Bird Research News

Vol.7 No.2

2010.2.18.

Blakiston’s Fish Owl

Shima-Fukuro (Jpn) Ketupa blakistoni

Morphology and classification
Classification: Strigiformes Strigidae
Total length:660-685mm (n=7) Tail length: 260-289mm (8)Wing length: 482-527mm (8)Tarsus length: 80.0-90.8mm (7)Culmen length: 33.1-38.0mm (9)Weight:♂ 3150-3450g (3) ♀ 3360-4600g (4)The measurements are after Yamamoto (1999).

Appearance:
Males and females are similar in plumage
coloration. They are ashy brown all over, 0with the white throat conspicuous whencalling. The face is slightly deeper ashy
brown. The chest, belly and flank are palegrayish brown. The flight feathers are darkbrown with nine beige lateral stripes. The
wing covert feathers are brown with wide
dark brown shaft-stripes and pale rustyred lateral stripes tinged with yellow. The
rectrices are brown with seven or eightcream horizontal bars.
Plumage coloration based on Yamamoto
Photo 1. Blakiston's(1999).
Fish Owl.

Vocalization:
Adult pairs frequently exchange calls. When males hoot "boh,boh", females call "boh" in response to the males. This bass duet
carries more than 1km. The young shriek "Bie-, bie-", when theybeg for food.

Distribution and Habitat
Distribution:
Blakiston's Fish Owls are distributed as a resident in the limitedareas of the Far East such as Magadan in Russia at 60ﾟN on thecoast of the Sea of Okhotsuk to the Ussuri River vally, southern
Sakhalin Island, northeastern China, Kunashirito and Shikotanto ofthe Kuril Islands, and Hokkaido,
northern Japan (Fig. 1). The world
population is estimated to be between
several hundred birds (Collar 2001)
and 800 birds (Slaght & Surmach2008).
Since
theirworldwide
extinction is concerned, they aredesignated as an Endangered Species
in the Red List of IUCN (IUCNFig. 1. Distribution ofSpecies Survival Commission 2008).
Blakiston's Fish Owls.

Habitat:Blakiston's Fish Owls feed on fish, uncommon diet for owls,
which restrict their range in the vicinity of a water system such asa river. They hunt primarily during the night in rivers, lakes,
marshes and occasionally on the sea shore. They roost in a broadleaved forest or a mixed forest of coniferous and broad-leaved
trees along a river during the daytime. Since the distribution islimited to a cold district, ice-free open water is extremely
important to their survival in winter.

Life history142

3 4 5 6
breeding season

78 9 10 11 12
non-breeding season

Breeding system:
Blakiston's Fish Owls are monogamous and they generally
maintain their pair-bond until they lose their parnter due mostly todeath. It is not uncommon for them to retain their pair-bond formore than ten years. They stay with their partner all year roundand they are assumed to hardly ever divorce, but Yamamoto(1999) reported a single case where a male territory owner wasreplaced by a male intruder following a battle.
In Hokkaido, they lay eggs from late February to mid-March,following copulation in early February in the coldest period ofwinter. Breeding duties are distinctly divided between the maleand female of a pair. The female takes full resopnsibility forbrooding the eggs and nestlings, while the male hunts and feeds
the female and nestlings. In the latter half of the nestling period,
however, the female also feed the young.

Nest:
Blakiston's Fish Owls generally nest in a cavity of broad-leavedtrees, but they need a large hollow of a tree with a diameter of 1m
because they are one of the largest owls of the world. In theTokachi region, south-central Hokkaido, they used Japaneselinden, Mongolian oaks and Katura trees (Cercidiphyllumjaponicum), while in the Nemuro region, eastern Hokkaido, theynested in Japanese Elm, Acer mono and Betula ermani (Yamamoto1999), and in the Shiretoko Peninsula, eastern Hokkaido Ulmus
lacinata was also used (Takenaka 1999). However, many
Blakiston's Fish Owls depend on nest boxes for breeding because
most broad-leaved trees large enough to nest have already beenfelled. They also nested in an old nest of Black Kites (Milvusmigrans) and on the ledge of a cliff (Yamamoto 1999).

Egg:
The clutch size is 1-2 eggs. The egg is laid at 2-5 day intervals.
The egg is white in color and 55.9-69.4mm by 49.0-52.8mm insize (n = 23) (Yamamoto 1999）.

