Interview with Dimitar Demerdjiev about the Eastern Imperial Eagle in Bulgaria

Date of the interview: 01 June 2011

In this interview Dimitar Demerdjiev from the Bulgarian Society for the Potection of Birds (BSPB) talks about biology and conservation of the Eastern Imperial Eagle in Bulgaria.
Dimiter is the Imperial Eagle Conservation Officer at the BSPB. The BSPB works very hard to protect this magnificent eagle in Bulgaria. See the links below the interview to learn more about their work. Also consider making a donation to the BSPB or become a member via their website (click on the English button at the top right).

Dimiter Demerdjiev with Eastern Imperial Eagle.
© Svetoslav Spasov

Markus Jais: What is the current population size for the Eastern Imperial Eagle in Bulgaria and how has the population developed during the last 20 years?
Dimitar Demerdjiev: The population of the Eastern Imperial Eagle in Bulgaria is estimated at 25-30 breeding pairs. In the period 2000-2011, there have been 27 known breeding territories, where Imperial Eagle pairs have bred. The annual maximum was recorded in 2009 - 20 pairs. In 2011, 19 territories are occupied by Imperial Eagle pairs. In the period 1994-2002, there were 14 known occupied nests, as the population was estimated at 20-25 pairs. During this particular period the species began to disappear from its mountain habitats. Since 2000, the Eastern Imperial Eagle has been recorded as a breeding species mainly in the southeastern part of the country, inhabiting hilly and lowland habitats. The increased number of pairs during the past decade is probably a result of intra-population processes supported by the conservation activities for the species undertaken in the country. The stable and relatively numerous population of the Eastern Imperial Eagle found in European Turkey contributes to the increase of the number of pairs in Bulgaria.

Markus Jais: How many pairs were successful and how many young have fledged in 2010?
Dimitar Demerdjiev: The year 2010 was not good for the Imperial Eagles in Bulgaria. There were only 10 successful pairs and 19 fledglings. The breeding success was not so bad but the number of the breeding pairs was unexpectedly low. The main reasons for that were natural factors such as severe storms during the summer and human factors such as disturbance in some of the non-guarded nests , and for the first time in Bulgaria – two nests were robbed by poachers.

Markus Jais: How many pairs do raise 2 or even 3 chicks? Is this dependent on the amount of food that is available?
Dimitar Demerdjiev: For the period 1994-2009 the clutch size (n = 114) had a mean value of 1.69 ± 0.6 chicks. Most of the clutches had 2 chicks (54.9 %), followed by those of one chick (38.1 %). Only 7 % of the clutches had 3 chicks. The breeding success of the eagles is strongly dependent on the food quantity and type. The highest mean breeding success (1.61 ± 0.78) was recorded with eagles feeding mainly on White Storks. The breeding success is also strongly related to the age of the breeding birds. The highest mean breeding success (1.13 ± 0.35) was recorded with pairs consisting entirely of adult birds, followed by “mixed” pairs (0.84 ± 0.52), and the lowest values were recorded with Imperial Eagles in immature plumage forming pairs (0.78 ± 0.69).

Markus Jais: How many birds die of electrocution?
Dimitar Demerdjiev: Thanks to the program for satellite telemetry, implemented by Bulgarian society for the Protection of birds (BSPB) in the framework of LIFE+ project “Conservation of Imperial Eagle and Saker Falcon in key Natura 2000 sites in Bulgaria” (Save the Raptors), we have proved that Imperial Eagles die from electrocution. Until now two juvenile eagles have been electrocuted, one in Bulgaria (just 1.8 km from the nest) and one in Turkey (Central Anatolia). Surveys carried out recently proved that a huge number of birds, mainly storks and raptors, fall victims to the risky (20 kV) power supply network. Perhaps there are much more Imperial Eagles dying of electrocution, but because of the small population size this could hardly be ascertained.

Eastern Imperial Eagle in flight

Eastern Imperial Eagle in flight.
© Daniele_Occhiato

Markus Jais: What is done to reduce mortality through electrocution? Are the power lines made safe?
Dimitar Demerdjiev: Some 500 risky electric poles of the most hazardous types are envisaged to be insulated within “Save the Raptors” project. Thus, all dangerous electric poles in the territories of at least four Imperial Eagle pairs will be made safe. However, this is not enough for definitive solution of the problem as immature eagles inhabit huge territories and new nesting locations will be established in the coming years. Measures on national scale should be taken in order to reduce the number of electrocuted raptors. Insulation of electricity poles in regions with globally threatened species, such as Imperial Eagle, and bird migration bottle neck sites should be with highest priority.

