This bird order comprises most of the diurnal birds of prey, such as hawks, eagles, and vultures.
List of Hybrids per Genus
Despite the fact that 13 species hybridize in the wild, there are no thorough studies on Accipiter. Two papers discuss the morphological and behavioral characteristics of two hybrids, namely Grey goshawk (A. novaehollandiae) x Brown Goshawk (A. fasciatus) in Australia (Olsen & Olsen, 1985) and Shikra (A. badius) x Levant Sparrowhawk (A. brevipes) in Israel (Yosef, Helbig & Clark, 2001). A study of two African species – African Goshawk (A. tachiro) and Red-chested Goshawk (A. toussenelii) found no evidence for hybridization (Louette, 2003). An apparent hybrid between Northern Goshawk (A. gentilis) and Cooper’s Hawk (A. cooperii) was reported in Tennessee (Gunther & Hopey, 2010).
Seven Aquila species hybridize with at least one other species. There is, however, one species pair that has received most attention: Lesser Spotted Eagle (A. pomarina) and Greater Spotted Eagle (A. clanga). The vulnerable status of the latter species links this situation to conservation issues. Hybrids and backcrosses can be identified based on a number of morphological features, such as nape patch and plumage index (Vali & Lohmus, 2004). Also, hybrid individuals might attain immature characteristics (Vali, 2010). Genetic analyses revealed extensive introgression and asymmetrical hybridization which could be attributed to mate choice based on size differences (Helbig et al., 2005; Vali et al., 2010). Introgression of Z-linked loci proved to be lower compared to autosomal loci (Backstrom & Vali, 2011). The two species use different habitats (Lohmus & Vali, 2005), but anthropogenic habitat alteration might favour hybridization (Maciorowski & Mirski, 2014). In the Biebrza River Vally (Poland), the proportion of broods producing hybrids increased by over 30% between 1996 and 2012 (Maciorowski, Mirski & Vali, 2015). Hybrid nestlings have the same conditional status as pure ones (Maciorowksi et al., 2018) Lastly, one study mapped the migration route of a hybrid individual, which followed a typical A. clanga migration strategy (Meyburg & Meyburg, 2007). The tracking of multiple hybrids revealed that their timing was similar to lesser spotted eagles while the wintering destinations were similar to greater spotted eagles (Vali et al., 2018).
Numerous Buteo species engage in hybridization, but few cases have been studied from a genetic point of view. A genetic study revealed gene flow between Common Buzzard (B. buteo) and Long-legged Buzzard (B. rufinus) and between Upland Buzzard (B. hemilasius) and Long-legged Buzzard (Jowers et al., 2019). Indeed, interbreeding of Long-legged Buzzard and Common Buzzard has been reported in Italy (Corso, 2009) and Gibraltar (Elorriaga and Munoz, 2013). Hybrids between Long-legged and Upland Buzzard have been documented in Asia (Pfänder & Schmigalew, 2001).
Common Buzzard also hybridizes with Rough-legged Buzzard (B. lagopus), as evidenced by sightings in Finland (Forsman and Lämsä, 2007).
Based on morphological and molecular analyses a museum specimen from Louisiana was identified as hybrid between Swainson’s hawk (B. swainsoni) and Rough-legged Buzzard (B. lagopus)(Clark & Witt, 2006). Swainson’s hawk also hybridizes with Red-tailed Hawk (B. jamaicensis), as shown by genetic tools (Hull et al., 2007).
In Utah, a Red-tailed Hawk x Ferruginous Hawk (B. regalis) hybrid successfully bred with a Red-tailed Hawk, indicating that these hybrids are fertile (Paprocki et al., 2019).
Intergeneric hybrids are rare in raptors, but a possible Common Buzzard (B. buteo) x Black Kite (Milvus migrans) has been sighted in Italy (Corse & Gildi, 1998). Another intergeneric hybrid between Red-shouldered Hawk (B. lineatus) and Common Black Hawk (Buteogallus anthracinus) was reported in California (Hug, 2016).
