There are three main categories among anthropogenic factors that pose a threat to the eastern imperial eagle. These are factors causing death of adults or fledged individuals, failure in breeding and habitat loss.
Factors causing death of adults or fledged individuals
Poisoning is one of the most severe problems threatening raptors in Europe.
Poisoning with chemicals belongs to two main categories: the first one is by the misuse of permitted, non-selective rodenticides and other poisoning chemicals, i.e. mixing of different chemicals, which enhances the effect of each other. It is not considered a direct poisoning. In cases like this, poisoning aims to kill rodents, however, after consuming poisoned prey imperial eagles may become infertile, get weak and die by accumulation of the poisoning agent (secondary intoxication), and also make their chicks sick leading to death. It is called secondary poisoning. The other main group of cases consists of the use of non-permitted, illegal poisons, which is considered to be direct poisoning. It usually aims the „unwanted” carnivores and birds.
Poisoned imperial eagles (Photos: Márton Horváth)
Lead poisoning is supposed to be another possible threatening factor; however, its frequency is unknown. Several studies showed that lead bullets developed intoxication in birds of prey. Consumed lead can cause poisoning in any age-groups. Eventually, the lead accumulates in the bones. In the case of the breeding population, after laying the eggs, the lead can get mobilized from the bones and do further damage. Weak or dead birds are rarely discovered, but the negative effect of poisoning is certainly in the order of higher magnitude than we could expect it from recoveries.
Being shot with pellets, eagles may die immediately or later due to the injury. Sometimes, the bird is lucky and the pellets get encapsulated in the body causing no furher problems. Shooting can affect all age-groups from eggs to adults. It is hard to assess the significance of shooting, but it can happen in nesting areas, foraging places, as well as temporary settlement areas all year round.
Shot white-tailed eagle (Photos: Budapest Zoo, Péter Barcánfalvi - HNP archives)
Unexperienced immatures can get hit on public roads or railways. Most often they crash with vehicles when flushed off a carcass close to the road. Accidents with trains can occur in cases, when the pair nests close to the railway. After fledging, young eagles often sit on the ground. Since the railway embankment is at higher ground, it is probably very attractive to them.
Medium voltage powerlines (20-35 kV) pose a serious threat to birds. When a bird lands on the pylon, it can easily get electrocuted by touching two wires or a wire and the grounded part of the pole at the same time. The bigger the bird, the higher chance for this to happen, though small raptors (kestrels) die in high numbers, as well. In most cases, electrocution causes immediate death. Young birds are more prone to this threat than adults.
Electrocuted imperial eagle (Photos: Imre Fatér)
Failed breeding attempt
Robbing for commercial purposes and own account have to be differentiated. Egg and chick robbing for collectors or falconers belong to the former, when the plunder can be marketed abroad, as well. The latter usually occurs, when local people (many times kids) take the eggs or the youngsters home without having any knowledge of the species. Emptying a nest bereaves the population of a clutch for that particular year, unless the pair starts a second clutch, which can happen if the robbing occurs at an early breeding stage. Illegally kept birds usually die lacking expertise and special conditions they require in captivity. Fortunately neither nest robbing nor catching of fledged Eagles is frequent, even though, it happens occasionally. Legal protection of birds of prey is well known by the public that makes keeping birds in captivity or trading them internationally hazardous.
Human disturbance is considered to be the most important threat to breeding success. Estimates put failed breeding attempts around 15% per year by human disturbance. Due to disturbance, Eagles tend to avoid large areas (including foraging, settlement and nesting areas) periodically. The main adverse effects are as follows:
- ordinary use of territory changes both in time and space, which means that birds may spend more time in sub-optimal habitat,
- change of nest site, less suitable site may be chosen,
- leaving the clutch, which perishes due to adverse weather conditions or predation,
- behavioural changes at chick-rearing stage, (e.g. less frequent feeding), negative effects on energy balance caused by less food and stress,
- chicks may jump out of nest or fledge earlier than they are supposed to,
- extreme cases can lead to territory desertion.
All in all, the most important negative effects are the lower breeding success and the individual mortality.
Lack of suitable nesting trees is a serious problem for the species regardless where it breeds, in the mountains or the lowlands. In wooded areas old stands are threatened most by logging, since those bring huge profit for the forestry. The situation is the worst in places that are not protected. Here, the nature conservation’s interest can hardly be put into effect even in cases of strictly protected species. Illegal logging threatens shelter-belts, groups of trees or lone trees in the lowlands.