Markus Jais: In some countries, Eastern Imperial Eagles are sometimes or even often poisoned. How is the situation in Bulgaria?
Dimitar Demerdjiev: Yes, unfortunately, Bulgaria also follows this trend. In 2004, a pair of Imperial Eagles and their chick (2 weeks before fledging) were found poisoned in their nest. In 2010, the male individual of a breeding Imperial Eagle pair was also found poisoned under the nest. Perhaps cases of poisoning are not rare, but it is hard to find the carcasses of the dead birds considering their habits and the big areas they inhabit.

Markus Jais: What other threats to the Eastern Imperial Eagle are there in Bulgaria?
Dimitar Demerdjiev: The most serious threats include: loss of habitats (breeding, foraging), disturbance caused by human activities, and poaching. A potential threat to the species is the construction of wind farms and photovoltaic facilities in the areas inhabited by Imperial Eagles.

Dead Eastern Imperial Eagle

A juvenile Imperial Eagle who died of electrocution in Turkey.
© Ivailo Angelov

Markus Jais: Does this also affect other species, for example Golden Eagles and White-tailed Eagles?
Dimitar Demerdjiev: Yes, of course. Especially the change in the habitats occurring in the last 5 years; this, perhaps, will have a negative impact on a huge number of bird species, not only raptors.

Markus Jais: How is the population of prey species like susliks? Is there enough prey for the eagles?
Dimitar Demerdjiev: There is a trend towards general decrease in the Souslik populations in the areas harboring Imperial Eagles. The most common prey of the Eastern Imperial Eagle is the Northern White-breasted Hedgehog (21.14 % of the food); (2) The second most common prey is the Souslik (15.2 %), followed by the Common Vole (8.19 %), the European Hare (6.96 %), and the White Stork (5.12 %); (3) Considering the biomass of the prey species, the European Hare ranks first (20.49 %), followed by the Northern White-breasted Hedgehog (19.95 %), the White Stork (16.34 %), the Domestic Fowl (6.38 %) and the carrion (4.88 %); (4) During the autumn-winter period the species feeds mainly on Common Voles (30.88 % of the prey, but only 1.15 % of the biomass), followed by the European Hare (8.31 % and 36.36 %, respectively); (5) The carrion is found to be an important food source in the autumn-winter period, providing 12.36 % of the biomass. Depending on the available food resources, the Imperial Eagles apply different strategies to survive. The pairs in Sredna Gora, Northern Sakar, and part of the Tundzha valley feed exclusively on Sousliks – the main prey species in the region. The eagles in Southern Sakar and Western Strandja have adapted to the most common prey species in their territories – namely, the hedgehog. In areas, where this species is not abundant enough, it could be replaced by various bird species (mainly White Storks, Yellow-legged Gulls), the European Hare, the European Glass Lizard, predators or carrion. A typical example of food adaptation is an Imperial Eagle pair in the Eastern Rhodope Mountains that started feeding mainly on birds.
The eagles kill White Storks and Yellow-legged Gulls. These are not juvenile birds killed in the nests or birds taken as carrion. These are mainly immature birds, but there are sometimes adult birds. In Southeastern Bulgaria, in regions inhabited by Imperial Eagles, there are flocks of dozens, sometimes hundreds of non-breeding White Storks during the summer. They are a suitable and easy prey for the Imperial Eagles. Once I had the chance to observe how a pair of Imperial eagles hunting together managed to kill a White Stork. The Eagles cut into the flying storks flock and and managed to single out onestork. Then, the Imerial Eagles diving litteraly as a Peregrine Falcon started hitting it one after another in the air. After 3-4 hits, one of the Eagles grabbed with its talons the back of the stork and the two birds fell to the ground. The other Eagle followed them and they started to rip up the already dead stork.

