Monitoring Eastern Imperial Eagle in the Khvalynsky National Park (Saratov Region, Russia)
Authors:   National Research Saratov State University, Khvalynsky National Park, Belyachenko A.V. 
Published: October 2023

The special structure of breeding territories, breeding parameters, and nutrition of the Eastern Imperial Eagle (EIE, Aqula heliaca) were studied in 2019–2023 in conservation (1,400 hectares), recreational (3,600 hectares), economic (20,600 hectares), and protective (114,900 hectares) areas of the National Park. 32 breeding territories were identified, 53 nests were discovered (including replacements and those newly build after old nests were destroyed), and the annual breeding of 17–26 pairs was established. In the rearing season, food remains and pellets were collected under 24 nests and 15 perches, and 4 occupied nests that had fallen from the trees were completely dismantled. Three types of EIE breeding habitats have been studied. About 21–24% of pairs used nests at the edges of mixed forests in conservation and economic zones of the National Park. Nests were located on centuries-old pine trees growing on steep ledges (30–50 m) between the Oligocene and Early Pliocene relief surfaces. The largest number of breeding territories (65–72%) were located in small river valleys, along the banks of ravines, streams, and watercourses of the protected area on a levelled Early Pliocene surface. Nests were located on large willows and black poplars. Habitats were surrounded by agrocenoses and were often located in close proximity to populated areas, roads, and railway tracks. Atypical breeding territories (4–14%) were associated with shelterbelts, anti-erosion plantations, and small isolated groves of the protected area. Large trees were cut down in the recreational area, and no EIE nests were found here. Reproductive rates were calculated based on the breeding cycles of all breeding pairs during the research period. 113 cycles were studied, during which 197 eggs were laid by adult birds, 166 nestlings hatched, of which 69 died, and the remaining 97 left the nests. The average EIE fecundity over 5 years was 0.86±0.043 nestlings fledged per pair, while eagles laid 1.74±0.071 eggs per nest. There are 7 known cases of clatches consisting of three eggs, but only in one case did all three nestlings leave the area at the end of the summer. EIE diet includes 20 bird species, 19 mammal species, and 1 reptile species. The most common species are Bobak Marmot (Marmota bobak) and young Common Magpies (Piсa piсa). Among the campophilous species EIE prey on young Montagu's Harrier (Circus pygargus) and Common Kestrel (Falco tinnunculus), Grey Partridge (Perdix perdix), Speckled Ground Squirrel (Spermophilus suslicus), European Hare (Lepus europeus), Northern Mole Vole (Ellobius talpinus), Greater Blind Mole-rat (Spalax microphthalmus), young foxes (Vulpes vulpes). Limnophilic species are represented in EIE diet by young Western Marsh Harrier (Circus aeruginosus) and Grey Heron (Ardea cinerea), Common Black-Headed Gull (Larus ridibundus), Garganey (Anas querquedula), Eurasian Beaver (Castor fiber), Muskrat (Ondatra zibethicus), European Water Vole (Arvicola terrestris). In forests and forest plantations EIE preys on Long-Eared Owl (Asio otus), Common Wood-Pigeon (Columba palumbus), European Pine Marten (Martes martes), European Polecat (Mustella putorius), Pygmy Field Mouse (Sylvaemus uralensis) and Yellow-Necked Mouse (Apodemus flavicollus). Near settlements EIE preys on Chicken (Gallus gallus), Domestic Cat (Felis catus), Brown Rat (Rattus norvegicus). In the last two years, the share of Common Raven (Corvus corax) increased in the diet. High food plasticity allows EIE to quickly adapt to changes in availability of trophic resources. On the other hand, the hunting skills of a particular pair are of great importance in successful rearing. Destruction of nests by pre-storm squalls must be noted among the natural abiotic factors that negatively affect the state of EIE population. Strong winds often break the crowns of old, rotten willows, pines, and nests fall to the ground (7 cases that led to the death of 9 nestlings). Sometimes too thin, but flexible, the tree sways unevenly in the wind with sharp longitudinal accelerations (catapult effect), which leads to eggs rolling out of the tray when adult birds are absent (3 cases of loss of 3 eggs) or even throwing 3–4-week-old nestlings directly into the crown, from where they can no longer get back to the nest (death of 2 nestlings). Biotic factors are of more variety. For example, on small rivers, large willows with EIE nests are gnawed by beavers and either immediately fall or break near the ground under the wind. Over the past two years, competition between EIE and ravens for breeding territories has intensified. For example, at the end of the winter of 2023, ravens built a nest near EIE breeding territory, on a nearby tree. As a result, EIE did not reproduce as ravens aggressively guarded their clutches. In another nest ravens pecked out two eggs in the absence of a young female eagle, and similarly, in another territory two eggs were damaged by magpies. Anthropogenic impact on EIE manifests through their systemic disturbance or depletion of food resources. For example, in 2021, the repair of railway tracks using heavy equipment 100 m away from the nest forced eagles to abandon the clutch. Another nest was abandoned as a result of cutting down 0.5 hectares of forest near the breeding territory. Widespread plowing of fallow and virgin lands by farmers in the protected area of the National Park led to the gradual degradation of the Bobak Marmot colonies, which brought five EIE breeding territories to the brink of extinction (only 6 nestlings fledged and 8 died of starvation in 2022–2023). Another three breeding territories were abandoned due to massive planting of apple orchards near the border of the conservation area, which undermined the Bobak marmot existence here as well. In the absence of the major food resource, the remaining pair flies 4.5 km from the conservation area to the city landfill, where EIE prey on rooks.