Golden Eagle

Appearance

The Golden Eagle is a large, dark brown raptor with broad wings. Its size is variable: it ranges from 66 to 100 cm in length and it has a typical wingspan of 1.8 to 2.34 m. In the largest race males and females weigh 4.05 kg and 6.35 kg.

In the smallest subspecies , the sexes weigh, respectively, 2.5 kg and 3.25 kg. The maximum size of this species is a matter of some debate, although the normal upper weight limit for a large female is around 6.8 kg and large races are the heaviest representatives of the ''Aquila'' genus.

Captive birds have been measured up to a wingspan of 2.81 m and a mass of 12.1 kg. The sexes are similar in plumage but are considerably dimorphic in size, with females rather larger than males. Adults are primarily brown, with gold on the back of the crown and nape, and some grey on the wings and tail.

Tarsal feathers range from white to dark brown. In addition, some birds have white "epaulettes" on the upper part of each scapular feather tract. The bill is dark at the tip, fading to a lighter horn color, with a yellow cere.

Juveniles have a darker, unfaded color, white patches in the remiges which may be divided by darker feathers, and a large amount of white on the tail with a black terminal band. Occasionally upper wing feathers of juveniles are also white, or birds lack white on the wing entirely. As the bird ages, the amount of white on wings and tail diminishes, and adult plumages is usually acquired by the fifth year.

Naming

There are six extant subspecies of Golden Eagle that differ slightly in size and plumage.
⤷  ''Aquila c. chrysaetos'' – The nominate subspecies. Eurasia except Iberian peninsula, east to western Siberia.
⤷  ''Aquila chrysaetos canadensis'' – North America.
⤷  ''Aquila chrysaetos kamtschatica'' Severtzov, 1888 – Eastern Siberia, from the Altay to the Kamchatka Peninsula. Often included in ''A. c. canadensis''.
⤷  ''Aquila chrysaetos daphanea'' Severtzov, 1888 – Southern Kazakhstan east to Manchuria and south-west China, along the Himalayas from northern Pakistan in the west to Bhutan in the east.
⤷  ''Aquila chrysaetos homeryi'' Severtzov, 1888 – Iberian peninsula and North Africa, east to Turkey and Iran.
⤷  ''Aquila chrysaetos japonica'' Severtzov, 1888 – Japan and Korea.

Status

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, the last comprehensive survey of Golden Eagles took place in 2003, and found 442 occupied territories. A less thorough survey in 2007 showed that in addition to large numbers of territories in the Scottish Highlands and the Inner and Outer Hebrides, there were a handful of birds in southern Scotland and northern England. Between 1969 and 2003 they nested in the Lake District, Cumbria.

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.

Behavior

Golden Eagles use their agility and speed combined with extremely powerful talons to snatch up prey including rabbits, marmots, ground squirrels, and large mammals such as foxes, wild and domestic cats, mountain goats, ibex, and young deer. They will also eat carrion if prey is scarce, as well as reptiles.

Birds, including large species up to the size of swans and cranes as well as ravens and Greater Black-backed Gulls have all been recorded as prey. They have even been known to attack and kill fully grown roe deer. The Eurasian subspecies is used to hunt and kill wolves in many native communities, where their status is regarded with great mystic reverence.

Golden Eagles maintain territories that may be as large as 155 square kilometres. They are monogamous and may remain together 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.

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 in diameter and 1 metre 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 eggs between January and September. 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. Even with eggs and small nestlings predation on the Golden Eagle is rare. The only known predators of Golden Eagle nests are wolverines and brown bears.

Food

The Golden Eagle is one of the most powerful predators in the avian world. While they do show strong local preferences for certain prey, Golden Eagles are first and foremost opportunists and virtually any small to mid-sized animal may be predated if encountered. Nearly 200 species of mammal and bird have been recorded as golden eagle prey. Prey selection is largely determined by the local availability and abundance of the prey species. Most prey taken are around half the weight of the predating eagle, with a typical prey weight range of 0.5–4 kg, though this eagle will sometimes fly with prey equal to or slightly heavier than its own weight.