What is the largest owl species?

Blakiston's fish owl, from far eastern Russia, northern Japan and China - a bird with a wingspan approaching two metres and a weight over four kilograms, which is heavy enough that it does not fly so much as haul itself between trees. Eurasian eagle-owls rival it and Blakiston's is generally the heaviest.

It is also not a proper owl in one important respect. It hunts fish, wading in shallow rivers, and it has given up the silent flight that defines the family - the fringed feather edges that muffle other owls are reduced, because a fish underwater cannot hear you coming and the feathers cost sound sensitivity and waterproofing. It is loud in flight by owl standards, which is a fair trade.

It needs very specific things and is endangered because of it: huge old-growth trees with cavities big enough to nest in, and rivers that do not freeze completely in winter. Logging removes the first and dams the second, and there are perhaps a couple of thousand left. Almost everything known about their behaviour comes from a small number of researchers spending winters in Primorye, which is one of the coldest and least accessible places anyone does fieldwork.