Diet of Eastern Imperial Eagle (Aquilaheliaca) in Bulgaria: composition, distribution and variation.

Nedko Nedyalkov,Dimitar Demerdzhiev,Stoycho Stoychev,Zlatozar Boev,Nikolay Terziev,Tseno Petrov,Dobromir Dobrev

doi:10.3897/bdj.10.e77746

Abstract

The Eastern Imperial Eagle (EIE) is a top predator exploiting different prey in different parts of its distribution. In this study, we summarise data collected over a long period of time (for 25 consecutive years), identifying key prey species in the different regions, as well as clarifying seasonal preferences in the eagle’s diet. Most studies on the EIE food composition covering different parts of the species distribution range analyse the breeding season, while data about the winter diet are scarce. To the best of our knowledge, this is the first study detailing the differences in EIE’s dietary preferences between the breeding and the winter periods. We identified 4891 specimens belonging to 196 different taxa, which represents the most comprehensive study considering the diet diversity of this threatened species. Mammals represented the largest proportion of the diet, followed by birds and reptiles. Northern White-breasted Hedgehog was the most common prey, accounting for 25.7% of the total prey caught and 26.75% of the biomass. The European Souslik was the second most important prey with 14.35% participation in the eagle’s diet, but with a 3.75% contribution to the biomass. As we predicted, prey composition and main prey species varied spatially and seasonally. Modelling differences in the EIE diet, we found that the “territory effect” had the strongest impact on the dietary variations. Diet diversity differed significantly between regions (F = 12.6, df = 4, p = 0.01). During the breeding season, eagles fed mainly on Hedgehogs (29.88%), Sousliks (16.85%) and Storks (7.74%), while the winter diet was predominantly small rodents (44.17%) and songbirds (13.96%). We found that top predators, such as EIE, have successfully adapted to a novel food source, which is abundant in the area. The detected flexibility in the diet of the species and its ability to switch to alternative prey, if available, when the primary prey decreased, should be considered when planning species conservation efforts. Investigating the temporal change of the main prey in the eagle’s diet is also crucial for further species conservation measures.

Highlights

The Eastern Imperial Eagle (Aquila heliaca), hereafter (EIE), is a large-size raptor species breeding from Central Europe, the Balkans, Central Asia and South Siberia to China and Mongolia (BirdLifeInternational 2021)
We identified 4891 specimens belonging to 196 different taxa (Suppl. material 1)
The great diversity of species in the food spectrum of the EIE proved its opportunism towards feeding

Summary

Introduction

The Eastern Imperial Eagle (Aquila heliaca), hereafter (EIE), is a large-size raptor species breeding from Central Europe, the Balkans, Central Asia and South Siberia to China and Mongolia (BirdLifeInternational 2021). While Sousliks (Spermophilus sp.) are predominant for the largest Eastern populations of Russia and Kazakhstan (Belik et al 2002, Karyakin et al 2008, Karyakin et al 2011, Katzner et al 2006), in the other parts of the species range, the diet of the EIE consists of different-sized mammals, birds and reptiles. The EIEs breeding in European Turkey feed mainly on Northern White-breasted Hedgehog (Erinaceus roumanicus), tortoises – Hermann's tortoise (Testudo hermanni) and Greek tortoise ( Testudo graeca) and Yellow-legged Gull (Larus michahellis) (Demerdzhiev et al 2014b), while in the Caucasus, reptiles, hedgehogs (Erinaceus spp.) and small rodents are predominant in the diet (Abuladze 1996, Horváth et al 2011)

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Results

Conclusion