The adult Great Black Hawk is almost entirely black, with long yellow tarsi. The tail is mostly black with a broad white median band (ridgwayi, the northern subspecies), or has a broad white basal half and a broad black distal half (urubitinga, the southern subspecies); but in all populations, when seen from below in flight the tail often gives the impression of being black with just one white tail band, due to the black undertail coverts. The upper tailcoverts are white. The bill is all black (ridgwayi) or black with a pale base (urubitinga), the cere is yellow, and the lores are whitish (ridgwayi) or tinged yellow (urubitinga). In flight, the long tarsi cross the white tail band. When perched, the wingtips fall well short of the tip of the tail. In the northern subspecies ridgwayi, the adult has white barring on the leggings (tarsal feathering). The immature is brown above and creamy buff below, with dusky streaks. The head and neck also are creamy buff, streaked on the crown and nape with dusky, but with no dusky lateral throat stripe.
Two congeners, Common Black Hawk (Buteogallus anthracinus) and Solitary Eagle (Buteogallus solitarius), are similar; field identification is more problematic in Central America, where all three species occur. Where sympatric, distinguishing characters between Great Black Hawk and Common Black Hawk are consistent, but where not sympatric, many Great Black Hawks show characters that are shared with Common Black Hawk, such as a yellowish tinge on lores and pale base to the bill. Common Black Hawk is smaller than Great Black Hawk, has a pale base to the bill (either bluish gray or yellowish), and has yellow lores (the lores typically are whitish or pale grayish in the northern subspecies of Great Black Hawk). Common Black Hawk has shorter tarsi: on the adult in flight, the tarsi barely reach the white tail band. Seen from below, adult Common Black Hawk in flight has white slashes on the base of the outer primaries, absent in Great Black Hawk. The undersurface of the wing of Common Black Hawk often shows a distinct black terminal band, contrasting with paler bases to the remiges; this band is narrower and less contrasting on Great Black Hawk. Seen from above, adult Common Black Hawk has dark uppertail coverts (white on Great Black Hawk). On the perched adult Common Black Hawk, the wing tips almost reach the tip of the tail (but the tail of Great Black Hawk extends much farther past the wing tips). Juvenile Common Black Hawk usually has a dark lateral throat stripe, which typically is absent in immature Great Black Hawks.
Solitary Eagle is larger than Great Black Hawk, with a proportionally shorter tail, and a wider wing base, creating a triangular silhouette never shown by Great Black Hawk. In southern part of the range, adult Solitary Eagle is paler gray than Great Black Hawk. Note that in South America, Great Black Hawk shows mostly white tail with black subterminal band, a feature not shown by any other large black raptor in that part of the range.
See also van Dort (2018) for an identification review of the three Buteogallus hawks in Central America.
Large hawk (see Measurements).
Adult: Head, body, and wing and undertail coverts are slate gray. Remiges with paler gray banding and a darker terminal band. In northern subspecies (ridgwayi) leggings are barred white (depending on the posture, not always visible), and the bill is entirely black (base of bill paler in subspecies urubitinga and in Common Black Hawk Buteogallus anthracinus). The uppertail coverts are white. Tail pattern differs between ridgwayi and nominate urubitinga, with the latter showing a white tail with one subterminal black band, while the tail of ridgwayi has two black bands (from below, looks black with a single with tail band). Size dimorphism slight, with females slightly larger than males (Gerhardt et al. 2012; see also Measurements). Nominate subspecies slightly larger than ridgwayi, and within populations of urubitinga, more southerly populations in temperate zones slightly larger than those closer to the equator (Gerhardt et al. 2012). Adult Common Black Hawks can usually be sexed based on the female's pale gray cheek; this cue does not apply to Great Black Hawk.
Juvenile: Pale buffy with dark markings behind eye, on breast, and on rest of under parts; malar region typically pale. Tail buffy with fine brown barring, also longer than tail of adult. In flight, shows obvious pale panels in primaries, as does juvenile Common Black Hawk.
Basic II: Similar to juvenile, but tail white with coarser black barring. In flight, note contrast between pale outer primaries and slightly darker inner primaries, and between darker basic II secondaries amid retained juvenile secondaries.
Complete annual molt of body, coverts and tail feathers, but not all primaries and secondaries replaced annually, resulting in staffelmauser molt patterns. Juveniles start molting into basic II plumage at around nine months of age (Clark and Schmitt 2017). Dickey and van Rossem (1938) suggested that "more than two years are necessary to reach maturity", but Clark and Schmitt recognize only two plumages before the definitive.
In ridgwayi, the irides are dull amber in younger birds, and dark brown to reddish brown in adults; adult urubitinga has irides from dark brown to reddish brown to deep red (Friedmann 1950). The bill is entirely black in ridgwayi, and black with a pale base in urubitinga. The cere is yellow. The lores are pale gray (ridgwayi) to tinged yellow (urubitinga), although some sources mention dark lores for ridgwayi (e.g. Dickey and van Rossem 1938, Ridgely and Gwynne 1989, Gerhardt et al. 2012). The long tarsi and toes are yellow, with black talons.
Total length: 51-61 cm (Howell and Webb 1995), 55–65 cm (Clark and Schmitt 2017); wingspan 115–130 cm (Clark and Schmitt 2017), 120-137 cm (Howell and Webb 1995)
Linear measurements: (from Friedmann 1950)
male (n = 11; specimens from Mexico, Belize, Honduras, Costa Rica, and Panama)
wing length: mean 376.4 mm (range 367-403 mm)
tail length: mean 243.3 mm (226-274 mm)
bill length (culmen from cere): mean 28.8 mm (range 26-31 mm)
tarsus length: mean 116.4 mm (range 112-126 mm)
length of middle toe, without claw: mean 47.2 (range 44.5-49 mm)
female (n = 7; specimens from Mexico, Honduras, and Costa Rica)
wing length: mean 388.8 mm (range 363-417 mm)
tail length: mean 248.5 mm (237-270 mm)
bill length (culmen from cere): mean 30.3 mm (range 29-32 mm)
tarsus length: mean 116.4 mm (range 108-127 mm)
length of middle toe, without claw: mean 48.3 (range 45-50 mm)
male (n = 5; specimens from Panama, Colombia, Brazil, Suriname, and Ecuador)
wing length: mean 391 mm (range 377-400 mm)
tail length: mean 244.6 mm (232-256 mm)
bill length (culmen from cere): mean 31.6 mm (range 30-33.5 mm)
tarsus length: mean 117.4 mm (range 114-128 mm)
length of middle toe, without claw: mean 50.5 (range 49-52.5 mm)
female (n = 4; specimens from Brazil and Suriname)
wing length: mean 409.5 mm (range 383-428 mm)
tail length: mean 251 mm (240.5-261 mm)
bill length (culmen from cere): mean 32 mm (range 30-34 mm)
tarsus length: mean 123.5 mm (range 119-128 mm)
length of middle toe, without claw: mean 50.5 (range 49-52.5 mm)
ridgwayi: male, 853.6 g, 996 g (Mexico, Belize; Paynter 1955, Russell 1962); female, 965.4 g, 1156 g (Mexico, Belize; Paynter 1955, Russell 1962); unsexed, 1197 g (Belize; Russell 1962)
urubitinga: male, 1250 g, 1306 g (Suriname; Haverschmidt 1962); male, 965-1306 g (n = ?, Suriname; Haverschmidt 1968); female, 1355-1560 g (n = ?, Suriname; Haverschmidt 1968)
subspecies?: range 960-1400 g (n = ?; Clark and Schmitt 2017)