Status and conservation of the golden eagle

In flight in Czech Republic

At one time, the golden eagle lived in a great majority of temperate Europe, North Asia, North America, North Africa, and Japan. Although widespread and quite secure in some areas, in many parts of the range golden eagles have experienced sharp population declines and have even been extirpated from some areas. The total number of individual golden eagles from around the range is estimated to range somewhere between 170,000 and 250,000 while the estimated total number of breeding pairs ranges from 60,000 to 100,000.[1][2] Few other eagle species are as numerous, though some species like tawny eagle, wedge-tailed eagle and bald eagle have total estimated populations of a similar size to the golden eagle’s despite having distributions which are more restricted.[3][4] The world’s most populous eagle may be the African fish eagle (Haliaeetus vocifer), which has a stable total population estimated at 300,000 individuals and is found solely in Africa.[3][5] On a global scale, the golden eagle is not considered threatened by the IUCN.[6]

Eurasia

In Europe, there are an estimated 6,000 to 10,000 breeding pairs. There was a great decline in Central Europe where they are now essentially restricted to the Apennine, Alps, and Carpathian Mountains. The strongholds in the continent are Spain, which holds an estimated 1,300 breeding pairs, Norway, which holds an estimated 860 to 1,040 breeding pairs and European Russia, which holds an estimated 500 to 1,000 breeding pairs.[7] Other European countries with stable and sizable populations include Italy, with an estimated 476–541 pairs, Switzerland, with 300–310 pairs and Romania, with an estimated 85–130 pairs.[7] The following nations are thought to have golden eagle populations that are increasing: Bulgaria with 150–170 pairs, Denmark with 1 known breeding pair, Finland with an estimated 300–350 pairs, France with approximately 390–460 pairs, Hungary with 3–5 known pairs, Ireland with 2 current pairs and Poland with approximately 35–40 pairs.[7][8] The following nations are thought to have decreasing golden eagle populations: Albania with about 50–200 pair, Croatia with approximately 90–110 pairs, England with no known current pairs, Greece with an estimated 100–200 breeding pairs and Latvia with somewhere around 5–10 pairs.[7][9][10] Several other European countries have a small number of golden eagles with less than 50 breeding pairs but with populations that are generally considered stable.[7] Despite their large population there, the golden eagle was considered near threatened in Spain in a 2003 report.[11] One of the authors of the previous study asserted that the population had increased in 2008 by perhaps 20% in Spain since the last survey in the late 1990s.[12] In Belarus, the population has reportedly declined considerably due to trapping, poisoning and the draining and development of upland bogs.[13] The golden eagle is considered Critically Endangered in the Czech Republic, where it was once quite common in the Beskydy and Krkonoše Mountains until logging hit the area hard around the time of World War II. All recent breeding attempts by the species in the Czech Republic are believed to have been unsuccessful.[14]

In Britain, the last comprehensive survey of golden eagles took place in 2003, and found 442 occupied territories.[15] A less thorough survey in 2007 showed that in addition to large numbers of territories in the Scottish Highlands and the Inner and Outer Hebrides, there were a handful of birds in southern Scotland and northern England.[16] The population is higher today in Scotland than it was in the 19th century, due to the heavy persecution at that time by sheep farmers, gamekeepers, and collectors.[1] There may have been as few as 190 pairs in the 1950s, though this survey may have not been complete.[17] Between 1969 and 2003 they nested in the Lake District, Cumbria.[15] In Ireland, where it had been extinct due to hunting since 1912, efforts are being made to re-introduce the species. In April 2007, a pair of golden eagles produced the first chick to be hatched in the Republic of Ireland in nearly a century. Forty-six birds were released into the wild in Glenveagh National Park, County Donegal, from 2001 to 2006, with at least three known female fatalities since then. It is intended to release a total of sixty birds, to ensure a viable population. The reintroduced golden eagles at the park produced a pair of fledglings for the first time in 2011.[18] The golden eagle is classified as bird of “High Conservation Concern” in Ireland.[19]

