How old is that eagle?

As you read this, eagle-viewing season is almost upon us. Adult resident bald eagles are already here; they stay here all year. Transient migrant adult and immature birds are already around, though not in great numbers yet. As January arrives, so do the bulk of migrant eagles as they seek open stretches of open water in order to forage for fish. As observers come from far and wide, the first-time viewers may be surprised that the bald eagle they see in a nearby tree looks nothing like the majestic white-headed eagle seen in pictures and paintings.

For the first 4 to 5 years of its life, a bald eagle is immature. Its feathers are varying shades of mottled brown and it will not breed and raise young until near the end of this part of its life. When a bald eagle fledges and flies out of the nest for the first time, it is fully grown as it makes that first take off with a six-and-a-half-foot wingspan, but its plumage is a dark brown with just a hint of mottling. During the first winter, it is still brown, but slightly lighter due to sun bleaching. By the second year, however, the immature eagle is very mottled, and some young show a very light phase with light colored breasts. Iris color changes from dark brown to light brown.

In the third and fourth years of its life, a bald eagle begins to look more like the classic adult with the white head and tail. This change is gradual, with the hint of a mottled white head and tail and a mottled brown body. Less mottling appears after each molt. By three-and-a-half to four years, the young eagle is a sub-adult. Just a hint of mottling appears, and a sub-adult may even be observed as a part of a breeding pair of eagles.

By four to five years, the last hint of mottling disappears, and the eagle becomes an adult. Once a bird is an adult, it is impossible to determine its age by visual signs.

Have fun eagle watching. Further information on watching can be found at the Eagle Institute in Lackawaxen, PA, or visit eagleinstitute.org .