Markus Jais: How does intensification of agriculture affect prey species and the eagles?
Dimitar Demerdjiev: Bulgaria’s accession to the European Union in 2007 and the launch of the programs for agriculture restoration were followed by a trend to cultivation and conversion of some of the territories of greatest significance for the species, formerly managed as pastures, into arable lands, vineyards, and orchards. Thus, compact and numerous Souslik colonies were destroyed and some of the pairs were left without their food resource. This trend could have a negative impact on the species, resulting in abandoned territories, especially the most affected ones, and considerably reduced quantities of the main food resources. There has already been such an example related to one of the mountain territories of the species, where huge meadows abundant in Sousliks have been cultivated and turned into potato fields since 2002. After 2005, the Sousliks within this territory have survived only in an area of about 3 ha, as their density in 2010 was only 7 individuals per ha. The pair inhabiting this territory feeds exclusively on Sousliks (representation of 33 %). Since 2005, the birds have inhabited the territory without breeding, and since 2009 there have been no sightings of the eagles in this region. The high adaptability of the Eastern Imperial Eagle in terms of food and prey species shows that in case of insufficient availability of Sousliks the species feeds on alternative prey that is abundant in the particular area. If there is no such alternative, however, the species cannot compensate the loss of its main food resource (Sousliks in this particular case), which might lead to the loss of the territory. This is particularly valid for the mountain ecotype Imperial Eagle pairs, specialized in feeding on Sousliks. In the autumn of 2003, the female individual of the only breeding pair in the Eastern Rhodope Mountains disappeared. Although the male bird did not leave the area, the territory remained unoccupied by a pair. The Sousliks rank second in the food spectrum of this pair. The area of the colony providing food for the birds was ploughed and overbuilt between 2004 and 2009 and, in fact, does not exist anymore.

Eastern Imperial Eagle.

Eastern Imperial Eagle.
© Svetoslav Spasov

Markus Jais: In some countries, lack of suitable nest trees is a problem? Is this also true for Bulgaria? Are artificial nests built and do the eagles use them?
Dimitar Demerdjiev: In Bulgaria the lack of suitable nesting substratum is a problem, too. There are territories providing abundant food resources, but the lack of tall trees leaves them unoccupied by Imperial Eagles. Sometimes the eagles nest on trees situated near roads or sites often visited by people because of the lack of other suitable sites. This results in serious disturbance and low breeding success. In 2008, BSPB began the construction of artificial nests to attract floaters to breed. Of all 18 nests built so far, one is occupied by a newly formed Imperial Eagle pair. A total of four different nests installed by Green Balkans and BSPB have been occupied by three Imperial Eagle pairs.

Markus Jais: Of what material are the nest platforms and how are they fixed on the trees?
Dimitar Demerdjiev: The nests are made of wood, resembling grids filled in with branches and twigs to make them look as natural as possible. They are attached to the trees as the bottoms are fixed with plain fine wire, which is then camouflaged. Then the nests are covered with branches and twigs carefully entwined into the base of the nests.

Markus Jais: Many windfarms are planned in Bulgaria. Can this be a problem for the Eastern Imperial Eagle and other large raptors in Bulgaria?
Dimitar Demerdjiev: Yes, if even a small part of the envisaged wind farms finds realization, this will probably cause huge losses for the species’ population. By 2011, in the Imperial Eagle breeding regions in Bulgaria, as well as in the temporary settlement areas, there have been numerous investment plans envisaging the construction of wind farms of various sizes. The possible impacts include: higher mortality caused by collision with the propeller blades of the wind turbines, deteriorated hunting habitats, lower quality of breeding territories, and disturbance. The risk of collision for newly fledged eagles is even higher than that threatening the adult individuals. The construction of wind farms will also have an indirect negative impact. “Chasing the birds away” results in habitat loss. Noise and rotation disturb the birds breeding and foraging in the area, thus affecting the breeding success and the physical health, and, on the other hand, increasing the mortality. The wind farm planned to be established in the southern part of SPA “Sakar” will affect at least 5 breeding pairs, which accounts for 25 % of the national population of the Eastern Imperial Eagle.

Markus Jais: You are tracking eagles with satellite transmitters. How many have been tracked or are tracked so far in Bulgaria and what are the results?
Dimitar Demerdjiev: Satellite tracking is of great importance to us, providing extremely interesting results. The first satellite tagging was done by BSPB in 2008. Since then, 14 more juvenile Imperial Eagles have been tagged with satellite transmitters by BSPB. The most shocking information received as a result of this activity was the low survival rate of juvenile individuals. Of the first eight eagles tagged with satellite transmitters, only one reached the age of two. Currently, only five of all fifteen satellite-tagged eagles are still alive and send signals. Of course, some of the transmitters might have stopped functioning. Yet, it has been confirmed that five of the birds have died of electrocution, poisoning, and shooting. Moreover, satellite tracking revealed the wintering areas of the juvenile Imperial Eagles from Bulgaria as well as the migration routes used by the individuals. They spend the winter period in the European part of Turkey, Anatolia, Syria, the Arabian Peninsula, and Africa. Few of them do not migrate and winter in Bulgaria. Another interesting observation is the wandering of the juvenile individuals before reaching maturity. Two of the satellite-tagged birds moved northwards and, crossing Ukraine, reached the Belarusian border. All eagle’s movements are publicly available on the Save the Raptros project web site (

