Verreaux's eagle-owl (Ketupa lactea), also commonly known as the milky eagle owl or giant eagle owl, is a large owl of the genus Ketupa in the family Strigidae. It is the largest African owl, measuring up to in total length. Widespread in sub-Saharan Africa, this eagle-owl is a resident primarily of dry, wooded savanna. The species is mainly grey in colour and is distinguishable by its bright pink eyelids, a unique feature not shared with any other owl species.König, C., & Weick, F. (2008). Owls of the World. A&C Black. .
Verreaux's eagle-owl is a highly opportunistic predator equipped with powerful talons. Just over half of its known diet is composed of mammals, but equal numbers of birds and even insects may be hunted locally, along with any other appropriately sized prey that is encountered.Brown, L. H. (1965). "Observations on Verreaux's Eagle Owl Bubo lacteus (Temminck) in Kenya." Journal of the East African Natural History Society, 25, 101-107.Avery, G., Robertson, A. S., Palmer, N. G., & Prins, A. J. (1985). "Prey of giant eagle owls in the de Hoop nature reserve, Cape province, and some observations on hunting strategy." Ostrich, 56(1-3), 117-122. This species is considered of Least Concern by IUCN, as it occurs over a wide range and has shown some adaptability to human-based alterations and destruction of habitat, also adapting to diverse prey when a primary prey species declines in a region. Although large in size and highly territorial, the Verreaux's eagle-owl does occur at fairly low densities, and some regional declines have been reported.
The common name commemorates the French naturalist Jules Verreaux. While still in his teens, Verreaux collected the type specimen that was later described by Temminck at the Rijksmuseum van Natuurlijke Historie.Hume, R. (1991). Owls of the world. Running Press, Philadelphia. 1991.
Taxonomy
There are no known subspecies in the Verreaux's eagle-owl, and there is remarkably little variation in their appearance across their considerable distribution. Reportedly, birds in the southern part of their range appear marginally larger on average but these size differences are quite subtle and may be considered as a mild case of Bergmann's rule.Andersson, C. J. (1872). Notes on the birds of Damara Land and the adjacent countries of South-West Africa. J. van Voorst. While genetic research has been undertaken for this species, its closest living relative in the genus Ketupa is not fully clear. At one time, the Verreaux's eagle-owl was mentioned as an owl with particularly mysterious genetic alliances among living owls.Olsen, Jery; Wink, Michael; Sauer-Gürth, Heidi & Trost, Susan (2002). A new Ninox owl from Sumba, Indonesia. Emu 102 (3): 223–231. Per Konig & Weick (2008), the species with studied genetic markers found to be most closely related are a dark-eyed species pair of Asian eagle-owls, the spot-bellied (Ketupa nipalensis) and barred eagle-owls (Ketupa sumatrana), but these are not particularly closely related to the Verreaux's.
Among species with available genomes to study for DNA characteristics, it has been revealed that the fish owls, in particular the brown fish owl (Ketupa zeylonensis), is the third most closely related species to the Verreaux's.Penhallurick, J. M. (2002). The taxonomy and conservation status of the owls of the world: a review. Ecology and conservation of Owls. CSIRO Publishing, Australia, 343-354. The Verreaux's eagle-owl along with 7 other species (including the aforementioned spot-bellied and barred eagle-owls) were formerly classified in the genus Bubo but they along with their fish owl cousins were found to be sufficiently divergent to qualify as the separate genus Ketupa.Wink, M., and H. Sauer-Gürth (2021). Molecular taxonomy and systematics of owls (Strigiformes) - an update. Airo 29:487–500. Salter, J. F., C. H. Oliveros, P. A. Hosner, J. D. Manthey, M. B. Robbins, R. G. Moyle, R. T. Brumfield, and B. C. Faircloth (2020). Extensive paraphyly in the typical owl family (Strigidae). The Auk: Ornithological Advances 137:1–15. Notably, Konig & Weick did not test the DNA of other African eagle-owls that may bear relation to the Verreaux's eagle-owl based largely on their solid dark brown eyes, namely Fraser's (Ketupa poensis) and Shelley's eagle-owl (Ketupa shelleyi) as opposed to other eagle-owls which have yellow to orange irises. Fraser's and the likely conspecific Usambara eagle-owls also have a small amount of bare skin around their eyes but this tends to bluish in colour and is not nearly as extensive as the pink seen in Verreaux's. Evidently, subsequent genetic testing appeared to confirm the relationship of Verreaux's eagle-owls with the Fraser's and Shelley's eagle-owls. Other large owls native to Africa, the fishing owls, also have uniform dark brownish eyes and are sometimes included with the genus Bubo but are now generally treated as a divergent genus. Scotopelia based on genetics. Pliocene fossil Bubo owls with clear similarities based on osteological characteristics to the modern Verreaux's eagle-owl (most are currently classified as Ketupa cf. lactea) from South Africa and Tanzania, indicate that the Verreaux's eagle-owl descended from slightly smaller ancestors that increased in size as they diversified from related species.Brodkorb, P., & Mourer-Chauviré, C. (1984). Fossil owls from early man sites of Olduvai Gorge, Tanzania. Ostrich, 55(1), 17-27.Pavia, M., Manegold, A., & Haarhoff, P. (2014). "New early Pliocene owls from Langebaanweg, South Africa, with first evidence of Athene south of the Sahara and a new species of Tyto." Acta Palaeontologica Polonica, 60(4), 815-828.
