Distribution, population status, habitats, and conservation of Lesser Spotted Eagle in Bulgaria

Abstract

The Lesser Spotted Eagle (Aquila [Clanga] pomarina) is a territorial raptor, distributed from Baltic region to Anatolia and Caucasus. Bulgaria is a part of the southern limit of the species distribution range. Since 2014, intensive field research in Eastern and Central Bulgaria identified an abundant and stable population of the species. For the period 2014–2023, 167 different active nests were found, and more than 450 occupied territories were mapped in Eastern and Central Bulgaria. Thus, the current population estimate is at least 1,000 breeding pairs. About 60% of the breeding population of the Lesser Spotted Eagle was situated in SPAs, but only 2.3% was located within Nature reserves, indicating insufficient protection of the species. The increasing anthropogenic pressure, mainly in terms of dramatic alteration of the species foraging and breeding habitats, and the lack of efficient legal protection pose a serious risk to the future of the Lesser Spotted Eagle in this part of the species distribution range. Most of the nests were situated at the edge of a forest, 19% were found in tree lines along the rivers, and only 2% were situated in single trees. The habitats varied from small forests and grasslands and significant percent of arable land to forests, small patches of arable land, and shrubs (less than 1%), as well as typical mosaic landscape with patches of cultivated crops, grasslands, and forest areas. The major threats to the habitats include plowing of grasslands, overgrowth of grasslands, forest management gaps, disturbance, construction of wind farms and solar parks, natural fires. Analysis of prey (n=523) from collected food remains (n=45 nests) shows that the main prey is Voles (Arvicolinae), accounting for 42.64% of all prey, followed by the Northern White-breasted Hedgehog (Erinaceus roumanicus), 13%. A parallel survey of the diet using photo traps (n=24 nests) and examining 141,985 photographs identified 1,357 different prey items. The results demonstrate again the dominant role of Voles (36%) as a main food resource, but followed by lizards (Lacertidae), 30%. The main conservation activities undertaken for the species in Bulgaria include appling biodiversity-friendly forest practices, improving breeding and foraging habitats, satellite tracking, restoration of breeding habitats through forest planting, insulation of hazardous electric poles, implementation of educational programs with children and local communities.