Identification

The Black Falcon is a medium-sized dark raptor and medium-large Falco, distinctively broader-winged than most congeners, and with a comparatively long, rather square-ended tail (length 45–56 cm; wingspan 97–115 cm; male mass 481–650 g, female mass 710–950 g). Measurements and descriptions are from Marchant and Higgins (1 Marchant, S., and P. J. Higgins, Editors (1993). Handbook of Australian, New Zealand and Antarctic Birds, Volume 2: Raptors to Lapwings. Oxford University Press, Melbourne, VIC, Australia. Close ), Debus (2 Debus, S. (2019). Birds of Prey of Australia, A Field Guide. Third edition. CSIRO Publishing, Melbourne, VIC, Australia. Close , 3 Debus, S. (2022). Australian Falcons: Ecology, Behaviour and Conservation. CSIRO Publishing, Melbourne, VIC, Australia. Close ), and Seaton et al. (4 Seaton, R., M. Gilfedder, and S. Debus (2019). Australian Birds of Prey in Flight, A Photographic Guide. CSIRO Publishing, Melbourne, VIC, Australia. Close ). Plumage changes slightly with age.

Adults (> 1 yr) are medium to dark chocolate-brown overall, sometimes with a slight grayish bloom or cast, and have an indistinct and thin dark malar stripe offset against a paler face; they often have a white chin, buff forehead and cheeks, finely barred underwings and undertail, and occasionally a pale-speckled breast. The extent of pale plumage highlights increases with age, up to at least 5 years (1 Marchant, S., and P. J. Higgins, Editors (1993). Handbook of Australian, New Zealand and Antarctic Birds, Volume 2: Raptors to Lapwings. Oxford University Press, Melbourne, VIC, Australia. Close ). The existence of an alleged rare sooty-gray morph has been questioned (5 Debus, S. J. S., and J. Olsen (2011). Some aspects of the biology of the Black Falcon Falco subniger. Corella 35:29–36. Close , 3 Debus, S. (2022). Australian Falcons: Ecology, Behaviour and Conservation. CSIRO Publishing, Melbourne, VIC, Australia. Close ). The bill is blue-gray and tipped black, the cere and orbital rings are pale gray, the irides are dark brown, and the feet are pale gray. Rarely, in the more speckled and barred individuals, the cere, orbital rings, and feet may be yellow (6 MacColl, C. and S. J. S. Debus (2022). Morphological variation in the Black Falcon Falco subniger. Australian Field Ornithology 39: 214–219. Close ). The sexes are similar, although females are slightly (5–14%) larger and considerably heavier. Juveniles (0–1 yr) are similar to adults, but in fresh plumage are darker sooty-brown, with rufous fringes to the dorsal plumage and sometimes pale fringes to the ventral plumage, and a pale tip to the tail; they also usually lack a pale forehead and cheeks and sometimes the pale barring under the wings or tail. They have a brown cere, which turns gray then pale blue-gray through the year, pale blue to pale blue-gray orbital skin, and pale olive-gray to pale blue-gray feet. Plumages are the same throughout the year, although fresh plumage gradually wears and fades. Juveniles are distinguishable from their parents by direct comparison and by molt stage (in flight), as they have complete flight and tail feathers from late spring to early autumn when adults are replacing theirs.

Distinguished from other Australian falcons, and other Australian raptors, by a combination of size, plumage, structure, and flight behavior. The Black Falcon is most likely to be confused with the darkest individuals of the Brown Falcon (Falco berigora).

Black Falcon is distinguished from a dark Brown Falcon by its more uniformly dark plumage, white chin, minimal (and finer) to no underwing and undertail barring, more powerful "square" shoulders, smaller head, short legs hidden by long thigh feathers, and larger feet (longer toes). The darkest Brown Falcon has conspicuous and broader pale barring in the wings and tail, producing a distinctly two-toned underwing; Brown Falcon also perches more upright with a "pot-bellied" profile on long legs, with more rounded shoulders, short thigh feathers, and shorter toes. The juvenile Peregrine Falcon (Falco peregrinus), of the Australian subspecies macropus, is distinctly more chunky in build than the sleek Black Falcon, and has pale underparts that are heavily streaked with dark brown. The Black Kite (Milvus migrans) has a pale carpal bar on the upperwings, "fingered" primaries in flight, a forked tail, barred wings and tail, and yellow bare parts. The juvenile Swamp Harrier (Circus approximans) has conspicuously long yellow legs, pale primaries on the underwings, a pale rump, and blunt wings that are held in a dihedral when gliding. At a distance in direct, non-hunting flight, Black Falcon may be confused with crows or ravens (Corvus spp.), but has more pointed wings and lacks the long bill.

In flight, Black Falcon is distinguished from Brown Falcon by its more rapid, shallow and short-amplitude (peregrine-like) flight action, sharply pointed wingtips, darker underwings, squarer and "stepped" tail tip (outermost rectrix noticeably shorter than the rest), toes not reaching the tips of the undertail coverts, and flat to slightly drooped wings when soaring or gliding. It lacks the Brown Falcon's "heavy" (greater amplitude), slower, and sometimes erratic flight action, blunt wingtips, two-toned (barred) underwings, rounded and often fanned tail, toes reaching the tips of the undertail coverts, and wings raised in a dihedral when soaring and gliding.

Black Falcon is mostly silent away from the nest, but has a Peregrine Falcon-like but more subdued, guttural, and measured cackling call; a creaking call that may be disyllabic or a more extended rattle; and a begging whine or lower, softer moan (see Vocalizations). Brown Falcon is much more vocal, commonly uttering raucous shrieking, cackling, and clucking calls.