The annual bald eagle count in Brackendale Provincial Park, where thousands of the birds often stop as they migrate north for the winter, has recorded its lowest number in its 30-year history.
Volunteers with the Brackendale Winter Eagle Festival went out in the Squamish River Valley, located about an hour's drive north of Vancouver, on Sunday. Volunteers once counted as many as 3,000 bald eagles, but this year they only spotted 411.
"A decrease in the salmon population in Squamish River is the main cause of the drop in the eagle number," said Glenne Campbell, an eagle-count organizer with the festival.
"We had adverse weather in the past year. The high temperature of rivers in the summer and the very rare frozen river in winter have made it very hard for the salmon to survive," she said.
The annual festival is a big draw for Brackendale, a small community just north of Squamish, where birdwatchers can easily view the eagles from a municipal dyke just across the Squamish River from the provincial park.
Eagles follow salmon and feed on salmon cadavers, and the abundant supply of the fish in the Squamish and Harrison rivers draws large numbers of the birds to the area.
Apart from climate change, David Hancock, eagle biologist and founder of Hancock Wildlife Foundation, said that overfishing and industrial hazards have also affected the salmon population.
In 2003, the eagle count in Brackendale dropped from 1,947 in the previous year to 577. The numbers returned to between 1,500 and 2,000 for several years, but dipped back below 1,000 in 2008.
B.C.'s Fraser Valley has also seen a dramatic decrease in eagles this year.
"We are supposed to have 7,000 to 9,000 eagles, but only about 2,000 eagles were counted in December," Mr. Hancock said.
"Eagles have to move to find food. Hopefully, they can find alternative food in other places, but it is very challenging for them and many eagles just perish."
The eagles scatter as they look for food, which makes them more difficult to track and count.
Mr. Hancock's foundation is working with Simon Fraser University to use cellphones to track where the rest of the eagles have moved to.