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Parabuteo unicinctusHarris's hawk

By Mary Truglio

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. (Johnsgard, 1990)

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. (Driscoll, 2000; Johnsgard, 1990)

  • Range elevation
    400 to 1,000 m
    1312.34 to ft

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. (Driscoll, 2000; Thomas and Gates, 1998; Wheeler and Clark, 1996)

  • Sexual Dimorphism
  • female larger
  • Range mass
    735 to 1047 g
    25.90 to 36.90 oz
  • Range length
    46 to 76 cm
    18.11 to 29.92 in
  • Range wingspan
    100 to 120 cm
    39.37 to 47.24 in

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. (Johnsgard, 1990)

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. (Driscoll, 2000; Johnsgard, 1990; Thomas and Gates, 1998)

  • Breeding interval
    Harris' hawks breed two to three times per year.
  • Breeding season
    Harris' hawks breed year round.
  • Range eggs per season
    3 to 15
  • Average eggs per season
    6
  • Average eggs per season
    3
    AnAge
  • Range time to hatching
    33 to 37 days
  • Range fledging age
    35 to 45 days
  • Average time to independence
    2-3 months

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. (Driscoll, 2000; Johnsgard, 1990; Thomas and Gates, 1998)

  • 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. (Klimkiewicz, 2002)

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. (Bednarz and David, 1988; Coulson and Coulson, 1995; Dawson and Mannan, 1991; Thomas and Gates, 1998)

  • Range territory size
    0.2 to 5.5 km^2

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.

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. (Bednarz and David, 1988; Coulson and Coulson, 1995; Johnsgard, 1990)

  • Primary Diet
  • 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. (Dawson and Mannan, 1991)

Ecosystem Roles

Harris' hawks are important predators in their ecosystem, controlling populations of many small mammal species. (Coulson and Coulson, 1995)

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. (Coulson and Coulson, 1995)

  • 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. (Driscoll, 2000)

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. (Johnsgard, 1990; Whaley, 1986)

Contributors

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

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

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cooperative breeder

helpers provide assistance in raising young that are not their own

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

fertilization

union of egg and spermatozoan

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polyandrous

Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scrub forest

scrub forests develop in areas that experience dry seasons.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

suburban

living in residential areas on the outskirts of large cities or towns.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

urban

living in cities and large towns, landscapes dominated by human structures and activity.

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

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.

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