Blakiston`s Eagle Owl

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. It is native to China, Japan, and the Russian Far East. This species is a part of the family known as typical owls (Strigidae), which contains most species of owl. Blakiston's fish owl and three other piscivorous owls are placed with some eagle-owls in the genus Ketupa. 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 on Hokkaidō, Japan in 1883.

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. Although found near the taiga zone, nest trees are generally deciduous and the species resides in mixed forests. 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.

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. 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, lamprey and salmon, 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 0.6 to 0.9 kg (1.3 to 2.0 lb). 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 (Cambaroides ssp.) and other crustaceans 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 crabs and secondarily frogs 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 eagles (Haliaeetus pelagicus) and white-tailed eagles (H. albicilla) on the coasts of the rocky Kuril Islands 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 mammalian prey are described from Japan and becomes most important to the diet during winter. Smaller mammals taken have included martens (Martes ssp.) and numerous rodents. Unidentified bats 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 hares (Lepus ssp.), rabbits, fox, cats (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 species. A case where a black-crowned night heron (Nycticorax nycticorax), a rare species in Japan, 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 (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 su…

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. 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, lamprey and salmon, 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 0.6 to 0.9 kg (1.3 to 2.0 lb). 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 (Cambaroides ssp.) and other crustaceans 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 crabs and secondarily frogs 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 eagles (Haliaeetus pelagicus) and white-tailed eagles (H. albicilla) on the coasts of the rocky Kuril Islands 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 mammalian prey are described from Japan and becomes most important to the diet during winter. Smaller mammals taken have included martens (Martes ssp.) and numerous rodents. Unidentified bats 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 hares (Lepus ssp.), rabbits, fox, cats (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 species. A case where a black-crowned night heron (Nycticorax nycticorax), a rare species in Japan, 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 (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 su…

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 (Ulmus ssp.), Japanese poplar (Populus maximowiczii), willow (Salix ssp.), Mongolian oak (Quercus mongolica), ash (Sorbus ssp.), and stone birch (Betula ermanii). Nest height range is 2–18 m (10–60 ft), but normally is at least 12 m (39 ft) off 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 (Milvus migrans) nests. Additionally, Blakiston's fish owl have now been recorded using temporarily abandoned nests of Steller's sea eagles. 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 6.2 cm (2.4 in) long and 4.9 cm (1.9 in) 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 1.96 kg (4.3 lb) in females and 1.85 kg (4.1 lb) 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).

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. 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 (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 genomes of typical Bubo and suggests that they are indeed more closely aligned with other fish owls. Blakiston's fish owl is the largest living species of owl. A pair field study of the species showed males weighing from 2.95 to 3.6 kg (6.5 to 7.9 lb), while the female, at up to 2.95 to 4.6 kg (6.5 to 10.1 lb), is about 25% larger. Around February, the average weight of Russian fish owls was 3.1 kg (6.8 lb) in seven males and 3.25 kg (7.2 lb) in five females, typically when their body mass at its lowest throughout the year. Blakiston's fish owl measures 60 to 72 cm (24 to 28 in) 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 Eurasian eagle-owl (B. bubo) is sometimes considered the largest overall living owl species. The three largest species of eagle-owl, all found in Siberia and the Russian Far East, are close in size to the Blakiston's fish owl. According to Heimo Mikkola, the very largest specimen of eagle-owl was 30 mm (1.2 in) 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 120 mm (4.7 in) 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 ave…

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. 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 (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 genomes of typical Bubo and suggests that they are indeed more closely aligned with other fish owls.