These birds are dark brown, with lighter golden-brown plumage on their heads and necks. It has a wingspan averaging over 2 m (7 ft) and up to 1 m (3 ft) in body length. They are extremely swift, and can dive upon their quarry at speeds of more than 150 miles (241 kilometers) per hour.
Golden eagles use their speed and sharp talons to snatch up rabbits, marmots, and ground squirrels. They also eat carrion, reptiles, birds, fish, and smaller fare such as large insects. They have even been known to attack full-grown deer.
Golden eagle pairs maintain territories that may be as large as 60 square miles (155 square kilometers). They are monogamous and may remain with their mate for several years or possibly for life. Golden eagles nest in high places including cliffs, trees, or human structures such as telephone poles. They build huge nests to which they may return for several breeding years. Females lay from one to four eggs, and both parents incubate them for 40 to 45 days. Typically, one or two young survive to fledge in about three months.
Description
Adult Golden Eagles range considerably in size, though some are among the largest eagles of the genus Aquila. Most subspecies of Golden Eagle vary in the range from 65 to 100 cm (26–40 in) in length, wingspan can range from 150 to 240 cm (60–96 in), and weight is from 2.5 to 7 kg (5.5–15.5 lb). The smallest-bodied subspecies is A. c. japonica while A. c. daphanea is the largest on average. However, wild specimens from Northwestern North America (A. c. canadensis) can exceed normal dimensions, as the largest recorded weighed 9 kg (20 lbs) and had a body length of 102 cm (40.1 in). As with many Accipitriformes, females are considerably larger than males, in the case of the Golden Eagle they weigh one-quarter to one-third more than male birds.
The plumage colours range from black-brown to dark brown, with a striking golden-buff crown and nape, which give the bird its name. The upper wings also have an irregular lighter area. Immature birds resemble adults, but have a duller more mottled appearance. Also they have a white-banded tail and a white patch at the carpal joint, that gradually disappear with every moult until full adult plumage is reached in the fifth year. Contour feathers may be moulted in a short time span.
Taxonomy and systematics
This species was first described by Linnaeus in his 1758 Systema naturae as Falco chrysaetos. The type locality is given simply as "Europa"; it was later fixed to Sweden.
The Golden Eagle is one of the large eagles in the genus Aquila, which are distributed almost worldwide. The latest research indicates it forms a worldwide superspecies with Verreaux's Eagle, Gurney's Eagle and the Wedge-tailed Eagle.
Feeding
Golden eagle predominant prey is leporids (hares and rabbits) and sciurids (ground squirrels, prairie dogs & marmots), the two groups normally comprising 50-94% of the diet of nesting eagles. Additional mammals regularly taken include mice, martens, foxes, young deer and mountain goats. The secondary important prey group for eagles are other birds. Various gallinaceous birds (largely phasianids, ptarmigans and grouse) are the most significant avian prey. However, virtually any bird, from a jay to a swan, is potential prey. During winter months when prey is scarce, Golden Eagles scavenge on carrion to supplement their diet. Sometimes when no carrion is available golden eagles will hunt down large prey, such as goat-antelopes and caribou. There is one confirmed report of a Golden Eagle snatching the cub of a Brown Bear, and several other unverified attacks. Golden eagles are avian apex predators, meaning a healthy adult is not preyed upon. There are records of golden eagles killing and eating large raptors such as Eurasian Eagle Owls, Gyrfalcons, Northern Goshawks and Buteo hawks, whether adults, nestlings or eggs. Falcons, jaegers and Buteos like Rough-legged Hawks, which are normally competitors, have worked together to group-mob Golden Eagles that have passed their adjacent nesting areas. More commonly, Golden Eagles kleptoparasitize, or steal prey, from other raptors. Despite being often smaller in size, they are capable of displacing large vultures, of both unrelated families, from carrion. However, the Bald Eagle and White-tailed Eagle can displace Golden Eagles in competition over food and vice versa. Golden Eagles have very good eyesight and can spot prey from a long distance. The Golden Eagle has a resolving power 8x more powerful than a human. The talons are used for killing and carrying the prey, the beak is used only for eating. They often have a division of labour while hunting, one bird driving the prey towards its waiting partner. On the other hand, the size difference between males and females allows more unpaired birds to live off the land, which is helpful to maintain a sufficiently large population for this large and slowly-maturing bird.
