Bonelli's Eagle Aquila fasciata Scientific name definitions

55–67 cm (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ); male 1400–2240 g, female 2100–3025 g (2 García, V., Moreon-Opo, R. and Tintó, A. (2013). Sex differentiation of Bonelli’s Eagle Aquila fasciata in western Europe using morphometrics and plumage colour patterns. Ardeola. 60(2): 261-277. Close ); wingspan 143–176 cm (2 García, V., Moreon-Opo, R. and Tintó, A. (2013). Sex differentiation of Bonelli’s Eagle Aquila fasciata in western Europe using morphometrics and plumage colour patterns. Ardeola. 60(2): 261-277. Close ). Medium-sized eagle with dark brown upperparts, white, lightly streaked underparts and predominantly dark underwing, with blackish median band; conspicuous white patch on center of back; tail with terminal dark band . Female  averages c. 10% larger and has more heavily streaked underparts. Irides yellow to yellow-orange, cere and feet yellow. Juvenile darker brown above, with rusty underparts and underwing coverts; irides hazel-brown (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ); lacks white patch on back and tail band; over years, underparts become progressively streaked darker, and then increasingly flecked with white, breaking into adult plumage during 4th year. Race <em>renschi</em> smaller (wing length 444–493 mm versus 458–560 mm in nominate race (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ) )and more heavily barred on wing and tail feathers.

Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.

This species and A. spilogaster previously placed in Hieraaetus, but recent molecular study indicated that both are closest to A. verreauxii and should be placed with it in present genus (3 Helbig, A. J., A. Kocum, I. Seibold, and M. J. Braun (2005). A multi-gene phylogeny of aquiline eagles (Aves: Accipitriformes) reveals extensive paraphyly at the genus level. Molecular Phylogenetics and Evolution 35:147–164. Close , 4 Lerner, H.R.L. and Mindell, D.P. (2005). Phylogeny of eagles, Old World vultures, and other Accipitridae based on nuclear and mitochondrial DNA. Molecular Phylogenetics and Evolution. 37(2): 327–346. Close ). Has often been considered conspecific with A. spilogaster. Race renschi suggested to constitute a separate species; recent study, however, found minimal genetic differentiation between it and nominate fasciata, suggesting only recent geographical isolation, and also advanced the possibility that presence of renschi in Lesser Sundas may be result of past introduction (5 Trainor, C.R., Debus, S.J.S., Olsen, J., Norman, J.A. and Christidis, L. (2013). Bonelli’s Eagle Aquila fasciata renschi in the Lesser Sundas, Wallacea: distribution, taxonomic status, likely origins and conservation status. Forktail. 29: 100–106. Close ). Two subspecies normally recognized.

Editor's Note: Additional distribution information for this taxon can be found in the 'Subspecies' article above. In the future we will develop a range-wide distribution article.

Mainly warm, sunny mountainous or broken terrain, normally with crags and cliffs. Vegetation cover variable: normally zones with extensive growth of bushes and shrubs, e.g. maquis, garrigue; sometimes with forest, but also barren slopes with virtually no vegetation. Sometimes visits flattish open areas, with pastures, cultivation or wetlands (mostly juveniles, or outside breeding season). Generally rather retiring, although relatively adaptable to fairly humanized zones. Nominate race occurs mainly from sea-level to 1500 m in Europe, up to 2000 m in NW Africa and up to 3750 m in Asia (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ); race renschi occurs in moist tropical forests from sea-level to c. 2000 m in Lesser Sundas (5 Trainor, C.R., Debus, S.J.S., Olsen, J., Norman, J.A. and Christidis, L. (2013). Bonelli’s Eagle Aquila fasciata renschi in the Lesser Sundas, Wallacea: distribution, taxonomic status, likely origins and conservation status. Forktail. 29: 100–106. Close ).

Sedentary and dispersive. Breeding pairs closely tied to home range, although somewhat less outside breeding season. Juveniles disperse once independent; in SW Europe, at least, tend to move to areas not occupied by adults, often agricultural zones, with fairly gentle relief, especially rich in prey; may travel hundreds of kilometres from natal areas. Seven nestlings (5 females, 2 males) fitted with satellite transmitters in Spain settled 80–536 km from their natal nests in the first six months after fledging (6 Cadahía, L., Urios, V. and Negro, J.J. (2005). Survival and movements of satellite-tracked Bonelli’s Eagles Hieraaetus fasciatus during their first winter. Ibis. 147(2): 415-419. Close ). Communal roosting occurs in dispersal areas of S Spain rich in prey (7 Moleón, M., Bautista, J. and Madero, A. (2011). Communal roosting in young Bonelli’s Eagles (Aquila fasciata). Journal of Raptor Research. 45(4): 353–356. Close ). Apparent vagrant photographed in NW Somalia in May 2010 was first record for the country (8 Cohen, C., M. S. L. Mills, and J. Francis (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. Close ).

