Golden Eagle Aquila chrysaetos
Version: 2.0 — Published September 17, 2020
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Originally described as Falco chrysaëtos Linnaeus, 1758 [type locality = Sweden].
The expansion of genomic sequencing and laboratory techniques has led to rapid growth in understanding the phylogeny of the Golden Eagle. Analysis of mitochondrial DNA (mtDNA) suggests that there is phylogeographic separation among eagles from central and southern Europe, and eagles from North America, Japan, continental Asia, and northern Europe (19). Within North America, there is evidence of weak genetic structuring of populations, with the ability to detect structure dependent on the resolution of the molecular markers used (85, 86, 87, 88). In some places, populations have experienced bottlenecks as a consequence of recent (89) or historical (90) isolation by distance resulting from island colonization. Likewise, recent analysis provides the hint of a heterozygote advantage, as adults are more likely to be heterozygous than are their offspring, whereby greater heterozygosity increases chances of survival to adulthood (86).
Variation across North America is not well known, but size varies considerably across the species’ Holarctic range. Bergmann’s rule, the tendency of intraspecific body size to increase with colder climates or increases in latitude (91, 92), has been documented for many species of birds (93, 94, 95, 96). Within subspecies, shows clinal variation, generally being larger at higher latitudes. That said, the largest subspecies is in mid-latitude montane areas of central Asia and the smallest in areas of similar latitude in Japan and Korea (32, 2). Overall plumage saturation (“darkness”) varies from palest in Europe and western Asia to darkest in Japan and Korea, with most other populations intermediate. Nape color is golden or brownish in the Western Palearctic and central Asia, but variations occur elsewhere (2; see Systematics: Subspecies). Information is lacking on the extent of variation in measurements and plumage characteristics in North America. Preliminary research suggests some morphological variation between migratory northern and more sedentary southern populations (TAM, EHC, M. Lanzone, M. Lockhart, T. Craig, unpublished data; Table 1; see Appearance: Measurements).
Six subspecies, following Mayer and Cottrell (97), Watson (2), Dickinson and Remsen (98; cf. 99, 32) are distinguished on the basis of size, color saturation of the body, and hue of the nape. One subspecies occurs in North America, one in Africa, and one in Japan. There are four subspecies in Eurasia, one of which is the same as that in Africa. Recent genetic evidence suggests that the Japanese subspecies is more closely related to the North American subspecies than either is to birds from Scotland (100).
Aquila chrysaetos homeyeri
A. c. homeyeri Severtzov, 1888 [type locality = Balearic Islands and Algeria].
Resident in the Iberian Peninsula and across North Africa (including scattered populations in mountains of Western Sahara (101) and the world’s southernmost population in the Bale Highlands of Ethiopia), through the Middle East and Arabian Peninsula to the Caucasus, Iran, and Uzbekistan.
Similar to A. c. chrysaetos, but smaller (median female wing length = 640 mm; 2), with darker body plumage and a browner, less golden, nape.
Aquila chrysaetos chrysaetos
A. c. chrysaetos (Linnaeus 1758) [type locality = Sweden]. Includes Falco fulvus Linnaeus, 1758; A. aurea Forster 1817; and A. c. melanastur Pelzeln, 1862.
Largely resident throughout Europe (except Iberian Peninsula), east to the Yenisey River in north-central Asia. Populations may be migratory, partially migratory, or non-migratory.
Body plumage medium brown with a golden nape; medium in size (median female wing length = 670 mm; 2).
Aquila chrysaetos daphanea
A. c. daphanea Severtzov, 1888 [type locality = ‘Turkestan’, a historic region of Central Asia bounded by the Gobi Desert, Tibet, Afghanistan, Iran, Caspian Sea, and Siberia]. Supercedes A. intermedia Severtzov, 1872 (indeterminate; see 102), and includes A. c. hodgsoni Ticehurst, 1931 (E. C. Dickinson, personal communication).
Resident in montane areas of central Asia, from the Pamir Mountains to central China and south to the Himalayas from northern Pakistan east to Bhutan.
Similar to A. c. chrysaetos, but larger (median female wing length = 700 mm; 2) and the nape is somewhat browner (intermediate between nominate subspecies and A. c. homeyeri).
Aquila chrysaetos japonica
A. c. japonica Severtzov 1888 [type locality = Hakabusakan and Hakodate, Japan].
Resident in Japan and Korean Peninsula.
Similar to A. c. kamtschatica, but markedly smaller (median female wing length = 630 mm; 2), and body plumage darker (toward fuscous) with a bright rufous nape.
Aquila chrysaetos kamtschatica
A. c. kamtschatica Severtzov, 1888 [type locality = Kamchatka, Russia]. Includes A. c. obscurior Sushkin, 1925.
Resident in northeastern Asia, east of the Yenisey River and south to Mongolia and northeastern China.
