Main mortality factors for the Eastern Imperial Eagle (Aquila heliaca Savigny, 1809) in Bulgaria

The Eastern Imperial Eagle is a globally threatened species, represented with not more than 35–40 pairs in Bulgaria. As a facultative scavenger feeding on carcasses and parts of dead domestic and wild animals, this species is extremely vulnerable to poisonous baits and toxic agents, intentionally or accidentally set up in its food. The present study identified electrocution and poisoning as the main mortality factors for the eagles in Bulgaria. We analysed a total of 56 cases among which 44 cases were related to the mortality of non-territorial eagles in different age classes, and we found 12 dead or distressed territorial birds recorded between 1992–2019. The main mortality factor was electrocution, accounted for 30.4% of fatalities. The poisoning was the cause of mortality in 12.5% of the non-territorial and 10.7% of the breeding birds. Some of the cases were laboratory confirmed as intoxication, while the others, based on the history, clinical symptoms and field evidence, indicated poisoning. The most commonly used toxic agents were anticholinesterase’s inhibitors. As a result of a timely therapy applied to the live birds found in distress with symptoms of poisoning, six eagles were successfully treated and released back in the wild. We found that mortality of eagles depended on the age of birds, breeding or dispersal grounds, while season had no significant effect.