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The Golden Eagle (Aquila chrysaetos)

The golden eagle, Aquila chrysaetos, is possibly the best known bird of prey in the Northern hemisphere, occurring throughout North America, Eurasia and Africa, with five sub-species recorded. Historically the golden eagle was widespread throughout the Holarctic but has since disappeared from heavily populated areas and still remains rare in many Eastern European countries with some populations still in decline: in Romania they are currently considered as vulnerable but are afforded strict protection. Golden eagles are territorial, holding territories up to 150km2 and although their habitat requirements are not specific, they are dependant on undisturbed nesting sites. Their habitats range from sea level up to several thousand feet occupying open terrain, mountains and plateaus but are rarely found in heavily forested areas, during harsh winters they will migrate southwards if food supplies decline.

Physical Characteristics

The golden eagle is a large bird with a wingspan of up to 7 foot and weighs between 3.2 – 6.4kg with the female being one quarter to one third larger than the male. Their name comes from a striking golden colour crown and nape in adult birds, with the rest of their plumage varying from a dark brown/black to dark golden brown colour. Immature birds have a more mottled appearance with white bands on the tail and at the carpal joints; these white patches gradually disappear with each moult until the adult plumage is reached at around five years. The feathers of adult birds extend the full length of the leg to the massive yellow talons, whereas those of immature birds extend only part way down the legs. Golden eagles reached sexual maturity around 5 years and live for around 15 – 20 years; however they have been recorded to live as long as 32 years.

Feeding

Golden eagles are considered as avian apex predators, meaning that healthy adult birds are not preyed upon. The prey of golden eagles is small to medium sized mammals and birds depending on the habitat, with carrion being an important supplement, they will also steal or kleptoparasitize prey from other raptors. The predominant prey of nesting birds, making up between 50 - 94% of the diet, are species belonging to the leporids (rabbits and hares) and sciurids (ground squirrels and marmots) groups. Other prey regularly taken include young deer, chamois, ibex and goats, however they will kill adults if food is scarce by driving them off cliff faces, they will also prey on gallinaceous birds (ground dwelling or game birds) such as grouse and ptarmigans. There are records of golden eagles taking other raptors such as Eurasian eagle owls and falcons and will displace vultures and other raptors from carrion. The eyesight of golden eagles has a resolution power around eight times greater than that of humans and can see in colour allowing them to spot prey from a long distance and use their talons for killing and carrying prey and a mating pair will often work together with one of the pair driving the prey towards the waiting partner. Although they are well adapted to hunting a wide variety of prey in numerous habitats, around 70% of hunts actually result in failure.

Reproduction

The golden eagles reach sexual maturity at around 5 years, at which point they will start to look for a mate with which they will pair for life. At this stage they will set up a territory and start to build nests or eyries of branches and grass when in use, either in the trees or more commonly on cliff faces, which they may use alternately in subsequent years. Their courtship display is performed in flight which involves plunging and looping together. After mating the female will typically lay 2 eggs a few days apart known as asynchronous laying, although 3 eggs are not uncommon, which are incubated for up to 45 days primarily by the female. When the chicks hatch they weigh around three ounces and are covered in white fluffy down. The parents will feed the chicks for an average of fifty days, however often it is only the older chick that will survive as it will typically be slightly bigger and stronger than the second chick due to a few days head start. The larger chick will normally win squabbles over food and the ‘Cain and Abel’ situation of the larger chick killing the smaller chick is commonly seen in this eagle. It is not clear why this happens as it appears to be unrelated to insufficient food or innate aggressiveness and may simply be the second egg acting as a reserve chick should anything happen to the first one. The chicks or eaglets fledge at around 72 – 84 days and remain dependant on their parents for up to 11 weeks.

Golden Eagle in human culture

Golden eagles have a long and sometimes colourful relationship with humans and their culture ranging from heraldry to falconry to religion. The golden eagle is currently the national bird of five countries, used in the coat of arms of a further three and is featured in the coat of arms of many other countries, including Romania. The golden eagle is the central element of the coat of arms and is a symbol of Latinity, courage, determination, power and grandeur and is also present on the coat of arms of Transylvania.

