Blakiston's fish owl

Blakiston's fish owl was formally described in 1884 by the English amateur ornithologist Henry Seebohm from a specimen collected near Hakodate on the island of Hokkaido in Japan. He placed the owl in the genus Bubo and coined the binomial name Bubo blakistoni. The specific epithet was chosen to honour the naturalist and explorer Thomas Blakiston who had supplied Seebohm with a specimen. 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==

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. In terms of structure, the Blakiston's fish owl is more similar to eagle-owls than it is to other fish owls but it shares a few characteristics with both types of owl. Like all fish owls, its bill is relatively long, the body relatively husky and wings are relatively long compared to eagle-owls. It also shares with other fish owls a comparatively long tarsi, although relative to their size the three smaller fish owl have a proportionately longer tarsus. Other than these few characteristics, a Blakiston's fish owl skull and skeleton is practically the same as that of a Eurasian eagle-owl. The talons of the Blakiston's fish owl are similar in shape and size to those of the Eurasian eagle-owls. It has been stated that the combination of wavy cross patterns on the underside of the Blakiston's plumage and its huge talons make it look strikingly like an outsized great horned owl (B. virginianus) from below. Two external characteristics that Blakiston's share with eagle-owls, but not with the other fish owls, is that its tarsi are totally feathered and that its wing beats are silent, although apparently the Blakiston's has relatively fewer sound-blocking combs on its wing primaries than the a comparable eagle-owl would. Among standard measurements, which at average and maximum are greater than any other living owl other than tail length, the wing chord measures , the tail measures , the tarsus is and the culmen is around . Superficially, this owl somewhat resembles the Eurasian eagle-owl but is more monochromatically brown to tan in colour. Like other fish owls but unlike most eagle-owls, the Blakiston's fish owl has relatively broad and ragged ear tufts which hang slightly to the side and that do not appear upright. The upperparts are buff-brown and heavily streaked with darker brown coloration. The underparts are a paler buff brown and less heavily streaked. The throat is white. The iris is yellow (whereas the Eurasian eagle-owl typically has an orange iris). The Eurasian eagle-owl and Blakiston's fish owl both occur in the Russian Far East and are potentially could compete for resources, although no scientifically observed interactions of any kind have been reported between these two largest owl species. It is likely, given the sizeable gap between the dietary preferences of the species (mainly aquatic animals in the Blakiston's, and mainly upland, terrestrial species in the eagle-owl), that competition for food is not normally a serious problem. Identification of the Blakiston's from other fish owls is not an issue as there is a gap of distribution of approximately between the ranges of the Blakiston's and the tawny fish owl (B. flavipes) and about separates the range of the Blakiston's and the brown fish owl (Ketupa zeylonensis). Improbably, early naturalist thought that the Blakiston's and brown fish owls belonged to the same species. The streaking on the underside of the brown and Blakiston's are similar and their songs sound more similar to each other than they do with the two songs of the other two species of fish owl, being deeper voiced with a dissimilar vocal pattern to the latter fish owl. Vocalizations differ among the recognized subspecies. In the nominate subspecies from Japan, the male calls twice and the female responds with one note, whereas the mainland subspecies has a somewhat more elaborate, four-note duet: HOO-hoo, HOBO-hoooo (here, the male call is in capital letters (HOO) and the female call in lower case (hoo)). The transliterations of the calls of owls from Russia, representative of the owl's vocal variations, are SHOO-boo and FOO-foo-foo. The territorial song or call in Russia in particular has been described as somewhat like a short, deep eagle-owl's call. Despite its slightly larger size, the Blakiston's fish owls voice is not as sonorous or as far-carrying as is the Eurasian eagle-owl's voice is. The fish owl's voice is rather deeper, however. As in most owls, vocal activity tends to peak directly before nesting activity begins, so peaks around February in this species. This duet of pairs of Blakiston's fish owl in the period leading up the breeding season is so synchronized that those unfamiliar with the call often think it is only one bird calling. When an individual bird calls, it may sound like hoo-hooo. Juveniles have a characteristic shriek, typically a startling and slurred phee-phee-phee. ==Subspecies==

Of the following four subspecies described in the literature, only the first two (B. b. blakistoni & B. b. doerriesi) are currently accepted by science. • 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 . • K. b. doerriesi (Seebohm, 1884). E. Siberia south to Vladivostok region and Korean border area. Now thought to include all non-Japanese Blakiston's fish owls. Larger than nominate with large white patch on top of the head; tail less marked and bars incomplete. The wing chord measures , the tail measures and a specimen had a tarsus of . • K. b. karafutonis (Kuroda, 1931). Sakhalin. Smaller than nominate race and darker, especially on back and ear-coverts; tail with narrower dark brown bars and the light bars more numerous (8–9 against 7 in nominate). • K. b. piscivorus (Meise, 1933). W. Manchuria. Paler overall than doerriesi, ground color of underparts grayish white (not buff-brown); tail-bars not fully creamy yellow, central rectrices having white inner webs almost to base; chin pure white. ==Habitat==

Blakiston's fish owl occurs in dense, minimally or undisturbed old-growth forest near waterways including floodplains or wooded coastlines. The species requires cavernous old-growth tree cavities for suitable nest sites. They are easily one of the largest birds to use tree hollows anywhere. 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. Slower-moving streams are equally likely to support these owls as the main river channels and they only need a few meters of open water to survive a winter. ==Feeding and behavior==

The Blakiston's fish owl feeds on a variety of aquatic prey. The main prey type is fish, with common prey including pike (Esox reichertii), catfish, trout and salmon (Oncorhynchus ssp.). Some fish these owls catch are quite large. Jonathan Slaght estimated that some fish caught are up to two to three times their own weight and has seen owls keep one foot on a tree root to be able to haul a large catch onto a bank. 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. In Russia, clutches are usually just one egg. Eggs are long and wide and are thus similar in size to Siberian eagle-owl eggs. The males provide food for the incubating female and later the nestlings. The incubation period is about 35 days and young leave the nest within 35–40 days but are often fed and cared for by their parents for several more months. Data on breeding success are scant: on Kunashir Island during a six-year period breeding success was 24%; with six fledglings resulting from 25 eggs. The average weight of fledgling owls was about 40% lighter than adult size, averaging in females and in males. Juveniles linger on their parents' territory for up to two years before dispersing to find their own. A study in Hokkaido found that male fledglings were about 10% more numerous than females but had a higher mortality rate post-fledgling. Blakiston's fish owls can form pair bonds as early as their second year and reach sexual maturity by age three. This unusually long pre-dispersal period may be why this owl is occasionally reported as gregarious, as sets of parents and juveniles will congregate but not unrelated owls. Once full-sized, these owls have few natural predators. However, they may be more vulnerable to attack from mammalian carnivores since, unlike other eagle owls which typically perch and hunt from trees or inaccessible rock formations, they hunt mainly on the ground along riverbanks. There are two records of natural predation on adults from Russia and none in Japan: one involved a Eurasian lynx (Lynx lynx) and the other an Asian black bear (Ursus thibetanus). ==Status==

in Tokyo. Blakiston's fish owl is classified as an Endangered Species by the IUCN. 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. ==Notes==