Harlan’s Hawk (B. harlani) has been considered a separate species and a subspecies of Red-tailed Hawk (B. jamaicensis). Hybridization between Harlan’s Hawk and Red-tailed Hawk has been documented (Clark 2018).
In Southern Siberia, Eastern Marsh Harrier (C. spilonotus) and Western Marsh Harrier (C. aeruginosus) hybridize. The situation was extensively described by Fefelov (2001). More Harrier species are known to interbreed, but they have not been studied in detail.
Allozyme analyses of Black Kite (M. migrans) and Red Kite (M. milvus) revealed low genetic distances, in contrast to their divergent phenotypes. This observation might be attributed to hybridization (Schreiber, Stubbe & Stubbe, 2000). A mixed pair of Black Kite female and Red Kite male produced hybrid offspring during breeding seasons 2017 and 2018 in Poltva, Ukraine (Literák et al., 2019).
There might be hybridization between European Honey Buzzard (P. apivorus) and Crested Honey Buzzard (P. ptilorhyncus) in Central Asia (Faveyts et al. 2011).
Backstrom, N. & Vali, U. (2011). Sex- and species-biased gene flow in a spotted eagle hybrid zone. BMC Evolutionary Biology 11.
Clark, W. S. & Witt, C. C. (2006). First known specimen of a hybrid Buteo: Swainson’s Hawk (Buteo swainsoni) x Rough-legged Hawk (B-lagopus) from Louisiana. Wilson Journal of Ornithology 118, 42-52.
Clark, W.S. (2018) Taxonomic status of Harlan’s Hawk Buteo jamaicensis harlani (Aves: Accipitriformes). Zootaxa 4425(2), 223-242.
Corso A. & Glidi R. (1998). Hybrids between Black Kite and Common Buzzard in Italy in 1996. Dutch Birding 20, 226-233.
Elorriaga, J. & Munoz, A. R. (2013). Hybridisation between the Common Buzzard Buteo buteo buteo and the North African race of Long-legged Buzzard Buteo rufinus cirtensis in the Strait of Gibraltar: prelude or preclude to colonisation? Ostrich 84, 41-45.
Faveyts, W., Valkenburg, M. & Granit N. (2011). Crested Honey Buzzard: identification, western occurrence and hybridisation with European Honey Buzzard. Dutch Birding 33, 149-162.
Fefelov, I. V. (2001). Comparative breeding ecology and hybridization of Eastern and Western Marsh Harriers Circus spilonotus and C-aeruginosus in the Baikal Region of Eastern Siberia. Ibis 143, 587-592.
Forsman, D., & Lämsä, E. (2007). Successful interbreeding between Common Buzzard and Rough-legged Buzzard in Finland. Linnut, 42, 36-37.
Gunther, K. A., & Hopey, M. E. (2010). Apparent Northern Goshawk (Accipiter gentilis) × Cooper’s Hawk (A. cooperii) Hybrid in Eastern Tennessee. North American Birds, 64, 2-4.
Helbig, A. J., Seibold, I., Kocum, A., Liebers, D., Irwin, J., Bergmanis, U., Meyburg, B. U., Scheller, W., Stubbe, M. & Bensch, S. (2005). Genetic differentiation and hybridization between greater and lesser spotted eagles (Accipitriformes : Aquila clanga, A-pomarina). Journal of Ornithology 146, 226-234.
Hug, L. (2016) Common Black Hawk x Red-shouldered Hawk in California. Western Birds 47, 325-326.
Hull, J. M., Savage, W., Smith, J. P., Murphy, N., Cullen, L., Hutchins, A. C. & Ernest, H. B. (2007). Hybridization among buteos: Swainson’s hawks (Buteo swainsoni) x red-tailed hawks (Buteo jamaicensis). Wilson Journal of Ornithology 119, 579-584.
Jowers, M.J., Sánchez-Ramírez, S., Lopes, S., Karyakin, I., Dombrovski, V., Qninba, A., Valkenburg, T., Onofre, N., Ferrand, N., Beja, P., Palma, L. & Godinho, R. (2019) Unravelling population processes over the Late Pleistocene driving contemporary genetic divergence in Palearctic buzzards. Molecular Phylogenetics and Evolution 134, 269-281.
