Facts & Profile

Golden eagle Aquila chrysaetos

The golden eagle (Aquila chrysaetos) is a bird of prey living in the Northern Hemisphere. It is the most widely distributed species of eagle. Like all eagles, it belongs to the family Accipitridae. They are one of the best-known birds of prey in the Northern Hemisphere.

Description & appearance

The golden eagle is a very large raptor, 66 to 102 centimetres (26 to 40 in) in length. Its wings are broad and the wingspan is 1.8 to 2.34 metres (5 ft 11 in to 7 ft 8 in). The wingspan of golden eagles is the fifth largest among living eagle species. Females are larger than males, with a bigger difference in larger subspecies.

Adults of both sexes have similar plumage and are primarily dark brown, with some grey on the inner wing and tail, and a paler, typically golden colour on the back of the crown and nape that gives the species its common name. Unlike other Aquila species, where the tarsal feathers are typically similar in colour to the rest of the plumage, the tarsal feathers of golden eagles tend to be paler, ranging from light golden to white.

This species moults gradually beginning in March or April until September or October each year. Moulting usually decreases in winter. Moult of the contour feathers begins on the head and neck region and progresses along the feather tracts in a general front-to-back direction. Feathers on head, neck, back and scapulars may be replaced annually. With large feathers of the wing and tail, moult begins with the innermost feathers and proceeds outwards in a straightforward manner known as "descendant" moult.

Voice, singing & call

While many accipitrids are not known for their strong voices, golden eagles have a particular tendency for silence, even while breeding. That being said, some vocalization has been recorded, usually centering around the nesting period. The voice of the golden eagle is considered weak, high, and shrill, has been called "quite pathetic" and "puppy-like", and seems incongruous with the formidable size and nature of the species. Most known vocalisations seem to function as contact calls between eagles, sometimes adults to their offspring, occasionally territorial birds to intruders and rarely between a breeding pair. In western Montana, nine distinct calls were noted: a chirp, a seeir, a pssa, a skonk, a cluck, a wonk, a honk and a hiss.

Habitat

Golden eagles are fairly adaptable in habitat but often reside in areas with a few shared ecological characteristics. They are best suited to hunting in open or semi-open areas and search them out year-around. Native vegetation seems to be attractive to them and they typically avoid developed areas of any type from urban to agricultural as well as heavily forested regions. In desolate areas (e.g., the southern Yukon), they can occur regularly at roadkills and garbage dumps. The largest numbers of golden eagles are found in mountainous regions today, with many eagles doing a majority of their hunting and nesting on rock formations. However, they are not solely tied to high elevations and can breed in lowlands if the local habitats are suitable. Below are more detailed descriptions of habitats occupied by golden eagles in both continents where they occur.

Hunting & diet

Golden eagles usually hunt during daylight hours, but were recorded hunting from one hour before sunrise to one hour after sunset during the breeding season in southwestern Idaho. The hunting success rate of golden eagles was calculated in Idaho, showing that, out of 115 hunting attempts, 20% were successful in procuring prey. A fully-grown golden eagle requires about 230 to 250 g (8.1 to 8.8 oz) of food per day but in the life of most eagles there are cycles of feast and famine, and eagles have been known to go without food for up to a week and then gorge on up to 900 g (2.0 lb) at one sitting.

The diet of golden eagles is composed primarily of small mammals such as rabbits, hares, ground squirrels, prairie dogs, and marmots. They also eat other birds (usually of medium size, such as gamebirds), reptiles, and fish in smaller numbers. Golden eagles occasionally capture large prey, including seals, ungulates, coyotes, and badgers. They have also been known to capture large flying birds such as geese or cranes. They have also been known to prey on other raptors, including owls and falcons.

Mating & Breeding

Golden eagles usually mate for life. A breeding pair is formed in a courtship display. This courtship includes undulating displays by both in the pair, with the male bird picking up a piece of rock or a small stick, and dropping it only to enter into a steep dive and catch it in mid-air, repeating the maneuver 3 or more times. The female takes a clump of earth and drops and catches it in the same fashion. olden eagles typically build several eyries within their territory (preferring cliffs) and use them alternately for several years.

Their nesting areas are characterized by the extreme regularity of the nest spacing. Mating and egg-laying timing for golden eagle is variable depending on the locality. Copulation normally lasts 10–20 seconds. Mating seems to occur around 40–46 days before the initial egg-laying. The golden eagle chick may be heard from within the egg 15 hours before it begins hatching. After the first chip is broken off of the egg, there is no activity for around 27 hours. Hatching activity accelerates and the shell is broken apart in 35 hours. The chick is completely free in 37 hours.

Chicks, juveniles & raise

In the first 10 days, chicks mainly lie down on the nest substrate. They are capable of preening on their second day but their parents keep them warm until around 20 days. They grow considerably, weighing around 500 g (1.1 lb). They also start sitting up more. Around 20 days of age, the chicks generally start standing, which becomes the main position over the course of the next 40 days. The whitish down continues until around 25 days of age, at which point it is gradually replaced by dark contour feathers that eclipse the down and the birds attain a general piebald appearance. After hatching, 80% of food items and 90% of food biomass is captured and brought to the nest by the adult male. Fledging occurs at 66 to 75 days of age in Idaho and 70 to 81 days in Scotland.

The first attempted flight departure after fledging can be abrupt, with the young jumping off and using a series of short, stiff wing-beats to glide downward or being blown out of nest while wing-flapping. 18 to 20 days after first fledging, the young eagles will take their first circling flight, but they cannot gain height as efficiently as their parents until approximately 60 days after fledging. In Cumbria, young golden eagles were first seen hunting large prey 59 days after fledging. 75 to 85 days after fledging, the young were largely independent of parents. Generally, breeding success seems to be greatest where prey is available in abundance.