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Bonelli's eagle ( Aquila fasciata) is a large bird of prey. The common name of the bird commemorates the Italian ornithologist and collector Franco Andrea Bonelli. Bonelli is credited with gathering the type specimen, most likely from an exploration of Sardinia. Like all , Bonelli's eagle belongs to the family Accipitridae. Its feathered legs marked it as member of the Aquilinae or booted eagle subfamily. This species breeds from southern Europe, Africa on the montane perimeter of the Sahara Desert, and across the Indian Subcontinent to Indonesia. In Eurasia, this species may be found as far west as Portugal and as far east as southeastern China and Thailand. It is usually a resident breeder.
Bonelli's eagle often occurs in hilly or mountainous habitats, with rocky walls or crags, from sea level to . Habitats are often open to wooded land and can occur in arid to semi-moist climate. It can be considered partially opportunistic, but is a specialist predator of the European rabbit, galliforms and pigeons. On evidence, when staple prey populations decline or are locally scarce, Bonelli's eagle switches to being an opportunistic predator of a wide variety of birds. Despite its persistence over a large range and its continued classification as a least concern species by the IUCN Red List, Bonelli's eagle has declined precipitously in various parts of its range, including almost all of its European distribution, and may face potential local extinction. Its decline is due to widespread habitat destruction, electrocution from electricity pylons as well as persistent persecution.
DNA research resulted in the two species being moved from the genus Hieraaetus to Aquila, along with another dissimilar species, the Cassin's hawk-eagle ( Aquila africana). Bonelli's, African hawk- and Cassin's hawk-eagles were found to be genetically closely related to the golden eagle ( Aquila chrysaetos) species complex, which also includes Verreaux's eagle ( Aquila verreauxii), Gurney's eagle ( Aquila gurneyi) and wedge-tailed eagle ( Aquila audax). These species are all conspicuously larger than Bonelli's and African hawk-eagles with differing proportions to their wings, tail and legs (in adaptation to their open country habits) and much darker coloured plumages. Furthermore, the four other traditional members of the genus Aquila have been revealed to be a separate species complex despite showing superficial similarity to the golden eagle group, i.e. being relatively large and long winged with usually dark colouring.
Beyond the nominate subspecies of Bonelli's eagle, which is found throughout its range in Eurasia, a second subspecies dwells in the Lesser Sunda Islands, A. f. renschi. The latter race is linearly smaller, and compared to other Bonelli's eagles tends to have more strikingly barred remiges and tail, the belly, thighs and crissum more boldly marked. At one time, its restricted and very isolated range have caused authors to suggest A. f. renschi may be a full species but recent studies have indicated that it is not genetically distinct enough to be considered a separate species. Furthermore, the most recent analysis couldn't rule out early introductions (possibly by ancient Falconry) at least playing a part in the species presence in the Lesser Sundas, as some other established wild birds on those islands are certain to have reached there by early human introductions.
Total length in fully-grown eagles of the species can vary from . Wingspan in males can vary from while that of the female may vary from .
Bonelli's eagle is intermediate in its wing lengths and tail length proportionately between the shorter-tailed and longer-winged eagles of open country and longer-tailed and shorter-winged forest eagles, which allows to vary its hunting between short-burst, agile surprise attacks in trees and ample ground-covering pursuits in the open.Whistler, H. (1940). How do large raptorial birds hunt their prey? Ibis, 4: 732–735.Brown, L. (1977). Eagles of the World. Universe Books. Its talons and feet are proportionately very large and presumably rather powerful for the eagle's size. In particular the elongated talon on its rear toe (used as a killing apparatus by almost all accipitrids), or Claw, is longer than that of the much larger eastern imperial eagle ( Aquila heliaca) and proportionately slightly larger even than its bigger Sympatry, the golden eagle. Hallux claw lengths in Bonelli's eagles from western Europe averaged in males and in females averaged , and could farther range up to .
The streaking on this eagle is normally strongest on the breast and upper flanks while the lower belly and crissum are typically either plain or only faintly marked. Juveniles are a lighter medium brown above with variable paler edges, sometimes with a creamy patch on the back (not the mantle as in the adults) and uppertail coverts. Generally, juveniles have a rusty-brown head with a darker brown around and behind their eyes. The juvenile eagle's crown is either darkly streaked or, occasionally, plain greyish. The tail of young birds is more clearly barred than the adults while the subterminal band is only negligibly thicker than the other bars. Like adults, the juvenile Bonelli's eagle's tail has a thin white tip. The juvenile is light rufous to warm buff below with minimal black streaks, which are normally confined to chest-sides.Forsman, D. (1999). The raptors of Europe and the Middle East: a handbook of field identification. London: T & AD Poyser.
In flight, Bonelli's eagle is a largish raptor with a well projecting head and broad, long and somewhat square ended wings which are slightly pinched in at body with a little tapering at tips. Feather molts can make the wings look quite variable in shape with some individuals appearing rather longer and narrower winged than others. In flight, the tail appears long and broad but if pinched in can appear surprisingly narrow. This species tends to fly with powerful but loose shallow beats. When gliding, they do so often on flat wings with well-spread feathers and the carpals pressed slightly forward but more so when entering a fast glide. This species soars infrequently on flat or slightly raised wings.Porter, R. F. (1981). Flight identification of European raptors. A&C Black. At nearly all times of the year, Bonelli's eagles quite often flies in pairs. In colouring, the flying adult is dark above with a variable amount of the white marking on the mantle. The tail has faded barring (rarely perceptible) on grey with a big blotchy subterminal band and a white tip above. The markings on the tail look more or less the same when seen both from below and above. Adult Bonelli's eagles have white lesser coverts which along with the greyish tail stand out in contrast against blackish central wing band over the greater and median coverts. Also the flight feathers are faintly and thinly barred light grey-brown with paler bases, which often become paler (to a whitish hue) on the primaries inside blackish tips and leading wing coverts. In flight, juveniles are brown above with slightly darker wing ends and tips to greater coverts and greyer primary windows. Occasionally, juveniles manifest a creamy patch on back and obscure narrow U above barred tail, which even if present are only sometimes visible. Below the juvenile's wing linings are light rufous to warm buff like the body colour. Usually juveniles appear with darker tips to greater coverts forming wing-diagonals (sometimes lacking or confined to carpal area) and a small but distinct area of white on primaries against the blackish tips. Until the 3rd year, the young eagles appear more like a 1st year juvenile than an adult, but begin developing more streaks below and darker greater underwing coverts. By the 4th year, the subadult Bonelli's are increasingly similar to the adult, with an increasing subterminal band, a whiter underbody and fairly prominent underwing-diagonals. However, subadults are often still appear with a mix of paler barred juvenile type feathers and plainer darker adult feathers on the flight feathers.
