As a child I was taught that birds fly south for the winter, at least here in the northern hemisphere. I always thought that the reason was to get away from the cold, after all who could blame them. As an adult I found out that the real reason that birds fly south is to find food.
In Minnesota we have a large population of nesting eagles, Alaska is the only state in the US that has more, so it is not difficult to find eagles through out the year. In winter though, many of the eagles that nest through out Minnesota as well as many from the neighboring states and Canada head south in search of open water where they can find food.
One of the spots where the eagles usually find open water is on the Mississippi River at Redwing, MN. The Excel Energy power plant at Redwing pumps warm water into the river which keeps the water open in this area. This provides an area where the bald eagles can fish and so they often gather here in large numbers, which is great if you are into nature photography and raptors.