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.Beebe, Frank (1984). A Falconry Manual. Hancock House Publishers, , page 81.
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, Antenor Ridgeway Nov. subgen. is on page 63. and introduced the generic name Parabuteo On page 248 , the heading is "Genus Antenor Ridgway", but the subspecies heading is "Parabuteo unicinctus var. harisii (Ridgway)". 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: Image Subspecies DistributionHarris's hawk (P. u. harrisi)Southwestern United States, Mexico, much of Central America, and western South America south to western Peru.Bay-winged hawk (P. u. unicinctus) Eastern and southern South America. 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.Blake, Ferguson-Lees and Christie cited in Birds of the world "Parabuteo unicinctrus" https://birdsoftheworld.org/bow/species/hrshaw/cur/systematics#subsp 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. Olmos Fábio & Robson Silva e Silva (2003). Guará-Ambiente, Flora e Fauna dos Manguezais de Santos-Cubatão Empresa das Artes, 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).Bednarz, J. C. and J. D. Ligon. (1988). A study of the ecological bases of cooperative breeding in the Harris' hawk. Ecology 69:1176–1187.
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 and generally have a wingspan of about .Clark, W. S. and B. K. Wheeler (1987). A Field Guide to Hawks of North America. Houghton Mifflin Co. Boston. 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 , with a range of , while the adult female average is , with a range of .Hamerstrom, F. (1978). "External sex characters of Harris' Hawks in winter". Raptor Res. 12:1–14. 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.Dawson, J. W. and R. W. Mannan. (1991). The role of territoriality in the social organization of Harris' hawks. Auk 108:661–672. No other bird of prey is known to hunt in groups as routinely as this species.Griffin, C. R. (1976). A preliminary comparison of Texas and Arizona Harris' Hawks (Parabuteo unicinctus) populations. Raptor Res. 10:50–54.
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
They nest in small trees, shrubby growth, or cacti. The nests are often compact, made of sticks, plant roots, and stems and are often lined with leaves, moss, bark, and plant roots. They are built mainly by the female. There are usually two to four white to blueish-white eggs sometimes with a speckling of pale brown or gray. The nestlings start light buff, but in five to six days turn a rich brown.
Very often, there will be three hawks attending one nest. This may include two males and one female. Whether or not this is polyandry is debated, as it may be confused with backstanding (one bird standing on another's back). Alternatively, they may consist of one male and two females. The non-breeding third bird acts as a helper for the pair, assisting with capturing prey, feeding chicks, and guarding chicks. The female does most of the incubation. The eggs hatch in 31 to 36 days. The young begin to explore outside the nest at 38 days, and fledge, or start to fly, at 45 to 50 days. The female sometimes breeds two or three times in a year. Young may stay with their parents for up to three years, helping to raise later broods. Nests are known to be predated by coyotes (Canis latrans), golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), great horned owls (Bubo virginianus), and flocks of common ravens (Corvus corax), predators possibly too formidable to be fully displaced by Harris's hawk's cooperative nest defenses. No accounts show predation on adults in the United States and Harris's hawk may be considered an apex predator, although presumably predators like eagles and great horned owls would be capable of killing them.Dawson, J. W. and R. W. Mannan. (1991). Dominance hierarchies and helper contributions in Harris' Hawks. Auk 108:649–660. In Chile, black-chested buzzard-eagles (Geranoaetus melanoleucus) are likely predators.Jiménez, J. E., & Jaksić, F. M. (1989). Behavioral ecology of grey eagle-buzzards, Geranoaetus melanoleucus, in central Chile. Condor 913–921.
The subspecies P. u. unicinctus breeds year-round, and reaches its "definitive" plumage after 4 annual moults (≥ 45 months). Young birds have a heavily streaked pattern across the body. This streaking pattern reduces with each moult, until moulting into the definitive plumage, at which point the body becomes uniformly dark in colour with minimal patterning.
Feeding The majority of Harris's hawks' prey are mammals, including ground squirrels, rabbits, and larger black-tailed jackrabbits (Lepus californicus). Birds from the size of small passerines such as diuca finch (Diuca diuca) to adult great egret (Ardea alba) and half-grown wild turkey (Meleagris gallopavo) can be taken.Ferguson-Lees, James, and David A. Christie. Raptors of the world. Houghton Mifflin Harcourt, 2001.Santander, Francisco J., et al. "Prey of the Harris' Hawk (Parabuteo unicinctus) during fall and winter in a coastal area of central Chile". The Southwestern Naturalist (2011): 417-422.Houcke, H.H. (1971). Predation By a White-tailed Hawk and a Harris' Hawk on a Wild Turkey Poult. Condor 4: 475. In one instance, a lone Harris's hawk successfully killed a subadult great blue heron (Ardea herodias).Woodward, H.D. (2003). Lone Harris' Hawk Kills Great Blue Heron. The Raptor Research Foundation 1:85–86. Reptiles such as lizards and snakes are additionally taken as well as large insects.
When hunting in groups, Harris's hawk can take large prey effectively, such as desert cottontail (Sylvilagus auduboni), the leading prey species in the north of Harris's hawk's range, usually weighing or less.Bednarz, J. C. (1988). A comparative study of the breeding ecology of Harris's and Swainson's hawks in southeastern New Mexico. Condor 90:311–323.Bednarz, J. C., J. W. Dawson, and W. H. Whaley. (1988). Harris' Hawk. Pages 71–82 in Proceedings of the southwest raptor management symposium and workshop. (Glinski, R. L., B. G. Pendleton, M. B. Moss, M. N. LeFranc, Jr., B. A. Millsap, and S. W. Hoffman, Eds.) Natl. Wildl. Fed. Washington, D.C. Even adult black-tailed jackrabbits weighing more than can be successfully taken by a pack of Harris's hawks.Coulson, Jennifer O., and Thomas D. Coulson. "Reexamining cooperative hunting in Harris's Hawk (Parabuteo unicinctus): large prey or challenging habitats?." The Auk 130.3 (2013): 548-552.