Eastern Imperial Eagle chicks in nest

Eastern Imperial Eagle chicks in nest.
© Nikolay Terziev

Markus Jais: What is the BSPB doing for eagle conservation and how can people help?
Dimitar Demerdjiev: BSPB has been implementing numerous activities for the conservation of the eagles. Some of the most significant ones include: searching for unknown nests and monitoring of the breeding population; identification of temporary settlement areas; identification of threats; nest guarding during the breeding period; satellite-tagging; development of plans and policies aimed at preserving the species’ habitats; purchase of land plots providing abundant food resources (Souslik colonies) and riparian habitats, where Imperial Eagles breed; construction of artificial nests; restoration of habitats; supplementary feeding of eagles during the breeding and the autumn-winter period; working with local farmers; education and awareness-raising activities. If interested, people can be involved as volunteers in any of the above activities. To support Imperial Eagles, however, people have to change their attitude and understanding! They have to realize that the human race is an inseparable part of the biological diversity. Therefore, we need to do our best to discontinue the devastation of the natural resources. BSPB invests lots of efforts to build adequate environmental awareness among young people. Properly educated, they will become wise decision-makers, taking good care of our Home.

Markus Jais: Is the BSPB working with other organisations in Bulgaria and other countries to protect the Eastern Imperial Eagle?
Dimitar Demerdjiev: Yes, BSPB works in close cooperation with all organizations implementing activities for the conservation of the Imperial Eagle. We have established good contacts with Green Balkans, BPPS, FWFF, etc., exchanging information and discussing joint actions and campaigns. We have also built excellent partnerships with RSPB / BirdLife UK, MME/BirdLife Hungary and Doḡa Dernegi/BirdLife Turkey.

Markus Jais: What other bird species will benefit from the conservation work for the Eastern Imperial Eagle?
Dimitar Demerdjiev: As an umbrella species, the conservation of the Imperial Eagle contributes to the protection of numerous other species (not only birds). The preservation of Imperial Eagle’s habitats directly contributes for conservation of all birds of prey, some of which are threatened, such as Saker Falcon (Falco cherrug), Lesser Kestrel (Falco naumanni), Lesser Spotted Eagle (Aquila pomarina), Booted Eagle (Aquila pennata), etc. Protection of natural and semi-natural grasslands has huge importance for general wildlife protection. Huge number of species with unfavorable conservation status depends on pastures and meadows for their survival - Sousliks, Corncrakes, Montague’s Harriers and land tortoises are just the tip of the iceberg.

Tagging an Eastern Imperial Eagle with a satellite Transmitter.

Tagging an Eastern Imperial Eagle with a satellite Transmitter.
© Svetoslav Spasov

Markus Jais: What should the Government (and maybe the EU) do to make sure the Eastern Imperial Eagle has a future in Bulgaria?
Dimitar Demerdjiev: The most important thing is preserving the habitats of the species. Any drastic change in the species’ habitats can have a negative effect on the status of the species. The numerous investment plans for construction of wind farms and photovoltaic facilities in the areas inhabited by Imperial Eagles threaten the survival of the species. A ban has to be imposed on the construction of such facilities within a specific buffer zone around the nests. The cultivation of territories managed as pastures for the past 20 years could also have a catastrophic effect. The authorities have to develop and adopt adequate measures to secure the preservation of the habitats.

Markus Jais: What was your most amazing experience with Eastern Imperial Eagles?
Dimitar Demerdjiev: Actually, searching for new facts and exploring the Imperial Eagle’s population is the most exciting part of my job. I enjoy being part of their life and discovering some novelties. To me, the most interesting experience is to analyze the different prey species of the Imperial Eagle. It is amazing how birds of the same species but placed in different living conditions could have so much distinction. This shows us new interesting facts about the species and we could better understand their behavior and needs, which helps us be more effective in their protection.

Markus Jais:Dimitar, thank you very much for the interview.

More information

BSPB - Bulgarian Society for the Protection of Birds

Conservation of Imperial Eagle and Saker Faclon in Bulgaria