The brown fish owl (Bubo zeylonensis or Ketupa zeylonensis) is an owl. Thisspecies is a part of the family known as typical owls, Strigidae, which contains most living owls. It inhabits the warm subtropical and humid tropical parts of continentalAsia and some offshore islands. Of the four living species of fish owl, it is the most widely distributed, most common and best-studied. It occupies a range of over 7,000 km (4,300 mi) from eastern China to Palestine.
The four fish owls were previously generally separated in the genus Ketupa. mtDNAcytochrome b sequence data is equivocal on which genus name is applied for them, and today they are commonly lumped with the horned and eagle-owls (Bubo) – which they also resemble osteologically very much – for sake of convenience. Depending on whether some little-studied tropical eagle-owls are closer to the fish-owls than to the typical eagle-owls, Ketupa might be a valid genus if these as well as the fishing owls (formerly Scotopelia) are included in it, although there are a number of osteological differences that suggest that fishing and fish owls are not directly related to each other.
This species is an all-year resident throughout most tropical and subtropical parts of the Indian Subcontinent to Southeast Asia and adjoining regions. West of its main range, it is patchily distributed to the Levant (possibly extinct) and southern Asia Minor (recently rediscovered). The typical habitat of brown fish owls is forest and woodland bordering streams, lakes or rice fields. It inhabits mainly the lowlands, from open woodland to dense forest as well as in plantations; in the Himalayasfoothills it ranges into submontane forest up to 1,500 m (4,900 ft) ASL or so but not higher. It frequently spends the day in stands of bamboo or other large shady trees. They be found around water reservoirs (or jheels in India), along canals, on the outskirts of villages and along sea coasts. Western birds are found in semiaridlandscape and may breed in oases in arid regions. Regardless of habitat, it rarely strays far from larger bodies of water such as rivers and lakes.
This species is a large owl, but it is intermediate in size between other fish owls. It ranges from 48 to 58 cm (19 to 23 in) in length and in wingspan from 125 to 140 cm (49 to 55 in). Weight can vary considerably, reportedly ranging from 1.1 to 2.5 kg (2.4 to 5.5 lb). Some of the variability is attributed to the range of sizes across the subspecies. Also, females are invariably at least somewhat larger than males and condition of birds is variable. It has prominent ear tufts but as in all fish owls, their tufts hang to the side of the head and have a scraggly look. The upperparts are rufous brown and heavily streaked with black or dark brown. The underparts are buffy-fulvous to whitish, with wavy dark brown streaks and finer brown barring. The throat is white and can be conspicuously puffed, while the facial disk is indistinct. The irides are golden yellow, the feet a duller yellow, and the bill is dark. Sexes do not differ in appearance except for size. Second-year fish owls of this species tend to be somewhat paler than full adults. Compared to the tawny fish owl, which they meet in range in Laos and Vietnam, it has a browner and less rufous overall color and a less pale face. The tawny also does not have barring as does the brown fish owl, it has feathering over two-third of its tarsus, whereas the brown is featherless on its legs, and has a yellowish band across its back absent in the brown species. Compared to the buffy fish owl, with which they may meet in the southeastern reaches of its range, the brown fish owl is slightly larger with a hue that's clearly browner and that species lacks the vermiculations and bars on the underside of the brown species.
Compared to eagle owls of similar length, fish owls tend to be even shorter in tail length and even heavier in build, have relatively larger wings (the tawny and Blakiston's being particularly chunky in shape), have considerably longer legs, and have a rough texture to the bottom of their toes. At least the latter two features are clear adaptations to aid these owls in capturing fish. Diurnal raptors who feed largely on fish have similar, if not identical, rough texture under their toes, which helps these birds grasp slippery fish. Unlike diurnal raptors who capture fish such as the osprey (Pandion haliaetus) as compared to most terrestrial raptors, the fish owls have large, powerful, and curved talons and a longitudinal sharp keel sitting under the middle claw with all having sharp cutting edges that are very much like those of eagle owls. Also, unlike fish-eating diurnal raptors will not submerge any part of their body while hunting, preferring only to put their feet into the water, although fish owls will hunt on foot, wading into the shallows. Unlike most owls, the feathers of fish owls are not soft to the touch and they lack the comb and hair-like fringes to the primaries, which allow other owls to fly silently in order to ambush their prey. Due to the lack of these feather-specializations, fish owl wing beats make sounds. The brown fish owl in particular is said to have a noisy wing beat, sometimes described as producing a singing sound, but another description claimed they could be "as silent as any other owl" in flight. The lack of a deep facial disc in fish owls is another indication of the unimportance of sound relative to vision in these owls, as facial disc depth (as well as inner ear size) are directly related to how important sound is to an owl's hunting behavior. Also different from most any other kind of owl, the bill is placed on the face between the eyes rather below it, which is said to impart this fish owl with a "remarkably morose and sinister expression". Similar adaptations, such as unwillingness to submerge beyond their legs and lack of sound-muffling feathers are also seen in the African fishing owls, which do not seem to be directly related. The brown fish owl has sometimes been regarded as conspecific with the Blakiston's fish owl (B. blakistoni), but there is an approximately 2,000 km (1,200 mi) gap in their distributions, not to mention a large number of physical differences not the least of which is the Blakiston's considerably greater size.
Its calls are described as a deep, trisyllabic tu-hoo-hoo, which is seemingly the territorial song emitted before breeding. It's call has been described as comparable to that of a distant Eurasian bittern (Botaurus stellaris). Other calls recorded for the brown fish owl have included a soft, "almost human-like" huphuphuphuphuphup or a loud huhuhuhuhuhuhu. Another call is a boom-uh-boom.