Bonelli's eagles are generally unmistakable when shape, flight and plumage are considered in combination. In poor light, it is possible to mistake one with a honey buzzard, one mainly in Europe and another mainly in Asia, as these raptors are extremely polymorphic and can come surprisingly close to approximating the plumage of various more powerful raptors. The wing shape in Bonelli's eagles can at times appear similar to that of honey buzzard but the latter raptor type are usually distinctly slimmer and slighter bodied with a much smaller, slimmer head. In flight, honey buzzards often have notched rather than square ended tails, less emarginated primaries and typically they fly with their wings held more at an angle. The sympatric species of honey buzzard tend to have bolder barring on the tail and underwings, broader dark trailing wing edges and all have no pale mantle patch or darker underwing-diagonals. An unlikely source of confusion is the Eurasian goshawk ( Accipiter gentilis), which is usually visibly smaller with much shorter wings, a slightly longer tail, different level flight style and many distinctive plumage characteristics. Distant juvenile Bonelli's could conceivably be mistaken for the long-legged buzzard ( Buteo rufinus), but the buzzard is also smaller and is shorter tailed with prominent dark carpal patches and dark trailing wing edges. Furthermore, the buzzard usually holds its wings in a noticeable dihedral when flying in a soar.Forsman, D. (2016). Flight Identification of Raptors of Europe, North Africa and the Middle East. Bloomsbury Publishing.
Another unlikely confusion species is the short-toed eagle ( Circaetus gallicus) which roughly matches the size of Bonelli's eagles but the short-toed has larger and differently rather wedge-shaped wings with a much less dark overall pattern as well as a shorter tail, a rounder head on a shorter neck and usually a dark rather than light throat. Also, goshawks, short-toed eagles and European honey buzzards usually frequent different habitats, more often living in more wooded and lowland habitats. Bonelli's eagles may be mistaken for pale morph adult booted eagle ( Hieraeetus pennatus) by inexperienced observers but, beyond being a third larger and more than twice as heavy, Bonelli's eagles are moreover distinct in plumage. Overall Bonelli's are much darker and streaker especially compared to the clearly paler flight feathers of booted eagles. Booted eagles are both whiter and more contrasting on the upperwing coverts, have whitish uppertail-coverts and have white on the wing's patagium. More similar in plumage is the juvenile Bonelli's eagle are the rare rufous morph of the booted eagle but the latter can still be told by the booted species' narrower wings and smaller size. In southern part of the Red Sea, vagrants (largely juveniles) may possibly come into range of the closely related and more similar African hawk-eagle, but the latter is somewhat smaller and comparatively short winged and longer tailed (the total length is similar between the species due to the African's longer tail but Bonelli's can be visibly larger bodied and rather heavier). In the African species, the adult plumage is a more contrasting, with dark slate grey upperparts, purer white underparts with dark streaking. In African hawk-eagles, juveniles compared to Bonelli's are darker above with pale wing-windows.Kemp, A., & Kemp, M. (2006). Sasol Birds of Prey; New Edition. Struik.
In southern Europe, they range patchily through different parts of Portugal and Spain into southern France as far north as the department of Drôme.Cugnasse, J.M., Ravayrol, A., Cramm, P., Goujon, C., Morvan, R., Nozerand, R., Pompidor, J.P. & Ricau, B. (1996). Large. in Muntaner J; Mayol J. "Biology and conservation of Mediterranean raptors, 1994": 371–379. Discontinuously, they are now seemingly solely left as breeding bird in Italy on the islands of Sardinia and Sicily.Toso, S. (1972). Observazioni di rapaci diurni in Sardegna. Rivista Italiana di Ornitologia, 42: 435–444. They at least were known to live in Aspromonte National Park in Calabria, near the far southwestern tip of the Italian peninsula, directly across the narrow Strait of Messina from Sicily.
Out of Europe, they may be found in western and southern Turkey, Syria (possibly but most likely extirpated), the isle of Cyprus, Lebanon, Israel, western Jordan, northeastern Egypt (rarely in northern half of Sinai Peninsula), possibly but not certainly in spots in the west and south of Saudi Arabia, and elsewhere in the Arabian Peninsula to Yemen, Oman, and the United Arab Emirates.Baumgart, W., Kasparek, M., & Stephan, B. (1995). Birds of Syria. M. Kasparek Verlag.Kassinis, N. (2010). Demographics of the Bonelli's eagle Aquila fasciata population in Cyprus. Bird Census News, 23(1–2), 21–27.Ramadan-Jaradi, G., Bara, T., & Ramadan-Jaradi, M. (2008). Revised checklist of the birds of Lebanon 1999–2007. Sandgrouse, 30(1), 22.Shirihai, H., Dovrat, E., Christie, D. A., & Harris, A. (1996). The birds of Israel (Vol. 692). London: Academic Press.Vaassen, E. W. Status and occurrence of Bonelli's Eagle, Hieraaetus fasciatus, in Turkey and Eastern Mediterranean–A Population Estimate. Raptor Research & Rehabilitation Center Turkey.Aspinall, S., & Hellyer, P. (2006). Important bird areas of the United Arab Emirates. British Birds, 99(11), 546.Jennings, M. C. (2004). Breeding birds in central Arabia 1978-2003. Sandgrouse, 26(1), 35-47. Elsewhere in the Middle East, their range includes eastern Iraq and west, south, and northeastern Iran, extending somewhat into Turkmenistan in the Kopet Dag range.Desfayes, M., & Praz, J. C. (1978). Notes on habitat and distribution of montane birds in southern Iran. Bonner Zoologische Beiträge, 29(1), 18–37.Bukreyev, S.A. (1998). Materials. Ornitologiya, 28: 154–158.
Further east into Asia, their distribution includes eastern Afghanistan and Pakistan through most of the Indian subcontinent, where generally it is uncommon but more locally common near Nepal. On the other hand, they are absent in eastern India and only occur as a vagrant to Sri Lanka and Bangladesh. In India, they are most regularly found in areas such as the Chambal river, Ranthambore National Park, the Chir zone of the lower Kumaon division, and in winter in the Keoladeo National Park of Bharatpur, Rajasthan. From central Myanmar, they range across into northwestern Thailand and northern Laos (though possibly only as a visitor rather than breeding in the latter two). In southern China, their resident range includes Yunnan, Guangxi, and Guangdong north to the Yangtze River, as well as rarely into Hong Kong.Round, P. D. (1983). Some recent bird records from northern Thailand. Nat. Hist. Bull. Siam Soc, 31(2), 123–138.Scharringa, J. (1994). A record of the Bonelli's Eagle Hieraaetus fasciatus in Thailand. Natural History Bulletin of the Siam Society, 42: 291.MacKinnon, J. R., MacKinnon, J., Phillipps, K., & He, F. Q. (2000). A field guide to the birds of China. Oxford University Press.Carey, G. (2001). The Avifauna of Hong Kong. Hong Kong Bird Watching Society. Their isolated population range is in the Lesser Sunda Islands, including at least Sumbawa, Timor, Wetar, Luang, and Flores, however records show they've turned up on as many as 20 islands in the Lesser Sundas.Trainor, C. R. (2002). The birds of Adonara, Lesser Sundas, Indonesia. Forktail, 93–100.
