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
A riparian zone or riparian area is the interface between land and a river or stream. In some regions, the terms riparian woodland, riparian forest, riparian buffer zone, riparian corridor, and riparian strip are used to characterize a ripar ...
areas.
[ It is native to China, Japan, and the ]Russian Far East
The Russian Far East ( rus, Дальний Восток России, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in North Asia. It is the easternmost part of Russia and the Asia, Asian continent, and is coextensive with the Far Easte ...
. This species is a part of the family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
known as typical owl
The true owls or typical owls (family (biology), family Strigidae) are one of the two generally accepted families of owls, the other being the barn owls and bay owls (Tytonidae). This large family comprises 230 living or recently extinct species ...
s (Strigidae), which contains most species of owl. Blakiston's fish owl and three other piscivorous
A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...
owls are placed with some eagle-owls in the genus ''Ketupa
''Ketupa'' is a genus of owls in the family Strigidae. The genus formerly contained just three species, the fish owls but based on the results from a genetic study published in 2020, the generic boundaries were altered. The genus now contains twe ...
''. Its habitat is riparian forest with large, old trees for nest sites near lakes, rivers, springs, and shoals that do not freeze in winter. Henry Seebohm named this bird after the English naturalist Thomas Blakiston, who collected the original specimen in Hakodate
is a Cities of Japan, city and seaports of Japan, port located in Oshima Subprefecture, Hokkaido, Japan. It is the capital city of Oshima Subprefecture. As of January 31, 2024, the city had an estimated population of 239,813 with 138,807 househol ...
on Hokkaidō
is the second-largest island of Japan and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by railway via the Seikan Tunnel.
The ...
, Japan in 1883.
Taxonomy
Blakiston's fish owl was formally described in 1884 by the English amateur ornithologist Henry Seebohm from a specimen collected near Hakodate
is a Cities of Japan, city and seaports of Japan, port located in Oshima Subprefecture, Hokkaido, Japan. It is the capital city of Oshima Subprefecture. As of January 31, 2024, the city had an estimated population of 239,813 with 138,807 househol ...
on the island of Hokkaido
is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...
in Japan. He placed the owl in the genus ''Bubo
A bubo (Greek βουβών, ''boubṓn'', 'groin') is adenitis or inflammation of the lymph nodes and is an example of reactive infectious lymphadenopathy.
Classification
Buboes are a symptom of bubonic plague and occur as painful swellings in ...
'' and coined the binomial name
In taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, altho ...
''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
The Eurasian eagle-owl (''Bubo bubo'') is a species of eagle-owl, a type of bird that resides in much of Eurasia. It is often just called the eagle-owl in Europe and Asia.
It is one of the largest species of owl. Females can grow to a total le ...
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''.[ However, the other fish owls are not believed by some authors to be divergent enough to support a separate genus either and so some authorities list fish owls as also included in the genus ''Bubo''.][
Given that it shares genetic material and osteological characteristics with the Eurasian eagle-owl, yet also seems to share some characteristics with the other three fish owls (especially the brown fish owl), the place of the Blakiston's fish owls in this evolutionary chain is ambiguous. Some authors have wondered whether the Blakiston's represents an intermediate step between traditional eagle-owls and the other fish owls, despite the current gap in distribution between Blakiston's and other fish owls.][ Whether other Asian eagle-owls with sideways slanting ear-tufts, namely the spot-bellied (''B. nipalensis''), the barred (''B. sumatranus''), and especially the somewhat superficially fish owl–like dusky eagle-owl (''B. coromandus'') are closely related to the fish owls and/or the Blakiston's is also unclear.][
Although a few authors also include them in ''Bubo'', the fishing owls of ]Africa
Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...
(generally classified in the genus ''Scotopelia'') seem to be fairly dissimilar. Based on external characteristics, osteology and preliminary genetic materials, the fishing owls are likely to have some convergently evolved characteristics to the fish owls and have no close relationship. Ultimately, given the lack of specific genetic studies for them, it is not clear how closely fishing owls are related to typical eagle-owls (to which fish owls are related).[
Recent genetic testing in Russia indicates a fairly large divergence from the ]genome
A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...
s of typical ''Bubo'' and suggests that they are indeed more closely aligned with other fish owls.[Spiridonova, L.N. & Surmach, S.G. (2018). ''Whole mitochondrial genome of Blakiston's fish owl ''Bubo'' (''Ketupa'') ''blakistoni'' suggests its redescription in the genus ''Ketupa''. ''Russian Journal of Genetics'', 54 (3): 369–373.]
