Golden eagle
The golden eagle 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. These birds are dark brown, with lighter golden-brown plumage on their napes. Immature eagles of this species typically have white on the tail and often have white markings on the wings. Golden eagles use their agility and speed combined with powerful feet and large, sharp talons to hunt a variety of prey, mainly hares, rabbits, and marmots and other ground squirrels.
Golden eagles maintain home ranges or territories that may be as large as. They build large nests in cliffs and other high places to which they may return for several breeding years. Most breeding activities take place in the spring; they are monogamous and may remain together for several years or possibly for life. Females lay up to four eggs, and then incubate them for six weeks. Typically, one or two young survive to fledge in about three months. These juvenile golden eagles usually attain full independence in the fall, after which they wander widely until establishing a territory for themselves in four to five years.
Once widespread across the Holarctic, it has disappeared from many areas that are heavily populated by humans. Despite being extirpated from or uncommon in some of its former range, the species is still widespread, being present in sizeable stretches of Eurasia, North America, and parts of North Africa. It is the largest and least populous of the five species of true accipitrid to occur as a breeding species in both the Palearctic and the Nearctic.
For centuries, this species has been one of the most highly regarded birds used in falconry. Because of its hunting prowess, the golden eagle is regarded with great mystic reverence in some ancient, tribal cultures. It is one of the most extensively studied species of raptor in the world in some parts of its range, such as the Western United States and the Western Palearctic.
Taxonomy and systematics
This species was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Falco chrysaetos. Since birds were grouped largely on superficial characteristics at that time, many species were grouped by Linnaeus into the genus Falco. The type locality was given simply as "Europa"; it was later restricted to Sweden. It was moved to the new genus Aquila by French ornithologist Mathurin Jacques Brisson in 1760. Aquila is Latin for "eagle", possibly derived from aquilus, "dark in colour" and chrysaetos is Ancient Greek for the golden eagle from khrusos, "gold" and aetos, "eagle".The golden eagle is part of a broad group of raptors called "booted eagles" which are defined by the feature that all species have feathering over their tarsus, unlike many other accipitrids which have bare legs. Included in this group are all species described as "hawk eagles" including the genera Spizaetus and Nisaetus, as well as assorted monotypical genera such as Oroaetus, Lophaetus, Stephanoaetus, Polemaetus, Lophotriorchis and Ictinaetus.
The genus Aquila is distributed across every continent but for South America and Antarctica. Up to 20 species have been classified in the genus, but more recently the taxonomic placement of some of the traditional species has been questioned. Traditionally, the Aquila eagles have been grouped superficially as largish, mainly brownish or dark-colored booted eagles that vary little in transition from their juvenile to their adult plumages. Genetic research has recently indicated the golden eagle is included in a clade with Verreaux's eagle in Africa as well as the Gurney's eagle and the wedge-tailed eagle. This identification of this particular clade has long been suspected based on similar morphological characteristics amongst these large-bodied species. More surprisingly, the smaller, much paler-bellied sister species Bonelli's eagle and African hawk-eagle, previously included in the genus Hieraaetus, have been revealed to be genetically much closer to the Verreaux's and golden eagle lineage than to other species traditionally included in the genus Aquila. Other largish Aquila species, the eastern imperial, the Spanish imperial, the tawny and the steppe eagles, are now thought to be separate, close-knit clade, which attained some similar characteristics to the prior clade via convergent evolution.
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Genetically, the "spotted eagles", have been discovered to be more closely related to the long-crested eagle and the black eagle, and many generic reassignments have been advocated. The genus Hieraaetus, including the booted eagle, little eagle and Ayres's hawk-eagle, consists of much smaller species, that are in fact smallest birds called eagles outside of the unrelated Spilornis serpent-eagle genus. This genus has recently been eliminated by many authorities and is now occasionally also included in Aquila, although not all ornithological unions have followed this suit in this re-classification. The small-bodied Wahlberg's eagle has been traditionally considered a Aquila species due to its lack of change from juvenile to adult plumage and brownish color but it is actually genetically aligned to the Hieraaetus lineage. Cassin's hawk-eagle is also probably closely related to the Hieraaetus group rather than the Spizaetus/Nisaetus "hawk-eagle" group which is not known to have radiated to Africa.
Subspecies and distribution
There are six extant subspecies of golden eagle that differ slightly in size and plumage. Individuals of any of the subspecies are somewhat variable and the differences between the subspecies are clinal, especially in terms of body size. Other than these characteristics, there is little variation across the range of the species. Some recent studies have gone so far as to propose that only two subspecies be recognized based on genetic markers: Aquila chrysaetos chrysaetos and A. c. canadensis.- Aquila chrysaetos chrysaetos – sometimes referred to as the European golden eagle. This is the nominate subspecies. This subspecies is found almost throughout Europe, including the British Isles, the majority of Scandinavia, southern and northernmost France, Italy and Austria. In Eastern Europe, it is found from Estonia to Romania, Greece, Serbia, Bulgaria and Kosovo in southeastern Europe. It is also distributed through European Russia, reportedly reaching its eastern limit around the Yenisei River in Russia, also ranging south at a similar longitude into western Kazakhstan and northern Iran. Male wing length is from, averaging, and female wing length is from, averaging. Males weigh from, averaging, and females weigh from, averaging. The male of this subspecies has a wingspan of, with an average of, with the female's typical wingspan range is, with an average of. This is a medium-sized subspecies and is the palest. As opposed to golden eagles found further east in Eurasia, the adults of this subspecies are a tawny golden-brown on the upperside. The nape patch is often gleaming golden in color and the feathers here are exceptionally long.
