Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • 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. (Driscoll, 2000; Johns­gard, 1990)

• Habitat Regions
• temperate
• tropical

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

• Other Habitat Features
• urban
• suburban
• riparian

• 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)

• Other Physical Features
• endothermic
• bilateral symmetry

• 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)

• Mating System
• monogamous
• polyandrous
• 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. (Driscoll, 2000; Johns­gard, 1990; Thomas and Gates, 1998)

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

• 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)

• Range lifespan
  Status: wild

  14.9 (high) years

• Average lifespan
  Status: wild

  179 months

  Bird Banding Laboratory

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)

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

• 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.

• Communication Channels
• visual
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• 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. (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)

• Known Predators

  • great horned owls (Bubo virginianus)
  • coyotes (Canis latrans)
  • common ravens (Corvus corax)

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)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Migratory Bird Act

  Protected

• US Federal List

  No special status

• CITES

  Appendix II

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.