Fewer estimates are known from Asia and North Africa. A stronghold population is in mountainous Turkey, where the large population included an estimated 2,000–3,000 breeding pairs persist. In Japan, there is an estimated 175–260 breeding pairs, with a total population of approximately 500 individuals. One study stated that food shortages and decreases in suitable foraging habitat are assumed to be responsible for an observed decline in population size and reproductive success in Japan.[20] In the Koreas, the golden eagle is known to be rarely observed and, in 2010, only 10 were seen in South Korea during winter birding censuses. Little is known in terms of population numbers elsewhere in Eurasia, with the IUCN estimating between 100 and 10,000 individuals each in China and in Russia, numbers that suggest the species occurs very sparsely in these massive countries.[21] In North Africa, the main occurrence is in Morocco, which is estimated to hold 200 to 500 breeding pairs. There appear to much fewer in other North African countries, with small, scattered populations in Algeria, Tunisia and Egypt, areas where no immature-plumaged eagles were observed in 2005.[22]

North America

In North America the situation is not as dramatic. It appears the greatest density of golden eagles anywhere in the world occurs in the Western United States and Western Canada. In total, the contiguous Western United States may hold up to 30,000 individual golden eagles, with a total of 70,000 to 100,000 individuals estimated across all of North America.[23][24][25] One estimate of the number of breeding pairs in the contiguous Western United States that excluded California, South Dakota, Montana and Oregon was 9,387.[26] The state with the largest known winter count of golden eagles is Montana with 13,138, followed by Wyoming with 10,072, Colorado with 7,081 and Utah with 5,993. Wyoming had the highest estimated set of breeding pairs 3,381–4,174, followed by 1,800 in Utah, 1,200 in Nevada and California and Idaho both with around 500 pairs (notably, Montana was not included in these particular studies, although the breeding population must include well over a thousand pair there).[27][28] In 6 out of 8 Canadian provinces where golden eagles breed, over 10,000 birds were observed in breeding bird surveys.[29] In 1981, it was estimated that there were 63,242 wintering individual golden eagles in the 16 Western United States (excluding Alaska).[25] However, there has still been a noticeable decline in some areas.

Threats

In modern times, almost all threats to golden eagles are attributable, directly or indirectly, to human activities.[30] In fact, all Aquila eagles in Eurasia face the same human-sourced threats as the golden eagle: habitat change, persecution, poisoning (often directed at other species) and collisions with man-made objects.[1] Certainly the most widespread unintentional threat to golden eagles by humans is urbanization and human-population growth which have made areas historically used by eagles unsuitable both in terms of habitat and prey availability. Habitat destruction in North America had, by the late 19th century, already driven golden eagles from some regions they used to inhabit.[31] In Southern California and the Colorado Front Range, this has been proved via long-term population and habitat surveys.[32][33] In Western China, the main threats to golden eagles are land development, the use of pesticides and apparent regular captures for falconry.[34] Fires since 1980 have caused large-scale losses of shrubs and jackrabbit habitat in areas used by eagles throughout the Intermountain West of North America. Wildfires that burned more 40,000 hectares of scrublands between 1981 and 1987 in the Morley Nelson Snake River Birds of Prey National Conservation Area affected nesting populations adversely. Nesting success at burned territories in Snake River Canyon declined after major fires. Abandoned burned territories have been subsumed by neighboring pairs, resulting in a decreased number of nesting pairs.[35] In a few cases, mankind has accidentally benefited golden eagles by logging previously heavily wooded areas. This has been recorded in the 1800s and 1900s in the Appalachian Mountains of the Eastern United States, where reforestation has now made the habitat unsuitable for nesting eagles, and in Washington state, which still holds breeding eagles in desolate areas that have been logged.[36][37] Afforestation, the commercial planting of non-native woodland, is a serious issue in Scotland, with the largest amount of it occurring in southwestern Scotland, especially in Argyll. During afforestation, the land is ploughed and in excess of 2,500 seedlings are planted per hectare, mainly with exotic conifers including Sitka spruce (Picea sitchensis) and lodgepole pine (Pinus contorta). The woodland canopy closes and ground vegetation dies, making these dark and gloomy places until harvesting in 40 to 50 years. More than 50% of land in Scotland at an elevation of 200–600 m (660–1,970 ft) has been planted as such. Afforestation requires removal of sheep and the fencing out or shooting deer, both important sources of carrion for golden eagles. Foraging areas of golden eagles have been confirmed to not include afforested areas.[1][38]

