What Is the Biggest Owl in the World? Eagle-Owls and Rivals

Blakiston’s fish owl or eagle-owl: which is bigger?

The answer depends on how you measure. There are three main contenders, and each wins in a different way:

• Heaviest on average: Blakiston’s fish owl (Bubo blakistoni, sometimes placed in the genus Ketupa). Females weigh about 2.95–4.6 kg (6.5–10.1 lb) and males 2.95–3.6 kg (6.5–7.9 lb).
• Equal top weight: the Eurasian eagle-owl (Bubo bubo). Its largest females reach the same 4.6 kg (10 lb), and the very longest eagle-owls are about 3 cm (1.2 in) longer than the longest fish owls. Many eagle-owls, though, are much smaller, especially in southern Europe.
• Longest: the great gray owl (Strix nebulosa), up to about 84 cm (33 in) from bill to tail, but weighing at most about 1.9 kg (4.2 lb).

Because Blakiston’s fish owl is heavier and broader-winged on average, ornithologists usually call it the largest living owl. In everyday terms, the two giants are a tie, and both are among the biggest nocturnal birds of prey on Earth.

Size table of the largest owls

The ranges are for wild adults and include both sexes. In every species the larger figures belong to females, since female owls are bigger than males.

Why the great gray owl looks so big

The great gray owl is a lesson in how feathers can fool the eye. It has a huge round face, the largest facial disc of any bird of prey, the longest tail of any owl and a thick coat of fluffy feathers that insulate it in the boreal forest. Underneath, its body is surprisingly slim, and it weighs less than half as much as a big eagle-owl.

That light build suits its hunting style. Great gray owls listen for voles moving under the snow, then plunge feet-first through the snow crust to grab them, even through about 60 cm (2 ft) of snow.

Why are these owls so big?

Large size helps owls in two ways. First, big bodies hold heat better, which matters in the long, cold winters of Siberia, Hokkaido and Scandinavia, where both giants live. Second, size lets them hunt big prey.

Blakiston’s fish owl catches fish such as salmon, trout and pike, as well as frogs and crayfish, wading in shallow water or diving from a perch on the bank. Some fish it catches may weigh more than the owl itself. The Eurasian eagle-owl takes mammals and birds up to the size of hares, herons and buzzards, and it is a top predator wherever it lives.

The biggest owls in North America

No owl in the Americas reaches the size of the two Eurasian giants, but three species stand out:

• The great gray owl is the longest owl in North America and in the world.
• The snowy owl is the heaviest North American owl, with large females weighing up to about 3 kg (6.5 lb).
• The great horned owl is the most widespread big owl, found from the Arctic tree line to South America, and is the New World cousin of the eagle-owl.

Our guide to owls of North America covers every species on the continent.

The smallest owls, for contrast

At the other end of the scale, the elf owl (Micrathene whitneyi) of the deserts of the southwestern United States and Mexico is usually named the smallest owl in the world. It is 12.5–14.5 cm (4.9–5.7 in) long and weighs about 40 g (1.4 oz). The long-whiskered owlet of Peru and the Tamaulipas pygmy owl of Mexico are of similar length.

That means a big female Blakiston’s fish owl can weigh more than 100 times as much as an elf owl. Even so, both belong to the same family, Strigidae, the typical owls.

Are the biggest owls endangered?

Not all of them. The Eurasian eagle-owl, great gray owl and great horned owl are all listed as Least Concern by the IUCN. The snowy owl is Vulnerable because of evidence of declines in parts of the Arctic.

Blakiston’s fish owl is the rarest of the giants. The IUCN lists it as Vulnerable, with an estimated 1,000–1,500 birds, including only a few dozen pairs in Japan. It needs old riverside forest with big hollow trees for nesting and rivers that do not freeze completely in winter. Logging, dams and riverside development have reduced its habitat, while some birds drown in fishing nets or are hit by cars. In Japan, large nest boxes and protection of river habitat have helped the small population.