Historically speaking, research published in People and Nature in 2024 by scientists from the University of Granada and Miguel Hernández University of Elche (UMH) indicates that Bonelli's eagle is a relative newcomer to Europe and the Mediterranean Basin and that they spread there with the help of humans around 50,000 years ago. Genetic analyses indicate that the Mediterranean Bonelli's eagle population likely comprised a few individuals around the last glacial maximum, which later thrived as the temperature in the Mediterranean Basin rose, and the human population grew and became sedentary.
Mechanistically, the three bilateral interactions among Bonelli's eagles, golden eagles, and the human population are jointly what allowed Bonelli's eagles to move from the Middle East into the Mediterranean Basin at this time – and also what prevented them from moving there sooner. Golden eagles are less tolerant of humans than Bonelli's eagles are. Additionally, between the two eagle species, the golden eagle is the dominant species, while Bonelli's eagle is the subordinate one. With these interactions in mind, the authors of the 2024 People and Nature study hypothesize and test with data-driven mathematical models that with the arrival of the first anatomically modern humans in Europe, some of the golden eagle territories closest to human settlements were abandoned, and these 'vacant' territories began to be occupied by Bonelli's eagles from the Middle East. That is, Bonelli's eagles could not have established themselves in the Mediterranean before the arrival of the first Homo sapiens because the competitive pressure exerted by golden eagles and other species would have been too overwhelming, but the arrival of humans displaced the golden eagles and provided an empty niche in the localities' ecosystems that Bonelli's eagles were then able to neatly fill.
Bonelli's eagles are mostly residential throughout their range but juvenile can disperse up to over several hundred kilometres. Sometimes, they are recorded at migration sites and at spots where not known to breed in winter.Franco, A. (1980). Observacion de Hieraaetus fasciatus en una corriente migratoria otonal de rapaces en Ceuta. Donana, Acta Vertebrat, 7: 263.Billet, J. (1994). Aigle de Bonelli. Survie et resistance en region Paca. 25: 18. Wanderings include around north of their regular range in France near the coast of English Channel, far from their normal haunts in Regensburg, Germany and, probably both from the Italian island populations, to northwestern Italy and Slovenia.Klose, A. (1979). Habichtsadler Hieraaetus fasciatus bei Regensburg. Anzeiger der Ornithologischen Gesellschaft in Bayern, 17: 177–178.Alessandria, G., & Boano, G. (2011). Le comparse dell'aquila di Bonelli Aquila fasciata in Italia nord-occidentale: eventi eccezionali o normale erratismo. Avocetta, 35, 3–12.Scott, R. E. (1997). Opazovanje kraguljega orla Hieraaetus fasciatus junija 1997 pri Predjamskem gradu. Acrocephalus, 18: 98–99. From their Iberian Peninsula range presumably, vagrants have been reported in the Canary Islands.Clarke, T. (2006). Field guide to the birds of the Atlantic islands. Christopher Helm. Beyond Sri Lanka, other areas the species has been known to vagrate (or perhaps rarely winter) in Asia have included Kazakhstan, the Korean Peninsula, Malaysia and Cochinchina in Vietnam, as well as a record in winter 1996 on the isle of Yamdena, the latter presumably from the Lesser Sunda population.Wassink, A., & Oreel, G. J. (2007). The birds of Kazakhstan. A. Wassink.Lee, W. S., Ku, T. H., & Park, J. Y. (2000). A field guide to the birds of Korea. LG Evergreen Foundation.Tordoff, A. W., & Eames, J. C. (2001). New additions to the list of birds of Vietnam. Oriental Bird Club Bulletin, 33, 37–38.Jeyarajasingam, A., & Pearson, A. (1999). A field guide to the birds of West Malaysia and Singapore. Oxford University Press.
In winter, Bonelli's eagle occurs at lower elevations and more open habitats in semi-deserts and plains, where it can appear surprisingly at home; it often prefers wetter habitats such as large river mouths, and , especially where these fall in existing home range, as prey is more likely to be concentrated in such areas. In some of the Indian subcontinent, Southeast Asia and the Lesser Sundas, Bonelli's eagle inhabits tropical rainforest that is much wetter and more humid than their typical habitats, and in such areas it is attracted to more sparse and rocky areas such as slopes and cliffs as well as alternately open mosaics and glades.
Bonelli's eagles will also occasionally stoop from a soaring height onto prey. Mostly, this predator takes birds from on or near the ground but some snatched them from bushes and, seldom, water. It has been known to have sufficient agility to catch some birds from active flight. In one case, a Bonelli's eagle was observed to fly below a Western jackdaw and swoop upwards to grab it from below. Pack hunter by a lifelong pair is quite common, almost exceptionally so in this species. One eagle tends to fly directly above the other, with several cases of one eagle scattering a bird flock for the other eagle to quickly single out, in a similar style to tandem-hunting ( Falco jugger). However, per Spanish studies, apparently tandem hunting neither improved hunting success nor were the eagles able to capture larger prey (in fact the estimated prey size by pairs was slightly lower than that taken by each mate hunting by itself) while hunting in tandem. It was hypothesized that tandem hunting is more important to the socio-sexual relations of the pair rather than capture of a significant amount of prey.Watve, M.G., Sant, N.R. & Joshi, V. (1995). Why Bonelli's Eagles hunt in pair: an assessment of individual and paired hunting successes. Journal of the Bombay Natural History Society, 91: 355–359. Compared to most other Aquilinae, Bonelli's eagle takes a great majority of its prey alive and seldom comes to carrion or Kleptoparasitism foods from other raptors. However, it will readily come to previously injured prey, especially shot by Hunting, and will readily take young animals across most prey classes. Also, in Keoladeo National Park, India, Bonelli's eagles were observed to habitually follow harriers, and other Aquila eagles in order to capture incidentally flushed during their flybys.Prakash, V. (1988). The general ecology of raptors in Keoladeo National Park, Bharatpur (Doctoral dissertation, Ph. D. thesis. Bombay University, Mumbai, India).
Overall, Bonelli's eagles take a fairly wide variety of prey. Across its wide range, their prey spectrum has been known to include perhaps up to nearly 200 prey species. Dietary studies have primarily been conducted in western Europe, though some study has gone into their food habits elsewhere (being well known in Cyprus and, less so, India).Iezekiel, S., Bakaloudis, D. E., & Vlachos, C. G. (2004). The diet of the Bonelli's eagle Hieraaetus fasciatus in Cyprus. In: Raptors worldwide: proceedings of the VI world conference on birds of prey and owls. Berlin: World Working Group on Birds of Prey/MME (pp. 581–87). Brown & Amadon (1986) considered Bonelli's eagles prey size range as nearly as extensive as the most massive Aquilinae, such as the golden eagle and the martial eagle ( Polemaetus bellicosus) (but mainly may have been describing the African hawk-eagle that was lumped at the time). Bonelli's eagles mainly hunts and , taking and other prey types on a more local and sporadic basis. In western Europe, it is considered something of a specialist predator on European rabbit and partridges, though other birds such as , gulls and sometimes are taken as much or more so depending on local prey population trends.