Literák, I., Skyrpan, M., & Andreyenkova, N.G. (2019). A mixed pair of black and red kites in Ukraine, including DNA analysis of hybrid offspring. Biologia, 1-6.
Lohmus, A. & Vali, U. (2005). Habitat use by the Vulnerable greater spotted eagle Aquila clanga, interbreeding with the lesser spotted eagle Aquila pomarina in Estonia. Oryx 39, 170-177.
Louette, M. (2003). Size, plumage, moult and supposed hybrids of African Goshawks (Accipiter tachiro/toussenelii group) in DR Congo. Ostrich 74, 18-29.
Maciorowski, G. & Mirski, P. (2014). Habitat alteration enables hybridisation between Lesser Spotted and Greater Spotted Eagles in north-east Poland. Bird Conservation International 24, 152-161.
Maciorowski, G., Mirski, P. & Vali, U. (2015). Hybridisation dynamics between the Greater Spotted Eagles Aquila clanga and Lesser Spotted Eagles Aquila pomarina in the Biebrza River Valley (NE Poland). Acta Ornithologica 50, 33-41.
Maciorowksi, G., Yosef, R., Väli, Ü & Tryjankowski, P. (2018) Nutritional Condition of Hybrid Nestlings Is Similar To That of Pure-Species Offspring of Spotted Eagles (Clanga clanga x C. pomarina). Journal of Raptor Research 52(4):484-490.
Meyburg, B. U. & Meyburg, C. (2007). Post-fledging behavior and outward migration of a hybrid Greater X Lesser Spotted Eagle (Aquila clanga X A. Pomarina). Journal of Raptor Research 41, 165-170.
Olsen, P. & Olsen, J. (1985). A natural hybridization of the Brown Goshawk Accipiter fasciatus and Grey Goshawk Accipiter novaehollandiae in Australia, and a comparison of the two species. Emu 85.
Paprocki, N., Watson, J.L., & Liguori, J. (2019). Successful Introgressive Breeding of a Ferruginous Hawk× Red-Tailed Hawk Hybrid with a Red-Tailed Hawk. Journal of Raptor Research, 53(2), 198-201.
Pfänder, P. & Schmigalew, S. (2001) Extensive hybridization of Long-legged Buzzard Buteo r. rufinus and Upland Buzzard B. hemilasius. Ornithologische Mitteilungen 53, 344-349.
Schreiber, A., Stubbe, M. & Stubbe, A. (2000). Red kite (Milvus milvus) and black kite (M-migrans): minute genetic interspecies distance of two raptors breeding in a mixed community (Falconiformes : Accipitridae). Biological Journal of the Linnean Society 69, 351-365.
Vali, U. (2010). Successful breeding of a ten-year-old hybrid spotted eagle Aquila clanga x A. pomarina retaining immature plumage characters. Ardea 98, 235-241.
Vali, U., Dombrovski, V., Treinys, R., Bergmanis, U., Daroczi, S. J., Dravecky, M., Ivanovski, V., Lontkowski, J., Maciorowski, G., Meyburg, B. U., Mizera, T., Zeitz, R. & Ellegren, H. (2010). Widespread hybridization between the Greater Spotted Eagle Aquila clanga and the Lesser Spotted Eagle Aquila pomarina (Aves: Accipitriformes) in Europe. Biological Journal of the Linnean Society 100, 725-736.
Vali, U. & Lohmus, A. (2004). Nestling characteristics and identification of the lesser spotted eagle Aquila pomarina, greater spotted eagle A. clanga, and their hybrids. Journal of Ornithology 145, 256-263.
Väli, U., Mirski, P., Sellis, U., Dagys, M. & Maciorowski, G. (2018) Genetic determination of migration strategies in large soaring birds: evidence from hybrid eagles. Proceedings of the Royal Society B 285,20180855.
Yosef, R., Helbig, A. & Clark, W. S. (2001). An intrageneric Accipiter hybrid from Eilat, Israel. Sandgrouse 23, 141-144.