Diet of Eastern Imperial Eagle (Aquila heliaca) in Bulgaria: composition, distribution and variation

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.

Human activities can hinder the breeding of a top avian predator: preliminary results

The Eastern Imperial Eagle (EIE) is a large-sized, globally threatened species with a wide distribution. The species is extremely vulnerable and sensitive to human disturbance and activities in the vicinities of its nests. We analyzed the effect of human disturbance in two territories of Eastern Imperial Eagles from Bulgaria in 2008–2009. We recorded 375 cases of different types of human activity in the vicinities of the two surveyed nests – 60 cases in nest A and 315 in nest B. The most common activity around the studied nests was the passing of light motor vehicles (n=100 cases). Our results highlight that the probability of EIE’s reaction is dependent on the type of activity, distance from the nest and the duration of the activity. However, eagles’ reaction is independent from the number of intruders. We found that with the decrease of the distance to the nest, the reaction progresses and is more acute. We found statistical differences between the distance belts and the majority of alert and flight reactions that were recorded at distances up to 300 m from the nests. We reported that humans walking around nests (mainly hunters, fishermen, tourists, people illegally extracting sand in the close vicinities of the nests) result in a large number of reactions of flight off by the eagles thus, leaving the nest unattended. More research on a large scale on this topic is needed including more accurate measures to address human disturbance in EIE territories. The findings will be applied to ensure higher breeding rates and species conservation.

Treatment of extremity fractures in 20 wild birds with a modified Meynard external fixator and clinical assessment of the results

The aim of this study is to evaluate the outcome of the treatment on twenty wild birds presenting with fractures that were stabilised with modified Meynard external fixators. The study material consisted of a total of twenty birds of eight different species, six white storks (Ciconia ciconia), one eastern imperial eagle (Aquila heliaca), one European honey buzzard (Pernis apivorus), one long-legged buzzard (Buteo rufinus), three common buzzard (Buteo buteo), one northern goshawk (Accipiter gentilis), one Armenian gull (Larus armenicus), and six yellow-legged gulls (Larus michahellis), which were diagnosed with fractures in their extremity bones following clinical and radiological examinations. The lesions of the twenty cases evaluated in the study were diagnosed as humerus fractures in nine cases, ulna fractures in three cases, tibiotarsus fractures in seven cases and a femur fracture in one case. The external fixators were removed between weeks five and nine postoperatively. While healing was seen in twelve of the twenty evaluated cases, the complete functional recovery occurred in six of these and they were released into nature. It was concluded that modified Meynard external fixator, which was made applicable for fractures in birds, could be an alternative method for fracture treatments in wild birds.

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.

Summary of raptor and owl ringing in Slovakia in the period from 2012 to 2019

Between 2012 and 2019, 6523 raptors and owls (30 species) were ringed in Slovakia. The most abundant was the common kestrel (2811 individuals), then the western marsh harrier (664) and saker falcon (517). The proportion of nestlings among all the ringed individuals was 84.4%. In the given period, 340 recoveries of raptors and owls (23 species) were recorded in the ringing station database. This number included 160 recoveries of individuals colour-marked and also recovered in our territory. There were 83 recoveries of birds ringed in Slovakia and resighted abroad. The last 97 recoveries were of individuals ringed abroad and recovered in Slovakia. In summary, most of the recoveries (of all types) were of Eastern imperial eagle (62 recoveries), then red-footed falcon (51) and common kestrel (43). Most of the recovery circumstances were ring reading (44% in total), recaptures (15%) and findings of bird cadavers. Regarding raptors or owls, collisions with vehicles (5%) and electrocutions (5%) were frequent causes of their deaths.

Eastern Imperial Eagle in Agricultural Lands in Kharkiv Region of Ukraine: the Results of Seventeen Years of Monitoring

A study on the population of Eastern Imperial Eagle (EIE) (Aquila heliaca) in the Kharkiv region of Ukraine was begun in 2003. About 40% of the region was surveyed during this study. In 2018-2020 an EIE counting was done on our study plots covering suitable nesting habitats of the species and 78 individuals of EIE were recorded. Comparing with 2005–2012 count when 81 EIEs were recorded and the population size was estimated as 50 breeding pairs it is possible to conclude that the population nowadays is stable. However, in some local breeding groups, the number is tending to decline. For instance, in the pine forests in the valley of the Siversky Donets river, the decline is caused by habitat destruction and human disturbance during the breeding period due to woodcutting. To prevent the future decreasing, since 2016 a new legislation prohibits logging activity in woodlands of Ukraine from the 1st of April till 15th of June. On the contrary, in the agricultural area in the south and southeast of the Kharkiv region, population growth was observed. In 2018–2020 we found 29 inhabited nests of Eastern Imperial Eagles located in agricultural open lands (16 nests), in vast oak forest (1 nest), and in pine forests of the Siversky Donets river valley (12 nests). In 2019, a significant difference was found in the breeding success of pairs inhabited agricultural lands (100% successful cases) that in pine forests (40%).