Black-and-chestnut Eagle

This is a fairly large eagle and very large raptor at 60 to 80 cm (24 to 31 in) in total length with a wingspan of 147 to 180 cm (4 ft 10 in to 5 ft 11 in). It is largest current member of the genus Spizaetus, with the smallest males somewhat larger than the largest female ornate hawk-eagles. Full grown weights for black-and-chestnut eagles have been reported as 1.5 to 3.5 kg (3.3 to 7.7 lb), making it among neotropic eagles around the same body size as the two largest Buteogallus and the black-chested buzzard-eagle, at least twice as heavy as other Spizaetus and slightly heavier than the notably longer crested eagle. Only the harpy eagle is considerably larger among all neotropical eagles, with most other eagles absent from the high elevation forest home of the black-and-chestnut eagle apart from the solitary eagle. For its genus and for many genera of forest-dwelling raptors in general, it has a proportionately short tail and proportionately long wings but still it is longer tailed and shorter winged than most true open country eagles. Females are notably larger as is typical in raptors, by about 4% to 14%, and longer tailed. The wing chord and tail length is 463 to 488 mm (18.2 to 19.2 in) and 283 to 300 mm (11.1 to 11.8 in) in males, respectively, and 508 to 528 mm (20.0 to 20.8 in) and 329 to 335 mm (13.0 to 13.2 in) in females. A small sample of these eagles measured 110 to 120 mm (4.3 to 4.7 in) in tarsus length. As an adult, this species is glossy black on the head and the back and a rich and somewhat streaky chestnut on the underside, much of the wing secondaries and even on its legs. The black-tipped white feathers on the wing primaries contrast strongly with the chestnut secondaries and underwing coverts. The adult's tail is grayish with a thick black subterminal band. Adult black-and-chestnut eagles have orange-yellow eyes and yellow bare parts but for the somewhat proportionately small gray bill. The juvenile bird is very different, being whitish over the head and body with a buffy wash underneath and scaly grey-brown on the back and mantle, somewhat more extensive than in other whitish juvenile Spizaetus. The wings are whitish on juveniles where adults are chestnut and the remaining wing feathers of the juvenile have a much more varying black-and-white pattern. The tail of juveniles has two strong black bands. The juvenile’s eye is blue-gray, later becoming yellow before becoming orangish at maturity. Maturity is obtained gradually over four years, about average for a large eagle but nearly twice as long as some other Spizaetus species. Adult black-and-chestnut eagles are practically unmistakable, unless seen only dorsally and then can be distinguished from the black hawk-eagle by its larger, much bulkier frame and distinctive tail pattern on a conspicuously relatively shorter tail. Black-and-chestnut juveniles are more reminiscent of juveniles of both other Spizaetus species but are distinctly larger, bulkier and proportionately shorter tailed than both and each species has somewhat distinctive juvenile patterns on the wing primaries and tail. The black-and-white hawk-eagle is particularly far smaller and, unlike the ornate hawk-eagle, is not known to take up occasional residency in cloud forests. Also juvenile pale morph crested eagles can appear surprisingly similar in flight to juvenile black-and-chestnut eagles but are conspicuously longer tailed with a stronger barring pattern. Furthermore, there is little to no overlap with the other species of the genus as well as crested eagles due to the distinct habitat used by the black-and-chestnut. The solitary eagle is unlikely to be mistaken, being much broader winged and lacks all chestnut pigment, furthermore having an almost inverse tail pattern to adult black-and-chestnuts on a rather shorter tail. Unlike other crested raptors, it is reported that the crest of the black-and-chestnut eagle is held upright during calm periods of time and in flight and more likely to be held flat in stressful circumstances.