Pellet analysis is considered the most reliable way to get a complete picture of Bonelli's eagle dietary habits. Despite its predaceous power, typically the average size of prey taken are within average range for a raptorial bird and it may take smaller prey on average than its mildly smaller cousin, the African hawk-eagle. In Sierra Morena, Spain, the mean size of prey taken was estimated at , while in Greece the mean prey size was estimated at .Alivizatos, H. & Bourdakis, S. Diet and breeding success of the Bonelli's Eagle (Hieraaetus fasciatus) in Greece: preliminary data. International Hawkwatcher, 5: 3–6. A subsequent study in Spain, however, posited the mean prey size as lower than in the past, stating that prey taken by males averaged an estimated and by females at , probably due to increased importance of and reduced numbers of . Thus, on average, prey sizes average about 20–45% of Bonelli's eagles own weight. Furthermore, the latter Spanish study found hunting success of Bonelli's eagles to average around 28.5%, a slightly higher hunting success rate than (20%) or lesser spotted eagles ( Clanga pomarina) (24%) but slightly lower than greater spotted eagles ( Clanga clanga) (34%).
Research determines that Bonelli's eagle are often attracted to scrub areas during hunting forays to catch sight of rabbits foraying out of vegetative cover. Since young juvenile and yearling rabbits are forced out to more open feeding spots by dominant adult rabbits, they are disproportionately often selected by Bonelli's eagles and other avian predators. Rabbits become more commonly caught during the summer when the young rabbits tend to disperse. On the contrary, 86.2% of the rabbits taken in southwest Portugal were reportedly adults. Most rabbits caught by Bonelli's eagle were estimated to weigh between (from the size of a kit to a smallish adult) per Spanish studies, with an estimated average weight in Spain of . A study in southeastern Spain estimated that the region's Bonelli's eagles claim about 337 rabbits during the breeding season and 237 rabbits during non-breeding during the course of a year, so despite their heavy predation barely make a dent on the overall population of rabbits (effecting less than 2.5% of the population at peak). The native western European population of wild rabbit has been heavily depleted by myxomatosis and rabbit haemorrhagic disease, having been reduced by an estimated 50–70%. While the overall numbers seemingly taken by them reduced by as much as a third between 1968 and 2009, on evidence Bonelli's eagle still sought them out and hunted rabbits preferentially even during the non-breeding season when their numbers dip to their lowest. In additional, significant numbers of other may be taken, extending to occasional ( Lepus granatensis) as well as accounts of Bonelli's eagles hunting ( Lepus europaeus) in the Greek isles and ( Lepus nigricollis) in the lower Himalayas.Handrinos, G., & Akriotis, T. (1997). The birds of Greece. Christopher Helm.Miranzo, B.M. (2017). Ecología espacial del águila de Bonelli ("Aquila fasciata") en Aragón. Universidad Complutense de Madrid, Departamento de Zoología y Antropología (Doctoral thesis).
Beyond gamebirds, are the other most significant avian prey type. The two larger European pigeons, the oft feral or domestic rock dove ( Columba livia) and the common wood pigeon ( Columba palumbus), are almost solely favoured among this group where encountered. In southwest Portugal, pigeons have surpassed rabbits (due to their disease-based decline) to become the most important prey. Here, attempts were made to parse the proportion of that were taken against the number of (since pigeon fanciers frequently persecute this eagle due its allegedly heavily predation of domestic birds). Of the 1497 prey items overall, feral pigeons were found to comprise 30.1% of the food by number and 26% of the biomass while the domestic types made up only 9.7% of the diet by number and 7.2% of the biomass. In Catalonia, Spain, unidentified pigeons made up 17.8% of the foods and 17.4% of the biomass while identified common wood pigeons made up a further 6.24% of the number and 6.54% of the biomass, while a smaller study from the same area boosted wood pigeons to make up 11.3% of 524 prey items. In Cyprus, rock and common wood pigeons collectively made up 27.7% of the diet.
In Provence, Eurasian magpie ( Pica pica) and western jackdaw ( Corvus monedula) made up 10.17% and 9.95% of the diet respectively. In Portugal, Eurasian jay comprised 7.5% by number but only 2.7% of the biomass. Corvids were the main prey for Bonelli's eagles in Georgia, with the Eurasian magpie comprising 12.3% of the diet, though largely young were reportedly taken, and ( Corvus corone) making up a further 10.76%. In the Aegean islands, carrion crows comprised 14.1% of the prey by number and 8.8% of the biomass, while south of Turkey in Cyprus, western jackdaw comprised 7.6% of the foods. Other avian prey groups taken in usually smaller numbers include , swifts, , European nightjar, European bee-eater, European roller, Eurasian hoopoe, , , and various , , Iberian grey shrike, Dunnock, at least 10 Old World flycatcher species, thrushes, Meadow pipit, , Emberiza, and . In total, about 130 bird species may be taken and birds as a whole almost always form the most ample part of the diet compared to other classes: 69.5% and 80.97% of the biomass in the south of France, 67.7% in Georgia and 62.6% in Catalonia.
Among , Bonelli's eagles have reportedly attacked red fox ( Vulpes vulpes) and ( Felis silvestris) (probably mostly kits and kittens of these two species) in western Europe as well as ( Martes foina) and assorted . Meanwhile, adult Bengal fox ( Vulpes bengalensis) have reportedly been caught in India. In France and Spain, mammals overall comprised 34.8% and 26.1% of the diet, respectively, whereas in Georgia they made up 15.4% of the diet. are usually secondary prey throughout the range. Though they are known to hunt , Bonelli's eagles rarely hunt them and generally seem to pursue by preference. In Cyprus, ( Laudakia stellio) comprised 5.9% of the food, unidentified Lacerta lizards 10.76% of diet in Georgia (and reptiles altogether adding up to 16.9% of the food by number). Relatively large adult specimens of ocellated lizard ( Timon lepidus), at in mean body mass, made up 3.97% of the biomass and 7.05% by number in Catalonia, Spain. Desert monitor ( Varanus griseus) and probably assorted other monitor lizards were reportedly amongst the leading prey for Bonelli's eagles in several parts of India. Minor prey includes Common toad and possibly a few other types of amphibian. Potentially and/or other may be taken but these may incidentally consumed (i.e. undigested food from the stomachs of prey).
