The successive plumage stages of Bald Eagles can be confusing. When I see an immature it is interesting to determine its age so I usually try to match it up with the patterns in the field guides. From watching the local nest we are rather familiar with the fledgling eaglets' first plumage.
At first, the young bird looks larger than the adult. It may actually weigh more, but this appearance is enhanced by the fact that the tail and flight feathers are actually longer than those of the adult. This assists the bird as it learns to fly, and gives its wings a broader (I call it "floppy" look). The newly fledged eaglet is quite dark brown all over. The head and upper neck are usually uniformly brown. We note that its eyes are dark and its beak and cere are black. Older birds have narrower wings and shorter tails and vary in the amount and distribution of white in their plumage, and their eye and beak colors change with age.
The field guide illustrations are not always distinctive, and It can be difficult to know what is meant by "age" when the earlier stages are illustrated. I found useful descriptive information in Clark & Wheeler's Peterson Field Guide "Hawks." It classifies the plumage molting stages as:
Immature, White-belly I, White-belly II, Adult Transition, and Adult, briefly summarized as follows:
Immature: (from fledging until almost a year old) "First Year"
Head uniform dark brown
Beak and cere black
Eyes dark brown
Back tawny brown, contrasts with darker flight feathers, some with whitish wash
Breast dark brown, usually contrasts with paler belly
Belly may have white streaking especially where breast and belly meet
Wing secondaries longer than adult
Tail longer than adult and dark
White-belly I (from 1 to 2 years old) "Second Year"
Molt begins in their first spring "almost a year old" -- (keep in mind that south Florida birds are then over a year old)
Head brown with lighter superciliary line
Eyes lighter brown to amber
Beak slaty color, cere lighter
Back shows more white, an upside down triangle
Breast mostly dark brown bib contrasts with belly,
Belly white with variable number of short dark streaks
Wings a few flight feathers replaced; new shorter secondaries
Tail molt complete, shorter
White-belly II (from 2 to 3 years old) "Third Year"
At 2 years of age they are similar to previous stage except that
Head has larger whiter superciliary line, cheek and throat whitish
Eyes whitish yellow
Beak lighter with dirty yellowish spots, cere more yellow
Back has upside-down white triangle
Breast bib is distinct
Belly white with dark streaks
Wings narrower with a few older long secondaries remaining
Tail short as in adult
Adult Transition (attained at age 3 and highly variable) "Fourth Year"
Head lightens, especial towards top but no as much down the neck
Body darkens
Eyes pale yellow
Beak and cere orange-yellow
Wings retain some white underneath and in "armpits"
Tail remains dark until spring of 5th year
Adult (over 4 years old and afterwards) "Fifth Year"
Head white
Tail and tail coverts white
Body dark brown with light edges to feathers
Beak and cere bright orange-yellow
Eyes pale yellow
For a year or more head may retain brown streaks and may have darker eye line like Osprey
Tail has dark terminal band for first year in adult plumage
Locked
