Characteristics

The adult Guiana Crested Eagle in normal phase has a greyish black crown, becoming more grey on the sides of the head and neck. The feathers, with the exception of the longest ones that form the crest, are narrowly tipped with greyish white. The mantle is black or brownish black; the upper-wing coverts, lower back and tail coverts are tipped with white. The tail is black with three narrow bands of grey and white and a pale tip. The throat and breast are brownish grey, paler on the throat with some black encroaching on the sides of the neck. The rest of the under surface, including the wing linings, is white or off-white, lightly barred with dark brown. The primaries are barred with black and marbled grey; the bars being darker and less noticeable on the upper surface of the wing. Females tend to be a little darker on the head and breast than are the males.
In the Taeniaus phase, the sides of the head and the upper breast are black - paler on the throat. The rest of the under parts are barred with black and white. Intermediates occur between it and the normal phase; in other words the amount of ventral barring varies from none to a great deal. Rarely, one is almost solidly black below as well as on the back.
The eyes are grey or greyish yellow; the area around eyes, the lores, and the cere are slaty black. The bill is black; the legs yellow. Immatures are white on the head and lower parts, some times lightly dusted with grey. The crest feathers are white at their base, then black, with a white tip. The back and wings are marbled and irregularly barred with black and white - paler on upper-wing coverts, which are white stippled with grey. The tail is marbled, grey and white, with seven or eight irregular black bars. As in the adult, the primaries are much barred. There is a smooth transition between this plumage and the adult, making it difficult to decide whether some specimens represent variations in the adult plumage, or are not fully adult.
The most noticeable feature of the Guiana crested eagle is the projecting occipital crest on its head. Unlike the Harpy eagle, which has a bifurcated or double crest, the Guiana crested eagle has a single, undivided crest. The crest consists of feathers uniquely colored with a white base, black center, and white tip. As with other birds' display behaviors, the crest—which can be raised and lowered—is thought to be used as a form of communication. Birds often communicate with vocal or visual displays, including colored plumage during breeding season or elaborate movement routines designed to attract potential mates. With birds such as the Guiana crested eagle, however, behavioral displays usually communicate greeting, threat, submission, or distraction. The crest's graded or variable display (it does not have to be completely raised or lowered, but can be somewhere in between) conveys the intensity of the eagle's impending actions. Even though the display of the occipital crest may be difficult to decipher for those studying this bird, the signals it communicates are likely to be unambiguous to others of its species.