JUVENILE

Feathers are fully grown but may still have a "soft" look
Looks almost like adult female (for most species)
Can fly well
Afraid of people
Beginning to feed itself. May have trouble finding enough to eat.
Is generally independent of parents.

ADULT

Feathers fully developed
Has a sleeker, smoother look about it
Some species have different coloring for male and female as this stage
Afraid of people
Claim and defend territory, generally during breeding season

Adult on the right
Juvenile on the left