Description
Blakiston's fish owl is the largest living species of owl.[ A pair field study of the species showed males weighing from , while the female, at up to , is about 25% larger.][ 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 gray owl
The great grey owl (''Strix nebulosa'') (also great gray owl in American English) is a true owl, and is the world's largest species of owl by length. It is distributed across the Northern Hemisphere, and it is the only species in the genus '' St ...
(''Strix nebulosa''), a species which has a significantly lower body mass.[ The ]Eurasian eagle-owl
The Eurasian eagle-owl (''Bubo bubo'') is a species of eagle-owl, a type of bird that resides in much of Eurasia. It is often just called the eagle-owl in Europe and Asia.
It is one of the largest species of owl. Females can grow to a total le ...
(''B. bubo'') is sometimes considered the largest overall living owl species. The three largest species of eagle-owl, all found in Siberia
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
and the Russian Far East
The Russian Far East ( rus, Дальний Восток России, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in North Asia. It is the easternmost part of Russia and the Asia, Asian continent, and is coextensive with the Far Easte ...
, are close in size to the Blakiston's fish owl. According to Heimo Mikkola, the very largest specimen of eagle-owl was longer in bill-to-tail length than the longest Blakiston's fish owl, while the top weight of the two species is exactly the same.[ The longest great gray owl was longer than the biggest Blakiston's fish owl but would be about 2.5 times lighter than the weight of the largest female Blakiston's.][ However, the average measurements of Blakiston's fish owl surpass the average measurements of the Eurasian eagle-owl in at least two of the major categories: weight and wingspan, making Blakiston's the overall largest species of owl.][ Even the large Siberian races of eagle-owl are slightly smaller on average than the Blakiston's, at least in terms of body mass and wing size.][ In the largest known body mass cited for a Eurasian eagle-owl population, the weights cited, for instance, were a mean for the males and a mean of for the females.][Mikkola, H. (1983). ''Owls of Europe''. T. & AD Poyser.] 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 .[ It is possible the largest specimens can attain a wingspan of approximately . 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
The great horned owl (''Bubo virginianus''), also known as the tiger owl (originally derived from early naturalists' description as the "winged tiger" or "tiger of the air") or the hoot owl, is a large owl native to the Americas. It is an extreme ...
(''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
The Russian Far East ( rus, Дальний Восток России, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in North Asia. It is the easternmost part of Russia and the Asia, Asian continent, and is coextensive with the Far Easte ...
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
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
, 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.[ The other two (''B. b. karafutonis'' and ''B. b. piscivorus'') were likely specimens of ''B. b. blakistoni'' & ''B. b. doerriesi'', respectively, and are presented here only for historical interest.][ The divergence of the Japanese birds of the nominate subspecies and the Russian subspecies was found to be extreme based on ]phylogeography
Phylogeography is the study of the historical processes that may be responsible for the past to present geographic distributions of genealogical lineages. This is accomplished by considering the geographic distribution of individuals in light of ge ...
, with a point of divergence of at least a half a million years.
*''K. b. blakistoni'' (Seebohm, 1884). Hokkaido
is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...
, N. Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
and Kuriles
The Kuril Islands or Kurile Islands are a volcanic archipelago administered as part of Sakhalin Oblast in the Russian Far East. The islands stretch approximately northeast from Hokkaido in Japan to Kamchatka Peninsula in Russia, separating the ...
. 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
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
south to Vladivostok
Vladivostok ( ; , ) is the largest city and the administrative center of Primorsky Krai and the capital of the Far Eastern Federal District of Russia. It is located around the Zolotoy Rog, Golden Horn Bay on the Sea of Japan, covering an area o ...
region and Korea
Korea is a peninsular region in East Asia consisting of the Korean Peninsula, Jeju Island, and smaller islands. Since the end of World War II in 1945, it has been politically Division of Korea, divided at or near the 38th parallel north, 3 ...
n 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
Sakhalin ( rus, Сахали́н, p=səxɐˈlʲin) is an island in Northeast Asia. Its north coast lies off the southeastern coast of Khabarovsk Krai in Russia, while its southern tip lies north of the Japanese island of Hokkaido. An islan ...
. 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
Manchuria is a historical region in northeast Asia encompassing the entirety of present-day northeast China and parts of the modern-day Russian Far East south of the Uda (Khabarovsk Krai), Uda River and the Tukuringra-Dzhagdy Ranges. The exact ...
