The river "flats" of the Chilkat River along the Haines Highway between miles 18 and 24 are the main viewing area for eagle watchers and considered critical habitat in the preserve. Bald eagles are attracted to the area by the availability of spawned-out salmon and open waters in late fall and winter.

The natural phenomena responsible for five miles of open water on the Chilkat River during freezing months is called an "alluvial fan reservoir". The Tsirku fan, which is a fan-shaped accumulation of gravel, rock, sand, and glacial debris, at the confluence of the Tsirku, Kleheni, and Chilkat Rivers acts as a large water reservoir.

During the warmer spring, summer and early fall seasons, water from snow and melted glacial ice flows into the alluvial fan. The fan receives water faster than it can flow out, creating a huge reservoir of water. When winter arrives, cold weather sets in and surrounding waters freeze. However, water in this large reservoir remains form 10 to 20 degrees (F) above surrounding water temperatures. This warmer water "percolates" into the Chilkat River and keeps it from freezing.

5 species of salmon spawn in these and other nearby streams and tributaries. The salmon runs begin in the summer and continue on through late fall or early winter. The salmon die shortly after spawning and it is their carcasses which provide large quantities of food for the eagles. This combination of open water and large amounts of food bring large concentrations of eagles into the Chilkat Valley beginning by early October and lasting through February.

Bald Eagle

The Bald Eagle is found only on the North American continent. Adult eagles generally weigh between nine and twelve pounds and have a wing span of seven feet. Females are slightly larger than males. Immature eagles are mottled brown and white. The distinct white head and tail of the mature bird is developed between four and six years of age.

Eagles feed mainly on fish, but water fowl, small mammals and carrion supplement their diet, especially when fish are in short supply. Eagles can fly up to 30 mph and can dive at speeds up to 100 mph. Their keen eyesight allows them to spot fish at distances of up to one mile.

Bald eagles mate for life. Courting behavior begins in early April and often involves spectacular aerial displays of eagles diving and locking talons. Eagles lay from one to three eggs, commonly two. The eggs usually hatch between late May and early June after a 34-35 day incubation period. The young usually leave the nest by early September.

The Chilkat Valley is year-round home for between 200 and 400 eagles. Over 80 eagle nests have been observed in the Eagle Preserve. By the time of the Fall Congregations, the resident eagles are through raising their young, although immature eagles may stay near their parents for a year or more. Over 3,000 bald eagles have been counted within the preserve during the Fall Congregation (October through February).