The Harris's Hawk can be found in semiopen habitats in the southwestern United States and northwestern Mexico, from Baja California, to southern Arizona, New Mexico and Texas, extending south through Central and South America to Chile and just into Patagonia (Johnsgard, 1990).
This is a large hawk with a long tail and broad wings. Harris's Hawk ranges in size from 18 to 23 inches (46-76 cm) in length and has a wingpan of 40 to 47 inches (100-120 cm). Adult plumage is uniformly chocolate brown with distinct reddish shoulders, upper and underwing coverts, and leg feathers. The tail is dark with white upper and undertail coverts and a white base and terminal band. Juveniles are similar to adults but are less distinctly colored and have a white belly with chocolate brown streaking. The tarsal feathers are pale with reddish barring and there is barring on the tail and wings. Females are larger than males, weighing an average of 1,047 grams and 735 grams, respectively (Driscoll, 2000; Thomas, 1998; Wheeler, 1996).
Mass: 735 to 1047 g
Length: 46 to 76 cm
Wingspan: 100 to 120 cm
female larger; bilateral symmetry
Records on longevity are collected from the Bird Banding Laboratory (BBL) in Laurel, Maryland. The maximum longevity record for the Harris' Hawk is 14 years, 11 months (Klimkiewicz, 2002).
Max Lifespan In Wild: 14.9 years (max)
Harris's Hawks utilize helpers to protect their nests from predators. They harass any animals threatening their nest and the young. They tend to become excited and will use an alarm call when predators come within their nesting area. Saguaros are used for perching to detect predators. The greatest threat to this species is the Great Horned Owl (Bubo virginianus). Groups consisting of 2-5 hawks will attack and harass an owl threatening the nest. The alpha male is most likely to strike the predator as the female stays behind to protect the nest. This establishment of helpers greatly increases the detection of predators and nest success (Dawson, 1991).Predators:
Harris's Hawks contribute to the ecosystem by controlling pest populations and the destruction of crops (Coulson, 1995).
The diet of the Harris's Hawk is versatile and varies with prey availability. These hawks feed mostly on small mammals such as rats and mice, but also takes birds and lizards. They commonly hunt in groups of about 5 hawks, increasing their success rate and enabling them to take larger prey such as cottontails and jack rabbits. These hunting groups consist of a 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. There is another member of the hunting group to capture the animal and to assume a posture known as mantling where they actually shield the prey with their wings to hide it. 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 (Coulson, 1995; Johnsgard, 1990; Bednarz, 1988).
The Harris's Hawk builds its nest 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 between late February and March. Females have the ability to breed all year long and can lay two to three clutches within a year. The incubation period takes 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. These hawks have been known to have several mates at a time. Harris's Hawks practice cooperative breeding, with family members helping with building nests, incubation, feeding, and defending the nest. This assistance increases nest success (Driscoll, 2000; Johnsgard, 1990; Thomas, 1998).
Number Produced: 3-5 to 9-15
Gestation Period: 33 to 37 days
Weaning: 35 to 45 days
These hawks are known to practice simultaneous polyandry. This is commonly found in areas where the habitat quality is rich as opposed to arid habitats where the chances of reproductive success is less, even when there are three hunting. It is also found to be common in Arizona where there is a significant amount of males contributing to the sex ratio, in comparison with areas such as Texas, where the sex ratio is not as skewed (Johnsgard, 1990).
Monogamous; polyandrous; cooperative breeder
Both the female and the male contribute to parental care. There is often a trio consisting of two males and a female which aid in the nest cycle (Johnsgard, 1990).
Male parental care; female parental care
The Harris's Hawk practices simultaneous polyandry. They form groups which aid in the nesting cycle. Most commonly these groups are trios are consisting of two males and a female; both males help with obtaining food and feeding the nestlings and provide nest protection. These groups also practice cooperative feeding. 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 (Johnsgard, 1990).
Harris's 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 (Johnsgard, 1990; Driscoll, 2000).Elevation: 400 to 1,000 m
The Harris's Hawk is of great benefit to farmers whose crops are destroyed by rodents. These hawks feed primarily on small rodents such as mice and rats and will alleviate a lot of destruction to crops (Coulson, 1995).
Controls pest population
The only negative aspect of these hawks is their habit of congregating on electrical transformers. This has become a great cost to electric companies who are being forced to reinsulate and, in some cases, build arms for perching to reduce the mortality rates (Driscoll, 2000).
Harris's Hawks are not listed as threatened or endangered, nor are they included on the list of Wildlife of Special Concern. However, they are protected from harassment and illegal shooting by the Migratory Bird Treaty Act. A population on the Colorado River is thought to have been extirpated due to their dependence on a riparian community which was altered by dam construction and disturbance from dredging as well as nest destruction. Real estate and agriculture threaten the species in Arizona. Recent declines in Texas populations resulted from the clearing of mesquite for agriculture and livestock grazing. Habitat loss is the major cause of decline of this species as well as excessive human disturbance. It is possible in areas such as Arizona for birds to live in cities where the native vegetation is protected, houses are spread apart and there is not an overabundant amount of asphalt and concrete. The status of these hawks is also threatened by the increase in falconry. Shooting can result in nest failure, abandonment and mortality. Electrocution is responsible for the loss of half of the population of breeding hawks. Electric companies need to contribute by insulating poles, wires and transformers to reduce mortality rate (Whaley, 1986; Johnsgard, 1990).