The brown fish owl was formally described in 1788 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.

Joan Gideon Loten, an administrator in the Dutch East India Company had provided Brown with a picture of the owl that had been drawn by the Ceylonese artist Pieter Cornelis de Bevere.

The Late Pleistocene Bubo insularis is typically considered to include the fragmentary remains originally described as Ophthalmomegas lamarmorae due to a mix-up with the fossil macaque Macaca majori and subsequently unstudied for many decades.

Its fossil bones suggest a bird the size of a large spotted eagle-owl (B. africanus), a bit smaller still than the smallest living fish owls.

It was certainly smallish but long-legged by eagle-owl standards, and its wing proportions differed conspicuously from a typical horned eagle owl.

Some consider it a specialized paleosubspecies of the brown fish owl that became extinct during the third Würm glaciation,[12][13] while others reported remains of B.

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.

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.

[19][18] The brown fish owl 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.

By number in the Melghat Tiger Reserve in India, freshwater crabs of the family Gecarcinucidae (of genus Barytelphusa) almost totally dominated the diet.

[citation needed] Birds hunted by brown fish owls have including lesser whistling duck (Dendrocygna javanica) and Indian pond heron (Ardeola grayii).

If this is correct, the different foot anatomy, more similar to that of a typical eagle-owl, would imply that the population had shifted back to terrestrial prey.

It has been conjectured that the owls disappeared with their prey due to climate change, but the giant pikas of Sardinia and Corsica still existed around 1750, finally succumbing to habitat destruction, introduced predatory mammals and overhunting soon thereafter.

Brown fish owls frequently nest in shady spots such as old-growth mango trees (Mangifera ssp.

Outside of the bare surface of large branches, nests are often in spots such as overgrown eroded ravines and steep riverbanks with natural holes.

Other nesting sites have included rock ledges, caves in shady cliff faces and stone ruins.

Due to this, it seems to be extinct as a breeding bird in Israel nowadays, attributable largely to damming practices leading to drying up of many waterways.

In Israel, it was decimated by the use of the rodenticide thallium(I) sulfate, which in addition to potential direct exposure through rodents also poisons surface waters.