Monday, May 21, 2012

Why do eagles migrate thousands of miles to feed on salmon?


Check out the feeding frenzy when the chum salmon arrive in the fall. This is only one half day of footage from our motion detecting cameras! Eagles pull out the salmon and other birds can access whatever is left.

video

But why do eagles migrate by the thousands to the Chilkat River from distant locations?

Well, it turns out that eagles often have plenty of food in the spring, summer, and early fall when things like herring, smelt, and salmon are widely available. But at the end of the fall and especially during winter, eagles have fewer food options just as they need more food to stay warm.

What is special about Southeast Alaska?

Where the Chilkat, Klehini, and Tsirku rivers meet in Southeastern Alaska is a unique geology that allows groundwater to percolate to the surface. This relatively warm water prevents this river from freezing, which allows chum and coho salmon to arrive much later than at other salmon runs.

Eagles that breed in distant locations migrate hundreds and thousands of miles to feed here in the fall and winter, but we have no idea where exactly they are coming from. Using global positioning system (GPS) transmitters, we can now follow the migratory behavior of these eagles for several years.

Our research will provide important insight on how much eagles from Canada and the continental US might depend on the salmon from this one location. By feeding on salmon over the fall and winter, these eagles can survive to return to their homes the following year. Thus, our project will highlight the impact that this one small salmon ecosystem might have on distant locations and how important it will be to protect this unique resource.

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