Satellite tracking of 22 juvenile Imperial eagles has allowed us at long last to know with certainty that non-safeguarded power grid poles are the most frequent cause of death for the juvenile birds.
These birds die most often due to electrocution by touching two conductors or a conductor and an earthed part of the facility. A large percentage of power lines in Bulgaria are a hazard for the large raptors and storks. Some of these lines are true death traps, killing scores of birds each year. The Imperial eagles like to perch on pylons. In some countries they even build their nests on long-distance line poles. Unfortunately, birds cannot differentiate between dangerous and safe pylons.
It is because of this particular reason that the BSPB has started working with all power distribution companies in Bulgaria in order to isolate the most dangerous poles near Imperial eagle nests. 390 dangerous pylons have been safeguarded during the project and work in this direction is still under way.
Widespread use of poisonous bait against predators during the 1950s is another reason for the disappearance of the Imperial eagles.
Another serious threat to raptors are the pigeon breeders who also set poisoned bait in order to eliminate the Goshawk and the Peregrine falcon, which are the most frequent attackers of pigeons. However, all raptors fall prey, although all of them are protected by law. In June 2011, the juvenile Imperial eagle named Sofia and tracked by satellite transmitter by the BSPB during the LIFE+ project “Save the Raptors”, was found dead near the town of Perushtitsa. The poisonous bait which had caused the death of the bird was found near Sofia's carcass.
The use of poison is strictly prohibited because it is a threat not only to domestic animals and wildlife, but also to humans. Unfortunately, poison baiting has not been discontinued.
Disturbance by humans is a frequent cause of failure to hatch. Many trees with nests in Bulgaria are in open spaces near arable lands. The eagles are accustomed to traditional agricultural activities such as grazing, plugging or movement of carts or automobiles along dirt roads. In Sakar we can see a shepherd and his flock passing underneath the nest without any response on the part of the brooding eagle. However, the appearance of machines unknown to the birds or of differently behaving people causes the birds to leave the nest.
Such cases are the appearance of a truck with workers, tourists, felling near the nest or shepherds shouting loudly. Leaving the nest causes death of the hatchlings due to cold or overheating.
This is why the BSPB has organised permanent guarding of the most endangered nests during the mating period, increasing the nesting success by 30%. Often, the nest guards prevent human disturbance and, also, save the young if they happen to fall from the nest or if they are brought to the ground by storm, as has been the case during the recent years.
Decreased souslik numbers
The European souslik (Spermophilus citellus) is an important part of the food spectrum of the Imperial eagle in Central and Eastern Europe. Eagles prefer this rodent because it lives in colonies and, where available, provides ample food.
Unfortunately, the souslik is also a globally endangered species and its numbers are dropping continuously. This is caused by the lack of suitable habitats – pastures maintained with low grass by traditional animal breeding.
Several cases of Imperial-eagle nest robbing have been registered during the past two years, with the juvenile birds or the eggs being taken from the nest. The goals of the robbers remain unclear, but perhaps this reflects a misguided interest toward nature. The taken eagles usually die since keeping them at home is not an easy task. But even if they survive, they are doomed to a life in captivity and are lost to nature forever. However, if they are released, they quickly starve to death because of their inability to hunt or, because they do not fear from humans, are killed by poachers.
Taking of wild animals from nature, and, especially, of a globally endangered species such as the Imperial eagle, is subject to extremely severe punishment by law. The Penal Code of the Republic of Bulgaria provides for imprisonment for up to 5 years and a fine of 1,000 to 5,000 for destruction, restraining or selling of wild animals endangered at the European or global level.
Should you witness or doubt any such crime, please, contact us at 02 846 59 19.
A large-scale campaign against raptors was started in the 1940s. These birds had been declared 'harmful' and exterminated on a mass scale. This elementary thinking had been the following: 'raptors eat hares and partridges and if we destroy them, there will be more for us.' Hunters had even been required to provide by the end of each year the legs of killed raptors to have their shooting license renewed. Of course, ecological science has subsequently shown that most raptors feed on rodents and are even 'useful' to us, humans. And those few who feed on game animals also occupy an extremely important place in nature. This was felt by hunters in Norway who had succeeded in exterminating raptors almost completely in the belief that this would increase the number of white partridges. The opposite happened – the numbers of partridges fell precipitously because of a contagious disease which had not been able to spread previously, as the sick birds had been eaten quickly by predators. Once the raptors had been killed, sick partridges managed to infect healthy partridges and the disease had become catastrophic.
Today, all raptors are protected by law. However, it is too late for many of the species. Some, such as the Bearded vulture, have disappeared completely from Bulgaria's nature. Others, such as the Imperial eagle and the Saker falcon are at the brink of extinction.
Traps placed near the carcass of a dead animal in order to catch wolves are a threat to eagles. The birds land near the carcass and may be killed or maimed by the traps. Several cases of Golden eagles suffering such fate have been registered in Bulgaria.
Rural depopulation and the dropping numbers of sheep and other livestock have allowed pastures to become overgrown. Certain grass and brush species develop wildly, growing tall and suppressing the growth of the other plants. Such conditions become unsuitable for the souslik. Souslik requires diverse plant species for food, and low grass not preventing them from running and from seeing their enemies. They disappear in overgrown pastures. And they are the Imperial eagles' main food. Where sheep are present in sufficient numbers, they graze the grass uniformly and do not allow excessive overgrowing of the pastures.
Intensive agriculture involving the use of many pesticides and introduction of monocrops has changed the hunting habitats of predatory birds and has reduced their key prey species. Furthermore, land aggregation required felling of many eagle-inhabited old trees between meadows.
Habitat changes caused by intensive forestry
Felling of old growth forests, selective felling of old trees and afforestation of pastures has destroyed the Imperial eagles; breeding and trophic habitats.
En-masse felling of poplars during the recent years is a serious threat. Imperial eagles in Bulgaria nets mainly on poplars - the only tall trees surviving in low-land areas in the country. Increased demand for poplar wood for export is the cause of large-scale legal and illegal felling. The lands of entire villages have remained without any poplars. Even two trees with Imperial eagles' nests have been felled while a third attempt was prevented at the last moment by nest guards.
The absence of trees suitable for nesting is forcing the eagles to nest in areas where they are frequently disturbed and where the hatchlings often die. For this reason BSPB experts have built 35 artificial nests in carefully selected locations allowing for sufficient food sources, limited disturbance and no dangerous power lines.
Fires can destroy inhabited nests directly. The number and size of fires in Bulgaria have increased drastically in the past decade. Some of the most devastating fires have occurred in regions of importance for the Imperial eagle. In 2000, a fire in Sredna gora was stopped within a few meters of the nest of an Imperial eagle.
The use of pesticides in agriculture is causing the death of many birds. A campaign to decrease shrews in 1989 lead to the poisoning of thousands of predatory birds throughout Bulgaria. Many Imperial eagles died at that time as well.
Strong winds and storms may cause nests to fall. In the 2000–2012 period, there have been fifteen registered cases of nests toppled over by strong winds in Bulgaria. Five chicks have died as a result, and one has received serious damages and could not be returned to nature.
In 2012, a nest with two young in the Sakar mountain area fell victim to a predatory mammal, most likely a pine marten.
Starvation and aggression in the nest
Sometimes, when food is insufficient, the stronger and larger eaglet kills its weaker sibling. It is possible, also, that the weaker eaglet may die due to systematic malnutrition, since the pair of eagles usually feed the larger eaglet in the event of limited food resources. Approximately 35% of eaglet losses are caused by aggression in the nest or by starvation.