HARRISON MILLS, B.C. – Along the Harrison River in British Columbia, thousands of eagles are gathering to gorge on salmon that have reached the spawning ground.
David Hancock, a biologist who has been studying eagles for about 65 years, says the world's largest congregation of bald eagles on the small community of Harrison Mills, about 100 kilometres east of Vancouver.
"Last Saturday morning I did a survey off the river and there were just over 7,000 eagles in the area," he said in a recent interview.
"This is the most we've had in November."
About 35,000 eagles gather in the lower Fraser Valley between November and February, and some days about 2,000 to 3,000 raptors move in, Hancock said.
"It's the biggest single accumulating area because the Harrison River is the single most productive river," said Hancock.
"It's the only river in Canada called a salmon stronghold river."
The Harrison River is a tributary of Fraser River and runs about 18 kilometers in length.
As rivers in Yukon, Alaska and northern British Columbia ice up food supplies are also free, which forces the eagles south.
"Our salmon are just beginning to die so the table is set down here," said Hancock.
But there are other factors that are contributing to the number of eagles that descend on the area.
"Sometimes the north does not freeze up and the eagles do not need to come," he added.
"Some years we do not get as many salmon so the table is not as generously set."
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The eagles remain in the area until February, although several of them are in Washington, Oregon and California as winter deepens.
Hancock said this year, the Harrison River does not have enough salmon
"This was not a good year for spawning," he said.
When the salmon carcasses are gone, he said the eagles feed on spawned herring and oolachin, a smelt.
In about four years the area may not see as many eagles because overhervesting means there will not be as many salmon carcasses for them to feed on, he said.
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Hancock said in the last two decades researchers have learned about the connection between the forests and the spawned salmon.
The carcasses of spawned salmon give nutrition to the soil, he added, which helps trees grow.
"Without those salmon there are no big forests," Hancock said.
"That's the lesson we learned in the last 20 years of ecology."