. 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
An old-growth forest or primary forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Natio ...
near waterways
A waterway is any navigable body of water. Broad distinctions are useful to avoid ambiguity, and disambiguation will be of varying importance depending on the nuance of the equivalent word in other ways. A first distinction is necessary betw ...
including floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
s or wooded
A woodland () is, in the broad sense, land covered with woody plants (trees and shrubs), or in a narrow sense, synonymous with wood (or in the U.S., the '' plurale tantum'' woods), a low-density forest forming open habitats with plenty of sunli ...
coast
A coast (coastline, shoreline, seashore) is the land next to the sea or the line that forms the boundary between the land and the ocean or a lake. Coasts are influenced by the topography of the surrounding landscape and by aquatic erosion, su ...
lines. 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.[ Although found near the ]taiga
Taiga or tayga ( ; , ), also known as boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches. The taiga, or boreal forest, is the world's largest land biome. In North A ...
zone, nest trees are generally deciduous
In the fields of horticulture and botany, the term deciduous () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed Leaf, leaves, usually in the autumn; to the shedding of petals, aft ...
and the species resides in mixed forests.[ Blakiston's fish owls typically require stretches of productive ]river
A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...
s that remain at least partially unfrozen in winter. In the frigid northern winters, open water is found only where the current
Currents, Current or The Current may refer to:
Science and technology
* Current (fluid), the flow of a liquid or a gas
** Air current, a flow of air
** Ocean current, a current in the ocean
*** Rip current, a kind of water current
** Current (hydr ...
is sufficiently fast-flowing or there is an upwelling of warm spring water
A spring is a natural exit point at which groundwater emerges from an aquifer and flows across the ground surface as surface water. It is a component of the hydrosphere, as well as a part of the water cycle. Springs have long been important f ...
.[ Slower-moving ]stream
A stream is a continuous body of water, body of surface water Current (stream), flowing within the stream bed, bed and bank (geography), banks of a channel (geography), channel. Depending on its location or certain characteristics, a strea ...
s 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
A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...
, with common prey including pike (''Esox reichertii''), catfish
Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...
, trout
Trout (: trout) is a generic common name for numerous species of carnivorous freshwater ray-finned fishes belonging to the genera '' Oncorhynchus'', ''Salmo'' and ''Salvelinus'', all of which are members of the subfamily Salmoninae in the ...
and salmon
Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...
(''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.[ The main prey suspected to be sought out in freezing winter months in flowing and brackish waters at the northeastern limits of their range were ]sculpin
A sculpin is a type of fish that belongs to the superfamily Cottoidea in the order Perciformes.Kane, E. A. and T. E. Higham. (2012)Life in the flow lane: differences in pectoral fin morphology suggest transitions in station-holding demand acros ...
, lamprey
Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...
and salmon
Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...
, likely largely juveniles of the latter two types. In the basin of the Bikin River, the mean body mass of fish caught was estimated at .[Pukinskiy, Y. B. (1973). ''Ecology of Blakiston’s Fish Owl in the Bikin river basin''. Byull. Mosk. Obshch. Prir. Otd. Biol., 78, 40–47.] 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.[ ]Crayfish
Crayfish are freshwater crustaceans belonging to the infraorder Astacidea, which also contains lobsters. Taxonomically, they are members of the superfamilies Astacoidea and Parastacoidea. They breathe through feather-like gills. Some spe ...
(''Cambaroides'' ssp.) and other crustacean
Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
s are known to be taken in some numbers, but the extent of their importance in the Blakiston's fish owl's diet is unknown. There is some evidence of sexual dimorphism in prey selection with males favouring frogs and smaller fish, while females preyed on larger fish.[ ]Freshwater crab
Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight family (biology), families. They show direct development and maternal care of a small number of offspring, in contrast to marine c ...
s and secondarily frog
A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...
s seem to be numerical as important, or sometimes more significant, as a source of food as compared to fish for the three smaller fish owl species, other than frogs during spring thus far this has not proven to be the case with the Blakiston's fish owl. The only owl species to which fish are more significant to their diet is the fishing owls of Africa. Blakiston's fish owls seem to co-exist with Steller's sea eagle
Steller's sea eagle (''Haliaeetus pelagicus''), also known as the Pacific sea eagle or white-shouldered eagle, is a very large Diurnality, diurnal bird of prey in the family Accipitridae. It was described first by Peter Simon Pallas in 1811. No ...
