The Harris’s hawk is a large bird, which weighs around 710g to 1,020g, and is 46cm to 76cm long. Their wingspan can be 100cm to 120cm. The female is usually around 40% bigger in size.
They have dark brown plumage, with chestnut brown shoulders, thighs, and wing linings. There is a white bar along the tips of the tail feathers, used for communication. The legs are long, un-feathered, and yellow in colour. Their legs are long to allow them to perch on plants such as cacti without damaging their body, and to protect from their prey items, and the skin is very tough. The wings are large and broad, as is the tail, used to help soar in thermals.
Its scientific name ‘parabuteo’ means buzzard-like, and ‘unicinctus’ means ‘once girdled’, referring to the belt of white feathers on the end of their tail.
Harris’ hawks are found in various habitats, from upland desert dominated by saguaros to mesquite, palo verde, and ironwood woodlands in the Colorado River valley. There is a population of hawks being reintroduced to the Colorado River that prefer to nest near water in mequite, willows and cottonwoods. In urban areas, they are seen utilizing washes, open lots, and open desert. These hawks may be found at elevations of 400 to 1,000 meters.
Most often, social groups of Harris’ hawks contain a single monogamous breeding pair. However, these hawks are known to practice simultaneous polyandry, where more than one male mates with one female and shares in the responsibilities of raising offspring. Polyandry is commonly found in areas where the habitat quality is rich as opposed to arid habitats where the chances of reproductive success are less, even when there are three adults hunting. It is also found to be common in Arizona where the sex ratio is significantly skewed towards males, in comparison with areas such as Texas, where the sex ratio is not as skewed.
Harris’ hawks build their nests in saguaros, palo verdes and mesquite trees at an average height of 5 meters. In urban areas, nests can be found on cottonwoods, ironwoods, palm trees and electrical towers. Nests are platforms made of sticks, weeds, twigs, and are usually lined with soft mosses, grasses and roots. Between two and four eggs are laid at a time. Females have the ability to breed all year long and can lay two to three clutches within a year. The incubation period lasts about 35 days and the males often share duties with the female during this period. Fledging occurs after another 40 days. The young birds tend to stay around the nest area for two to three months longer.
Harris’ hawks are non-migratory and diurnal. They form complex social groups, which aid in the nesting cycle. Most often these groups are trios consisting of two males and a female, but groups of four or five hawks are not uncommon. There is a strict dominance hierarchy within groups of Harris’ hawks. The breeding, or alpha, female, is dominant to all other hawks in the group. Occasionally there is a second female who is subordinate to the alpha female but dominant to all other males in the group. The breeding, or alpha, male is dominant to all other males in the group. Commonly the group contains a beta male, who may attempt, often unsuccessfully, to mate with the alpha female. Finally, there may be several gamma birds, which are subordinate to the alpha and beta individuals. These gamma birds may be either male or female, and usually they are sexually immature individuals. Often they are the juvenile offspring of the alpha pair. All members of the group help with obtaining food, defending the breeding territory, and providing nest protection. These groups also hunt cooperatively. They are able to depend on much larger prey when hunting in groups. This aspect of group hunting and food sharing increases survival rates for birds as individuals.
The diet of Harris’ hawks is versatile and varies with prey availability. These hawks feed mostly on small mammals such as rats and mice, but also take birds and lizards. They commonly hunt in groups of about five hawks, increasing their success rate and enabling them to take larger prey such as cottontails and jack rabbits. These hunting groups consist of a breeding pair and other helpers, with the female dominating. They are fast flyers and once they have spotted their prey, they land and take turns trying to scare and actually flush the prey animal until it darts from beneath its hiding place. Another member of the hunting group captures the animal and assumes a posture known as mantling, in which the hawk shields the prey with its wings to hide it from other birds. It has been suggested that group hunting is encouraged by the dense brush and thorny nature of their habitat. There is some evidence that these hawks may feed on carrion if food availability is low