Conservation Status

The golden eagle’s former range spanned the Northern hemisphere throughout North America, Europe and Asia breeding throughout the plains, forests and mountains. As a result of persecution and poisoning the species has experienced a decline in numbers and range and in some cases extinction, for example in Ireland. The biggest decline has been seen in Central Europe where this species is now restricted to mountainous areas such as the Apennine, Alps and Carpathian mountain ranges. There are two main causes that have been mirrored across the globe for the decline in numbers; these are poisoning and habitat destruction.
Habitat destruction has been the major driving force behind the declines, where by the late 19th century eagles had been driven from huge areas they used to inhabit and restricting them to more remote locations and restricting the amount of available territories and also food. Increasing humans populations are resulting in intense industrialization and deforestation for the growing of food crops is resulting in dramatic decline of suitable territories for juvenile eagles including an increase in power lines. There have been increasing cases of electrocution of eagles by power lines in Europe, although some countries (for example Germany) now have laws in place to ensure that all power lines are bird friendly, it is in the rural areas that overhead power lines pose the greatest threat especially to juvenile eagles as they look to set up their own territories. As we become more “environmentally aware” and look at alternative or renewable energy sources such as wind turbines, we are actually potentially increasing the risks to these birds. It is now estimated that around 100 golden eagles a year die at Altamont Pass in North America and several hundred have died worldwide as a result of flying into the turbine blades. The disturbance that is caused during the building of the wind farm is also of concern as they lead to destruction of nest sites and also habitat, although in some areas the habitat may recover, the eagles have not been shown to return. There is some hope though; as natural heritage and conservation organizations are now being consulted during the planning stages it is helping to safe guard some of the most important habitats for these birds.
Poisoning, both indirectly through pollution and directly though bate, and persecution pose the greatest threat to these birds in some areas with approximately 50% of golden eagle deaths now being attributed to humans. In the 20th Century the use of chemicals that accumulate through the food chain such as DDT and other insecticides were a major contributory factor in the decline in numbers, and although many of these insecticides are now banned, the eagles still suffer from poisoning, but now it is the eagles themselves that are the targets. Many farmers believe that eagles are responsible for the death of young livestock and although illegal, is still a regular occurrence. Eagles are also poisoned or shot on grouse moors and private estates where sport hunting of black grouse takes place as they are believed to be responsible for a decline in grouse numbers and as a result, huge swaths of suitable golden eagle territory remain uninhabited by them. As eagles, especially young ones, frequently feed on carrion they are easy targets for poisoning. In some countries, nests are still robbed of their eggs by egg collectors or for selling on the black market.
In Romania, golden eagles used to be common sight in mountainous areas such as the Carpathians, until the beginning of the 20th century, but as with most other countries huge declines were seen as a result of persecution, poisoning and pesticides. There are believed to be around 40-60 breeding pairs in the whole of the Carpathian Range, but no definite numbers for the Transylvania Carpathians. What is encouraging is the level of protection that these birds are afforded with all hunting illegal under the Bern Convention and proposed monitoring and public education of both the birds and also of their nest sites and habitats. The Carpathian Mountains are considered as one of the last refuges for this endangered bird in Europe.

So what now?

Despite declines in numbers, on-going persecution and habitat destruction, the golden eagle is listed as least concern on the IUCN red list; however, this is largely due to the large Asian and American populations. This said, in many countries, including Romania the golden eagle is considered endangered and does require further research and protection to safe guard the small populations that are hanging on. A greater understanding of their needs and also the impacts of what we would term “environmentally or ecologically friendly” energy alternatives is required along with close monitoring of territories to provide an understanding of what human activities cause disturbance. Only then can we effectively plan and implement conservation strategies for this majestic bird.

References

Brandes, D. Windpower and Migrating Raptors: An Unresolved Issue.

Drewitt, A.L., & Langston, R.H.W., (2006). Assessing the impacts of wind farms on birds. Ibis, 148, pp. 29-42.

Munteanu, D. rare, Vulnerable, Endangered Birds In Romania.
http://www.plural-magazine.com/article-rare-vulnerable-endangered-birds-in-romania.html

Pedrini, P. and Sergio, F.(2001) 'Golden Eagle Aquila chrysaetos density and productivity in relation to land abandonment and forest expansion in the Alps', Bird Study, 48: 2, 194 - 199
Pedrini, P., & Sergio, F. (2002). Regional conservation priorities for a large predator: golden eagles (Aquila chrysaetos) in the Alpine range. Biological Conservation, 103, pp. 163-172.

Romania Web Directory. http://www.romania.org/romania/coat-of-arms.html

Witkowski Z.J., Król W., Solarz W. (eds.). 2003. Carpathian List Of Endangered Species.
WWF and Institute of Nature Conservation, Polish Academy of Sciences, Vienna-Krakow