The Mississippi River is a popular wintering area for bald eagles because of abundant food and open water, particularly at locks and dams and power plants that keep the river from freezing. Gizzard shad and other fish often are stunned as they pass through the gates of the dam. In addition to food, eagles need places to roost during the night and perch during the day. Bald eagles generally roost together in large mature trees surrounded by a buffer of smaller trees. Roosts are chosen by the eagles to provide protection from the weather and avoid disturbances.
Roosts are also generally close to a source of food.
Daytime perches are usually within 60 yards of the water s edge. Large cottonwoods tend to be used most frequently, although the eagles will choose smaller trees that are closer to the water. On mild days eagles may be seen standing on the ice. During the winter, bald eagles are under pressure to consume enough food and expend as little energy as possible in order to maintain body heat. If fishermen, bird watchers, or boaters get too close to the eagles, the birds will waste valuable energy flying away.