Cases of golden eagles taking over prior Bonelli's eagles territories have been reported but usually golden eagles only takes up the prior Bonelli's territory when the latter vanishes due to unrelated (often anthropogenic) causes not direct competition or usurpation. A minor negative effect has been probably correlated with golden eagles not infrequently attacking and displacing juvenile and subadult Bonelli's eagles and can tend to be behaviourally dominant in keeping with its larger size. This in turn presumably hampers the ability of Bonelli's to expand their range after declines and stabilize their population.Fernandez, C., & Insausti, J. A. (1990). Golden eagles take up territories abandoned by Bonelli's eagles in Northern Spain. Journal of Raptor Research, 24, 124–125.Dobado-Berrios, P.M., Álvarez, R. & Leiva, A. (1998). El Águila Perdicera en la provincia de Córdoba. Quercus, 154: 48–49.Ontiveros, D. (2000). Ecología de una población de Águila Perdicera (Hieraaetus fasciatus) del sureste ibérico: plan de conservación. Tesis doctoral. Universidad de Granada. Granada.Cheylan, G. (1973). Notes. Alauda, 41: 203–212. Further east, in Israel, Bonelli's and golden eagles are competitors as well. In the dry, barren Negev desert, golden eagles nests were found apart and Bonelli's were scarce. In the Judean desert, which has more annual rainfall and more available prey, the distance between golden eagle nests averaged and Bonelli's eagle easily outnumbered them. Apparently, Bonelli's eagle exceptionally outcompeted its larger cousin here due to a subtle topographic variation in the habitat.Bahat, O. 1989. Aspects in the ecology and biodynamics of the Golden Eagle (Aquila chrysaetos homeyeri) in the arid regions of Israel. Master's Thesis. Tel Aviv University Tel Aviv, Israel. In Spain, Bonelli's eagles share cliff habitats beyond golden eagles also with ( Falco peregrinus), , Eurasian eagle-owls ( Bubo bubo) and three species of vulture. The eagles tend to dominate the smaller carnivorous birds in most circumstances, even the swifter peregrine.Martínez, J. E., Martínez, J. A., Zuberogoitia, I., Zabala, J., Redpath, S. M. & Calvo, J. F. (2008). The effect of intra- and interspecific interactions on the large-scale distribution of cliff-nesting raptors. Ornis Fennica, 85 (1): 13–21. However, the still larger griffon vulture ( Gyps fulvus) was apparently a routine territory and nest usurper of other birds of prey, displacing golden eagles, ( Gypaetus barbatus) and ( Neophron percnopterus) from their nests as well as 9 out of 23 eyries built by Bonelli's eagles in the study area. Despite their prior claimed "dominance" over the swift falcons, at least three cases have been observed of peregrine falcons usurping Bonelli's eagle (presumably through routine harassment and dive-bombing) nests in Spain. Beyond golden eagles, peregrines and griffon vultures, ( Strix aluco) have been known to take over old Bonelli's eagle nests.Gálvez, M., Aris, S., Baques, J. M. (1998). Nidificacion de cárabo común Strix aluco en nido abandonado de aguila perdicera Hieraaetus fasciatus. Butlleti del Grup Catala d'Anellament, 15: 43–45.
European rabbits have a huge range of predators in the Iberian peninsula, with at least 30 different species known to hunt the once densely populated lagomorph. Besides the overlapping ranges of Bonelli's and golden eagles, most other birds of prey that hunt rabbits extensively are partitioned from the potential depletive effect of competition by differences in habitat preferences, hunting techniques and temporal activity. Beyond the specialized mammalian predator, the Iberian lynx ( Lynx pardinus), some of the other most specialized predators of wild rabbits are Bonelli's eagles, golden eagles, Spanish imperial eagles ( Aquila adalberti) and Eurasian eagle-owls. A comparative study indicated that the golden eagle diet was comprised 40% by rabbits, while they made up 49% for eagle-owls, 50% for Spanish imperial eagles and 61% for Bonelli's eagle.Voous, K.H. 1988. Owls of the Northern Hemisphere. The MIT Press, 0262220350. Elsewhere, higher import has been applied for rabbits in the local diet of golden eagles as well as for Spanish imperial eagles.Sánchez, R., Margalida, A., González, L. M., & Oria, J. (2008). Biases in diet sampling methods in the Spanish Imperial Eagle Aquila adalberti. Ornis Fennica, 85(3), 82–89. The mean size of rabbits taken increases more or less with the size of the avian predator: for , for Bonelli's eagles, for Eurasian eagle-owls and for golden eagles.
Along with northern goshawks, golden eagles and Eurasian eagle-owls, Bonelli's eagle is considered a "super predator" in the European region due to its habit of hunting other predators. In contrast to the other birds of prey, they are somewhat less commonly at high predator status compared to goshawks (most common predator of other diurnal raptors in studies), golden eagles (most common predator of mesopredator mammals), and eagle-owl (most common predator of other owls). However, they are relatively common predators of other diurnal birds of prey, per overall analysis they took such prey somewhat more regularly than did golden eagles in Europe. Among the other accipitrids that Bonelli's eagle have been known to hunt include the Indian spotted eagle ( Clanga hastata), European honey buzzard ( Pernis apivorus), red kite ( Milvus milvus), black kite ( Milvus migrans), western marsh harrier ( Circus aeruginosus), Montagu's harrier ( Circus pygargus), hen harrier ( Circus cyaenus), Eurasian sparrowhawk ( Accipiter nisus), shikra ( Accipiter badius), Eurasian goshawk, long-legged buzzard and common buzzard ( Buteo buteo).Gil-Sánchez, J. M. (1998). Selección de presa por el Águila-azor Perdicera (Hieraaetus fasciatus) durante el periodo de nidificación en la provincia de Granada (SE de España). Ardeola, 45(2), 151–160.Sant, N., Shelke, V., & Shelke S. (2013). On the breeding biology of the Indian Spotted Eagle Aquila hastata. Indian Birds, 8 (2) 29–32. Among falcons, they have been known to prey upon common kestrel ( Falco tinnunculus), lesser kestrel ( Falco naumanni) and peregrine falcon and as for owls, tawny owl ( Strix alucco), little owl ( Athene noctua), long-eared owl ( Asio otus), short-eared owl ( Asio flammeus) and most impressively of all, in at least one instance, an adult Eurasian eagle-owl.López-López, P., García-Ripollés, C., Giménez, J., & Urios, V. (2016). A case of predation of a Eurasian Eagle-Owl by a Bonelli's Eagle. Journal of Raptor Research, 50(4), 422–425. Although usually classed as an apex predator, as in most cases of apex predators in competitive environments, Bonelli's eagles sometimes infrequently fall victim to interspecific killings and predation as well.Resano-Mayor, J., Hernández-Matías, A., Real, J., Moleón, M., Parés, F., Inger, R., & Bearhop, S. (2014). Multi-scale effects of nestling diet on breeding performance in a terrestrial top predator inferred from stable isotope analysis. PLOS ONE, 9(4), e95320. Eurasian eagle-owls have been known to prey on Bonelli's nestlings a few times and possibly also an adult at least once.Bayle, P. (1987). De´couverte des restes d'un aigle de Bonelli Hieraaetus fasciatus juvenile dans une aire de Hibou Grand-duc Bubo bubo en Provence. Faune de Provence, 8:49–53. In one case, a subadult male golden eagle preyed upon an adult male Bonelli's eagle. are also counted amongst the predators of nests taking eggs in southeastern Spain.Gil-Sánchez, J.M.; Molino-Garrido, F., Valenzuela-Serrano, G. (1996). Selección de hábitat de nidificación por el Águila perdicera (Hieraaetus fasciatus) en Granada (SE de España). Ardeola, 43: 189–197.
Nesting locales are often high on cliff ledge or alternatively at (usually over ) above the ground in large trees. Very rarely, nests may be on the perimeter of buildings.Ontiveros, D., & Pleguezuelos, J. M. (2003). Physical, environmental and human factors influencing productivity in Bonelli's eagle Hieraaetus fasciatus in Granada (SE Spain). Biodiversity & Conservation, 12(6), 1193–1203. The trees selected are often the tallest and/or most densely foliaged in a given stand. Their close cousin, the African hawk-eagle, usually nests on trees and rarely utilizes crags and alternate nesting sites as does Bonelli's.
