Parabuteo unicinctus is a medium-large bird of prey that breeds from the southwestern United States south to Chile, central Argentina, and Brazil. It contains two subspecies, the Harris's hawk (P. u. harrisi) and the bay-winged hawk (P. u. unicinctus). The species is also occasionally referred to as the dusky hawk and known in Latin America as the peuco. Harris's hawk is notable for its behavior of hunting cooperatively in packs consisting of tolerant groups, while other raptors often hunt alone. Harris's hawks' social nature has been attributed to their intelligence, which makes them easy to train and has made them a popular bird for use in falconry.
Etymology The name is derived from the Greek para, meaning beside, near or like, and the Latin buteo, referring to a kind of buzzard; uni meaning once; and cinctus meaning girdled, referring to the white band at the tip of the tail. John James Audubon gave this bird its English name in honor of his ornithological companion, financial supporter, and friend Edward Harris.
Taxonomy Robert Ridgway placed Harris's hawk in its own new subgenus Urubitinga (Antenor) in 1873, and introduced the generic name Parabuteo in 1874. Richard Bowdler Sharpe also separated Harris's hawk to a monotypic genus, Erythrocnema, in 1874. In his Catalogue of Birds in the British Museum, Sharpe gives an extensive synonymy, with various authors having earlier placed P. u. harrisi in three genera and P. u. unicinctus in eleven.
Subspecies There are two subspecies of Harris's hawk:
The range of the two subspecies overlap in northern South America, coexisting as far south as Peru. It is unknown if they interbreed where they coexist. P. u. unicinctus is smaller than the northern subspecies, with proportionately longer tail and wings, and the adult's dark brown ventrum is streaked or flecked with white or whitish. Additionally, the wing underside of fully mature P. u. harrisi is completely dark in colour, while that of fully mature P. u. unicinctus is patterned and lighter in colour. The species has a white band at both the base of the tail and edge of the tail. These white bands are broader in P. u. harrisi. A recent suggestion to raise these subspecies to species status was rejected by the South American Classification Committee, as the current body of knowledge of the subspecies' relation to each other was considered insufficient. A third subspecies P. u. superior sometimes accepted in the past in the northwest of the species' range (Arizona to Baja California) was believed to have longer tails and wings and to be more blackish than P. u. harrisi; however, the sample size of the original study was quite small, with only five males and six females. Later research concluded that there is not as strong a physical difference as was originally assumed. Other ecological differences, and evidence of a latitudinal cline, were also brought up as arguments against the validity of the subspecies segmentation.
Distribution and habitat Harris's hawks live in sparse woodland and semi-desert, as well as marshes (with some trees) in some parts of their range (Howell and Webb 1995), including mangrove swamps, as in parts of their South American range. Harris's hawks are permanent residents and do not migrate. Important perches and nest supports are provided by scattered larger trees or other features (e.g., utility poles, woodland edges, standing dead trees, live trees, boulders, and saguaros). The wild Harris's hawk population is declining due to habitat loss; however, under some circumstances, they have been known to move into developed areas.
Description
This medium-large hawk is roughly intermediate in size between a peregrine falcon (Falco peregrinus) and a red-tailed hawk (Buteo jamaicensis). Harris's hawks range in length from 46 to 59 cm (18 to 23 in) and generally have a wingspan of about 103 to 120 cm (41 to 47 in). These hawks have a brownish plumage, reddish shoulders, and tail feathers with a white base and white tip. They exhibit sexual dimorphism with the females being larger by about 35%. In the United States, the average weight for adult males is about 701 g (1.545 lb), with a range of 546 to 850 g (1.204 to 1.874 lb), while the adult female average is 1,029 g (2.269 lb), with a range of 766 to 1,633 g (1.689 to 3.600 lb). They have dark brown plumage with chestnut shoulders, wing linings, and thighs, white on the base and tip of the tail, long, yellow legs, and a yellow cere. The vocalizations of Harris's hawk are very harsh sounds. The lifespan of Harris's hawk is 10–12 years in the wild, though up to 25 years has been recorded in captivity.
Juvenile
The juvenile Harris's hawk is heavily streaked with white or buff on the underparts, and appears much lighter than the solidly dark-breasted dark adults. When in flight, the undersides of the juveniles' wings are buff-colored with brown streaking, and the primary feathers are whitish except at their tips, giving a pale panel on the outer wing; the tail band is also paler than on adults. They can look very unlike adults at first glance, but the identical chestnut plumage is an aid for identification.
Behavior
This species occurs in relatively stable groups. A dominance hierarchy occurs in Harris's hawks, wherein the mature female is the dominant bird, followed by the adult male and then the young of previous years. Groups typically include from two to seven birds. Not only do birds cooperate in hunting, but they also assist in the nesting process. No other bird of prey is known to hunt in groups as routinely as this species. Social behaviour is most well documented in the northern subspecies P. u. harrisi. Individuals tend to be larger with more pronounced social behaviours in the southwestern U.S., where environmental conditions are harsher, than in the southeastern U.S. P. u. unicinctus was once thought to be significantly less social than the northern subspecies, but increasing records of social behaviour in the subspecies since the late 1990s suggests a greater extent of sociality in the subspecies than previously recognized.
Breeding
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