Lesser spotted eagle

The eagle of the forests

The lesser spotted eagle is smaller than most other eagles in Bulgaria. Still, its wingspan can reach 145 cm, but it weighs no more than 1600 grams.

As with many raptors, females and males look alike, with just a minor difference in size, so there is almost no sexual dimorphism. However, differences can be observed between the young and the adult birds. The young of the lesser spotted eagle are chocolate brown with a prominent golden patch on their nape. The adults have brown plumage.

In the breeding season the lesser spotted eagle often emits a squealy ‘wiiik, wiiik’, and in the other seasons it is identified by its repetitive ‘k-ye k-ye’ call that resembles the yelps of a small dog.

© Bogdan Boev/Lesser spotted eagle

A long-distance migrant

Lesser spotted eagles are found in Europe and Asia and they spend the winter in Africa. The greater part of their population lives in Europe – more than 95 per cent of it. The breeding population is estimated to be between 14 000 and 19 000 pairs. Lesser spotted eagles are typical ‘long-distance migrants’, with individuals from the northern populations covering nearly 10 000 km to reach their wintering grounds. The species spends the winter south of the equator. Its migration route passes through the Bay of Burgas, the Bosphorus and the Gulf of Aqaba.

During migration lesser spotted eagles form sparse flocks of up to several dozen birds in mixed groups with buzzards, kites and other eagles. The birds make stops along their long journey to rest and to recover their energy.

The eagle’s home in Bulgaria

Lesser spotted eagles are found in higher densities on Derventski Hills, in Sakar Mountain, at the western foothills of Strandzha Mountain, along the lower and middle course of Tundzha River, in Eastern Balkan Mountain, as well as in the Eastern Rhodope Mountains. Scattered habitats are found in Dobrudzha, in the Danube Plain, the Thracian Valley, the Western Rhodope Mountains, as well as in the mountains Sredna Gora, Vitosha, Plana.

On Sakar Mountain and the neighbouring Derventski Hills its numbers are slowly rising, whereas its population on Strandzha Mountain is in decline due to a degradation of its feeding grounds, mostly by succession of the open lands due to social-economic changes in the region.

The breeding population of the lesser spotted eagle in Bulgaria is estimated to be more than 600 pairs. Lesser spotted eagles prefer broad-leaf and mixed forests close to open spaces – mainly pastures, meadows, arable land and water bodies. They like habitats with a mosaic structure.

The eagles’ menu

Lesser spotted eagles feed on small mammals, mainly voles and other prey of similar size: rodents, amphibians, reptiles, small birds and insects. The pairs on Sakar Mountain catch also hedgehogs which is regarded as a feeding adaptation for the species.

© Bogdan Boev/Hedgehog

One young per year

Lesser spotted eagles are monogamous – the pair stays together until the death of one of the partners. They build their nest on high trees. The female lays 1–3 eggs, most often 2. Both parents incubate the eggs for 33–43 days. The young leave the nest at 49–56 days of age. Pairs raise one chick per year, very rarely two.

Conservation status

The lesser spotted eagle is protected by the law. It is included in the Bulgarian Red List as ‘vulnerable’, and in the IUCN Red List as ‘least concern’.

© Bogdan Boev/Lesser spotted eagle

Threats to the lesser spotted eagle

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Logging in old-growth forests, selective felling of old trees and afforestation of pastures lead to the destruction of the breeding and feeding habitats of the lesser spotted eagle.
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Intensive agriculture uses a lot of pesticides, and introduces monocultures (huge fields of only one plant species). This leads to a decrease in the numbers and diversity of the animals that the eagle feeds on.
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A recently emerged threat is the use of shredders to clear scrub away from pastures. The process damages the lesser spotted eagle’s habitats and directly destroys the animals that he uses as prey.

Helping the eagle

According to research lesser spotted eagles prefer to nest at the forest edge, near open spaces with scrub-grass communities in the forests, or near agricultural land in the vicinity of territories with available and accessible food resources. Good practices and models for the improvement and sustenance of feeding grounds and food resources for the species include:

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restoration of abandoned grass and scrub-grass communities;

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transformation of arable land into pastures or implementing favorable schemes for culture rotation;

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restoration of scrub vegetation;
pasture rotation and effective management;

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construction of food trenches and other methods to increase the abundance of animals that the species uses as a source of food.

The practices for the creation, restoration and sustenance of forest landscape structures and sections of the forest edge near open spaces include:

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the creation and restoration of forest shelter belts that are important as rest stops during migration, as well as in the breeding season of the lesser spotted eagle;

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restoration and sustenance of transitional tree-scrub vegetation (ecotone) as a key habitat for the species that form the diet of the lesser spotted eagle.

© Bogdan Boev/Lesser spotted eagle

Satellite tagging of lesser spotted eagles

In the summer of 2020 for the first time in Bulgaria three young lesser spotted eagles of the local population were tagged with GPS/GSM transmitters. The transmitters are fitted on the young eagles when they are about to leave the nest and have already reached the size and strength of adult birds. The transmitters are small devices that are fitted on the back of the birds with specially designed straps. They weigh only 70 g so the birds get used to them and they can carry them all their life. The transmitters have solar panels to charge their battery so they have a long life span.

Tagging lesser spotted eagles with transmitters will contribute to revealing the model of dispersion of the young individuals, their migration routes, their rest stops; it will also facilitate the collection of important data about the threats they face in their wintering grounds, as well as along their migration route.

Satellite tracking will enhance research on the habitats lesser spotted eagles use and prefer, as well as on the life span of the species. The collected data will contribute for the preparation of a demographic model for the species, and it will outline the main directions for a more effective conservation not only regionally but globally too.

You can follow the stories of Kubrat, Tervel and Svoboda – the three lesser spotted eagles that were tagged with transmitters, – on the map here.

Safe electricity pylons and poles

There are several ways to make power lines safe for the birds:

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By mounting special insulation on potentially dangerous electricity pylons we can prevent the birds from being electrocuted when they touch the line and the pylon simultaneously.
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The replacement of bare lines with fully insulated ones (the so-called PAS System) protects the birds from electrocution along the entire length of the overhead line.
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Installing perches on transmission towers – they provide a safe perch for the birds away from the conductors.
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Replacement of overhead power lines that are dangerous for the birds with underground lines. This approach completely eliminates the risk of electrocution or collision for the birds and guarantees a reliable energy supply for people.

Taking steps with regards to dangerous electricity poles and pylons is an exceptionally urgent measure for the protection of many species of birds, as uninsulated power lines are the most common cause for the death of young birds. In Bulgaria a great percentage of the power distribution lines pose a risk for birds, large raptors and white storks in particular. Some of them are true death traps that kill dozens of birds every year.

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