[order] ACCIPITRIFORMES | [family] Accipitridae | [latin] Aquila fasciata | [authority] Vieillot, 1822 | [UK] Bonellis Eagle | [FR] Aigle de Bonelli | [DE] Habichtsadler | [ES] Aguila-azor Perdicera | [NL] Havikarend

Subspecies

 

Genus

Physical charateristics

 

A slim, medium-sized eagle, with rounded, rather short, wings and a long tail. The dark upper side contrasts strikingly with the clear white under side, the spots being hardly visible at a distance. In flight the wings appear dark in contrast to the white body below, and have a white leading edge, a blackish bar at the base of the flight quills, a conspicuous grey patch at the carpal joint, and a dark trailing edge contrasting with the paler flight quills. Immatures are more difficult to distinguish from other medium-sized brown eagles, but the pale chestnut under side is a good guide.

Listen to the sound of Bonellis Eagle

Copyright remark: Most sounds derived from xeno-canto

Range

 

Eurasia, Oriental Region : Spain to India to South China, also North AF

Habitat

 

In Europe Bonelli’s Eagle is restricted to the Mediterranean regions. It lives in mountainous areas and other rugged terrain at medium to low altitude - sea level to 1500 m, averaging 660 m with only 11 % of pairs nesting above 1000 m. It tends to prefer short or sparse vegetation, such as garigue, dry grassland and rocky habitats but the vegetation cover of its habitat can be highly variable including forests and parkland as well as bushes and scrub. It is also often found in mosaics of open habitat with non-intensive crops, vineyards, olive groves, non-irrigated orchards, small woodlands and pasture. The average distance between pairs is 11.9 km although neighbouring pairs may breed only 2 km apart.

Reproduction

 

In nuptial display, the pair circle over the breeding site and perform a vigorous undulating display, with steep downward plunges and upward swoops, seldom assisted by wing-flapping. At the onset of the breeding season the pair soars over the breeding site, occasionally calling. The birds are generally more noisy at this time, and display continues to a lesser extent through most of the breeding season.
Nests are usually built on crags, often in trees and occasionally on buildings. When in trees they are usually in the largest, leafy tree in the area, often in a river valley, and at between 30 and 120 feet above ground. They are very large structures for the size of the bird, up to six feet across by two feet thick. The nests are used year after year, starting quite small (three feet across by eighteen inches deep), growing larger and more massive according to age and site. Sticks up to one inch in diameter or more are used, and the whole thing looks like the nest of a much bigger eagle. Pairs may have from one to five nests from which to choose.
Normally two eggs are laid, dates varying with location. Incubation is by both sexes, but the female has the greater share, about 90% of the daylight hours and all night. The male feeds her on or near the nest, not necessarily every day. She may also feed on her own kills in spells off when the male shares the duties. The incubation period is 42-43 days. The downy young are at first helpless like other young eagles. The first feathers appear through the down at 25-35 days, and cover the body by 45 days. At this stage the eaglets can normally feed themselves. One eaglet generally kills the other in the early fledging period, but in about 20% of nests both survive. The fledging period is about 65 days. When the young hatch both parents brood them closely at first, the female taking the greater share. The female remains much near the nest even after she has ceased to brood the young, and at all stages this eagle is likely to spend more time on the nest with the eaglet than some others. For some time after the young fly from the nest the family may be seen together. Most young move rapidly away from the nest site, and accompany their parents on the wing for up to two months after they leave the nest.

 

Breeding success is high (82 %), though 30 % of the pairs do not lay. Productivity is 0.82 chicks/pair and 1. 56 fledging per successful nest but there are appreciable differences between years and regions.

Feeding habits

 

The Bonelli’s Eagle preys on medium-sized mammals and birds of a wide range of species. Rabbits and partridges are the preferred prey but it also preys on hares, squirrels, rodents, pigeons, corvids and lizards. In recent years, declines in both rabbits and partridges have caused diet changes and less profitable prey is becoming important. Carrion feeding is rare.

Conservation

 

This species has a large global range; the total size has not yet been quantified, but the Extent of Occurrence in Africa alone is estimated to be 510,000 km2. It has a large global population estimated to be 10,000-100,000 individuals (Ferguson-Lees et al. 2001). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.
The Bonelli’s Eagle Hieraaetus fasciatus is endangered at a European level having undergone large declines throughout almost all of its European range between 1970 and 1990, reducing the population to 862-1072 breeding pairs.
The declines have exceeded 50% over twenty years in some areas and in Spain, which holds up to 65% of the European population, the population appears to have declined by 25% from 1980 to 1990. This downward trend is contrary to that of other big eagles, such as the Spanish Imperial Eagle and Golden Eagle, whose populations are either stable or recovering. It is thought to be due to persecution, electrocution by powerlines, disturbance at nest sites and loss and deterioration of dry grassland and garrigue habitats. The global population is not concentrated in Europe. In Europe the species irregularly distributed in the Mediterranean basin. The global range of the Bonelli’s Eagle extends from the Iberian Peninsula and NW Africa across southern Europe, the Middle East and Arabian Peninsula through Afganistan to India, south China and Indonesia. The birds of Europe are sedentary, and the population of the European Union can be estimated at 800-900 breeding pairs.

 

Throughout the Old World regions Bonelli’s Eagle is a bird of wooded mountain ranges, not necessarily at very high altitudes, but extending from sea level to 6,000-7,000 feet. The African race prefers savannah country, not necessarily mountainous, forest edges, cultivation, and thorn-bush, provided there are some big trees. It is diflicult to define the habitat precisely. It is always wooded, usually mountainous, and usually in the rainfall range 20-45 inches per annum. This is not a bird of deep forests or of open desert or steppe country. It is normally resident throughout the year, but the birds from the northern fringe of the range migrate south to warmer climates in winter and appear in migration streams through the Pyrenees, Asia Minor and other places.
Wherever it occurs it is a bold and rapacious bird, living on a wide range of prey, all taken alive. It spends a lot of its time soaring over its chosen nesting area, and the pair can frequently be seen together outside the breeding season, and will often roost together on an outstanding tree, even when they have been apart most of the day. Its normal method of hunting is from cover inside a tree, by a quick dash, but it will also catch prey by quartering hill slopes like other eagles, or make a stoop from a soaring position. It can catch birds on the wing, but most of its prey is taken on the ground. Several pairs or individuals may be found together at particularly favourable places where large numbers of game-birds may congregate, as for instance at a water-hole in dry country. Its range of prey is almost as great as that of the Martial Eagle Polemaetus bellicosus or Golden Eagle Aquila chrysaetos, eagles of twice its weight. It has exceptionally powerful feet for its size, the hind claw being very long, longer than that of the Imperial Eagle Aquila heliaca which is much heavier.

 

Migration

 

Resident and dispersive. Adults present all year in loose vicinity of breeding area, though less attached to territory July-November. In Europe, young become independent July to early August and soon leave nest vicinity, though occasionally remain in area into October or even later. Dispersal mainly southward, and some appear late summer in low-lying areas along Mediterranean. In central and south Spain, frequently seen autumn-winter 25-50 km from nearest possible nesting localities. Irregular occurrences west and north France, and rare vagrants further north, also mainly July-December. Slight evidence of southward autumn movement across Mediterranean; few birds involved, and probably continuance of dispersal rather than migration.

Distribution map

 

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