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Harris Hawk

Parabuteo unicinctus

  1. Not Evaluated
  2. Data Deficient
  3. Least Concern
  4. Near Threatened
  5. Vulnerable
  6. Endangered
  7. Critically Endangered
  8. Extinct in the Wild
  9. Extinct

About Us

The Harris Hawk is one of the most popular birds used in the sport of falconry. It was named the Harris Hawk by John James Audubon, a famous nineteenth century naturalist, named after his friend and fellow naturalist Edward Harris. It first featured in his famous illustrated book ‘Birds of America’, of which we have one of few existing copies here at Woburn Abbey.  Although it is called a ‘hawk’ it is not actually part of the hawk family, but is more closely related to the buzzard family. Its scientific name ‘parabuteo’ means buzzard-like, and ‘unicinctus’ means ‘once girdled’, referring to the belt of white feathers on the end of their tail.

Here at Woburn we have two Harris hawks, Ziggy and Hugo. Ziggy enjoys flying with Hugo, just like he would do in the wild, as Harris hawks hunt in packs known as casts. His favourite things to do are fly low over the audience’s heads, or to catch his food in the air!

Distribution
United States and parts of South America
Habitat
Dry bush country, desert, canyons and scrub land
Height
46 - 76cm in length
Weight
710 - 1,020g
Lifespan
Wild 11 years, in captivity up to 25 years
Threats
Accidental electrocution and habitat loss

Physical Features

The Harris’s hawk is a large bird, which weighs around 710g to 1,020g, and is 46cm to 76cm long. Their wingspan can be 100cm to 120cm. The female is usually around 40% bigger in size.

 They have dark brown plumage, with chestnut brown shoulders, thighs, and wing linings. There is a white bar along the tips of the tail feathers, used for communication. The legs are long, un-feathered, and yellow in colour. Their legs are long to allow them to perch on plants such as cacti without damaging their body, and to protect from their prey items, and the skin is very tough. The wings are large and broad, as is the tail, used to help soar in thermals.

Juveniles have similar colouration, but have a more streaked brown body, and have buff coloured wing linings, and barring on the tail. The beak is yellow with a black tip.

There are three subspecies of Harris’s hawk, all with geographical and slight physical differences. They can also be called the bay-winged hawk, due to the colouration of the underside of the wings.

Their hearing is said to be similar to that of a human, however their vision is far superior. During daylight it is said to be eight times better than a human’s vision. They use this vision when hunting their prey, and can focus on a small prey item from a long distance before homing in on it to hunt. It is said that they could read a newspaper headline from a whole football pitch length away. Their head features a sharp bony ridge above each eye, called the supra-orbital ridge, which shields their eyes from the sun.

Diet and Hunting Behaviour

The Harris’s hawk’s diet is consists mainly of small mammals, such as jackrabbits, rats and mice, but they will also take birds and lizards. If food is scarce they may take carrion.

If food is abundant or an item of food left partially uneaten, they will often cache, or store food, for later times.

They are diurnal hunters, meaning they are active during the day time. They will spend most of their time perching or resting in their home range, before going out on hunting trips.

Harris’s hawks are very unusual amongst birds of prey, because they live in family groups, known as casts. Even more unusually is the Harris’s hawk’s ability to hunt cooperatively in this group. They will often hunt smaller prey items alone, but for larger prey items such as the jackrabbit the whole cast will come together to take down a prey item for the group. They have the nickname ‘wolves of the sky’ due to this pack mentality when hunting.

There is a strict hierarchy within the group, with females being the dominant sex. The young males usually form the main hunting party, working together to flush out and scare prey items, either by diving from the air, or by running on the ground to flush them out of vegetation. They will take it in turns to do this until the prey item is tired enough to be caught easily. Females will also join the hunt, but usually taking the role of the final move of killing the prey after the males have flushed it out and tired it out first. The individual who catches the prey will then perform a behaviour known as mantling, where they will cover the food with their wings and tail spread out over it to protect it from being stolen. The females will take their pick of the food, before letting the males eat.

Harris’s hawks are also experts at taking birds in flight. They will grab a bird at high speed, using feet designed not to let go. The tendons in the toes work on a ratchet system, so that once an item is in the feet they cannot let it go, only grip tighter the more it moves.

Harris’s hawks can be very territorial, keeping territories form 0.2 to 5.5 square kilometres in size. The size of this range will depend on food and resource availability. This territory will be defended from other groups.

 

The strong feet and talons are used to catch the prey, and in most cases kill it with the grip. They will then use the sharp hooked end of the beak to tear up their food to eat it.

