Which owl is generally considered the largest owl species by body mass?

Blakiston’s fish owl is generally considered the largest owl species by body mass.

The species, Ketupa blakistoni, is a huge fish owl of northeastern Asia. It lives beside forested rivers and streams, especially in Russia, Japan, China, and parts of the Korean Peninsula. Its diet includes fish, amphibians, crustaceans, and other aquatic animals, although it can also take birds and mammals.

The owl depends on mature riverside forests because it nests in large tree cavities and hunts along waterways. This habitat requirement makes logging, river modification, and loss of old trees serious threats. It is also vulnerable to declines in fish and to human disturbance near breeding sites.

The Eurasian eagle-owl is often mentioned in comparisons because it is another exceptionally large owl. However, measurements differ by sex and by whether researchers compare body mass, length, or wingspan. Blakiston’s fish owl is especially notable for mass and overall bulk.