Shelley's eagle-owl

Shelley's eagle-owl (Bubo shelleyi) is a species of owl in the family Strigidae. Despite its large size, it is a very little-known, rarely studied owl that seems to occur in very small numbers.

Shelley's eagle-owl
Illustration by Keulemans, 1875
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Strigiformes
Family: Strigidae
Genus: Bubo
Species:
B. shelleyi
Binomial name
Bubo shelleyi
(Sharpe & Ussher, 1872)

Description

This dark eagle-owl is among the largest owls in the world and by far the largest eagle-owl found in the African rainforests. The total length of the species is 53 to 61 cm (21 to 24 in).[2] The wing chord measured from 420 to 492 mm (16.5 to 19.4 in), the tail measures 233 to 266 mm (9.2 to 10.5 in), the tarsus at 76 to 84 mm (3.0 to 3.3 in) and the total bill at 56 to 62 mm (2.2 to 2.4 in).[3] A single male was reported to have weighed 1,257 g (2.771 lb), with females presumably attaining rather higher weights.[4] Going on standard measurements, the Shelley's eagle-owl would appear to be even larger than the aforementioned total length and body mass would suggest.[2][3] In the key aspects of wing and tarsal lengths, Shelley's eagle-owl would appear to be broadly similar in size to the Verreaux's eagle-owl, which is usually considered to be Africa's largest owl species, and it may be one of the largest tropical owls in the world.[3] The bill of the Shelley's is proportionally massive and seemingly the second longest of any living owl behind only the Blakiston's fish owl.[3]

It is dark sooty black-brown above overlaid with light barring. The underparts are whitish with heavy dark barring. Lighter and darker morphs are known. The light morphs have an off-white to pale tawny facial disc, with a prominent rim marked with a blackish-brown border. In the light morph, the crown and mantle are dusky brown overlaid with buffy-whitish bars. The dark morph is much darker brown above with sparse orange-buff barring, a darker facial disc and a scaly looking brownish chest. The tail and the flight feathers of all are barred with brownish colouration of light and dark. The eyes are dark brown and the feet and almost the entirety of the toes are feathered.[2] The juvenile of the Shelley's eagle-owl has large areas of white about the head with sooty barring.[5]

Identification

It is the only large, heavily built, eagle owl in Africa with such barred patterning. Other eagle-owls co-exist with the Shelley's eagle-owl in the rainforest but conspicuously differ in most outward respects. The Akun eagle-owl is much smaller and less barred with pale yellow eyes and bare, yellow toes. Fraser's eagle-owl is also considerably smaller, has less barring, a warmer tawny overall colouration, and bare, bluish-grey toes. The similarly sized Verreaux's eagle-owl does not usually co-exist but some abutting ranges in West Africa may occur. The Verreaux's does not occurs in deep forest and the Shelley's has never been recorded outside of it but its conceivable that either may seldom visit Forest-savanna mosaics. If overlaps do occur, the Verreaux's is significantly paler, subtler and greyer with conspicuous pink eyelids.[2][6]

Distribution and habitat

This species is found in Central and Western Africa. It has been found in widely scattered locations, perhaps isolated by habitat destruction.[1][7] One isolated population is thought to live in a small area centered in inland Liberia as well adjacent extreme southeast Sierra Leone, western Ivory Coast and the southeastern tips of Guinea.[1][7] An isolated population may persist in a spot of southern Ghana.[1] The largest probable population is in all of southern Cameroon (also possibly extreme southern Nigeria), much of the non-coastal parts of Equatorial Guinea and Gabon, the northern and southern parts of the Republic of the Congo and a large swath of northern Democratic Republic of the Congo, perhaps reaching extreme eastern Uganda.[1][7] It is a resident of lowland, tropical rainforests and has never been collected outside densely forested and old growth areas.[2]

Behaviour

The Shelley's eagle-owl is a nocturnal bird which spends its days roosting in dense foliage, reportedly often at quite low levels in trees.[2] Few living wild specimens have ever been studied and the species has never been known to be photographed in the wild.[6] Persistent singing by the species has been heard in March, at least in Liberia.[2][5] The typical call is a loud, wailing kooouw (very different and much higher pitched from the typical calls of other eagle-owls of large size, which often call with sonorous hoots) given at intervals of several seconds. A loud peeping sound has also been reported, possibly in times of stress.[2] Heard far more often than it is seen, Shelley's eagle-owls are said to vocalize most persistently at or just before dawn and around dusk.[8]

Breeding

Details of the species' breeding habits are not generally known and only incidental observations have been made. In Democratic Republic of the Congo various stages of development were witnessed in different months: recently fledged young in April, a large nestling in September and a juvenile in mesoptile plumage in early November.[2][5] Additionally, an adult was seen roosting with a probable juvenile in December in the Cameroon.[5]

Feeding

The powerful talons and feet of the species suggest that its preferred prey consists of medium-sized mammals and large birds. The only confirmed wild prey was a large, unidentified flying squirrel.[9] In captivity, Shelley's eagle-owls require about 110 g (3.9 oz) of food a day, mainly consisting of rodents.[5]

Status and conservation

Only 20 specimens of this species are known to have been collected. Further studies, especially of the life history of Shelley's eagle-owls, are badly needed.[5] Based on this, it appears to be a very local and very rare bird.[2] Due to its location in dense rainforest, it is clear that the species is threatened by any habitat loss within its native range. The habitat destruction of the Guinean Forests of West Africa has been rampant as well as in the Congolian rainforests, thus compromising nearly all of this species' range.[1][5] A very rough estimate of 1,500-7,000 individuals, and almost certainly less than 10,000 individuals, was claimed to be living in the wild.[1][5] Due to the epidemic levels of clearcutting and seemingly very low population densities, this species was uplisted to Vulnerable by the IUCN in 2018, after an initial uplisting in 2004 to Near Threatened.[1]

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References
  1. BirdLife International (2018). "Bubo shelleyi". IUCN Red List of Threatened Species. 2018. Retrieved 17 December 2018.CS1 maint: ref=harv (link)
  2. König, Claus; Weick, Friedhelm (2008). Owls of the World (2nd ed.). London: Christopher Helm. ISBN 9781408108840.
  3. Weick, F. (2007). Owls (Strigiformes): annotated and illustrated checklist. Springer Science & Business Media.
  4. Dunning, John B. Jr., ed. (2008). CRC Handbook of Avian Body Masses (2nd ed.). CRC Press. ISBN 978-1-4200-6444-5.
  5. Holt, D. W., R. Berkley, C. Deppe, P. L. Enríquez, J. L. Petersen, J.L. Rangel Salazar, K.P. Segars, K.L. Wood, and J. S. Marks (2020). Shelley's Eagle-Owl (Bubo shelleyi), version 1.0. In Birds of the World (J. del Hoyo, A. Elliott, J. Sargatal, D. A. Christie, and E. de Juana, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA.
  6. Owls of the World: A Photographic Guide by Mikkola, H. Firefly Books (2012), ISBN 9781770851368
  7. Voous, K. H. (1966). The distribution of owls in Africa in relation to general zoogeographical problems. Ostrich, 37(sup1), 499-506.
  8. Borrow, N. & Demey, R. (2010). Birds of Ghana. Christopher Helm, London.
  9. Fry, C. H., S. Keith, & E. K. Urban (eds) (1988). The Birds of Africa. Vol. 3. Academic Press.
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