s, only about 400 breeding pairs of bald eagles remained in the lower 48 states.

"DDT kept those pairs that remained from producing enough young to sustain the population, especially in those areas where it was widely used, such as northeastern Oregon," said Isaacs.

Until the mid-1970s, bald eagles were found only in a few places in Oregon and southwest Washington - Upper Klamath Lake, the Cascade Lakes, the lower Columbia River, and along the coast.

By the late 1970s, the bald eagle population started to recover, he said.

"The biggest increases occurred in areas where eagles were most common to begin with," said Isaacs. "But there have also been substantial increases where they were formerly rare, such as along the Willamette River and in central Oregon."

Isaacs also gives major credit to the federal Endangered Species Act for eagle recovery. Bald eagles were listed as a threatened species in Oregon under the ESA in 1978. The act protects not just the eagles, but also their habitat.

The eagles' success stems as well from educational outreach programs and conservation organizations including the Klamath Basin Bald Eagle Conference, Eagle Watch and the Oregon Eagle Foundation, he added.

Eagle biologists estimate that there were at least 700 and up to 1,000 pairs of bald eagles in Oregon and the lower Columbia River around 1800. Isaacs is hopeful that these levels could be reached again.

"I think we could see the bald eagle population double again," he said. "Just last week, we received a report of a pair of bald eagles building a new nest at Wallowa Lake, where an old nest, abandoned since the 1940s, has persisted as a reminder that the bald eagles once nested there."

Scientists estimate that there are about 6,000 breeding pairs of bald eagles in the lower 48 states and about 100,000 nesting pairs in Canada and Alaska combined.