Description
Despite the alternative common name of giant eagle-owl, Verreaux's eagle-owl is not the largest owl or eagle-owl in the world. It is, however, a very large and powerful owl species. This species is both the largest owl found in Africa and the world's largest owl to occur in the tropics. Among all the world's owls, it is the fourth heaviest living owl, after Blakiston's fish owl (Ketupa blakistoni), the Eurasian eagle-owl (Bubo bubo) and the tawny fish owl (Ketupa flavipes). In addition, it is the fourth longest extant owl (measured from the bill to the tip of the tail), after the great gray (Strix nebulosa), Blakiston's fish and Eurasian eagle-owls.CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), .Tana, P. G., Vazquez, A., & Chavez, C. (1997). "Notes on a nest of the Tawny Fish Owl (Ketupa flavipes) at Sakatang Stream, Taiwan.". Wilson Bulletin, 66, 135-136.Bull, E. L., & Duncan, J. R. (1993). "Great Gray Owl: Strix nebulosa". American Ornithologists' Union. Based on body mass and wing chord length, Verreaux's eagle-owl is about the same size as "medium-sized" races of Eurasian eagle-owl, such as those from Central Asian steppe (B. b. turcomanus) and the Himalayas (B. b. hemachalana), slightly smaller than most northern Eurasian races, considerably smaller than Siberian and Russian eagle-owls, and somewhat larger than the smallest Eurasian eagle-owl subspecies, such as those from the Iberian Peninsula (B. b. hispanus) and the Middle East (B. b. omissus or nikolskii).Vaurie, C. (1960). "Systematic notes on Palearctic birds. No. 41, Strigidae, the genus Bubo." American Museum Novitates; no. 2000.Rothschild, W. & Hartert, E. "Notes on eagle-owls". Novitates Zoologicae, A Journal of Zoology.Vaurie, C. (1963). "Systematic notes on Palearctic birds. No. 52, Supplementary notes on Bubo bubo". American Museum Novitates; no. 2132.Qinghu C., Jianping S. & Zhigang J. (2008). "Summer diet of two sympatric species of raptors upland buzzard (Buteo hemilasius) and Eurasian eagle owl (Bubo bubo) in Alpine meadow: Problem of coexistence." Pol. J. Ecol, 56(1), 173-179.
Verreaux's eagle-owl ranges from in total length.Field Guide to the Birds of East Africa: Kenya, Tanzania, Uganda, Rwanda, Burundi by Stevenson & Fanshawe. Elsevier Science (2001), This species has been reported as having an average wingspan of , but Mikkola referenced this as the wingspan of a smaller male.J. del Hoyo, A. Elliott and J. Sargatal, eds. Handbook of the birds of the world. Volume 5. Barn-owls to Hummingbird. Barcelona: Lynx Edicions.Owls of the World: A Photographic Guide by Mikkola, H. Firefly Books (2012), The largest known wingspan from a wild female measured nearly .Mendelsohn, J. M., Kemp, A. C., Biggs, H. C., Biggs, R., & Brown, C. J. (1989). Wing areas, wing loadings and wing spans of 66 species of African raptors. Ostrich, 60(1), 35-42. While female owls are almost always larger than males, Verreaux's eagle-owl stands out as one of the most sexually dimorphic living owl species, some studies showing the female can average 35% heavier than the male. In comparison, the females of the nominate subspecies of Eurasian eagle-owls and great horned owl (Bubo virginianus) are reported to average approximately 20% and 25% heavier than the males, respectively.Earhart, C. M. and N. K. Johnson. 1970. Size dimorphism and food habits of North American Owls. Condor 72:251-264. The full range of reported body mass in the species ranges from in males against a body mass of in females.Weick, F. (2007). Owls (Strigiformes): annotated and illustrated checklist. Springer Science & Business Media.Biggs, H.C., Kemp, A.C., Mendelsohn, H.P., & Mendelsohn, J.M. (1979) Weights of South African raptors and owls. Durban Museum Novitas, 12: 73-81. In one study, 4 males were found to have averaged while 6 females averaged . Another study found 5 males to have averaged approximately while five females averaged .Musindo, P. T. (2006). Morphological variation in bills and claws in relation to Prey type in Southern African Birds of Prey (Orders Falconiformes and Strigiformes) (Doctoral dissertation, University of Zimbabwe). Unusually large sizes have been claimed in captivity with claims that specimens measuring up to in length and in wingspan but these are unverified and possibly misreported as these figures match the largest Eurasian eagle-owls. Males heavier than any in the wild have been verified in captivity to weigh up to . Among standard measurements, the female is reported to measure from , averaging , in wing chord, in the tail, while the same measurements in the male are from , averaging , and from in tail length. In both sexes, the tarsus has measured and the bill (in a small sample) . Based on wing chord size compared to body mass and other linear dimensions, the Verreaux's eagle-owl averages somewhat larger in the size of its wings relative to its body size than most other eagle-owls, excluding the Asian fish owls which are also relatively long-winged.