s (''Haliaeetus pelagicus'') and white-tailed eagle
The white-tailed eagle (''Haliaeetus albicilla''), sometimes known as the 'sea eagle', is a large bird of prey, widely distributed across temperate Eurasia. Like all eagles, it is a member of the family Accipitridae (or accipitrids) which also ...
s (''H. albicilla'') on the coasts of the rocky Kuril Islands
The Kuril Islands or Kurile Islands are a volcanic archipelago administered as part of Sakhalin Oblast in the Russian Far East. The islands stretch approximately northeast from Hokkaido in Japan to Kamchatka Peninsula in Russia, separating the ...
but nothing is known how they relate with these larger fish-eating raptors, the presence of which has sometimes been theorized as partially the cause of the restricted range of the Blakiston's due to competition for similar food resources. However, in other raptor communities, diurnal raptors and owls can co-exist successfully given their distinct times of activity. Furthermore, Blakiston's fish owl generally dwells in forested areas while sea eagles are more likely to forage near more open wetland or coastal areas.[
A wide variety of ]mammal
A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...
ian prey are described from Japan and becomes most important to the diet during winter.[ Smaller mammals taken have included ]marten
A marten is a weasel-like mammal in the genus ''Martes'' within the subfamily Guloninae, in the family Mustelidae. They have bushy tails and large paws with partially retractile claws. The fur varies from yellowish to dark brown, depending on ...
s (''Martes'' ssp.) and numerous rodent
Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
s.[ Unidentified ]bat
Bats are flying mammals of the order Chiroptera (). With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most birds, flying with their very long spread-out ...
s have turned up occasionally in Blakiston's fish owl pellets in the Russian Far East, although bats were much more prominent in the diet of Eurasian eagle-owls there (79 eagle-owl pellets and 10 fish owl pellets had bat remains, respectively).[ Large mammals are sometimes taken by this species, including ]hare
Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores and live Solitary animal, solitarily or in pairs. They nest in slight depressions called forms, and their young are precociality, able to fend for themselves ...
s (''Lepus'' ssp.), rabbit
Rabbits are small mammals in the family Leporidae (which also includes the hares), which is in the order Lagomorpha (which also includes pikas). They are familiar throughout the world as a small herbivore, a prey animal, a domesticated ...
s, fox
Foxes are small-to-medium-sized omnivorous mammals belonging to several genera of the family Canidae. They have a flattened skull; upright, triangular ears; a pointed, slightly upturned snout; and a long, bushy tail ("brush").
Twelve species ...
, cat
The cat (''Felis catus''), also referred to as the domestic cat or house cat, is a small domesticated carnivorous mammal. It is the only domesticated species of the family Felidae. Advances in archaeology and genetics have shown that the ...
s (''Felis catus'') and small dogs (''Canis lupus familiaris'').[ Fewer records are known of bird predation, but they are known to capture avian prey such as hazel grouse (''Tetrastes bonasia'') and a variety of ]waterfowl
Anseriformes is an order of birds also known as waterfowl that comprises about 180 living species of birds in three families: Anhimidae (three species of screamers), Anseranatidae (the magpie goose), and Anatidae, the largest family, which i ...
species. A case where a black-crowned night heron
The black-crowned night heron (''Nycticorax nycticorax'') r black-capped night heron commonly shortened to just night heron in Eurasia, is a medium-sized heron found throughout a large part of the world, including parts of Europe, Asia, and Nort ...
(''Nycticorax nycticorax''), a rare species in Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
, was chased in flight by a male fish owl was observed but the heron managed to evade capture. A similar case of a fish owl chasing a grey heron
The grey heron (''Ardea cinerea'') is a long-legged wading bird of the heron family, Ardeidae, native throughout temperate Europe and Asia, and also parts of Africa. It is resident in much of its range, but some populations from the more norther ...
(''Ardea cinerea'') has also been reported.[
The two most common hunting methods for Blakiston's fish owl are wading through river shallows and perching on the river bank and waiting for movement in the water. Other waterside perches may include logs.][ In this behavior, an individual may wait for four hours until it detects prey and the species is perhaps most often witnessed while hunting in this method. Upon identifying prey, fish owls either drop directly into the shallow water or sail a short distance.] It also takes carrion, as evidenced by fish owls in Russia being trapped in snares set for furbearing mammals, which use raw meat as bait.[ While small prey such as frogs and crayfish are taken back to an habitual perch for immediate consumption, larger prey such as fish and waterfowl are dragged onto a bank and finished off before being flown off with.]
