Imperial eagle (Aquila heliaca)

The imperial eagle is a large, dark-colored species of eagle. Adult individuals have dark brown plumage, with pale yellow-cream colored crowns and napes. Shoulder feathers are white. The tail is gray with a black band at the tip. The beak and legs are yellow, with a black tip on the beak. Juveniles are lighter brown in color and exhibit white spotting on the wing coverts.

Body length ranges from 72 to 83 cm. Wingspan varies between 185 and 205 cm in males and 200 and 220 cm in females. Body weight ranges from 2.4 to 2.7 kg in males and 3.1 to 4.5 kg in females. In the wild, they can live up to approximately 26 years, and in captivity, their lifespan may exceed 40 years.

Behavior

The imperial eagle is generally solitary but can be observed in loose groups of more than ten individuals during migration periods. It soars using thermal air currents, glides efficiently, and can make rapid movements during hunting. It typically flies with calm, broad wingbeats and may execute sudden dives to capture prey.

Kaşif Şahgaga (Source: AA)

Biology and Habitat Preference

This species inhabits steppe-forest transition zones and can nest in open areas, plains, agricultural lands, near wetlands, and steppes. Its upward shift to higher elevations is considered a consequence of habitat loss and human pressure.

Nests are typically built on tall trees at heights of 10 to 20 meters above ground. The nest diameter is approximately 1.2 to 1.5 meters, with a depth of 60 to 70 cm. Females usually lay two eggs per year. After the incubation period, chicks hatch and become capable of flight within about 60 days. Due to food competition, survival rates are typically limited to only one chick.

Diet

The imperial eagle is a carnivorous species that feeds primarily on small mammals (field vole, rat, hamster, rabbit), birds (duck, pigeon, crow), reptiles (snake, turtle), some insects, and carrion. It locates prey on the ground, captures it with its talons, and carries it away.

Distribution

The breeding range of the imperial eagle extends across a wide geographic area between Central and Eastern Europe and Central Asia. It regularly breeds in countries such as Austria, Hungary, Slovakia, Russia, and Kazakhstan, outside of Türkiye. During migration, it is also observed in regions such as North Africa, South Asia, and the Middle East.

The population in Türkiye is estimated to consist of between 42 and 180 breeding pairs. Detailed studies in the Thrace region indicate a population of approximately 30 to 50 pairs.

Threats

Major threats to the imperial eagle include agricultural pesticides, habitat loss, power transmission lines, illegal logging, vehicle collisions, decline in prey populations, and illegal hunting. High-voltage power lines and poisoning are particularly significant causes of mortality. Additionally, the placement of wind energy plants along the eagles’ flight routes can lead to collision-related deaths.

Photo: İbrahim Yozoğlu (Source: AA)

Imperial Eagle Population

The imperial eagle typically begins breeding at the age of four. Pairs form lifelong bonds; if one partner dies, the surviving bird may find a new mate the following year. Pairs often establish long-lived nests that are maintained and reused over many years. Dry branches and large tree limbs are used in nest construction. The nest diameter is approximately 120 to 150 cm, with a depth of 60 to 70 cm.

Egg-laying generally occurs in spring. Females typically lay two eggs per year, occasionally three or four. Both parents participate in incubation, which lasts an average of 43 days. Usually, both eggs hatch, but due to food competition, only one chick typically survives. This behavior is linked to the species’ characteristic “siblicide.” The earlier-hatched and stronger chick dominates the sibling, securing its survival.

Chicks acquire flight capability approximately 60 days after hatching. However, they continue to be fed by their parents for about two weeks after leaving the nest, during which time they develop their flying and hunting skills.

Feeding Behavior and Diet Composition

The imperial eagle (Aquila heliaca) is a fully carnivorous predator. It usually hunts alone, though it may occasionally hunt with its mate. It primarily captures prey on the ground and is less agile than other raptors when pursuing birds in flight.

During hunting, it typically soars over open areas and attacks with a sudden dive upon spotting suitable prey. It also perches on tall trees at forest edges to survey the surroundings and swoops down when an opportunity arises. Its vision is highly developed, enabling it to detect prey from great heights.

After capturing prey, it kills it with its powerful, curved talons, carries it, and usually brings it back to the nest for consumption. It actively uses both its feet and beak during the processes of capturing, killing, and transporting prey.

Prey Types and Diet Composition

The diet of the imperial eagle varies according to geographic region and season. It feeds on small and medium-sized mammals, birds, reptiles, carrion, and occasionally insects. Commonly consumed mammals include the suslik (Spermophilus sp.), hedgehog (Erinaceus concolor), European hare (Lepus europaeus), blind mole rat (Nannospalax leucodon), and field mouse (Apodemus sp.). Important avian prey includes gull, pigeon, duck, and quail. Reptiles such as turtle and snake are also part of its diet.

Habitat Preferences

The imperial eagle (Aquila heliaca) is ecologically specialized to steppe-forest transition zones and prefers extensive, semi-open, mosaic-type habitats. Its habitats generally include wooded steppes, gallery forests, steppes, and isolated tall trees in agricultural areas. These habitats provide suitable conditions for both nesting and hunting.

Nests are typically built on large trees at heights of 10 to 25 meters above ground. In the absence of suitable trees, some individuals have been recorded nesting on low shrubs or human-made structures. Nests in the same area may be reused for many years and grow larger over time.

In Thrace, studies have found that imperial eagles most frequently build nests on Quercus pubescens (downy oak), Quercus cerris (Turkey oak), Quercus frainetto (Hungarian oak), Populus nigra (black poplar), and Salix spp. (willows). These trees are often found as solitary specimens within agricultural lands, providing the eagles with unobstructed views of their surroundings.

The structure of vegetation surrounding the nest and hunting areas is important. Imperial eagles prefer open agricultural fields containing clusters or individual trees. They rarely nest in dense, closed-canopy forests. This preference is linked to both ease of hunting and the concentration of prey in such habitats.

Global and National Distribution

The global distribution of the imperial eagle extends from Austria to Mongolia, covering the central and southern parts of Eurasia. Breeding populations are concentrated primarily in Kazakhstan, Russia, Hungary, Slovakia, and Türkiye. During migration, it is also observed in regions such as North Africa, the Indian subcontinent, and Southeast Asian countries.

The total number of breeding pairs in Europe ranges between 850 and 1300. The two largest populations are in Russia (900–1000 pairs) and Kazakhstan (750–800 pairs).

Estimates of the population size in Türkiye vary. Earlier studies suggested 35–70 pairs, while more recent assessments indicate a possible range of 42 to 180 pairs.

Field studies in Thrace have revealed a population of approximately 30 to 50 pairs in the region.

This migratory species is observed over a vast geographic range during winter, from northern Africa to Kenya, India, and southern China. In Europe, it is primarily known as a summer visitor.