Harris's hawk

Appearance

This medium-large hawk is roughly intermediate in size between a peregrine falcon and a red-tailed hawk. Harris's hawks range in length from 46 to 59 cm and generally have a wingspan of about 103 to 120 cm. These hawks have a brownish plumage, reddish shoulders, and tail feathers with a white base and white tip.

They exhibit sexual dimorphism with the females being larger by about 35%. In the United States, the average weight for adult males is about 701 g, with a range of 546 to 850 g, while the adult female average is 1,029 g, with a range of 766 to 1,633 g. They have dark brown plumage with chestnut shoulders, wing linings, and thighs, white on the base and tip of the tail, long, yellow legs, and a yellow cere. The vocalizations of Harris's hawk are very harsh sounds.

The lifespan of Harris's Hawk is 10–12 years in the wild and 20–25 years in captivity.

Distribution

Harris's hawks live in sparse woodland and semi-desert, as well as marshes in some parts of their range, including mangrove swamps, as in parts of their South American range. Harris's hawks are permanent residents and do not migrate. Important perches and nest supports are provided by scattered larger trees or other features.

The wild Harris's hawk population is declining due to habitat loss; however, under some circumstances, they have been known to move into developed areas.

Behavior

This species occurs in relatively stable groups. A dominance hierarchy occurs in Harris's hawks, wherein the mature female is the dominant bird, followed by the adult male and then the young of previous years. Groups typically include from two to seven birds. Not only do birds cooperate in hunting, but they also assist in the nesting process. No other bird of prey is known to hunt in groups as routinely as this species.

Habitat

Harris's hawks live in sparse woodland and semi-desert, as well as marshes in some parts of their range, including mangrove swamps, as in parts of their South American range. Harris's hawks are permanent residents and do not migrate. Important perches and nest supports are provided by scattered larger trees or other features.

The wild Harris's hawk population is declining due to habitat loss; however, under some circumstances, they have been known to move into developed areas.

Reproduction

They nest in small trees, shrubby growth, or cacti. The nests are often compact, made of sticks, plant roots, and stems and are often lined with leaves, moss, bark, and plant roots. They are built mainly by the female. There are usually two to four white to blueish-white eggs sometimes with a speckling of pale brown or gray. The nestlings start light buff, but in five to six days turn a rich brown.

Very often, there will be three hawks attending one nest: two males and one female. Whether or not this is polyandry is debated, as it may be confused with backstanding. The female does most of the incubation. The eggs hatch in 31 to 36 days. The young begin to explore outside the nest at 38 days, and fledge, or start to fly, at 45 to 50 days. The female sometimes breeds two or three times in a year. Young may stay with their parents for up to three years, helping to raise later broods. Nests are known to be predated by coyotes, golden eagles, red-tailed hawks, great horned owls, and flocks of common ravens, predators possibly too formidable to be fully displaced by Harris's hawk's cooperative nest defenses. No accounts show predation on adults in the United States and Harris's hawk may be considered an apex predator, although presumably predators like eagles and great horned owls would be capable of killing them. In Chile, black-chested buzzard-eagles are likely predators.

Food

The majority of Harris's hawks' prey are mammals, including ground squirrels, rabbits, and larger black-tailed jackrabbits. Birds from the size of small passerines such as diuca finch to adult great egret and half-grown wild turkey can be taken. In one instance, a lone Harris's hawk successfully killed a subadult great blue heron. Reptiles such as lizards and snakes are additionally taken as well as large insects.

When hunting in groups, Harris's hawk can take large prey effectively, such as desert cottontail, the leading prey species in the north of Harris's hawk's range, usually weighs 800 g or less. Even adult black-tailed jackrabbits weighing more than 2,000 g can be successfully taken by a pack of Harris's hawks.

Undoubtedly because it pursues large prey often, this hawk has larger and stronger feet, with long talons, and a larger, more prominent hooked beak than most other raptors around its size. Locally, other buteonine hawks, including the ferruginous hawk, the red-tailed hawk, and the white-tailed hawk also hunt primarily cottontails and jackrabbits, but each is bigger, weighing about 500 g, 300 g and 200 g, respectively, more on average than a Harris's hawk.

In the Southwestern United States, the most common prey species are desert cottontail, eastern cottontail, black-tailed jackrabbit, ground squirrels, woodrats, kangaroo rats, pocket gophers, Gambel's quail, scaled quail, northern bobwhite, cactus wren, northern mockingbird, desert spiny lizards, and skinks In the tropics, Harris's hawks have adapted to taking prey of several varieties, including those like chickens and European rabbits introduced by man. In Chile, the common degu makes up 67.5% of the prey.While most raptors are solitary, only coming together for breeding and migration, Harris's hawks will hunt in cooperative groups of two to six. This is believed to be an adaptation to the lack of prey in the desert climate in which they live. In one hunting technique, a small group flies ahead and scouts, then another group member flies ahead and scouts, and this continues until prey is bagged and shared. In another, all the hawks spread around the prey and one bird flushes it out. Harris's hawks will often chase prey on foot, and are quite fast on the ground and their long, yellow legs are adapted for this, as most hawks do not spend as much time on the ground. Groups of Harris's hawks tend to be more successful at capturing prey than lone hawks, with groups of two to four individuals having ~10% higher success rates per extra individual.