These owls are primarily active at dusk and dawn. During the brood-rearing season, these owls are relatively more likely to be seen actively hunting or brooding during the day. For an owl, it spends unusual amounts of time on the ground. Occasionally, an owl may even trample out a regular footpath along riverbanks it uses for hunting.[ Early reports of concentrations of as many as 5–6 owls near rapids and non-freezing springs are dubious, as these owls are highly territorial.][
]
Breeding
This bird does not breed every year due to fluctuations in food supply and conditions. Courting occurs in January or February. Laying of eggs begins as early as mid-March, when ground and trees are still covered with snow.[ These owls prefer nesting in hollow tree cavities in Japan][ and Russia.][ Mature forests with a mixture of coniferous and deciduous trees is usually the preferred nesting habitat.][ In Russia, trees selected for nesting can consist of ]elm
Elms are deciduous and semi-deciduous trees comprising the genus ''Ulmus'' in the family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical- montane regions of North America and Eurasia, ...
(''Ulmus'' ssp.), Japanese poplar (''Populus maximowiczii''), willow
Willows, also called sallows and osiers, of the genus ''Salix'', comprise around 350 species (plus numerous hybrids) of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions.
Most species are known ...
(''Salix'' ssp.), Mongolian oak (''Quercus mongolica''), ash (''Sorbus'' ssp.), and stone birch (''Betula ermanii''). Nest height range is , but normally is at least of the ground. Reports of nesting on fallen tree trunks and on the forest floor are very rare occurrences at best and possibly untrue. Other than nest cavities, there are very isolated records of nesting on cliff shelves and in old black kite
The black kite (''Milvus migrans'') is a medium-sized bird of prey in the family Accipitridae, which also includes many other diurnal raptors. It is thought to be the world's most abundant species of Accipitridae, although some populations have ...
(''Milvus migrans'') nests.[ Additionally, Blakiston's fish owl have now been recorded using temporarily abandoned nests of ]Steller's sea eagle
Steller's sea eagle (''Haliaeetus pelagicus''), also known as the Pacific sea eagle or white-shouldered eagle, is a very large Diurnality, diurnal bird of prey in the family Accipitridae. It was described first by Peter Simon Pallas in 1811. No ...
s.
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
Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...
and none in Japan: one involved a Eurasian lynx
The Eurasian lynx (''Lynx lynx'') is one of the four wikt:extant, extant species within the medium-sized wild Felidae, cat genus ''Lynx''. It is widely distributed from Northern Europe, Northern, Central Europe, Central and Eastern Europe to Cent ...
(''Lynx lynx'')[ and the other an ]Asian black bear
The Asian black bear (''Ursus thibetanus''), also known as the Asiatic black bear, moon bear and white-chested bear, is a medium-sized bear species native to Asia that is largely adapted to an arboreal lifestyle. It is distributed from southeast ...
(''Ursus thibetanus'').[
]
Status
Blakiston's fish owl is classified as an Endangered Species
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching, inv ...
by the IUCN
The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
. 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.[ Globally and included more recent detailed analysis from Russia, it is estimated that the population consists in total consists of about 1,000–1,500 individuals, or about 500–850 pairs. In the ]Primorye
Primorsky Krai, informally known as Primorye, is a federal subject (a krai) of Russia, part of the Far Eastern Federal District in the Russian Far East. The city of Vladivostok on the southern coast of the krai is its administrative center, an ...
, it is estimated that 200 to 400 individuals remain. During surveys in 2016-2019 on Kunashir Island
Kunashir Island (; ; ), possibly meaning ''Black Island'' or ''Grass Island'' in Ainu, is the southernmost island of the Kuril Islands. The island has been under Russian administration since the end of World War II, when Soviet forces took po ...