The Harris’s hawk will produce a pellet every day, a small package of all the parts of their food they cannot digest fully, such as the bones and fur or feathers, regurgitated. This removes the indigestible parts of food, but also cleans the digestive tract of any debris and bacteria.

Social Structure and Communication

The Harris’s hawk is not a very vocal species, with only a few calls. The most common calls are an extended, harsh call or a low, growling sound. When protecting a nest or food they will be very vocal.

During hunting the tail feathers are used to communicate silently. The white band across the bottom of the tail is visible from a distance, especially to a species with such good vision. Hawks will flick the tail as a signal that everyone is in position and ready to hunt.

Females will be allowed to feed first, and will even perch higher than the males to show dominance. During hunting the female will usually take the role of making the final blow to kill the prey, after the males have done all of the work to flush out and tire them first. The entire group will help hunt, but will also help to protect the territory, and protect the nest. It is thought that this social structure developed due to the harsh conditions of their habitat, with little food and resources, making cooperation the only viable way to survive.

Harris’s hawks do something called ‘back-stacking’. If there is no room to perch, they will sit on top of each other, up to four birds high. It is the dominant bird who will be at the bottom of the stack, if they approach a perch with a subordinate bird on it, they will move to allow the dominant bird to perch, and stack on their back instead.

Breeding

The social structure of Harris’s hawks is very complex compared to most birds of prey. They live in large family groups, of between four and twelve individuals, called a cast. This cast will contain a dominant breeding female, and either one or two breeding males. It is the females who are dominant, within a very strict hierarchy.

The female will often mate with two males, and allow both to help in the incubation of the eggs and the rearing of the young. Although they have two partners, they will usually pair with both of these for life, staying in the small family group.

Harris’s hawks usually nest in a tall tree, cactus, or yucca, at a heights of 5 to 20 metres. They will occasionally nest in electrical pylons in some urban areas too. The nest is a platform of sticks and plant material, lined with mosses and grasses. The female will lay two to four eggs, which both her and the male, or two males, will take in turn to incubate. They will hatch at around 35 days. After they hatch the entire group will assist in the rearing of the young, and will all protect the nest and young. They will fledge at 40 days old, and will stay in the area of the nest for two or three months after, learning to hunt from other group members. Juveniles may stay with the family unit for up to three years, helping rear subsequent young, and learning, before moving on the breed on their own. As the female is larger, a female hatchling takes more to feed, and so as a strategy to maximise survival the first hatchling is always a male, meaning there is more food for the other chicks.

Breeding usually occurs from February to June, and can include the female laying up to three clutches in this time, providing food is readily available. Courtship involves aerial displays from the male, performing high vertical dives towards the female.

The Harris’s hawk reaches sexual maturity at around a year old, and can live up to 11 years in the wild, or 25 in captivity.

Husbandry

All of our birds of prey are flown daily. This has many benefits to the animal. Firstly it allows the animal to exercise, keeping them fit, and developing flying muscles. It also allows them to perform their natural behaviours, for some of our birds of prey this may include various hunting techniques such as catching prey mid-flight, and chasing down ground prey, or killing a (rubber) snake.

Each bird has a varied diet, just as it would in the wild, mimicking the varying nutritional properties of each food type and the quantities.

Threats and Conservation

The natural predators of the Harris hawk are few, but include great horned owls, coyotes, and common ravens. The young are most vulnerable, but the nest is usually well protected by all members of the group, with lookouts who give warning calls when predators approach, and with the breeding males often attacking predators near the nest, while the female guards it.

Although they are not classed as endangered, in some parts of their range they are rare. There have been some re-introductions of populations in some states. Habitat loss and human disturbance are the main causes of decline for Harris’s hawks in the USA. Populations in Arizona and Texas have suffered greatly due to these causes. Accidental electrocution is also a problem, with birds perching on electrical wires. It happens often enough that some electrical companies have added extra insulation to cables in prone areas, or even added arms to pylons for perching birds to stop damage to their equipment.

They can benefit humans, by acting as pest control around agricultural crops, eating all of the rodents.

In the USA the Harris’s hawk is protected from harassment and illegal shooting by the Migratory Bird Treaty Act.

They are listed as appendix II of CITES, which means the trade and export of this species is heavily regulated and controlled to protect them.

Fun Facts

Harris’s hawks do something called ‘back-stacking’. If there is no room to perch, they will sit on top of each other, up to four birds high!
 
Their eyesight is said to be eight times better than a humans, and if they could read, they would be able to read a newspaper headline from a whole football pitch length away!

They have long legs, covered in tough skin, to allow them to perch on cacti!