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How and why has the number of golden eagles fluctuated in Scotland?
Since the early 20th century golden eagles in Scotland have recovered, having reached a low point of perhaps as few as 150 pairs. Now there are over 420 pairs and the population is stable -- confirmed by three national censuses in the past 20 years. There are still threats and the population is yet prevented from reaching its full potential. Although fully protected by law since 1953, eagles in Scotland are still killed illegally each year.
Jeff Watson spots a golden eagle. |
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Most man-induced deaths occur through eating poisoned bait, set illegally to control foxes and crows but consumed by eagles, especially in winter when they are great scavengers, feeding on dead sheep and deer and other easy pickings. Poisoned baits are laid by gamekeepers who believe they must control predators on the commercial grouse moors that occur mostly in the drier climate of eastern and southern Scotland. This mortality leaves many gaps in the golden eagle range and is a major factor limiting the expansion of the population south into the border (between Scotland and England) country and to England where only one or two pairs survive.
Apart from human persecution, the fate of eagles in Scotland is determined by land-use practices, and their effect on the eagle's food supply. Populations are most dense in the west of the country where there is abundant winter food in the form of sheep and deer carrion. Here golden eagles occupy territories as small as 18 square miles, whereas in the east they range over areas of 50 to 60 square miles. In summer, eagles need live prey, as opposed to carrion, to feed their growing chicks. Such prey as red grouse, mountain hare, and rabbit are generally more plentiful in the east of the range and consequently the birds here, so long as they are free from persecution, tend to breed more successfully. Typically in the west of Scotland breeding success is around 0.3 chicks per pair per year and in the east nearer 0.7 chicks. Broods of two chicks are not uncommon in the east but very rare in the west.
Two land uses other than grouse moor management influence the fate of eagles in Scotland. In the southwest Highlands large-scale commercial forestry plantations in open mountain country have displaced the favored open-country prey of eagles and led to population declines, notably in places like Kintyre but also in my native Galloway. In the northwest of Scotland there are potential long-term problems resulting from over-grazing of the upland vegetation by excessive numbers of sheep and deer. This has led to loss of heather -- the principal food plant for grouse and hares -- and as a result there is often little other than carrion for eagles to feed upon.
Where else do golden eagles live? How are golden eagles in Scotland different from in other parts of the world?
The golden eagle has a circumpolar distribution in the northern hemisphere, known as a Holarctic distribution, and occurs generally between latitudes 30-60 degrees north. Typically it is a bird of mountain regions, ranging from Scotland and Scandinavia, the Alps and the mountains of Spain, eastwards to the great Himalayas, and with a Eurasian outpost in Japan. In North America it is most abundant in the west with the heartland in the Rockies from Alaska south to Mexico. One population occurs almost at the Equator in the Bale Mts of southern Ethiopia.
In some flat landscapes golden eagles can thrive so long as their prey is plentiful and there is some vertical structure to the vegetation and nest sites are present. For example there are eagles in the flat peatlands of the Baltic where they nest in pine trees in isolated forest stands that are surrounded by open peatlands with abundant capercaillie and small roe deer as prey. It is the size of available prey that is important to golden eagles. There needs to be plentiful food in the weight range of 2 to 6 pounds. This is often provided by species of grouse or hare, as in Scotland, but can be substituted by some unusual prey like tortoises in the eastern Mediterranean, large lizards in North Africa, and even hedgehogs on the Swedish island of Gotland. In the United States jackrabbits are important food, especially in hot desert areas to the south. In Scotland, and throughout much of this range these eagles nest on crags in mountains. Where cliffs are lacking then they will build huge structures in sturdy trees such as pines.
The golden eagle over much of western Europe is one of the larger races, outsized by the massive Himalayan race in which the female can weigh up to 13 to 15 pounds. The smallest of all is the island race in Japan where females weigh it at just over six pounds. The North American race is also rather small, and tends to be darker than the eagles of Western Europe, looking especially black on the front and underside.
Adult golden eagles are more or less uniform dark brown, sometimes paler on the upperside where flight feathers can be bleached by the sun. Juvenile and immature eagles have large white patches on the wings and the tail, sometimes retaining these until they are three or four years old. These dramatic and huge black-and-white flight feathers are used by Native American Indians in their traditional war bonnets. There is a hugely fascinating, almost religious association between some Native American tribes and the golden eagle. In the Tien Shan Mountains of central Asia there is today a strong living tradition that involves men hunting with golden eagles from horseback; here their quarry is the Corsac fox (hunted for its fur), and the antelope (hunted for meat). Some even report these horse-borne eagles catching wolves!
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Eagle IQ
Learn all about the majestic golden eagle. |
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Interview
Discover one man's passion for this bird. |
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Birds of Prey
What makes a bird a "bird of prey"? |
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Resources
Web links and books related to the program |
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