Normally medium-sized birds and mammals ; adaptable, eating most readily available prey. Diet well known in SW Europe: prefers rabbits and partridges; if these are scarce, will switch to other, normally secondary, prey, e.g. pigeons , corvids, gulls, squirrels and other rodents, or lizards. In Israel takes mainly partridges and pigeons, with few mammals or reptiles. Large prey unusual, although Asian Houbaras (Chlamydotis macqueenii), storks, herons, buzzards and foxes reported. Diet in the non-breeding season comprised of 55·5% mammals (51·7% rabbits), 43% birds (18% partridges, 16% pigeons) and 1.5% lizards in S Spain and 14% mammals (9·8% rabbits), 86% birds (49% pigeons) and no lizards in NE Spain (9 Moleón, M., Gil-Sánchez, J.M., Real, J., Sánchez-Zapata, J.A., Bautista, J. and Sánchez-Clemot, J.F. (2007). Non-breeding feeding ecology of territorial Bonelli’s Eagles Hieraaetus fasciatus in the Iberian Peninsula. Ardeola. 54(1): 135-143. Close ). Non-breeding “floaters” in S Spain fed mostly on European rabbits (Oryctolagus cuniculus), Red-legged Partridges (Alectoris rufa) and pigeons (Columba sp.) (10 Caro, J., Ontiveros, D. and Pleguezuelos, J.M. (2011). The feeding ecology of Bonelli’s Eagle (Aquila fasciata) floaters in southern Spain: implications for conservation. European Journal of Wildlife Research. 57(4): 729-736. Close ). Very agile flight, capturing most of prey on ground, but also birds in flight; sometimes pairs hunt together. Of 110 attacks observed in SE Spain from 1985–2008, 28·2% were successful; surprise was the most important factor in attack success, and attack success declined with increasing group size of prey (11 Martínez, J.E., Zuberogoitia, I., Gómez, G., Escarabajal, J.M., Cerezo, E., Jiménez-Franco, M.V. and Calvo, J.F. (2014). Attack success in Bonelli’s Eagle Aquila fasciata. Ornis Fennica. 91(2): 67-78. Close ).

Generally silent, except during the breeding season. In display flight, gives a repeated shrill “iuh” or a more drawn-out whistling “eeeuu”  (falling somewhat in pitch at the end) (12 Beaman, M., and S. Madge (1998). The Handbook of Bird Identification for Europe and the Western Palearctic. Christopher Helm, London, UK. Close ). Also a fluting, low-pitched “klu-klu-klu...” or “ki-ki-ki...” in alarm, and other barking, gurgling and grunting sounds at or near nest (1 Ferguson-Lees, J., and D. A. Christie (2001). Raptors of the World. Christopher Helm, London, UK. Close ).

