Harris's Hawk Life History

Habitat

Habitat Scrub

Harris's Hawks live in semiopen desert lowlands—often among mesquite, saguaro, and organ pipe cactus—and in some savannah and wetland habitats. Territories include high perches such as trees, boulders, and power poles, which the birds use as lookouts, feeding platforms, and for nesting. Access to water is important in hot environments, and birds generally choose areas that include water features such as springs, water catchments and cattle tanks. As development has expanded and human persecution of hawks has declined, Harris's Hawks have moved into urban and suburban areas throughout their range.

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Food

Food Mammals

Harris's Hawks feed mostly on medium-sized mammals such as hares, rabbits, ground squirrels, and other rodents. They may also take quail, medium-sized birds, and reptiles. Individuals in a group of hawks often take turns eating downed prey. They may cache prey in trees to be eaten later. Groups of Harris's Hawks sometimes defend larger carcasses against interlopers who would take the prey for themselves.

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Nesting

Nest Placement

Nest Tree

Nests are located in almost any relatively tall, sturdy structure, including native saguaro cactus, mesquite trees, cliffs, and introduced trees such as palm, eucalyptus and pine. Nests may also be found on artificial structures such as electrical transmission towers, weather antenna, windmill platforms, and artificial nesting platforms.

Nest Description

Nest are bulky structures made up of sticks and parts of cactus, and lined with the same as well as grass, feathers, and down. The breeding pair constructs the nest, with the bulk of the work done by the female. Material may be added throughout the nesting season. Nests can sometimes take on an elliptical shape and are from 18 to 24 inches across, and about 9 inches deep. The inner cup measures about 6 to 14 inches in diameter and 1 to 4 inches deep. More than one nest may be constructed or repaired in a given year, and unused sites are often turned into feeding platforms. Only the breeding female has a brood patch and she does most of the incubation, brooding, and shading of the eggs and nestlings. Other members of the group deliver prey. Depending on available prey, Harris's Hawk may have more than one brood per year.

Nesting Facts
Clutch Size:1-5 eggs
Egg Length:2.2-2.3 in (5.5-5.8 cm)
Egg Width:1.6-1.7 in (4.2-4.4 cm)
Incubation Period:31-36 days
Nestling Period:44-48 days
Egg Description:Very pale bluish that fades to white, may have a few pale brown or lavender spots.
Condition at Hatching:Helpless and covered in cinnamon colored down.
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Behavior

Behavior Aerial Dive (ground/talons)

Harris's Hawks are highly social raptors, often found in groups with complex social hierarchies that engage in cooperative hunting and breeding. Groups can consist of up to seven individuals, including both related and unrelated adults of different ages. These birds may help a monogamous breeding couple, or the group may include multiple breeders. These gregarious hawks employ some of the most sophisticated cooperative hunting strategies known in birds, and they feed according to dominance hierarchies within the group. Group members perch in tight proximity, and territories are occupied and defended year-round. Aggressive encounters are infrequent and relatively benign between members of a group, usually taking the form of foot grabbing. A hawk may display aggression by holding its body level to the ground, drooping its wings, and raising the feathers on its head, neck and back. They are agile flyers that, when hunting, may also take to the ground, running and hopping to seize prey. They soar at high altitudes, sometimes plunging into dramatic dives, or even hovering and flying backwards. Sky dancing, consisting of a dramatic dive, may be used as a territorial display, or by males courting females. In one peculiar behavior known as backstanding, hawks may alight onto the back of another for minutes at a time, possibly in hopes of securing the particular perch for themselves.

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Conservation

Conservation Low Concern

Harris's Hawks are fairly common, but their populations have declined by around 2% per year between 1968 and 2015, according to the North American Breeding Bird Survey resulting in a cumulative decline of 62%. Partners in Flight estimates the global breeding population at 920,000. The species rates an 11 out of 20 on the Continental Concern Score, which means it is not on the Partners in Flight Watch List and is a species of low conservation concern. Harris's Hawks are vulnerable to habitat loss due to urbanization and oil and gas development, which reduces habitat quality and prey availability. Brush control programs that eliminate mesquite habitat may also threaten populations in some areas. An additional side effect of urbanization is a shift away from natural perches—hawks increasingly perch on power poles, which often results in electrocution, sometimes killing several members of a group. Thankfully, electric utility companies are working to retrofit many utility lines to reduce electrocution risk for raptors.

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Credits

Crossley, R., J. Liguori, and B. Sullivan. (2013). The Crossley ID Guide: Raptors. Princeton University Press, New Jersery, USA.

Dwyer, James F. and James C. Bednarz. 2011. Harris's Hawk (Parabuteo unicinctus), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A. and A. S. Love (2016). Longevity records of North American birds. Version 2016.1. Patuxent Wildlife Research Center, Bird Banding Laboratory, Laurel, MD, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski, Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley guide to birds, second edition. Alfred A. Knopf, New York, USA.

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