The Breeding of Harris Hawks in the wild

A female Harris Hawk will mate with two males & the nest may be made in cooperation of several other birds. Nests are made in the tops of trees or on the top of a tall Yucca or Cactus.

Up to 5 eggs are laid & incubation is done by the female (33-36 days). Sometimes two clutches of eggs are laid in a season, between early March to late June.

Feeding of the young is done as a joint effort by the female & both of the males. The young are fully fledged in 7-8 weeks from hatching, though the young may stay with the parents for up to 1 year.

One study has shown that the polyandry (mating with more than one male) exhibited by the female Harris Hawks is not due to an imbalance in the ratio of males to females, the ratio is roughly 50:50. Whilst it is not certain why the polyandry exists, one theory suggests that the amount of available food may be an issue. Some studies have shown that in areas of large amounts of food, the males (who usually provide most of the food during the early part of the breeding season) are more likely to mate with more than one female (polygamy) as they are able to provide food for both. In areas of a low source of food, polyandry is more likely, as the chances of survival for the young is improved with two or more males providing the food.

Harris Hawks naturally hunt cooperatively & are usually more successful hunting in this manner, this has been suggested as a major reason for the female Harris Hawks taking two mates.

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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 coloured down.

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NEST DESCRIPTION
A Harris Hawk 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.

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.