A record number of bald eagles have been counted at Hanford this winter, possibly attracted by the record fall Chinook run.
Hanford scientists spotted 60 eagles during boat trips on the Columbia River in December, said Michael Sackschewski, an environmental scientist for Mission Support Alliance.
During the '50s just two or three eagles would be seen during the winter at Hanford, he said. That grew to about 20 a year during the '70s and then 40 per year during the '90s.
By 2011 and 2012 researchers were counting about 50 eagles each year.
Some of that increase came as populations across the lower 48 states rebounded from near extinction from hunting and pesticide poisoning in the mid-20th century.
But this year's record-breaking number also may be because of the larger than usual number of salmon in the Columbia River, Sackschewski said.
More upriver fall Chinook returned than any time in the past 75 years, according to Washington State Department of Fish and Wildlife.
Hanford biologists have counted twice the normal number of redds, or fall Chinook spawning nests, in the river, Sackschewski said.
Unusually cold weather in December also may have made them easier to spot, since they may have been more likely to stay in one place, he said.
Bald eagles primarily use the Hanford Reach of the Columbia River as a wintering area from mid-November to mid-March, eating fish and waterfowl, according to the last bald eagle monitoring report for the Hanford nuclear reservation issued in May.
The younger eagles may depart first after much of the spawned Chinook salmon carcasses are gone, with the adult eagles staying and likely feeding on waterfowl.
Eagles have been seen many years building nests of sticks high in trees near the river and defending territories at Hanford, but the nesting attempts typically end in mid-March with the birds leaving to build nests elsewhere.
However, just last year two bald eagles hatched at the Hanford nuclear reservation, the first time that was known to happen in more than 50 years.
The nesting pair and juveniles remained at Hanford into the summer and one of the young was seen on a Columbia River island midsummer.
Beginning in the fall of 2011 Mission Support Alliance biologists began a project to document the use of night roosting areas, which had not been done systematically at Hanford, according to the Department of Energy.
Surveys are conducted at dusk from a half hour before sunset until dark, with surveyors in vehicles outside quarter-mile buffer zones using spotting scopes and binoculars to count the number of eagles and record whether they are adults or juveniles.
Bald eagles are considered juveniles until they are about 5 years old, when their mottled brown-and-white plumage turns to dark brown and they develop the distinctive white head and tail of an adult.
Workers are restricted from entering a quarter-mile buffer zone around a roosting area from mid-November to mid-March unless they get permission for an occasional midday visit for a task such as collecting a sample from a groundwater monitoring well.
Protections also are in place to keep workers away until nests are abandoned or, as was required for the first time last year, eaglets are fledged.
Bald eagles were removed from the federal threatened and endangered species list in 2007, but they remain protected by Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act.
The roosting areas are used year after year and biologists may see 15 to 20 birds in one tree, Sackschewski said.
Because of the intensive monitoring in recent years, two-long protected roosting locations were dropped near the former K Reactors and the Hanford town site because they were not regularly used, but a few other sites have been added to the list of night roosting areas. Hanford uses the state definition of a roosting area -- at least three eagles seen on at least two nights for multiple years.
Much of the environmental cleanup along the Columbia River has been completed, and most of the roosting areas are not near active cleanup sites, Sackschewski said.
However, some wells used to pump up contaminated groundwater to be treated are near roosting sites.
-- Annette Cary: 582-1533; email@example.com; Twitter: @HanfordNews