The spot-bellied eagle-owl (Ketupa nipalensis), also known as the forest eagle-owl is a large bird of prey with a formidable appearance. It is a forest-inhabiting species found in the
The spot-bellied eagle-owl, like its close relative, the
fish owls" that were also considered to be included in Ketupa, the barred and the spot-bellied species are not closely tied to riparian habitats and piscivorous eating habits.[2] However, all eagle-owls and fish owls (as well as the snowy owl (Bubo scandianus)) we're at one point deemed insufficiently distinct to warrant separate genera and until fairly recently authors generally treat all within the genus Bubo.[2][3] Due to its forest-dwelling habits and some superficial characteristics, it has been wondered by some authors if the spot-bellied eagle-owl is related to the rainforest-dwelling eagle-owls of Africa, namely the Fraser's (Ketupa poensis) and similarly-sized Shelley's eagle-owl (Ketupa shelleyi).[4] However, more extensive genetic research indicates paraphyly with no recent common ancestor between the Ketupa owls and the more "typical" Bubo owls. Therefore the Ketupa owls (including the spot-bellied eagle-owl) are now widely considered as belonging to a distinct genus.[5][6]
Description
A painting of the spot-bellied eagle-owl.
The spot-bellied eagle-owl is a large species of owl. It measures from 50 to 65 cm (20 to 26 in) in length.
culmen length.[11][12] The subspecies of spot-bellied eagle-owl found on Sri Lanka, K. n. blighi, is linearly about 10% smaller than the birds found further north in India but about the same size as owls from the southern tip of India.[4]K. n. blighi has a wing chord length of 370 to 455 mm (14.6 to 17.9 in), a tail length of 184 to 240 mm (7.2 to 9.4 in), a longer tarsus than northern birds at 63 to 68 mm (2.5 to 2.7 in) and a culmen length of 43 to 48 mm (1.7 to 1.9 in). One bird from Sri Lanka had a middle talon of 44.2 mm (1.7 in), a toe length of 50.6 mm (2.0 in) and a wingspan of 143 cm (56 in).[2][8] The reported talon length above is very large relative to the size of this owl – the Eurasian eagle-owls found in Spain (Bubo bubo hispanus), although relatively small compared to other Eurasian eagle-owl races, were shown to have smaller talon lengths than the Sri Lankan spot-bellied eagle-owl.[13] Other than size, the only feature that distinguishes northern birds from Sri Lankan birds is an ill-defined band of honey-brown colour on the pectorals.[4]
A spot-bellied eagle-owl in Sri Lanka, which are similar to mainland birds but smaller.
The spot-bellied eagle-owl is overall a stark, grayish-brown bird, with dark, coarse brown coloration over the back and upper wings. The throat and underparts are mainly pale fulvous in color with black and white horizontal stripes along the flanks of the body that become broad spots on the abdomen and undertail coverts. On the wings, the primaries are dark brown with lighter brown stripes and the secondaries are more heavily barred with buff-brown coloration. The lores are covered in bristly feathers and the cheeks are brownish-white with black feather shafts. The large ear-tufts slant off to the sides.
Strix widely found in the Indian subcontinent and Southeast Asia, is around 35% smaller.[2][3][4] Furthermore, the colouring and markings of the spot-bellied eagle-owl are distinctive from all but the barred eagle-owl, which it does not co-exist with in the wild. The barred and spot-bellied eagle-owls are immediately distinguished in the field from other eagle-owls by their pale-looking, sideways slanting ear-tufts, and the degree of feathering on the legs and feet. This species pair unlike sympatric eagle-owls has horizontal rather than vertical underside markings (which coalesce somewhat in the barred eagle-owl to barring, but appear as almost continuous spotting on the spot-bellied eagle-owl) over a much paler ground colour, while the back is slightly grayer looking, lacking any warmer brown or tawny tones.[4]
Voice
This owl is noted for its strange, human-sounding call, and it has been suggested that it is the same as the
cryptid known as ulama or "Devil Bird" in Sri Lanka.[14] A local name is Maha Bakamuna ("large horned owl"). According to http://www.cryptozoology.com, in July 2001 it was confirmed that ulama description perfectly matches spot-bellied eagle-owl. This call consists of a scream, which rises and then falls in tone. The territorial call of the species consists of low hoots with two-second intervals between hoos.[2] The voice is booming, deep and carries quite far. It is usual for forest-dwelling owls (and many different kinds of birds) to have an extensive and complex range of vocalizations since vision is more limited than in open or semi-open habitats.[4] However, the spot-bellied eagle-owl has relatively small ear openings, even for a member of the genus Bubo, suggesting that some territorial behaviour is carried out visually instead of auditorily.[15]
Distribution and habitat
An adult Spot-bellied Eagle-Owl seen right after heavy rains in Sigiriya, Sri Lanka.
The spot-bellied eagle-owl is nocturnal and often spends its day hidden in the dense foliage of large forest trees. However, they have been observed on the move and even hunting during the day, especially in forests with minimal human disturbance. Their activity normally picks up at dusk as they begin to hunt.[2] In larger forest owls, a partially diurnal behaviour is not uncommon. The bright whitish colouration, overlaid with brownish cross-bars, forming a brow over the eyes to the front of the ear-tufts is theorised to play a primary role in expression of behavioural intent.[4]
Diet
This is a very powerful and bold predatory owl, which is assuredly at the top of the avian food chain in its forested range. However, no extensive study of its dietary habits is known. Even in larger eagle-owls such as the
toque monkeys (Macaca sinica), and one apparently caught an Indian flying fox (Pteropus giganteus) from its tree roost.[20][21][22] Due to the capture of diurnal prey such as giant squirrel, partial daytime foraging habits have been inferred for the spot-bellied eagle owl.[23] They will also opportunistically prey upon snakes, lizards (including large monitor lizards) and fish.[11][12] Like several of the eagle-owls and fish owls but unlike most owls, the spot-bellied eagle-owl has been recorded as feeding on carrion. Thus far, they've been seen feeding on the carcases of goats (Capra aegagrus hircus) and tigers (Panthera tigris).[19]
Breeding
A young spot-bellied eagle-owl, which tend to be paler than adults.
