About Golden Eagles
Where they can be found
Golden Eagles can be found at various latitudes in the northern hemisphere all around the world. In North America, most eagles that breed north of the Mt Lorette watch site are migratory. Those that breed at more southern latitudes tend to stay in the same area year-round, although there can be some movement when not on territory. While most Golden Eagles in Alberta fly south for the winter, a few can be found year-round as far north as the Edmonton area, in some prairie locations, and in the foothills in southern Alberta.
Identification
Adult Golden Eagles are large, dark brown raptors. They have golden feathers on the back of the head and nape, as well as on the leading edge of the wing. Paler brown feathers appear on the scapulars, which show as two pale (tawny) diagonal bars across the upper wing in flight. The tail feathers are faintly barred, and the tarsi are feathered down to the feet. These eagles reach their adult plumage around their fifth summer. Juvenile birds have white at the base of the tail feathers, and white patches of various size in the wings (at the base of the inner primaries and outer secondaries). As the birds grow older, the amount of white in the tail and the wings is gradually reduced, although some may retain small amounts of white into adulthood. The amount of white in the wings of immature birds is highly variable, and not a particularly good indication of age. The tawny bar on the upper wing appears in the second summer, so if an eagle lacks this feature, we know it is a juvenile.
Physical characteristics
Females weigh 3.6-6.7 kg (8-15 lb), and are, on average, larger than the males, which weigh 2.8-4.6 kg (6-10 lb). The wingspan ranges from 190 cm to 227 cm, or roughly 2 metres.
Confusingly similar birds
The only raptors in our area that are similar in size to the Golden Eagle are Bald Eagles and Turkey Vultures. Turkey Vultures are quite rare at the Mt Lorette site, but should be easily distinguished from a Golden Eagle by the very small, red head, black plumage, very broad wings, and a very different flight style – soaring Turkey Vultures hold their wings in a substantial “V” shape, they teeter from side to side, and when flapping their wings, the wings seem quite floppy. The underside of the flight feathers is a silvery colour that contrasts with the black of the rest of the wing and body.
Bald Eagles are more problematic. They are roughly the same size as a Golden Eagle, but with slight structural differences that can help with picking them out with some experience, as well as some notable plumage differences. Bald Eagle wings look more like planks, whereas the Golden Eagle wing has more of an S-shaped curve to the trailing edge due to slightly longer secondaries (the inner flight feathers). When soaring or gliding, the wings of a Bald Eagle are held in more of a horizontal position, whereas a Golden Eagle wing will have a slight dihedral or V shape. Bald Eagles have larger heads and shorter tails, so a Bald Eagle looks more balanced front-to-back than a Golden Eagle. Close up, the bill of a Bald Eagle can be seen to be substantially larger than a Golden Eagle’s, and this contributes to the large head appearance when viewed from a distance. In terms of plumage, Bald Eagles are mostly dark brown, but all of them have some white feathers, the distribution of which differs from year to year until they become adults, and also differ from Golden Eagles. Adult Bald Eagles are all brown except for the head and tail, which are white. Juvenile Bald Eagles are all brown, except for some white on the underside of the wings, close in to the body and never in a patch on the outer wing as a juvenile Golden Eagle would have. As a Bald Eagle grows older, it develops white on the belly, and the head and tail gradually turn white. By the third year, the belly and underwings will be losing that white colour and becoming brown like an adult. By its fourth summer, it will look almost like an adult, but will still have traces of brown in the head and tail. Most will have attained their adult plumage by their fifth summer.
Size differences between eagles
So, what’s larger – a Bald Eagle or Golden Eagle? The answer may be surprising – they are roughly the same size. There is much variation within each species, with the females larger than the males on average. But there is overlap in size between males and females and also between Golden Eagles and Bald Eagles. In a very general sense, Bald Eagles tend to be a bit heavier, and Golden Eagles tend to have longer wings, as might be expected for a species that needs some flying agility to capture prey animals like hares.
Taxonomic relationship
Interesting fact – in the world of bird taxonomy, Golden Eagles and Bald Eagles are not closely related to each other – Bald Eagles are more closely related to hawks like the Red-tailed Hawk than to Golden Eagles. On the evolutionary tree, the branch with Golden Eagles diverged from the Bald Eagle branch more than 20 million years ago. The word “eagle” is a general term applied to raptors with large wingspans. Bald Eagles belong to a group of eagles whose diet is primarily fish and are called fish-eagles. Golden Eagles belong to a group of eagles sometimes called “true eagles”, or “booted eagles” due to the feathers on their legs down to the toes. The scientific name for Golden Eagle is Aquila chrysaetos – the word “aquila” is Latin for “eagle”, which may mean that these “true eagles” were simply the first birds to be named as eagles. The word “chrysaetos” is derived from the Greek words “khrūsós” (gold) and “āetós” (eagle).
