Brown Fish-Owl

The brown fish-owl (Ketupa zeylonensis) is a large, powerful owl associated with rivers and other freshwater habitats across a broad swathe of Asia. Adults are about 48–58 cm long, have a wingspan of roughly 125–140 cm and weigh about 1.1–2.5 kg; females are generally larger than males. The plumage is warm brown to rufous-brown above and paler below, heavily marked with dark streaks and fine barring. Long ear tufts, bright yellow eyes and a poorly defined facial disc give the species a distinctive expression.

Brown fish-owls need access to water, but the surrounding landscape can vary enormously. They occur along wooded rivers and streams, around lakes, reservoirs and marshes, in mangroves and tropical forest, and even along watercourses in comparatively dry and rocky country. The species occurs mainly in lowlands but has been recorded to about 1,900 m. Mature trees, cliffs or other sheltered structures provide daytime roosts and nesting sites close to feeding areas.

In India the species occurs from lowland forests and tiger-reserve landscapes to wooded foothills and human-modified wetlands. The combination of open water for hunting and large trees or rocky cavities for shelter is more important than any single forest type. Because the species is resident, degradation of a productive river or wetland can affect the same local pair throughout the year.

The name fish-owl is accurate in the sense that the species is strongly tied to aquatic prey, but fish are far from its only food. Brown fish-owls take freshwater crabs and other crustaceans, frogs, fish, reptiles, rodents, birds and other animals living in or near water.

A 2023 study from two sites in the foothills of the Western Ghats in Goa analysed 104 pellets and found a strikingly crab-dominated diet: crabs made up 75.5% of identified prey, while the remainder included frogs, fish, snakes, birds, scorpions and insects. This shows how strongly local prey availability can shape the diet. A 2013 study of a breeding pair in Gujarat recorded 192 feeding flights over 23 nights and identified 18 different prey types.

Brown fish-owls usually hunt from rocks, branches or other perches beside or above the water. When prey is detected they drop or glide low toward the surface and seize it with the feet, and they can also wade into shallow water to take prey directly.

The feet are specialised for this aquatic hunting style. Rough, prickly scales on the soles and large, strongly curved talons help the owl hold wet, slippery prey once it has been caught.

Brown fish-owls are primarily nocturnal, with much activity concentrated after dusk and before dawn, although birds may also move or hunt in twilight and occasionally by day. During daylight they usually roost quietly in dense foliage, on large shaded branches, in rock recesses or other sheltered sites near water.

Pairs are resident and communicate with deep calls, sometimes duetting. The willingness to use reservoirs, dams and other modified water bodies helps explain why the species can persist in some human-influenced landscapes, provided that suitable roosts, nest sites and prey remain.

Breeding timing varies geographically but generally falls in the drier part of the year on the Indian subcontinent. Brown fish-owls do not build elaborate nests. They use large tree hollows and cavities, rock ledges or crevices, steep banks and sometimes old nests built by other large birds. Sites are usually close to water and may be reused.

A study published in 2015 from Kerala followed nine breeding attempts at the same nest site from 2007 to 2015. Breeding there extended from mid-November to mid-April. Seven clutches contained one egg and two contained two eggs. Incubation lasted 32–37 days and chicks remained in the nest for 43–49 days. Seven of the 11 eggs laid during the study period produced fledged young. Repeated use of the same nest site over several years shows that brown fish-owls can be strongly faithful to a suitable breeding site.

The small clutch and long period before the young leave the nest make adult survival and secure nesting sites especially important.

The brown fish-owl is classified as least concern on the IUCN Red List and retains a large range. In India, monitoring data updated in 2025 show a much less favourable trend, with an estimated long-term decline of about 39% and a current decline of roughly 3.4% per year.

Threats vary locally and include degradation of rivers and wetlands, removal of mature waterside trees, disturbance of nest and roost sites, entanglement in fishing nets and direct persecution. Because the owl depends on aquatic food webs, pollution and changes to river flow can affect it indirectly by altering prey communities.