Description
Size and form
Bonelli's eagle is a fairly large bird of prey and a medium-sized eagle. When still classified as a member of the genus Hieraaetus, it was considered the largest extant species therein, however, as a member of Aquila it is amongst the smallest-bodied species.Naoroji, R., & Schmitt, N. J. (2007). Birds of prey of the Indian subcontinent. Om Books International.Brown, Leslie and Amadon, Dean (1986) Eagles, Hawks and Falcons of the World. The Wellfleet Press. . Amongst the currently accepted species of Aquila eagles, it is of similar size to the tawny eagle ( Aquila rapax) (albeit with rather shorter wings than the tawny), slightly larger than the African hawk-eagle and notably larger than the Cassin's hawk-eagle. CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), . Like most birds of prey, Bonelli's eagle displays reverse sexual dimorphism as the female is larger than the male to the contrary of most other kinds of birds, in this case she may average about 10% larger overall.
(1999). 9780198546610, Oxford University Press. ISBN 9780198546610 (2025). 9781530890071, CreateSpace Independent Publishing Platform. ISBN 9781530890071 Prior claims put the weight of this species as , however this probably slightly underrepresents both their size and the sexual dimorphism of this eagle. (1980). 9780198575054, Oxford Univ. Press. ISBN 9780198575054 A large sample of full grown males from western Europe were found to average , with a range of (sample size of 91), while 87 females were found to average , with a range of . Mature males from western Europe were found to have averaged in total length and in wingspan while mature females averaged in total length and in wingspan. Although the linear measurements reportedly increase slightly in average size in the eastern part of the range, body weight was similar or slightly lower at a mean of and for males and females from the Indian subcontinent, respectively, though the sample size is unknown in this case.Dementiev, G. P., Gladkov, N. A., Ptushenko, E. S., Spangenberg, E. P., & Sudilovskaya, A. M. (1966). Birds of the Soviet Union, vol. 1. Israel Program for Scientific Translations, Jerusalem.
Bonelli's eagles in general form appear to have a medium-sized head on a fairly long neck, a strong bill, a mid-to-longish tail and exceptionally long and well feathered legs. The combination of its well-proportioned, stout body and elongated legs may lend to descriptions of the species as "athletic" in appearance.Rasmussen, P. C., & Anderton, J. C. (2005). Birds of south Asia: the Ripley guide. Washington, DC. This eagle often perches with a very upright carriage, at times openly on a rock, a crag, tree branches or some form of post but also in the foliage of tree cover, especially when actively hunting. When perched, the wing tips tend to fall a bit short of the tail tip. Among standard linear measurements, the wing chord of males varies from , with an average in western Europe of , in tail length from , with an average of , in Tibiotarsus length from , with an average of and in Beak length from , with an average of . Meanwhile, females vary in wing chord from , in tail length from , with an average of , in tarsus length from , with an average of , and in total bill length from , with an average of .Ali, S., & Ripley, S. D. (1983). Handbook of the Birds of India and Pakistan: Together with Those of Bangladesh, Nepal, Bhutan and Sri Lanka. Oxford University Press. Two males from the A. f. renschi race measured in wing chord length and a single female measured .
Colouring and identification
Adult are dark brown above, from a cold hue similar to dark chocolate to an umber hue depending on their state of molt as well as to some extent individual and regional variances, with pale margins to most feathers. These pale margins are especially broad on the median wing coverts (which thus appear lighter brown overall). Adults also have a variably sized, irregular white patch on the mantle that can vary from nearly absent (though almost never completely so) to being quite large and extending to the upper back. The adult's tail is grey with obscure darker brown thin bars, with a broad blackish subterminal band and creamy white tip. The adult Bonelli's head is dark brown with a paler, often streaky neck and a white throat. The underside has a cream base colour with variable amounts of sparse blackish-brown streaks or drop shaped markings. (1993). 9780195637311, Bombay Natural History Society. ISBN 9780195637311 The adult female averages darker and more heavily patterned than the adult male, particular on the underside, a case of colour sexual dimorphism otherwise seemingly rare in Aquilinae.
(2025). 9788866940005, Ricca Editore. ISBN 9788866940005 By their 2nd summer, the young eagles are still largely the same in colouring but tend to become more patchy below with increased heavy streaking. During the gradual further development through subsequent molts, the immature eagles develop a thicker subterminal band and a paler ground colour below. Among the bare parts, adult's eyes are yellow to yellow-orange while those of the juvenile are hazel-brown. Adult plumage is obtained between the 4th and 5th years. At all ages, the cere and feet are both pale yellow.
Vocalizations
Bonelli's eagle is largely silent outside of breeding season and is a somewhat infrequent vocalizer even in the context of breeding. Its calls are less well studied than those of the African hawk-eagle, which although a tropical species, also generally ceases to call outside of the breeding season.Steyn, P. (1983). Birds of prey of southern Africa: Their identification and life histories. Croom Helm, Beckenham (UK). 1983. The main call of Bonelli's eagle is done during the courtship display and, sometimes, also at the nest. Its main call consists of a loud, shrill, somewhat far-carrying scream, yuiii-yuiii-gii-gii or a drawn-out heeeeii-heeeeii with slight regional or even individual variations. Its call is farther carrying than the "puppy-like" one of the golden eagle and is reminiscent in pitch of that of the red-tailed hawk ( Buteo jamaicensis). The call may be given by both sexes. However, the female Bonelli's eagle calls most intensely when the male is delivering prey unlike the preference for vocalizing in aerial display as the male usually does. Other recorded vocalizations have included a fluted, low-pitched klu-klu-klu as well as a repeated ki ki ki in alarm. Also other barking, gurgling and grunting sounds have been reported by researchers at or near the nests.
Distribution and habitat
Bonelli's eagle has a spotty and sparse worldwide distribution currently. It is distributed in northwestern Africa from the Anti-Atlas in Morocco northeasterly through the lower parts of the Atlas Mountains in northern Algeria and northern Tunisia and probably formerly northern Libya.Meade-Waldo, E. G. B. (1903). XVIII.—Bird-Notes from Morocco and the Great Atlas. Ibis, 45(2), 196–214.Jourdain, F.C.R. (1915). Notes on the bird-life of eastern Algeria. Ibis 3: 133–159.Bundy, G. (1976). The birds of Libya. BOU Check-list, 1, 102. Beyond its African breeding range, the IUCN Red List and others have mapped out a semi-regular wintering range for Bonelli's eagles, in coastal west Africa from southern Morocco down through Western Sahara, Mauritania and northwestern Senegal, rarely also east to Mali, although little more is reportedly known about this population and its origins and altogether the species is considered largely non-migratory.Borrow, N., & Demey, R. (2001). A guide to the birds of western Africa. Princeton, NJ.Global Raptor Information Network. 2020. Species account: Bonelli's Eagle Aquila fasciata. Downloaded from http://www.globalraptors.org on 12 Aug. 2020. Additionally, it has been recorded as a vagrant in east Africa in Somalia.Cohen, C., Mills, M. & Francis, J. (2015). First records for Somalia of Bonelli's Eagle Aquila fasciata, Short-toed Snake Eagle Circaetus gallicus and Red-breasted Wheatear Oenanthe bottae. Bulletin of the African Bird Club, 22(2): 225–228.