Habitat
Golden Eagles can live in a wide variety of habitats, from sea level to high mountains. Perhaps it is easier to describe the places they’re not usually found: urban areas, agricultural areas, burned forests, and dry deserts. For breeding in western Canada, they nest on cliffs or bluffs along rivers, or in mountainous terrain. They will also nest in trees and in some areas even on the ground. In winter they are usually found in more open habitats.
What do they eat?
The diet of Golden Eagles around the world is quite diverse. In western North America their diet is primarily small to medium-sized mammals (hares, rabbits, ground squirrels, marmots), supplemented with birds like grouse or ptarmigan. However, when their favoured prey items are not available, they will hunt other small mammals and birds. They will also scavenge on carcasses, particularly when on their wintering grounds.
More specifically, eagles that breed in the northern mountains, the northern tundra, and southern Arctic ecoregions prey primarily on ground squirrels, when the squirrels are not hibernating. When the squirrels are not available, the major prey items are snowshoe hare, arctic hare, and ptarmigan.
Migration
In the fall this is generally related to the ability to find food on the breeding grounds in the north – once there is snow cover and some of those smaller mammals go into hibernation, and with the loss in daylight hours for hunting, it is harder for the eagles to find food, and most must go south. There are exceptions – for example, some eagles have been known to over-winter in Alaska when snowshoe hares have been abundant. What specifically triggers the northward migration in spring is not known. In songbirds, it is known that short distance migrants like robins respond to changes in temperature and thus greening up of grass and trees. However, long distance migrant songbirds such as the ones that overwinter in South America, move north in response to the length of daylight. Are Golden Eagles responding to changes in daylight? It’s not known yet, but they do have a strong fidelity to their breeding grounds and have the instinct to head back there at some point. In addition, eagles that are resident in the areas where the migrants spend the winter will want to reclaim their territories for breeding and will push out the visitors. We have noted that satellite tagged adult eagles tend to inch northward when the weather is warm in late winter, but even if they have moved some distance north from their wintering grounds, they don’t really do any large movements to the north until early to mid-March.
Migration timing
Golden Eagles move south from August to December, with the peak of migration occurring around or a little after Canadian Thanksgiving at our count site. In the spring, they start moving in late February and continue into May. The peak occurs around the equinox. In spring most birds in the first three or so weeks are adults. The younger, non-breeding birds take their time going north.
Life Span
This is difficult to determine, but it is estimated that in the Rockies 50% of eagles live just 3 years, 25% live 6 years, 5% live 13 years, and 1% live more than 20 years. Golden Eagles in captivity have been known to live up to 46 years! Another analysis shows that there is an annual survival rate of 70% for first year birds, 77% for second year birds, 84% for third years, and 87% for birds more than 3 years of age.
Breeding
Golden Eagles are assumed to be monogamous, meaning that mated pairs generally stay together for life. They build nests on cliffs or in trees, and the nests are usually re-used from year to year. On average, two eggs are laid (sometimes more, sometimes fewer), and while often only one of the young will survive, two may fledge in years of high food abundance. Pairs typically attempt only one brood per season. This means that the rate of reproduction for these birds is quite low.
Conservation
The Golden Eagle is currently classified as “Least Concern” by the International Union for the Conservation of Nature, although it has experienced sharp declines in Europe and Asia. In western North America recent data point to a stable or slightly declining trend in population. The most recent Raptor Population Index analysis by the Hawk Migration Association, using migration data up to 2023 (including our data), shows declines at raptor migration count sites across the western half of the continent. At this point it is not known if the decline is due to a declining population, or whether it is due to changes in migration patterns.
Causes of mortality
Loss of nesting habitat, illegal poaching, collisions with vehicles and power lines, expanded energy development, electrocution, lead poisoning, rodenticide poisoning, and loss of food sources due to land development, and wildfires are all factors leading to a decline in population.
References: most of this information comes from the Golden Eagle account at Birds of the World (birdsoftheworld.org/bow/species/goleag), supplemented with information from ielc.libguides.com/sdzg/factsheets/goldeneagle/summary, and local observations.