, 28 pairs of Blakiston's fish owls were registered. In Russia, fish owls are killed by fur-trappers, drown
Drowning is a type of suffocation induced by the submersion of the mouth and nose in a liquid. Submersion injury refers to both drowning and near-miss incidents. Most instances of fatal drowning occur alone or in situations where others presen ...
in nets set for salmon, and are shot by hunter
Hunting is the human practice of seeking, pursuing, capturing, and killing wildlife or feral animals. The most common reasons for humans to hunt are to obtain the animal's body for meat and useful animal products ( fur/ hide, bone/tusks, ...
s.[ In Japan, death by hunting is unlikely, but fish owls have been hit by cars and killed by power lines.][ Additionally, cases of exposure to ]lead
Lead () is a chemical element; it has Chemical symbol, symbol Pb (from Latin ) and atomic number 82. It is a Heavy metal (elements), heavy metal that is density, denser than most common materials. Lead is Mohs scale, soft and Ductility, malleabl ...
or lead poisoning
Lead poisoning, also known as plumbism and saturnism, is a type of metal poisoning caused by lead in the body. Symptoms may include abdominal pain, constipation, headaches, irritability, memory problems, infertility, numbness and paresthesia, t ...
, possibly from bioaccumulation
Bioaccumulation is the gradual accumulation of substances, such as pesticides or other chemicals, in an organism. Bioaccumulation occurs when an organism absorbs a substance faster than it can be lost or eliminated by catabolism and excretion. T ...
but also perhaps lead bullets in carrion
Carrion (), also known as a carcass, is the decaying flesh of dead animals.
Overview
Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...
, have been reported in these owls in at least Japan. Given their very small global population, ongoing deaths are unlikely to be sustainable.[ Local conservation efforts in Japan have been undertaken including education, installation of large nest-boxes and supplemental feeding.][ Biologists have found the presence of Blakiston's fish owls as good indicators of the health and disturbance level of a forest and of fish populations.][ An additional concern was a clear lack of ]genetic diversity
Genetic diversity is the total number of genetic characteristics in the genetic makeup of a species. It ranges widely, from the number of species to differences within species, and can be correlated to the span of survival for a species. It is d ...
found in Russia's fish owls upon the testing of their genome, with similar concerns expressed in Japan as well as evidence of inbreeding
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely genetic distance, related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genet ...
.[ 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.][Hayashi Y. (200(). ''The habitat maintenance is the most important, is it not? :conservation of the Blakiston's Fish Owl''. in ''Conservation of rare birds of Japan''. (Satoshi Yamagishi ed.) pp. 75–98, Kyoto University Pub., Kyoto.]
Importance to indigenous peoples
Blakiston's fish owl is revered by the Ainu peoples of Hokkaido, Japan, as a Kamuy
A ''kamuy'' (; ) is a spiritual or divine being in Ainu mythology, a term denoting a supernatural entity composed of or possessing spiritual energy.
The Ainu people have many myths about the ''kamuy'', passed down through oral traditions and r ...
(divine being) called Kotan koru Kamuy (God that Protects the Village). In Russia, the species is considered a food source by the Evens
The Evens /əˈvɛn/ ( Even: эвэн; pl. эвэсэл, ''evesel'' in Even and эвены, ''eveny'' in Russian; formerly called ''Lamuts'') are a people in Siberia and the Russian Far East. They live in regions of the Magadan Oblast and ...
people in northern Siberia
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
and the northern Russian Far East
The Russian Far East ( rus, Дальний Восток России, p=ˈdalʲnʲɪj vɐˈstok rɐˈsʲiɪ) is a region in North Asia. It is the easternmost part of Russia and the Asia, Asian continent, and is coextensive with the Far Easte ...
.[ In the past, fish owls were hunted as a favoured food source by the Udege peoples in ]Primorye
Primorsky Krai, informally known as Primorye, is a federal subject (a krai) of Russia, part of the Far Eastern Federal District in the Russian Far East. The city of Vladivostok on the southern coast of the krai is its administrative center, an ...
due to their high fat content,[ and their wings and tails were dried and used as fans to disperse biting insects while hunting;] however, the practice has locally fallen out of favour.[
]
Notes
References
External links
*
Images and videos of the Blakiston's fish owl ''(Ketupa blakistoni)''
at ARKive
ARKive was a global initiative with the mission of "promoting the conservation of the world's threatened species, through the power of wildlife imagery", which it did by locating and gathering films, photographs and audio recordings of the wor ...
"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
xeno-canto is a citizen science project and repository in which volunteers record, upload and annotate recordings of bird calls and sounds of orthoptera and bats. Since it began in 2005, it has collected over 575,000 sound recordings from more th ...
{{Taxonbar, from=Q1137288
Ketupa
Birds of Manchuria
Birds of North Asia
Birds of Japan
Natural monuments of Japan
Birds described in 1884
Taxa named by Henry Seebohm
Apex predators