Similar to A. c. daphanea, but, on average, slightly smaller (median female wing length = 690; 2) and the nape is rufous brown instead of golden brown.
Aquila chrysaetos canadensis
A. c. canadensis (Linnaeus, 1758) [type locality = Hudson Bay, Canada].
Resident and migratory populations across North America, from Alaska and northern Canada south to northern Mexico. Populations from central Canada and northward are usually migratory, but may overwinter in Alaska when suitable food is available (CLM, EHC, TEK, TAM). Some individuals from California and New Mexico migrate north for part of the year (103, 104).
Similar in appearance to A. c. japonica, but somewhat paler overall and larger (median female wing length = 650 mm; 2).
Within the family Accipitridae, aquiline eagles are widespread globally and include the genus Aquila, as well as a number of other genera. Aquila are medium to large eagles with feathering to the toes—hence, they are called the “booted” eagles (105, 106). A recent phylogeny supports 5 major clades within the booted eagles and places 11 species within the genus Aquila (107). Many of the large species in the genus, including A. chrysaetos, are similar morphologically and isoenzymatically (108). Within Aquila, the relationship of A. chrysaetos to other members of the genus is uncertain. It is not clear if it is more closely related to a clade that includes A. audax (Wedge-tailed Eagle of Australia), A. gurneyi (Gurney’s Eagle of New Guinea and Wallacea), A. verreauxii (Verreaux's Eagle of sub-Saharan Africa), A. spilogaster (African Hawk-Eagle of tropical Africa), and A. fasciata (Bonelli's Eagle of southern Europe and the Maghreb east to the Indian subcontinent and to Southeast Asia), to a clade containing A. nipalensis (Steppe Eagle of Eurasia), A. rapax (Tawny Eagle of Africa and India), and A. heliaca (Imperial Eagle of the grassland-forest interface of Eurasia), or to both both of these clades together (109, 107). Association with the second clade is supported by anecdotal evidence of the Golden Eagle in the Altai Region of Russia forming mated pairs and successfully reproducing with Imperial Eagle (I. Karyakin, unpublished data) and photographic evidence of potential hybrids in Europe (110).
The genus Aquila is Latin for "eagle" and the specific epithet, chrysaetos, is Greek for “golden.” The common name is derived from the pale golden feathers on the head and nape.
There are Pleistocene-era records of Golden Eagles in North America from Oregon, California, Utah, Nevada, New Mexico, Texas, and Mexico (111, 112, 29). More than 690 Golden Eagle specimens representing that era were found at the Rancho La Brea tar pits in southern California, and the Golden Eagle was the most abundant bird species recovered there (113). Golden Eagle remains also were found at archaeological sites inhabited by prehistoric Native Americans in Utah (114) and New Mexico (115). Aquila remains are reported in fossils from the Upper Miocene in Nebraska (116), and from the late Pliocene in Florida and Arizona (117). Fossil bones of two species, A. pliogryps and A. sodalist, were found in collections made in southwestern Oregon (118).
The late Pliocene Aquila fossil remains from Florida and Arizona (117) were ~10–15% larger than modern female A. chrysaetos eagles. However, there is no evidence of changes in morphology from Golden Eagle fossils from California in the late Pleistocene, but these birds differed significantly from Holocene Golden Eagles (113). These ancestral Golden Eagle specimens may have been, on average, larger and with more robust skulls than modern day Aquila eagles in North America (119). There appears to be considerable overlap and gradation between contemporary Golden Eagle and Pleistocene fossil records in North America.
Fossil Golden Eagle records are also widespread elsewhere in the world. Golden Eagle remains are regularly found at Neanderthal sites (120). Prehistoric humans in northeastern Italy and in the middle Rhône Valley in southern France used Golden Eagle talons during the Middle Palaeolithic period (late Pleistocene; 121). Golden Eagle fossils from the Pleistocene have also been recorded from Portugal, Spain, France, Italy, Greece, on islands in the Mediterranean, and in Bulgaria; see Marco (122) for a review of the fossil record and specific references.
Other Pleistocene Aquila eagles have been found in the Galilee region of Israel, on the southeastern island of Sicily, Italy, and in midwestern and southern Bulgaria (122). Late Pliocene fossils of an Aquila eagle are described from northwestern Bulgaria. This bird was larger but closely related to Golden Eagles (123). A fossil Aquila record from the Mid-Miocene in Northern Territory, Australia is the oldest of the genus for that country (124). Aquila-like remains are reported in fossils from the Upper Eocene or Lower Oligocene in Europe (125) and from the Quaternary in Cuba (126). The latter fossil was originally described as an Aquila, but was later redescribed and assigned to the genus Buteogallus (127).