Spatial and temporal differences in migration strategies among endangered European Greater Spotted Eagles Clanga clanga

GPS-tagging a Greater Spotted Eagle by Valery Dombrovski

Author(s): Väli, Ü., Dombrovski, V., Maciorowski, G., Sellis, U. & Ashton Butt, A.

Published: November 2021   Pages: 14pp

Journal: Bird Conservation International

Digital Identifier No. (DOI): 10.1017/S0959270921000411

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A new collaborative research study involving BTO has used GPS to track the movements of one of Europe’s rarest birds of prey, the Greater Spotted Eagle, shedding light on the pressures this species faces outside of the breeding season.

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Understanding connectivity between migratory bird breeding and wintering grounds is essential for range-wide planning of conservation activities. We used GPS-tracking to explore the migration of twenty-eight Endangered Greater Spotted Eagles, Clanga clanga from three remaining European breeding populations towards their wintering range, and to identify population and sex-specific patterns in selection of wintering sites. The tracked eagles wintered in three continents, 46% in Africa (mostly Eastern Sahel), 43% across southern Europe (mostly Greece) and 11% in Asia (the Middle East). Migratory connectivity was weak (rM = 0.16) and the population spread across the wintering range was large (1917 km). The three studied populations differed in their migration strategy, with Northerly, Estonian breeders all wintering in Southern Europe and Polish and Belarusian breeders divided between Southern Europe and Africa. Migration strategy was different between Belarusian males and females, with males more likely to winter in Africa than Europe, and on average, migrating 2500 km further south than females. Migration to Africa took longer, but was partly compensated by higher migration speeds. Greater Spotted Eagles wintered in wetland sites throughout their wintering range, with fifteen of twenty-nine birds wintering in internationally or nationally protected sites (including twelve Ramsar sites). Nearly a third of European winterers stayed in the same Greek national park, perhaps indicating a limitation of suitable sites in Europe due to wetland loss or degradation. This highlights the importance of protected wetlands to this species, but also shows their vulnerability to future wetland degradation. Only two of fourteen wintering sites in Africa were under protection, showing a potential mismatch between protection of females and males in their wintering grounds.

The Greater Spotted Eagle is a Critically Endangered species, with fewer than 1,000 breeding pairs remaining in Europe. A summer visitor to the continent, the species' wintering distribution is poorly understood but has been thought likely to be restricted by suitable wetlands that provide sufficient food.

Prior to this study, a number of wintering sites had been identified across the Mediterranean coast but Greater Spotted Eagles have also been recorded in the Middle East and Northeast Africa. However, differences in wintering grounds between and within existing populations are little known, hampering efforts to conserve and identify threats to this species outside the breeding grounds.

Scientists fitted GPS tags to adult Greater Spotted Eagles breeding in Estonia, Poland and Belarus, and analysed where these birds wintered from the resulting tracks. This revealed the extent of the wintering range and differences in wintering regions between the different breeding populations and between males and females.

Estonian birds all wintered across southern Europe, whereas Polish and Belarusian birds wintered in Southeast Europe, the Middle East or Africa. In Belarusian eagles, males were more likely to winter further south than females, with the majority of males wintering within a narrow belt in Eastern Sahel (South Sudan and Ethiopia) and females in coastal wetlands in Southeast Europe (southern Greece) and Turkey. This may also have been the case for Polish eagles, but there is uncertainty due to the small number of birds tracked. The majority of the tracked eagles wintering in Europe were restricted to a small number of protected areas, highlighting the importance of these locations for this species. However, only two of the 12 wintering sites in Africa have protected status, both within the same national park. The reliance on ecologically intact wetlands hints at one of the mechanisms of decline of this species, as the majority of wetlands in southern Europe have been destroyed or degraded, with over 63% of Greece’s wetlands lost between 1950 and 1985.

This distinct wintering grounds of females and males could have impacts on the conservation of the species. Most of the tracked females wintered at sites that are formally protected, whereas males did not. This could lead to a sex-biased survival if African wetlands were degraded. In contrast, past habitat loss in Europe relative to Africa may have reduced numbers of females relative to males. Furthermore, protected areas can be insufficiently protected and eagles in some European protected areas are threatened by hunting or dangerous power lines. Ultimately, an imbalanced sex ratio could increase hybridization rates with Lesser Spotted Eagles (a more common, closely related species) and thereby increase the extinction risk for the Greater Spotted Eagle.


The authors thank Kordian Bartoszuk, Denis Kitel, Kazimierz Krzywicki, Triin Leetmaa, Riho Ma ̈nnik, Paweł Mirski, Renno Nellis, Ain Nurmla, Ju ̈rgen Ruut, Dmitry Shamovich, Alexander Sobolev and all the other people who assisted in tagging eagles. The GPS-tracking was financially supported by the projects LIFE04NAT/EE/000072 and LIFE08NAT/PL/000511; Estonian Ministry of Foreign Affairs (project’ Knowledge-based conservation of the globally vulnerable Greater Spotted Eagle in Belarus’); Estonian Environmental Investments Fund; Estonian Environmental Board; and Endangered Landscapes Programme. The Endangered Landscapes Programme is managed by the Cambridge Conservation Initiative and is funded by Arcadia, a charitable fund of Peter Baldwin and Lisbet Rausing.
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