Booted Eagle (Hieraaetus pennatus)

Identification

The Booted Eagle is a small eagle, whose silhouette in flight resembles that of the Common Buzzard, but it is more slender and exhibits distinctive characteristics.

• Plumage: The species is dimorphic, existing in two main forms and intermediates:
  • Pale morph: The underparts are white, often with some grayish-brown streaks on the chest and around the eye. The underwing coverts are white and contrast sharply with the black or brownish-black flight feathers.
  • Dark morph: The underparts and underwing coverts are uniformly dark brown, sometimes slightly lighter towards the leading edge of the wing.
  For both forms, the three inner primary flight feathers are often lighter and translucent, forming a clear "window" or panel in the hand of the wing when viewed from below. The upperparts are generally dark brown, with a light brownish band on the shoulders and a whitish patch on the rump that contrast with the darker flight feathers and tail. A specific diagnostic criterion is the presence of small white patches at the leading edge of the wing, visible from the front, often called "landing lights" or "braces."
• Head: It is relatively massive. In the pale morph, it is light fawn-colored and streaked, while in the dark morph, it is light brown streaked with brown. The forehead is white.
• Eyes: The iris is dark brown in juveniles and reddish in adults.
• Beak: Short, strong, and hooked, adapted for its carnivorous diet.
• Legs: Yellow, ending in powerful talons. Its tarsi are fully feathered, which gives it its name and is characteristic of eagles.
• Juvenile: Young birds resemble adults but often have more rufous underparts with more pronounced dark streaks, and a rufous head.
• Silhouette and Flight: It is the smallest of the eagles. Its wings are long, broad, with almost parallel edges, and have 5 to 6 fingered primary feathers. Its tail is long (almost equal to the wing width) and square-cut. In soaring flight, it holds its wings slightly arched and carried forward. In gliding flight, the wings are slightly below horizontal and the "hand" even lower. Its flight is graceful and faster than that of a buzzard.

Scientific Dimensions and Records (Booted Eagle)

These figures highlight that despite its modest size for an eagle, the Booted Eagle possesses impressive characteristics.

Song and Calls

The Booted Eagle is generally a discreet bird outside the breeding season. However, it becomes more vocal in spring during courtship displays and near the nest.

Its calls can include:

• Contact and Alarm Calls: It emits sharp, piercing calls, often transcribed as "kih kih kih," whose high pitch is surprising for an eagle and reminiscent of a falcon or a sparrowhawk.
• Courtship and Territorial Calls: During the courtship display, the male may emit an insistent "pee-peee" or a rapid series of "pee-pee-pee-peee." At the nest, vocalizations like "klia-klia-klia-ki-ki" are common. The male has a higher-pitched call than the female.
• Silence: Outside the breeding season, it is mostly silent.

Habitat and Distribution of the Booted Eagle

The Booted Eagle has a wide, discontinuous distribution range, extending in a narrow band from the Maghreb and Spain eastward to Lake Baikal, as well as an isolated and sedentary population in the Cape Province of South Africa.

It is mainly found in:

• Semi-forested habitats: It avoids large uniform forests, preferring open or fragmented pine or deciduous forests interspersed with fallow land, cultivated areas, hedgerow landscapes, or clearings.
• Medium-altitude mountain areas: These environments offer varied hunting grounds (hedgerow meadows, moors) and mixed slope forests. It can nest from sea level up to 1,600 m (5,200 ft) altitude.
• Forests with varied terrain: It adapts to all kinds of forest facies, provided the woodland is not too artificial or too dense.

Northern populations are migratory, wintering in the Indian subcontinent and sub-Saharan Africa. Sedentary populations also exist in the Balearic Islands and certain regions of Southern Africa.

Distribution Map

Diet

The Booted Eagle is a formidable carnivorous predator, with a very varied and eclectic diet.

It mainly feeds on:

• Birds: Its diet is essentially ornithophagous, capturing a wide diversity of small to medium-sized species, such as larks, sparrows, starlings, thrushes, blackbirds, jays, or pigeons.
• Small mammals: It can also catch mammals up to the size of a rabbit, such as rats, voles, hares, shrews, mice, or squirrels.
• Reptiles: Lizards are among its occasional prey.
• Insects: Insects can supplement its diet, which it sometimes catches while walking.

The Booted Eagle hunts by soaring at high altitudes, circling, then plunging in a swift dive on its prey, talons first, to capture it on the ground or in low flight. It can also hunt from ambush from a perch at the edge of open areas. Occasionally, it raids the nests of other species.

Reproduction

The Booted Eagle is monogamous, forming pairs that often remain bonded for life and return to the same nesting site each year. Sexual maturity is not well known but is estimated to be reached around two years of age.

• Nest: Unlike falcons, the Booted Eagle builds its nest. It is almost always located in a tree (often mature pines or oaks in Spain), occasionally on a rock face, at a height of 6 to 16 meters (20 to 52 ft). The nest is built by both adults with branches and twigs; the female regularly brings green branches during the nesting period. It may also reuse old nests of other large birds.
• Courtship Display: The breeding season begins with spectacular aerial displays, including chases, dizzying dives, and ascents, often accompanied by calls. These begin after returning to the breeding sites, around mid-April in some regions.
• Eggs: The female typically lays 1 to 3 eggs (most often 1 or 2), white in color with brown spots, between April and May. Incubation lasts approximately 29 to 40 days, primarily by the female who is fed by the male.
• Raising the Young: Chicks hatch covered in white down. They are fed by both parents. Fledging occurs between 35 and 60 days after hatching. After leaving the nest, they remain dependent on adults for several weeks (6 to 9 weeks) to learn to hunt. There is only one brood per year.

Conservation Status

The Booted Eagle is classified as "Least Concern" (LC) by the IUCN (International Union for Conservation of Nature) globally (last assessed in 2018). This classification is due to its very wide distribution range and an estimated global population of between 150,000 and 195,000 mature individuals, considered stable. In Europe, the population is estimated between 23,300 and 30,300 pairs.

However, this global status should not mask persistent local threats and past declines:

• Habitat Loss and Degradation: The decline and destruction of its forest and semi-forest habitats, deforestation, poor forest management (rejuvenation of stands), and fires are significant threats.
• Human Disturbance: The construction of roads, forest tracks, tourist or recreational activities near breeding sites can disturb nesting.
• Power Lines: Electrocution on power grids represents a significant cause of mortality.
• Pesticides: The use of pesticides and other biocides, particularly in wintering areas, can affect reproduction and prey availability.
• Hunting and Persecution: Historically, the species has suffered from direct hunting and nest destruction, practices now prohibited but which have had a notable impact in certain regions.
• Wind Turbines: The development of wind energy installations, especially in migration corridors, is a potential threat due to collisions.

Conservation measures are being implemented to protect the Booted Eagle, including its legal protection (Annex I of the EU Birds Directive, Annex II of the Bern and Bonn Conventions, Annex II of CITES), monitoring of nesting areas, improved forest management, and actions to reduce collisions with infrastructure.

Frequently Asked Questions (FAQ)

References

1. Wikipedia - Booted Eagle