9788875850111 ISBN 9788875850111 In southeastern Europe, an isolated population possibly persists in Croatia as well as in northern and southern Macedonia (with the further possibility of spilling over into Kosovo) and spottily through different areas of Greece (possibly spilling over the borders in the west in Albania and in the east in Bulgaria), as well as Crete.Kralj, J., & Barišić, S. (2013). Rare birds in Croatia. Third report of the Croatian Rarities Committee. Natura Croatica: Periodicum Musei Historiae Naturalis Croatici, 22(2), 375–396.Hallmann, B. (1985). Status and conservation problems of birds of prey in Greece. Conservation Studies on Raptors, ICBP Technical Publication, 5, 55–59.Susic, G., Marinkovic, S., Mandic, R. & Kovacic, D. (1983). Bonelli's Eagle (Hieraaetus fasciatus Vieillot, 1822) on the Island of Krk. Larus: 200–202.Marinkovic, S. & Orlandic, L. (1989). Bonelli Eagle (Hieraaetus fasciatus V.) in Yugoslavia. Larus, 40: 179–183.
Habitat
Bonelli's eagle usually lives at an elevation of or lower in Europe, in the Himalayas at and up to in Bhutan, at in the Atlas Mountains.
It tends to dwell in similar habitat types across its range and lives in lands hugging large bodies of water, largely the Mediterranean Sea and northern Indian Ocean. To a lesser extent, it lives near the coast of the Atlantic and the and near the Caspian Sea. Despite often being near seas and oceans it mostly occurs in fairly Aridity habitats and in quite sunny areas. It prefers rocky areas including lower mountains, foothills with plentiful and steep sided ; it is very skilled at hunting in craggy, irregular rocky terrain.Baccetti, N. & Spagnesi, M. (1987). Rapaci Mediterranei III: Atti del Quarto Colloquio Internazionale sui Rapaci Mediterranei. Supplemento alle Ricerche di Biologia della Selvaggina, 12: 1–316. Usually, extensive garrigue-type habitat such as low bushes or more substantial vegetation such as scattered trees are a common feature of residential ranges but also at times even denser . Such scrubby areas are key since they hold prey concentration in Mediterranean habitats. However, excessive ground cover may limit hunting success, so it avoids dense scrub. In the Mediterranean region, it visits Pinus or sclerophyll forests, but avoids deep forests. In Spain and Sicily, it shows a preference for agricultural arable land and other human-modified habitats, probably because it preys on . However, it avoids urban areas. It may additionally range into timbered or even virtually barren slopes or semi-desert, especially in Israel and India where moister intersect with . Juveniles may take up temporary residence over dry cultivation, small wetland areas, or surprisingly deep woodlands.
Behaviour and ecology
This species is very aerial, often given to soaring and circling over its home range. Like most raptorial birds, it mainly lives solitarily or in a breeding pair. Bonelli's eagle is a powerful predator, and has been described as rather "bold and rapacious". Its primary hunting methods recall those of a powerful Accipiter such as a Northern goshawk. Most commonly, this eagle still-hunts, often either utilizing a concealed tree perch or a lofty spot in irregular rocky terrain to watch for prey activity. Upon spotting its quarry, it often dashes out rapidly to take birds as they take off or a mammal as it runs for cover, at times making lengthy tail-chase that may continue between trees or into tree stands or bushes. Not infrequently as a latter part of a tail chase, these eagles (again reminiscent of a goshawk) will occasionally walk on the ground to obtain their prey.Marmasse, A. & Vilatte, M. (1995). Prey. Faune de Provence, 16: 123. Bonelli's eagles also hunt in a quartering flying style relatively close to the ground (in a fashion reminiscent of a harrier) or patrols hillsides for prey activity.
Rabbits and other lagomorphs
More than any other, the European rabbit ( Oryctolagus cuniculus) is considered the most important prey species for most European Bonelli's eagles. In the largest European studies, the rabbit is usually the leading prey species: such as in Catalonia, Spain where rabbits comprised 22.54% of 2254 prey items (and 33.3% of the prey biomass) and in Provence, France where rabbits made up 16.4% of 2742 prey items.Mayor, J.R. (2014). Study of the Feeding Ecology of Bonelli's Eagle: Effects of Diet on Body Condition, Vital Rates and Demography. Universitat de Barcelona (Doctoral dissertation)Morvan, R. (2010). Aigle de Bonelli (Hieraaetus fasciatus) : présentation de l'espèce et des causes de son déclin. Rev. sci. Bourgogne-Nature, 11: 228–235. In the third largest western European study, rabbits were secondary in number to pigeons (at 18.4% of 1641 prey items) but were still the largest contributors of biomass, at 33.2%. Even where non-native, such as the Aegean islands of Greece, the European rabbit dominated the foods of this eagle, comprising 40.8% by number and 46.6% by biomass of the foods. In Spain, it was found that about three-quarters of studied floating juvenile Bonelli's eagles were hunting rabbits almost exclusively, apparently as they were easier to capture despite their larger size than bird prey.
Gamebirds and pigeons
The main secondary wild prey species associated with Bonelli's eagles is the red-legged partridge ( Alectoris rufa). Although at times capable of evading the attentions of eagles, this partridge occurs in conveys in the same mixed scrub that hold rabbits and is taken whenever the eagles are lucky enough to have the element of surprise. About 383 red-legged partridges were estimated to be hunted annually in one study area of southwestern Spain. In the large Spanish study of Catalonia, French study of Provence and in southwest Portugal, the red-legged partridge made up 9.57%, 11.6% and 17.2% of the diet by number, respectively. More so than any other prey type outside of western Europe, such as partridges seem to be globally the most favoured prey type where available for Bonelli's eagle. In Cyprus, a review of 528 prey items, revealed that the Chukar partridge ( Alectoris chukar) was the main prey at 31.4% of the diet. More than a dozen gamebirds have been detected in the foods of this species from Asia with at least a half dozen genera turning up in a few reviews of their ecology in India. At times, even adult Indian peafowl ( Pavo cristatus), potentially weighing up to , have been dispatched by this species. In the Lesser Sunda Islands, most eye-witness accounts of their hunting habits indicate that wild (or, on some islands, introduced) green junglefowl ( Gallus varius) as well as Chicken ( Gallus gallus) are likely to be the most important prey.