Death by collisions with man-made structures and objects can be a serious local issue. Electrocution or collision with power lines has become an increasingly significant cause of mortality since the early 20th century. Apparently, juveniles birds are more susceptible than adults, being generally less cautious and physically adept.[39] Due to attempts to perch on or by flying into power lines, a total of 134 and 115 golden eagles were killed by power lines in the western United States in 1972 and ’73, with a peak of 66 in Utah in 1972.[40] Today, golden eagles still regularly meet their demise due to power lines in the United States and the species was considered the bird-of-prey in North America most likely to be killed by them.[41] 266 examined golden eagle deaths from 1980 to 1990 in Spain showed that 14 of the deaths (5%) were from electrocution and 57 (21%) were from wire collision.[42] Compared to the United States and Spain, in some other parts of the range such as Scotland and Scandinavia, electrocutions and wire-collisions are rare due to fewer high power-poles in the desolate areas that the golden eagles occupy.[1] Controversially, the US Fish and Wildlife Service has permitted that a "wind-farmer" in central Oregon could legally cause the incidental killing of golden eagles by large wind turbines. Such turbines have set up as an alternative source of energy but are often fatal for high-flying birds such as raptors.[43] Wind turbine blades appear to move slowly from a distance but at close range move so quickly as to appear a nearly invisible blur. It is estimated that up to 70 golden eagles may be killed locally by turbines each year in west-central California, almost all of them being juveniles as opposed to adults which tend to remain on their home ranges that largely occur outside of the wind farm area.[44][45] There are mounting concerns of the effect of wind turbines in Europe as well, since construction of new ones is increasing in Scotland and Spain.[46][47] Collisions with automobiles rarely claim golden eagle lives, though instances of this can increase in desolate areas during winter, when road-side prey or carrion may attract the eagles. In California's Diablo Range, 5% of 61 radio-tagged birds died from vehicle collisions.[44] Where disturbance is regular, breeding failure for golden eagles is significantly more frequent. This was certainly inferred in the 1982 Scottish breeding bird survey when disturbances were heavy in the Highlands.[1] Sheep farmers and egg-collectors are the leading cause of disturbances at the nests. Recreation, forest management and development projects such as road construction, mining or power generation are other potential sources of disturbances. When disturbed by humans at the nest, the parents frequently leave their nest for a period of up to two hours, reduced provisioning rates, endangered eggs or young to predation, as well as overheating, chilling or desiccation.[48] Human intrusion within 750–1,500 m (2,460–4,920 ft) of nests can cause disturbance.[49] Nesting success was found to be reduced in Norway during years where the Easter holidays fell early, apparently due to the volume of vacationers in the countryside in these years during the pivotal early stages of nesting.[50] During a study in Wrangell – St. Elias National Park and Preserve of Alaska, experimenters camped within 400 m (1,300 ft) of active nests, which led to reduced food delivery and nest attendance by the parents, then at 800 m (2,600 ft), at which distance the disturbance of nesting behavior seemed to decrease considerably.[51] The topography of the landscape and location of the nest can affect how closely the nest can be approached without disturbance.[52] Mining and various types of energy development occur in eagle nesting and wintering habitat. The practice of surface coal mining threatens the limited nesting sites in Wyoming.[53] In the Italian Apennines, high levels of nesting failures have been contributed directly to disturbance, thanks to increased tourism in remote mountain areas, construction of new roads and mining.[54] Aggressive behavior by golden eagles due to a human presence near the nest is considered exceptional and usually only result in minor injuries if any, as a particularly bold eagle may rarely attempt to dissuade a human trespasser.[55][56] Golden eagles are somewhat sensitive to human disturbance even while not nesting. Experimental studies showed that pedestrians, which caused flushing at 105–390 m (344–1,280 ft), were more likely to cause wintering golden eagles in Colorado to flush than vehicles, at 14–190 m (46–623 ft). This study showed that golden eagles were more sensitive to human disturbance during winter than several other raptor species, including bald eagles.[57]

