Parabuteo unicinctus

Geographic Range

Harris' hawks can be found in semi-open 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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

Habitat

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.

• Habitat Regions
• temperate temperate
• tropical tropical

• Terrestrial Biomes
• desert or dune desert or dune
• savanna or grassland savanna or grassland
• scrub forest scrub forest

• Other Habitat Features
• urban urban
• suburban suburban
• riparian riparian

Physical Description

These are large hawks with long tails and broad wings. Harris's hawks range in length from 18 to 23 inches (46 to 76 cm) and have wingspans of 40 to 47 inches (100 to 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 weigh an average of 1,047 grams, and males are smaller, weighing an average of 735 grams.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• female larger

Reproduction

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.

• Mating System
• monogamous monogamous
• polyandrous polyandrous
• cooperative breeder cooperative breeder

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.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Both the female and the male contribute to parental care. Harris' hawks practice cooperative breeding, with several birds helping with building nests, incubation, feeding, and defense. This assistance increases nest success. There is often a trio consisting of two males and a female which aid in the nest cycle.

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

Records on longevity are collected from the Bird Banding Laboratory (BBL) in Laurel, Maryland. The maximum longevity record for Harris' hawks is 14 years, 11 months.

Behavior

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.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• sedentary sedentary
• territorial territorial
• social social

Home Range

Harris' hawks establish and defend territories that range from 0.2 to 5.5 square kilometers in size. Territory size depends on the availability of food and other resources.

Communication and Perception

Like all hawks, Harris' hawks have keen vision and hearing. They are known to make hissing noises, give alarm calls, and probably communicate visually as well.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical

Food Habits

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.

• Primary Diet
• carnivore carnivore
  • eats terrestrial vertebrates

• Animal Foods
• birds
• mammals
• reptiles

Predation

Great horned owls ( Bubo virginianus ) pose the greatest predation threat to this species, but coyotes ( Canis latrans ) and common ravens ( Corvus corax ) also threaten young hawks. Female Harris' hawks utilize helpers to protect their nests. The helpers perch in saguaros and scan the surroundings for predators. They tend to become excited and will use an alarm call when predators come within their nesting area. Groups consisting of 2 to 5 hawks will attack and harass any predator 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.

Ecosystem Roles

Harris' hawks are important predators in their ecosystem, controlling populations of many small mammal species.

Economic Importance for Humans: Positive

Harris' hawks are of great benefit to farmers whose crops are destroyed by rodents. These hawks feed primarily on small rodents such as mice and rats and therefore alleviate a lot of destruction to crops.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

The only negative impact of these hawks is their habit of congregating on electrical transformers, where they are often electrocuted. 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 of hawks.

Conservation Status

Harris's Hawks are not listed as threatened or endangered. They are included in CITES appendix II and 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. Shooting can result in nest failure, abandonment and mortality. Electrocution is responsible for the loss of half of the population of breeding hawks. 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.

Additional Links

Encyclopedia of Life

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Mary Truglio (author), University of Arizona, Jay Taylor (editor), University of Arizona.

References

Bednarz, J., J. David. 1988. A Study of the Ecological Basis of Cooperative Breeding in the Harris' Hawk. Ecology , 69(4): 1176-1187.

Coulson, J., T. Coulson. 1995. Group Hunting by Harris' Hawks in Texas. Journal of Raptor Research , 29(4): 265-267.

Dawson, J., R. Mannan. 1991. Dominance Hierarchies and Helper Contribution in Harris' Hawks. Auk , 108(3): 649-660.

Driscoll, J. 2000. "AZGF Nongame Field Notes - Harris' Hawk (Parabuteo unicinctus)" (On-line). Accessed March 27, 2002 at http://www.gf.state.az.us/w_c/nongame_harris_hawk.shtml .

Johnsgard, P. 1990. Hawks, Eagles, and Falcons of North America . Washington and London: Smithsonian Institution Press.

Klimkiewicz, M. 2002. "Longevity Records of North American Birds" (On-line). Accessed April 18, 2002 at http://www.pwrc.usgs.gov/bbl/homepage/long2890.htm .

Thomas, A., C. Gates. 1998. "North American Raptors: Harris' Hawk" (On-line). Accessed March 27, 2002 at http://library.thinkquest.org/18166/harris'_hawk.html .

Whaley, W. 1986. Population Ecology of the Harris' Hawk in Arizona. Journal of Raptor Research , 20(1): 1-15.

Wheeler, B., W. Clark. 1996. North American Raptors . New York: Academic Press.