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Blakiston's fish owl (Ketupa blakistoni), the largest living species of owl, is a fish owl, a sub-group of eagle-owls that specialize in hunting in riparian areas.

Blakiston's fish owl is more closely related to the Eurasian eagle-owl than to the subgenus Ketupa of fish owls it was formerly believed to be closer to. This was shown by osteological and DNA-based tests in 2003 by ornithologists/taxonomists Michael Wink and Claus König, author of Owls of the World.

Description

thumb|left|Illustration by J. G. Keulemans

Blakiston's fish owl is the largest living species of owl. Around February, the average weight of Russian fish owls was in seven males and in five females, typically when their body mass at its lowest throughout the year. Blakiston's fish owl measures in total length, and thus measures slightly less at average and maximum length than the great grey owl (Strix nebulosa), a species which has a significantly lower body mass. The maximum wingspan of the Blakiston's fish owl is also greater than any known eagle-owl. The wingspan range known for Blakiston's fish owls is . The Blakiston's is noticeably larger than the other three extant species of fish owl.

  • K. b. blakistoni (Seebohm, 1884). Hokkaido, N. Japan and Kuriles. Lores of facial disc tawny-brown with narrow black shaft-stripes; above eyes, around bill base and on forehead a row small, stiff almost completely white feathers; chin largely white. Rest of head and underparts brown with blackish-brown shaft-stripes and buff feather tips; back is darker. The mantle is somewhat lighter and more rufous and with blackish-brown bars as well as dark brown shaft-streaks. Wings deep brown with numerous buff yellow bars. Tail dark brown with 7–8 cream-yellow bars. Underparts light buff-brown with blackish-brown shaft streaks and narrow light brown wavy cross-bars. The wing chord measures , the tail measures and the tarsus measures . Blakiston's fish owls typically require stretches of productive rivers that remain at least partially unfrozen in winter. In the frigid northern winters, open water is found only where the current is sufficiently fast-flowing or there is an upwelling of warm spring water. In the basin of the Bikin River, the mean body mass of fish caught was estimated at . In Russia, amphibians are taken in great quantity in spring, especially Dybowski's frog (Rana dybowskii), and may come to seasonally outnumber fish in the diet during that time.

Nest cavities have to be quite large in order to accommodate these birds. Clutch size is 1 to 3, usually 2. It is endangered due to the widespread loss of riverine forest, increasing land development along rivers and dam construction. The current population in Japan has been estimated at approximately 100–150 birds (20 breeding pairs and unpaired individuals), whereas on mainland Asia the population is higher, at times variously estimated at several hundred or perhaps up to thousands of individuals. In the Primorye, it is estimated that 200 to 400 individuals remain. In Russia, fish owls are killed by fur-trappers, drown in nets set for salmon, and are shot by hunters. Given their very small global population, ongoing deaths are unlikely to be sustainable. Evidence has been found of a gradual recovery of the Blakiston's fish owl population in Hokkaido but Japanese conservationists are vexed by the lack of suitable habitat and recommend land use changes to encourage the growth of the population.

Importance to indigenous peoples

Blakiston's fish owl is revered by the Ainu peoples of Hokkaido, Japan, as a Kamuy (divine being) called Kotan koru Kamuy (God that Protects the Village). In Russia, the species is considered a food source by the Evens people in northern Siberia and the northern Russian Far East. however, the practice has locally fallen out of favour.

  • Images and videos of the Blakiston's fish owl (Ketupa blakistoni) at ARKive
  • "Blakiston's Fish Owl Kotan Koru Kamui: The God of the Village" by Mark Brazil, at JapanVisitor
  • Calls of a Blakiston's fish owl at Xeno-canto