Laying mainly from Feb to mid-Mar in Mediterranean region; Dec throughout much of Indian Subcontinent. Territorial at all times. Nests on cliff ledges, or less often in trees, habit varying with region. Tree-nesting, particularly in  Eucalyptus, is becoming relatively frequent in SW Iberia (13 Dias, A., Palma, L., Carvalho, F., Neto, D., Real, J. and Beja, P. (2017). The role of conservative versus innovative nesting behavior on the 25-year population expansion of an avian predator. Ecology and Evolution. 2017: 1–13. Close ). Nest bulky, up to 200 cm wide, 100 cm deep; built of sticks and lined with green leaves . Normally various nests per pair, often close together and even on same cliff face; used alternately. Clutch size 1–2 eggs, rarely 3, laid at intervals of 2–3 days; incubation 37–41 days, mainly by female; chicks brooded and fed by female; at first only male brings prey to nest; chicks have first and second down white; fledging c. 60–70 days; juveniles may stay in territory several months more; seven nestlings carrying satellite transmitters dispersed from their natal areas at an average age of 142 days (6 Cadahía, L., Urios, V. and Negro, J.J. (2005). Survival and movements of satellite-tracked Bonelli’s Eagles Hieraaetus fasciatus during their first winter. Ibis. 147(2): 415-419. Close ). Normally 1 or 2 chicks fledge: averages in Mediterranean 1·1–1·5 chicks per clutch, 1·4–1·6 per successful breeding attempt. Cases of siblicide recorded (14 Hernández-Matías, A., Real, J., Parés, F. and Llacuna, S. (2016). Siblicide in Bonelli’s Eagle (Aquila fasciata). Journal of Raptor Research. 50(1): 125–128. Close ). Sexual maturity possible before adult plumage acquired, very occasionally in second year. High juvenile mortality, sometimes of over 50% in first year. On basis of long-term study (1990–2008) of marked birds in France, annual survival 0·48 for fledglings, 0·57 for 1- and 2-year-olds, 0·87 for 3-year-olds and older birds (15 Hernández-Matías, A., Real, J., Pradel, R., Ravayrol, A. and Vincent-Martin, N. (2011). Effects of age, territoriality and breeding on survival of Bonelli’s Eagle Aquila fasciata. Ibis. 153(4): 846-857. Close ). Recorded up to 20 years old in captivity.

Not globally threatened (Least Concern). CITES II. In decline in Europe, with some regional stabilization, but in 1980s, in Spain , home to bulk of European population, perhaps up to 116 pairs disappeared. This contrasts with stability or recovery of Spanish populations of other eagles, especially Aquila chrysaetos and A. adalberti, which presumably face similar difficulties and threats. In areas of high density of A. chrysaetos, present species suffers somewhat, perhaps as a result of competition. Trends unknown in Africa and Asia. In early 1990s, c. 900 pairs in Europe: 679–755 in Spain, c. 75–90 in Portugal, 29 in France, c. 15 in Italy, 50–70 in Greece, and fewer than 60 in rest of Balkans. By 2015, BirdLife International estimated 1100–1200 pairs in Europe, including c. 750 pairs in Spain, 128–150 in Portugal and 100–140 in Greece. (Re)introduced to Mallorca, Balearic Islands and hacking programmes are also helping to boost populations on the Spanish mainland. Estimates in N Africa of 500–1000 pairs in Morocco, perhaps 200 pairs in Algeria, and c. 100 pairs in Tunisia. In Turkey c. 50 pairs; in Israel, after slight recovery, 19 pairs in 1980s. Almost extirpated in former USSR; widely distributed but rare or uncommon in Indian Subcontinent. Race <em>renschi</em> very poorly known and rarely recorded; reported as relatively common on Wetar I, Banda Sea, Indonesia (16 Trainor, C. R., Imanuddin, F. Aldy, P. Verbelen, and J. S. Walker (2009). The birds of Wetar, Banda Sea: one of Indonesia’s forgotten islands. BirdingASIA 12:78–93. Close ).

Causes of decline not wholly understood, but species obviously affected by direct persecution and accidents with powerlines, which cause much mortality, particularly amongst juveniles; on the S France population the survival probability, especially in juveniles and immature birds, increased in 1990–2009 after the insulation of dangerous power lines (17 Chevallier, C., Hernández-Matías, A., Real, J., Vincent-Martin, N., Ravayrol, A. and Besnard, A. (2015). Retrofitting of power lines effectively reduces mortality by electrocution in large birds: an example with the endangered Bonelli’s eagle. Journal of Applied Ecology. 52(6): 1465–1473. Close ); also important are degradation and transformation of habitat, reduction in numbers of prey species, and a large increase in human interference and disturbance in breeding areas. In study of seven territorial individuals in E Spain tracked by satellite telemetry over period of 4–5 years, annual home range was 205·6 km² (extremes 44·7–704·8 km²) and average core area 44·4 km² (range 31·8–91·9 km²), with only slight temporal variation in home-range size, but wide variation in use of space (27·3% of total home range used during all seasons, 30·3% used only during a single season, whereas area around nest, main hunting areas and roosting sites utilized regularly every year at all seasons); individuals strongly territorial, even outside breeding seasons, but also made long trips (more than 15 km) well beyond territorial boundaries (assessed for first time by GPS); strong association between topographical landmarks and home-range segregation noted (18 Pérez-García, J. M., Margalida, A., Afonso, I., Ferreiro, E., Gardiazábal, A., Botella, F. and 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. Close ).