The intentional killing of golden eagles has been a huge conservation hurdle for the species. While illegal in most countries today, hunting, trapping and poisoning may still occur clandestinely across almost the entire range. During 1948, in Carter County, Montana, 286 golden eagles were shot and killed in the month of March alone. At the time $5 was offered by the Montana Fish and Game Commission for each eagle killed, a bounty initiated by pressure from sportsmen and ranchers who believed that eagles were killing large numbers of sheep and “antelopes”.[58] Approximately 20,000 golden eagles were killed from light aircraft in the Southwestern United States in the 1940s, with the rate of such shooting in Texas having continued at over a thousand a year (5,000 from 1942 to 1947).[59] In the United States, the golden eagle was given federally protected status in 1963. Allegedly, in 1972, over 800 golden eagles were shot from aircraft in Wyoming and Colorado.[60] [61] In Switzerland more than 100 golden eagles were reportedly shot each decade until the species was legally protected in 1953.[62] In Scotland, many estate managers would pay gamekeepers to hunt down any and kill all eagle species in the 1800s and early 1900s. On one estate in Caithness, Scotland, allegedly 295 eagles (including both golden and white-tailed eagles) were shot and trapped from the years of 1820 to 1826.[63] Occasionally, golden eagles may be caught in trap lines laid out to capture mammalian predators.[64] Today, some authorities believe many game managers still try to deliberately destroy the contents of nests in spring or intentionally disturb the eagles during their nesting process.[1] In a study conducted in Scotland, areas were broken down between low disturbance areas (with a low human presence and limited history of persecution), moderate areas (where minor disturbances occur, mainly unintentionally from hill-walkers or rarely intentionally by egg-collectors) or severe disturbance areas (where persecution, heavy disturbance and considerable egg-collecting is believed to still occur). In low disturbance areas, about 45% of nests failed, in moderate disturbance areas about 74% failed and in severe disturbance areas 93% of nesting attempts failed.[65] 73 out of 147 inaccessible nesting sites in this study (50%) produced fledglings, whereas more accessible nests produced fledglings in only 21 out of 68 nests (31%).[65] The golden eagle became legally protected in 1980 in Spain but the species is still regularly killed there today. In 266 golden eagle deaths from 1980 to 1990, 59% (157 specimens) had died from shooting or trapping and 8% (21 specimens) died from poisoning.[42]

Poisoning, both intentional and unintentional, is perhaps the most insidious man-made threat to golden eagles. The usual targets of carrion-poisoning are species such as coyotes, red fox and gray wolves, which are considered pest that threaten livestock (a charge usually vastly exaggerated by the human imagination). However, golden eagles are occasionally targeted as well for the same reasons. The main cause of mortality for golden eagles in Britain has been poisoning, with a number of 51 eagles verified to be killed by poisoning from 1980 to 2008 probably being far lower than the actual amount killed as such.[1][66] A disproportionate amount of golden eagle poisonings in Scotland from 1981 to 2000 were linked to grouse moors (where grouse are kept for the pleasure of shooting) and were probably cases of gamekeepers deliberately poisoning eagles and foxes to keep their stock of grouse high.[67] It is estimated that the adult survival rate is reduced by 3 to 5% in Scotland by intentional poisonings.[66] In the 1980s, California ground squirrels, due to the perception among cattle rangers that they are agricultural pests, were poisoned by the anticoagulant rodenticide, Chlorophacinone. In turn, the poisonings caused golden eagles, as one of the major natural predator of California ground squirrels, to die in turn.[68] At least 10 individuals died in 1971 from eating Thallium(I) sulfate–laced pronghorn set out by sheep ranchers in Wyoming; despite public outcries, poisoning by sheep ranchers continued into the 1980s.[61] In the 20th century, organochloride and heavy metal poisonings were also commonplace, but these have declined thanks to tighter regulations on pollution. In southern Idaho, 10 out of 17 golden eagles examined were found to have had exposure to lead.[69] As a whole, the golden eagle is less susceptible than most raptors to organochlorine pesticides because of mammal-feeding habits, as opposed to predominantly bird-eating species like peregrine falcons and fish-eating species like bald eagles, both of which had huge population declines in the 20th century due to the use of pesticides like DDT . Eggs from golden eagle nests that were collected after 1946 in North America had shell thicknesses similar to (of less than a 10% difference) those collected in earlier years.[70] However, in Scotland egg shell thickness did decrease by around 10% from 1951 to 1965.[71] A dead golden eagle collected on the island of Lewis had the highest concentration of organochlorine known from a modern bird in Scotland.[72] The higher effects of organochlorines in Scotland may be due to the fact that birds there consume a relatively high quantity of seabirds, as opposed to North America, where this practice is rare.[1]

