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 Indian subcontinent and Southeast Asia. This species is considered part of a superspecies with the barred eagle-owl (Ketupa sumatrana), which looks quite similar but is allopatric in distribution.
Taxonomy The spot-bellied eagle-owl, like its close relative, the barred eagle-owl, is one of the species that would have to be moved into Ketupa if that genus is to be retained, according to mtDNA cytochrome b sequence data (Olsen et al. 2002). Unlike 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. However, all eagle-owls and fish owls (as well as the snowy owl (Bubo scandianus)) were at one point deemed insufficiently distinct to warrant separate genera and until fairly recently authors generally treat all within the genus Bubo.Owls of the World: A Photographic Guide by Mikkola, H. Firefly Books (2012), 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).Voous, K.H. 1988. Owls of the Northern Hemisphere. The MIT Press, 0262220350. 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.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
Description
The spot-bellied eagle-owl is a large species of owl. It measures from in length. It is the sixth longest owl in the world on average and has the ninth longest wings of any living owl. The widely reported weight range for this species is , but this is probably towards the low end (possibly from K. n. blighi) or is possibly representative only of smaller males.CRC Handbook of Avian Body Masses, 2nd Edition by John B. Dunning Jr. (Editor). CRC Press (2008), . That body mass range is similar to that of the larger race of barred eagle-owl, which are in all races considerably smaller going on total length, standard measurements and appearance. One female shot near Haputale in the Badulla District of Sri Lanka, where the owls are smaller than to the north, was found to have weighed .Legge, W. (1886) A History of Birds of Ceylon, Volume 2. Perhaps a more correct average weight range for the species is .Grimmett, R., Inskipp, C., & Inskipp, T. (2013). Birds of the Indian Subcontinent: India, Pakistan, Sri Lanka, Nepal, Bhutan, Bangladesh and the Maldives. Bloomsbury Publishing. A large owl, presumed as an eagle-owl, recorded on the illegal wildlife trade from India purportedly weighed .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. The ear-tufts of the spot-bellied are very long and conspicuously of variable length, giving them a somewhat scraggly appearance at the tips. The ear-tufts of the spot-bellied eagle-owl measure in length. The spot-bellied eagle-owl has feathered legs and feet, like most eagle-owls, but the terminal digits of the toes are bare before the talons. The feet and talons are as formidable as any eagle-owl, being very large, heavy and powerful for their size. This species typically measures in wing chord length, in tail length, in tarsal length and in culmen length.Spot-bellied Eagle-Owl - Bubo nipalensis . Avis.indianbiodiversity.org. Retrieved on 2012-08-23.Harding, W. A., & Percy Moore, J. (1927). The Fauna Of British India Including Ceylon And Burma. 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. K. n. blighi has a wing chord length of , a tail length of , a longer tarsus than northern birds at and a culmen length of . One bird from Sri Lanka had a middle talon of , a toe length of and a wingspan of . 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. 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.
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. Juveniles birds are distinct from adult birds, being a much paler grayish-cream overall with fairly heavy brownish barring. Distinguishing the spot-bellied eagle-owl is relatively straightforward, since other Indian and southeast Asian eagle owls do not generally dwell in deep forests as does this species. The spot-bellied is the largest of the owls in its range other than the tawny fish owl (Ketupa flavipes), which is restricted in both habitat and diet to mountain streams. The brown fish owl (Ketupa zeylonensis), which is quite different in colouring if seen reasonably well, is slightly smaller linearly than the spot-bellied eagle-owl and is found in more wetland-based (and often somewhat more degraded) habitats. The subspecies of Eurasian eagle-owl (Bubo bubo hemachalana) found in the Himalayas may inhabit higher elevations of the same mountains where the spot-bellied eagle-owl dwells in the lower elevations in the forested foothills but there their ranges barely abut. The Indian eagle-owl (Bubo bengalensis) (typically found in wooded vicinities of rocky areas) is around 10% smaller than the spot-bellied; the dusky eagle-owl (Ketupa coromanda) (typically found in woods near wetlands) is around 15% smaller; and the brown wood owl, the largest Strix widely found in the Indian subcontinent and Southeast Asia, is around 35% smaller. 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.
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.Glossary . Cryptozoology. Retrieved on 2012-08-23. 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. 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. 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.Kelso, L. (1940). Variation of the external ear-opening in the Strigidae. The Wilson Bulletin, 24-29.
Distribution and habitat
This species is distributed through the Lower Himalayas from Kumaon east to Burma, thence to central Laos and central Vietnam. They are found throughout the Indian subcontinent and peninsular Southeast Asia, reaching the southernmost limits of their range in Sri Lanka and 12 degrees north in southern Thailand. The spot-bellied eagle-owl dwells mainly in primary or older second growth forests. Potentially, they can come to inhabit nearly all varieties of land-based habitats but prefer those such as dense, evergreen forests or moist deciduous forests within their range, though they do extend into tropical valleys, terrai and shola in the lower hills of India. Although often considered uncommon to somewhat rare, recent photographic evidence indicates that they are widely found in different parts of India and may simply avoid detection, so long as appropriate wooded habitat remains.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. They are found in a range of climates from the temperate woodlands of Nepal to the humid, tropical rainforest of Southeast Asia. However. the spot-bellied eagle-owl is mainly a species of tropical and subtropical foothills, mostly distributed at elevations of , but it can be found from sea-level to , the latter in the Transhimalayas.
Behaviour
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. 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.
Diet