Bald Eagles

A Bald Eagle becomes sexually mature at the age of four to five years. Prior to that it undergoes substantial changes in appearance which enables its age to be estimated. All the variations can be seen around the Lake, as local eagles do not migrate.

Adult Bald Eagles mate for life. In February, they show serious breeding behaviour: they add new sticks to their existing nests and mate. By the end of March, eggs have been laid. Chicks hatch late in April. By mid-July, the young have fledged.

Appearance of a Bald Eagle by Age
Age Head Body Image
 in nest
plumage: grey down ⇒ brown feathers
beak, cere: blackish
iris: sepia
plumage: grey down ⇒ brown feathers unavailable
 ½ yr
plumage: blackish brown
crown: slight bleaching by winter
beak, cere: uniformly dark grey
iris: sepia
underparts: buff brown mottled dark
wing coverts: dark brown
wing pits: mottled white
tail: sooty black mottled white
Basic I
 1½ yr
plumage: brown
crown: tan
beak, cere: mainly dark grey
iris: lightens to buff–brown
tail: brown
body, wings: dark brown
wing pits: mainly white
mantle: mottled white triangle
breast: mainly olive
belly: darker than breast
Basic II
 2½ yr
plumage: the osprey–head look
crown: light grey
auriculars: brown band to eye
throat: extensive white
beak: blackish grey, buff–yellow cere
iris: light cream
tail: smokey grey going to
mottled brown at tips
body, wings: brown occasionally
mottled white
wing pits: variable, mottled white
Basic III
 3½ yr
plumage: striking shift to white
crown: brown flecking, also around and behind eye
beak, cere: mainly yellow, brown line forward of nares
iris: pale yellow
tail: white, terminal brown strip
body, wings: dark brown with
scalloped buff feather margins; slight
white flecking on chest and wing pits
Basic IV
 4½ yr
plumage: same as III except almost no brown mottling on head tail: white
body, wings: same as III
 5½ yr ⇒
plumage: white
beak: yellow
iris: pale yellow
tail: white
body, wings: dark brown with
scalloped buff feather margins
Descriptions are given of the Bald Eagle in the winter when its appearance is not in the transition which takes place during the protracted molt (feather replacement) of spring and summer. This table relies heavily, but not exclusively, on McCollough, Mark, 1989, “Molting sequence and aging of Bald Eagles”. Consult it for more detail, and good drawings.

I probably would not have gone to the trouble of building this reference had I known at the time about the Jim Butler’s good summary presented at Squamish Ecology. Consult this also.