Other birds
Other medium-sized birds are taken widely by Bonelli's eagles. A popular dietary choice in western Europe was yellow-legged gulls ( Larus michahellis), weighing an estimated . In the 2,724 prey items in Provence, this gull was second only to the rabbit in number, comprising 14.6% of the diet. Other are taken by Bonelli's eagles as well as wide diversity of other , including rails, Eurasian stone-curlew, northern lapwing, , Procellariformes, and .Resano, J., Bayle, P., Real, J., Hernández, A., Vincent-Martin, N. & Ravayrol, A. (2012). Analyse du régime alimentaire de l'Aigle de Bonelli Hieraaetus fasciatus (Vieillot, 1822) pendant la saison de reproduction 2010 en France. Université de Barcelone – Equip de Biologia de la Conservació, 1: 95–101. Water birds taken Bonelli's eagles may vary in size from wading birds as small as common sandpiper ( Acitis hypoleucos) and diving birds as small as ( Tachybaptus ruficollis) to those as large as adults of ( Ciconia leucocephala), greylag goose ( Anser anser) (though reportedly taken while injured by buckshot in India), and common crane ( Grus grus). , of a dozen or more species and up to the size of the common raven ( Corvus corax), are taken in considerable numbers in differing parts of the range.
Other assorted prey
Beyond the high significance of rabbits (and sometimes other lagomorphs), other mammals are rarely as important or diverse in the diet of Bonelli's eagles as birds are. A couple of rodents can be locally significant secondary prey, however. The red squirrel ( Sciurus vulgaris), with a mean estimated mass in Spain of , was reported in almost all western Europe studies, with about 130 reported as taken in studies from Provence, France. The black rat ( Rattus rattus), of similar size to the squirrel at an average of about was an important secondary food source in islands south and east of Greece, being the second most common prey species in Cyprus (15.5% of 528 prey items) and fifth most important prey species in the Aegean islands. In northwestern Africa such as Morocco, it was reported that the fat sand rat ( Psammomys obesus), another rodent of similar size, was amongst the favourite foods locally for Bonelli's eagles.Amezian, M., Irizi, A., Errati, A., Loran, H., El Khamlichi, R., Morandini, V., González, D. G., Garrido, J. R. (2015). Spanish Imperial Eagles and other eagles found electrocuted in Morocco and proposition of correction measures. Other rodent species known in the diet of Bonelli's eagles have included other , Common gundi, assorted mice, , dormice and blind mole rats.Burger, J., Hiessler, N., Ponchon, C., & Vincent-Martin, N. (2013). Plan national d'actions en faveur de l'Aigle de Bonelli, Aquila fasciata (2014–2023). In Ministère de l'environnement et du développement durable et de l'energie. Beyond a few species of , additional mammalian prey for this species, although seldom taken, can be relatively large. They have been known to attack the young of various ungulates include blackbuck ( Antilope cervicapra), chinkara ( Gazella bennettii), ( Capra aegagrus hircus) and domestic sheep ( Ovis aries).Kumar, S. (1993). Bonelli's Eagle (Hieraatus fasciatus) killing a Blackbuck (Antilope cervicapra) fawn. Journal of Raptor Research, 27(4), 218–219. In the Aegean islands, live-caught but often young and small goat kids comprised 8.5% of the foods and 24.3% of the biomass at nests.
Interspecies predatory relationships
Bonelli's eagles frequently occur in range with multiple other eagles and competing predators. Almost certainly the most direct competitor from their European range to the Middle East is their much larger cousin, the golden eagle. Habitat preferences overlap between these two eagles with both species favouring rocky habitats, though the golden eagle regularly dwells at slightly higher elevations with (though is as adaptive to low elevations as Bonelli's so long as habitat is favourable and undisturbed). Competition between the eagles has been reported in particular from Spain, in areas such as Sierra Morena. Both species excluded each other from mutual territories and had broadly overlapping food habits. However, Bonelli's eagle took more birds and golden eagle more singularly hunted rabbits. Mean distance between nests on a plot of was found to be for 8 pairs of golden eagles and for 10 pairs of Bonelli's. The two can co-exist with sufficiently large ranges as long as they are able to maintain their own range, with the existence of trophic segregation (by size and the more avian based diet of Bonelli's) and the lag in the breeding periods, as these natural mechanisms would allow the coexistence of both species in the mountain.
Breeding
Pair formation and nest distribution
Bonelli's eagles, like most but not all raptorial birds, generally lives solitarily or in pairs. They usually mate for life.Wilhelm, J. (1986). On. Ciconia, 10: 43. Territories are maintained through aerial displays which often involve calling, single or mutual high circling and, most frequently, sky-dancing in the area of eyrie. During this species' sky-dances, one or other of the eagle pair plunges headlong from a great height, with its wings almost closed, before checking and rising again on stiff wings, circling to regain original altitude and diving again. The sky-dance sequence may be repeated up to 5–10 times. Occasionally but usually infrequently, territorial exclusions escalate into talon grappling between a territorial bird and an intruder.Simmons, R. E., & Mendelsohn, J. M. (1993). A critical review of cartwheeling flights of raptors. Ostrich, 64(1), 13–24. Aerial display extend with diminished frequency into the incubation and early nestling periods. In Spain, the average estimated size of a pairs home range was a very large , though only 27.3% of their home ranges on average were used in all seasons.Pérez-García, J. M., Margalida, A., Afonso, I., Ferreiro, E., Gardiazábal, A., Botella, F., & Sánchez-Zapata, J. A. (2013). Interannual home range variation, territoriality and overlap in breeding Bonelli's eagles (Aquila fasciata) tracked by GPS satellite telemetry. Journal of Ornithology, 154(1), 63–71.Martínez-Miranzo, B., Banda, E., Gardiazábal, A., Ferreiro, E., & Aguirre, J. I. (2016). Differential spatial use and spatial fidelity by breeders in Bonelli's Eagle (Aquila fasciata). Journal of ornithology, 157(4), 971–979. Home ranges in Portugal were estimated to average up to .Ferreira, A. (2011). Microhabitat factors affecting nest site selection and breeding success of tree-nesting Bonelli's Eagles (Aquila fasciata) (Doctoral dissertation). On Cyprus, the mean nearest neighbor distance was with 0.52–0.65 pairs per . Contrary to many other raptor species, it was found that were no significant relationship between the density of their main prey species and the distance of the neighbouring pairs.Ontiveros, D., & Pleguezuelos, J. M. (2000). Influence of prey densities in the distribution and breeding success of Bonelli's eagle (Hieraaetus fasciatus): management implications. Biological conservation, 93(1), 19–25. A dead or missing mate may be quickly replaced and mature adults have additionally been seen breeding with subadults.
Nests
The breeding season of Bonelli's eagles is from late January/February to July in the western part of the range and November–August/September (peaking December–May) in the Indian subcontinent and Myanmar. Both members of the pair may dwell around the eyrie for up to 2–3 months before breeding. Their nest is a huge structure of branches and sticks, scarcely smaller than those built by eagles twice the size of this species, though rarely as great in depth as some old nests of the larger eagles. Often the nest completely obscures the sitting female from view unless it is seen at the same level or higher than the nest. Nest size can average up to across and deep but with repeated use the nest can range up to in both directions (record sized nest in India was in height). Tree nests tend to average larger than those placed on cliff ledges. One nest in the Gir forest was used periodically used over the course of 30 years. While they may line their active nest with greenery, it is less frequent and sparser where present than in many other birds of prey.