Reproduction
Golden Eagles usually mate for life. They build several eyries within their territory and use them alternately for several years. These nests consist of heavy tree branches, upholstered with grass when in use. Old eyries may be 2 metres (6.6 ft) in diameter and 1 metre (3.3 ft) in height, as the eagles repair their nests whenever necessary and enlarge them during each use. If the eyrie is situated on a tree, supporting tree branches may break because of the weight of the nest. Certain other animals – birds and mammals too small to be of interest to the huge raptor – often use the nest as shelter. Their predators are just the right size for Golden eagle prey, and therefore avoid active eyries.
The female lays one to four (usually two) eggs between January and September (depending on the locality). The eggs vary from all white to white with cinnamon or brown spots and blotches. They start incubation immediately after the first egg is laid, and after 40 to 45 days the young hatch. They are covered in fluffy white down and are fed for fifty days before they are able to make their first flight attempts and eat on their own. In most cases only the older chick survives, while the younger one dies without leaving the eyrie. This is due to the older chick having a few days' advantage in growth and consequently winning most squabbles for food. This strategy is useful for the species because it makes the parents' workload manageable even when food is scarce, while providing a reserve chick in case the first-born dies soon after hatching. Golden eagles invest much time and effort in bringing up their young; once able to hunt on their own, most golden eagles survive many years, but mortality even among first-born nestlings is much higher, in particular in the first weeks after hatching.
Congregation and Migration
As with many raptors, golden eagles congregate once a year. In Eurasia and North America, this congregation usually occurs in the Autumn (while congregations of bald eagles is a late-winter / early-spring phenomenon). The largest known congregation, in number of birds present, of the golden eagle is in the state of Montana in October. The congregation site is the east slope of the Bridger Mountains and adjacent Bridger Canyon. The mountain range is on the edge of the Rocky Mountain chain, where it borders parts of the Great Plains and several island ranges. Golden eagles from all over North America congregate here before migrating for the winter.
Status and conservation
At one time, the Golden Eagle lived in temperate Europe, North Asia, North America, North Africa and Japan. In most areas this bird is now a mountain-dweller, but in former centuries it also bred in the plains and the forests. In recent years it has started to breed in lowland areas again e.g. in Sweden and Denmark.
There was a great decline in Central Europe where they are now essentially restricted to the Apennine, Alps and Carpathian Mountains. In Britain, there were about 420 pairs in 2007, the majority of these in the Scottish highlands, and between 1969 and 2004 they bred in the Lake District, Cumbria. Golden Eagles can still often be seen soaring above mountains in Scotland, and are slowly returning to Northern England.
In Ireland, where it had been extinct due to hunting since 1912, efforts are being made to re-introduce the species. Forty-six birds were released into the wild in Glenveagh National Park, County Donegal, from 2001 to 2006, with at least three known female fatalities since then. It is intended to release a total of sixty birds, to ensure a viable population. In April 2007, a pair of Golden Eagles produced the first chick to be hatched in the Republic of Ireland in nearly a century. The previous attempt to help the birds breed at the Glenveagh National Park had failed.
In North America the situation is not as dramatic, but there has still been a noticeable decline. The main threat is habitat destruction which by the late 19th century already had driven Golden Eagles from some regions they used to inhabit. In the 20th century, organochloride and heavy metal poisonings were also commonplace, but these have declined thanks to tighter regulations on pollution. Within the United States, the Golden Eagle is legally protected by the Bald and Golden Eagle Protection Act.
Available habitat and food are the main limiting factor nowadays. Collisions with power lines have become an increasingly significant cause of mortality since the early 20th century. On a global scale, the Golden Eagle is not considered threatened by the IUCN mainly thanks to the large Asian and American populations.