This species'
nesting season is from December to March, however, an egg has been recorded as late as June in Cachar. Most nesting sites are in large, spacious tree hollows. Alternately, they use abandoned stick nests made by other large birds, in many cases those previously built by eagles, vultures or kites. They've additionally been recorded as nesting in caves and sheltered fissures of rock walls. In this species, only one egg has ever been recorded per clutch and this is only one of three amongst all owl species (besides the buffy fish owl (Ketupa ketupu) and the barred eagle-owl) where this is known to be the case.[24] The egg is white and round ovoid in shape with a smooth surface, averaging 61.2 mm × 49.9 mm (2.4 in × 2.0 in) in size, and are thus around the same size as the eggs of the largest living owls, the Eurasian eagle-owl and Blakiston's fish owl (Ketupa blakistoni). It has been reported that both sexes engage in incubation but this may not be the case (male owls generally do little to no incubating in eagle-owls), with the male more likely temporarily covering the eggs while the female flies off for a short period. Few further details are known of their breeding biology, including the brooding and fledging stages due to this species reportedly being very fierce and aggressive in defence of their nests.[2] Anecdotes have claimed that some rather serious injuries have been incurred in the process of approaching spot-bellied eagle-owl nests, thus caution and distance from active nests is recommended.[12][25][26]
Status
This species is generally uncommon, likely needing large hunting and breeding territories and thus occurs at low densities. However, it continues to occur over a large range and is not thought to be conservation dependent. Areas where deforestation occurs are likely to be vacated by this species, which is perhaps the only widespread threat faced by this owl.
^ abcdefghijklmnVoous, K.H. 1988. Owls of the Northern Hemisphere. The MIT Press, 0262220350.
^Salter, J. F., Oliveros, C. H., Hosner, P. A., Manthey, J. D., Robbins, M. B., Moyle, R. G., Brumfeld, R. T. & Faircloth, B. C. (2020). Extensive paraphyly in the typical owl family (Strigidae).The Auk, 137(1), ukz070.
^WInk, M., & Sauer-Gürth, H. (2021). Molecular taxonomy and systematics of owls (Strigiformes) - an update. Airo 29:487-500
^ abcLegge, W. (1886) A History of Birds of Ceylon, Volume 2.
^Grimmett, R., Inskipp, C., & Inskipp, T. (2013). Birds of the Indian Subcontinent: India, Pakistan, Sri Lanka, Nepal, Bhutan, Bangladesh and the Maldives. Bloomsbury Publishing.
^Ahmed, A. (2010). Imperilled custodians of the night: a study of the illegal trade, trapping, and utilization of Owls in India. TRAFFIC India/WWF-India.
^ abcdeHarding, W. A., & Percy Moore, J. (1927). The Fauna Of British India Including Ceylon And Burma.
^del Mar Delgado, M.; Penteriani, V. (2004). "Gender determination of Eurasian Eagle-Owls (Bubo bubo) by morphology". Journal of Raptor Research. 38: 375–377.
^Kelso, L. (1940). Variation of the external ear-opening in the Strigidae. The Wilson Bulletin, 24-29.
^Deshmukh, A. J. (2008). Photographic record of Forest Eagle-Owl Bubo nipalensis from Kanha National Park, Madhya Pradesh, India. Indian Birds, 4(1), 18.
^Srinivasan, S. (2013). Spot-bellied Eagle Owl Bubo nipalensis in northern Eastern Ghats, Andhra Pradesh, India. Hist. Soc, 29(2), 503-518.
^Choudhury, A. (2001). Some bird records from Nagaland, north-east India. Forktail, 91-104.
^ abcNandini, R. 2005 Predation by Forest Eagle-Owl Bubo nipalensis on Mouse Deer Moschiola meminna. Bull. BO C, 47, 121-122.
^Kannan, R. (1994). Forest Eagle Owl (Bubo nipalensis Hodgson)–a predator of the Indian Giant Squirrel (Ratufa indica). Journal of the Bombay Natural History Society, 91, 454.
^Dittus, W. P. (1975). Population dynamics of the toque monkey, Macaca sinica. Socioecology and psychology of primates, 42, 125-151.
^Roy, O., Chakraborti, T. M., & Chakraborty, R. (2018). Spot-bellied Eagle-Owl Bubo nipalensis feeding on Indian Flying Fox Pteropus giganteus. Indian Birds, Correspondence.
^Ramanujam, M. E., & Singh, T. (2017). A comparative study of the diet of the Indian Eagle Owl Bubo bengalensis (Franklin, 1831) from two distinct habitats in the Tamil Nadu-Puducherry area, southern India. Journal of Threatened Taxa, 9(3), 9892-9902.
^Hume, R. (1991). Owls of the world. Running Press, Philadelphia, PA. 1991.
^Ramanujam, M. E. (2004). Inter-specific intimidatory behaviour of adult Indian Eagle Owls Bubo bengalensis (Franklin) in defence of their nestlings. Zoos’ Print Journal, 19(2), 1343-1345.
.jpg)