The reason why golden eagles are intentionally killed is usually due to the fear of loss of livestock and game species. As previously described, most feeding on ungulates is probably only as a carrion. The findings of virtually every study of losses of stock to golden eagles has revealed that the actual amount of livestock killed by the eagles is negligible and financial restitution from conservation organizations should not be necessary, including those studies funded by the farming organizations or governmental programs seeking to justify the “control” of golden eagles.[1] In Scotland, studies have revealed that an estimated 0.5–8% of lamb mortality is attributable to golden eagle predation. This equates to the raptors killing about 0.15–2.4% of a given flock of sheep. Starvation and accidents are actually the primary cause of lamb deaths in Scotland, with occasional fox, crow and dog predation also occurring.[73][74][75] On the Western Isles of Scotland, a closely studied relationship between the nesting golden eagles and the local sheep flocks showed that 1 to 3% of lamb deaths were attributable to this species.[76] In North America, sheep predation is generally even rarer than in Eurasia but some flocks of sheep in Montana have experienced a relatively heavy rate of loss, more than 10% in some cases, determined to be caused by golden eagle predation in harsh-weather years that lower the numbers of jackrabbits and cottontails.[77] Some organizations have attempted to relocate golden eagles from areas where lamb predation was semi-regular. In Montana, over 400 eagles (most seemingly migratory specimens) were relocated at a cost of over $100,000. Similarly, 16 breeding eagles were relocated in Wyoming after relatively heavy levels of lamb depredation. In each case, relocation has failed as the eagles find their way back to their own home ranges or wintering grounds in a matter of a few weeks, showing that the eagles have a strong homing ability.[77][78] In northern Norway, among 36 deaths out of 263 first-year, radio-collared lambs in a free ranging sheep flock died, 17 from wolverine predation, 8 were from disease, 5 from golden eagle predation, 3 from Eurasian lynx predation and 2 from Red fox predation.[79] In Sweden, the hunting of semi-domestic reindeer by golden eagles has been analyzed. Of an estimated 120,000 reindeer born every year in that nation, golden eagles are reported to kill less than 500 of them, amounting to less than 0.4% loss.[80] Jeff Watson advocated that, instead of trying to kill the golden eagle, that sheep-farmers should encourage population growth in prey like rabbits, hares and ground squirrels, as golden eagles will generally ignore livestock if wild prey is abundant.[1]