- Aquila chrysaetos homeyeri Severtzov, 1888 – commonly known as the Iberian golden eagle. This subspecies occurs in almost the entirety of the Iberian Peninsula as well as the island of Crete, though it is absent from the rest of continental Europe. It also ranges in North Africa in a narrow sub-coastal strip from Morocco to Tunisia. A completely isolated population of golden eagles is found in Ethiopia's Bale Mountains, at the southern limit of the species' range worldwide. Although this latter population has not been formally assigned to a subspecies, there is a high probability that it belongs with A. c. homeyeri. This subspecies also ranges in much of Asia Minor, mainly Turkey, spottily through the Middle East and the Arabian Peninsula into northern Yemen and Oman to its eastern limits throughout the Caucasus, much of Iran and north to southwestern Kazakhstan. Male wing length is from, averaging, and female wing length is from, averaging. Weight is from with no known reports of average masses. This subspecies is slightly smaller and darker plumaged than the nominate subspecies, but it is not as dark as the golden eagles found further to the east. The forehead and crown are dark brownish, with the nape patch being short-feathered and a relatively light rusty color.
- Aquila chrysaetos daphanea Severtzov, 1888 – known variously as the Asian golden eagle, Himalayan golden eagle or berkut. This subspecies is distributed in central Kazakhstan, eastern Iran, and the easternmost Caucasus, distributed to Manchuria and central China and along the Himalayas from northern Pakistan to Bhutan and discontinuing in northeastern Myanmar. This subspecies is the largest on average. Male wing length is from, averaging, and female wing length is from, averaging. No range of body weights are known, but males will weigh approximately and females. Although the wingspan of this subspecies reportedly averages, some individuals can have much longer wings. One female berkut had an authenticated wingspan of, although she was a captive specimen. It is generally the second-darkest subspecies, being blackish on the back. The forehead and crown are dark with a blackish cap near the end of the crown. The feathers of the nape and top-neck are rich brown-red. The nape feathers are slightly shorter than in the nominate subspecies and are similar in length to A. c. homeyeri.
- Aquila chrysaetos japonica Severtzov, 1888 – commonly known as the Japanese golden eagle. This subspecies is found in northern Japan and undefined parts of Korea. Male wing length is from, averaging, and female wing length is from, averaging. No range of body weights are known, but males will weigh approximately and females. This is, by far, the smallest-bodied subspecies. It is also the darkest, with even adults being a slaty-grayish black on the back and crown and juveniles being similar, but with darker black plumage contrasting with brownish color and white scaling on the wings, flank and tail. This subspecies has bright rufous nape feathers that are quite loose and long. Adult Japanese golden eagles often maintain extensive white mottling on the inner-webs of the tail that tend to be more typical of juvenile eagles in other subspecies.
- Aquila chrysaetos canadensis – commonly known as the North American golden eagle. Occupies the species' entire range in North America, which comprises the great majority of Alaska, western Canada, Western United States and Mexico. The species is found breeding occasionally in all Canadian provinces but for Nova Scotia. It is currently absent in the Eastern United States as breeding species east of a line from North Dakota down through westernmost Nebraska and Oklahoma to West Texas. The southern limits of its range are in central Mexico, from the Guadalajara area in the west to the Tampico area in the east; it is the "Mexican eagle" featured on the coat of arms of Mexico. It is the subspecies with the largest breeding range and is probably the most numerous subspecies, especially if A. c. kamtschatica is included. Male wing length is from, averaging, and female wing length is from, averaging. The average wingspan in both sexes is about. Males weigh from, averaging, and females typically weigh from, averaging. The subspecies does not appear to follow Bergmann's rule, as specimens of both sexes from Idaho had a mean weight of and where slightly heavier than those from Alaska, with a mean weight of. It is medium-sized, being generally intermediate in size between the nominate and A. c. homeyeri, but with much overlap. It is blackish to dark brown on the back. The long feathers of the nape and top-neck are rusty-reddish and slightly narrower and darker than in the nominate subspecies.
- Aquila chrysaetos kamtschatica Severtzov, 1888 – sometimes referred to as the Siberian golden eagle or the Kamchatkan golden eagle. This subspecies ranges from Western Siberia, across most of Russia, including the Altay, to the Kamchatka Peninsula and the Anadyrsky District. This subspecies is often included in A. c. canadensis. Male wing length is from, averaging, and female wing length is from, averaging. No weights are known in this subspecies. The coloration of these eagles is almost exactly the same as in A. c. canadensis. The main difference is that this subspecies is much larger in size, being nearly the equal of A. c. daphanea if going on wing-length.