Thirty-five thousand birds of any kind is a sight to behold, but when those thirty-five thousand birds are bald eagles, the spectacle does have a way of focussing the mind.
The great gathering of bald eagles—technically, a “convocation”—in the Fraser Valley in early December was a natural wonder that lit up the news. People in Ontario especially, who have been witnessing a slow recovery of bald eagles and are thrilled to spot one or two at a time in cottage country, were justifiably amazed. But what does this many bald eagles in one place mean? Are they really hungry? Are they planning something? Should we bring all our small pets indoors?
To begin, large numbers of bald eagles in B.C. are not unknown. Vancouver’s Ladner landfill, for example, attracts up to two thousand snacking bald eagles at a time. And as Dave Bradley, B.C. program manager for Bird Studies Canada, points out, there have been similar gatherings in Brackendale, on the Squamish River, during winter months, where 1,300 birds (but at times up to 3,000) typically have turned up.
The eagles gather at Brackendale for the same reason they’ve converged in the Fraser Valley: to feast on salmon. The difference is that salmon runs are so much larger on the Fraser River than on the Squamish, hence the staggering number of eagles in the Fraser Valley event. Overall, the Fraser Valley convocation is a good news story, says Bradley. It’s another testament to the bald eagle’s rebound from the devastation of DDT and the days when they were routinely shot for eating salmon. It’s also a potential good news story for salmon (although the salmon may not see it that way).
Eagles gathering in such large numbers is unusual, and typically only occurs when there is abundant prey. “Think of Grizzly Bears feeding on Salmon in Alaska — they would never tolerate the close proximity of each other unless there were enough prey to go around. It’s the same story with the eagles.” The fact that so many eagles are gathering in one place suggests that there are plenty of salmon running right now. If there’s a correlation between large numbers of eagles and large numbers of salmon, the proof will come in comparing the eagle counts with the salmon stock estimates made by the Department of Fisheries and Oceans.