Conservation

The golden eagle is not threatened at the species level but efforts need to be taken to prevent extinctions from many northern countries. The primary efforts undertaken to conserve the species have been, in order of prevalence from highest to lowest: conservation education and awareness, policy protection, directed land management, legislation and law enforcement and the provision of indentures.[1] In Scotland, only 3 out of 16 regions in Scotland occupied by golden eagles since 1982 have been deemed favorable for conservation status, based upon the extent of local persecution, prey abundance and habitat change.[46] The United Kingdom has put in place deterrent legislation to prevent behavior around the nest with the potential to cause harm and acts of willful harm to white-tailed eagles and some have advocated using the same policies for golden eagles.[46] Education in this region mainly is undertaken by the Royal Society for Protection of Birds (RSPB). To curb the destructive practice of afforestation, some locals have switched to planting native Caledonian pine forests instead, likely resulting in much less harm to the native fauna possibly including golden eagles.[81] While conservation efforts in Scotland have previously included the setting aside Sites of Special Scientific Interest (SSSIs), these are usually too small to benefit golden eagles. More recently, the United Kingdom government has instead taken from governmental policies enacted in Continental Europe the idea of Special Protection Areas (SPAs), which offers strong legal protection of single species. Potentially more than 7,000 km2 (2,700 sq mi) may be set aside in Scotland as SPA for golden eagles.[82] Some education of mountain-climbers in country holding breeding golden eagles has been undertaken by the Mountaineering Council of Scotland.[83] Within the United States, the golden eagle is legally protected by the Bald and Golden Eagle Protection Act.[4] In the United States, many studies of the effects of industrialization and development have been undertaken by the very companies attempting to develop near areas holding golden eagles, in order to understand and hopefully minimize harmful effects. For example, Swan Falls electric power-plant in southern Idaho has funded research into the effects of reconstruction activities on breeding raptors (including the golden eagles), the Arch Mineral Corporation has funded studies attempting to test and successfully relocate golden eagle nests and KENETECH Windpower and the National Renewable Energy Laboratory have funded research into the effects of turbine-based wind energy on golden eagles.[44][84][85] In the 1970s in the United States, bounds were made to reduce the number of golden eagles to die from electrocution and wire-collisions. The primary change has been to raise the central insulator more than 1 m (3.3 ft) above the cross-arm and to position the ground-wire at a lower height on the pole, both likely to reduce the probability of golden eagles striking the wires with their wings. Also, the power company may place an insulating tube from 1 to 2 m (3.3 to 6.6 ft) on either side of the pole attachment or, especially if the previous modifications are not feasible, install raised perches at the top of the power pole.[86] In Spain, the issue of electrocutions is more intractable because all pylons were made out of metal, which makes them much more dangerous to wildlife flying into them.[87]

Effects on conservation-dependent species

On the conservation front, the golden eagle is itself unintentionally contributing to the conservation crisis of another animal, the island fox, a small insular relative of the gray fox found only in the Channel Islands of California. Golden eagles did not start nesting in these islands until the 1960s. The predominant theory on why they did not previously occupy them was that territorial bald eagles deterred them until DDT use decimated the local bald eagle population.[88] This critically endangered canid had evolved without major natural predators but the large breeding population of golden eagles in California has spilled in numbers over to the islands and is there feeding partially on the foxes, whose already declining population cannot support sustained predation.[89] Also in North America, attempts to reintroduce endangered whooping cranes by mixing them with flocks of sandhill cranes have been largely unsuccessful in part due to natural predators picking off the unnaturally unwary birds. Although the chief predator has been bobcats, golden eagles are one of the other predators that are habitually killing the birds.[90] The golden eagle may be a competitor and, rarely, a predator of the recently reintroduced California condors in central Arizona and southern California, but the pressure exerted by the eagles on condors are seemingly minor, especially in contrast to manmade conservation issues for the species such as lead poisoning from bullets left in hunter-killed ungulate carcasses.[91][92] In Scotland, the common hen harrier has been the subject of much unfavorable attention due to the fact that it is a habitual predator of the chicks of red grouse, a subspecies considered to be near threatened in the nation. One of the methods to control harrier numbers has been proposed is to encourage a population increase of golden eagles, which may also hunt grouse but are unlikely to cull young grouse and tend to outcompete and sometimes hunt the harriers themselves.[93]

References

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  35. ↑ Kochert, M.N.; Steenhof, K.; Carpenter, L.B.; Marzluff, J.M. (1999). "Effects of fire on Golden Eagle territory occupancy and reproductive success". Journal of Wildlife Management. 63 (3): 773–780. doi:10.2307/3802790. JSTOR 3802790.
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