Incubation and nestling periods and fledging rate:
The incubation period is 35-38 days. The eggs hatch from lateMarch to mid-April. In one of the study sites of the Tokachiregion, eggs were laid every year for 21 years
from 1989 to 2009, but they did not hatch for
10 years, which showed a low hatching rate.
Females continue to brood the nestlings forabout two weeks after hatching. The nestlings
usually fledge 48-60 days after hatching, but
Yamamoto (1999) reported a 69-day nestling
period. In one of the study sites of the Tokachiregion, the fledging rate of nestlings was 89%
from 1989 to 2009 (n = 18 birds). The young
usually fledge from mid-May to early June, but
Photo 2. Nestling
the parent birds continue to feed them untilof about 50
autumn or occasionally even towards thedays oldwinter.

Diet and foraging behavior
The diet of Blakiston’s Fish Owls consist principally of salmonid
fish, such as pink salmon (Oncorhynchus gorbuscha) and Japanesechar (Salvelinus leucomaenis) which go upstream in autumn anddolly varden trouts(Salvelinus malma) which spend their lifetimein a river (Takenaka 1999, Yamamoto 1999). Also they often
capture stone loach (Barbatula barbatula), sculpins (Cottuspollux) and lamprey (Lampetra reissneri). Food items of the mostimportance next to fish are amphibians such as frogs andsalamanders, followed by birds (ducks), small mammals (mice andshrews) and crustaceans (crawfish) or uncommonly beetles, whichshows the diversity of their prey.

Bird Research News

Vol.7 No.2

2010.2.18.

© Japan Bird Research Association
Sumiyoshi 1-29-9, Fuchu, Tokyo, Japan

Topics of ecology, behavior and conservation● Dispersal, homecoming and inbreeding
When Blakiston's Fish Owl juveniles are ready to support
themselves, they depart from their natal site for a new habitat in thefirst or second spring after fledging, but some female young return tothe natal site repeatedly. In the study site, for instance, a female
returned to the natal site every winter until she became five years ofage, even though she lived with her husband in their own territory,
which suggests that her parents remembered her for a long time.
Some single females return to the natal site and stay there for good.
For instance, a five-year-old daughter who happened to return to thenatal site immediately after her mother disappeared paired with herfather in the natal territory and continued to breed for 12 years(Hayashi 2009). This female bird committed another sin. She pairedwith her own grandson who returned to the natal site after her father
disappeared and raised young twice successfully (Hayashi 2009).
Moreover, brothers and sisters of different ages met and paired in thesite where they arrived after dispersal from their natal site, whichsuggests that it is not so uncommon for Blakiston’s Fish Owls toinbreed in Hokkaido.

● Decline and conservation of the population
Specimens and other data show that Blakiston's Fish Owls used to be
widely distributed in Hokkaido including Sapporo, Hakodate andObihiro (Hayashi 1999). They have been declining in number anddiminishing in range because they have lost their food and nesting
resources due to the modification of fluvial environment and timber
harvesting during the high economic growth period as well as theexploitation of run-up salmons for artificial hatching farms. Japanese
breeding population of Blakiston's Fish Owls is currently about 35pairs, which occur mainly in eastern Hokkaido. They are listed
among a "Critically Endangered" category as a species at anextremely high risk of extinction in the immediate future (WildlifeDivision, Nature Conservation Bureau of the Ministry of theEnvironment 2002).
Since 1984, the Ministry of the Environment has conducted theconservation program of Blakiston's Fish Owls which includes thethree projects of 1) breeding pair support by creating feeding ponds,2) the installation of nest boxes and 3) the banding of fledglings forindividual identification to allow long-term monitoring of thepopulation. These time- and labor-consuming efforts have steadily
produced results. Over 200 nest boxes have been installed, and thebreeding sites of the Nemuro and Tokachi regions have become asupply source of young as a result of the feeding project started at an
early period. A high fledging rate of nestlings is supported by safe
nest boxes and artificial feeding. In a breeding site of the Tokachiregion, for example, a pair delivered food to a nestling 470 times intotal until it fledged, and provisioned fish represented about 50% of
the delivery frequency and more than 90% of the food weight (Fig.
2). Wild fish occur
frog stone loach
Rana pirica 0.5%
othersquite sparsely in theunknown
5.1%
breeding
grounds
where Blakiston's Fish
Fishlamprey
artificially fed
Owls depend heavily
17.7%
47.0%
on artificial feeding stone loach
Fish artificially fed(Takenaka 1999), and 7.7% frog
94.4%
Rana pirica
therefore they can
16.6%
hardlyproduceFeeding frequency (470 times)
Feeding quantity (50.3 kg)
offspringwithout
artificial feeding.
Fig. 2. Food items of a nestling.

● Conservation issues
While stop-gap measures such as artificial feeding and nest box
installation have taken effect, the habitat conservation has always

バードリサーチ生態図鑑
lagged behind. The high frequency of inbreeding due to the shortageof suitable breeding habitats would have been caused by theinsufficient food resource in the surrounding areas except for thepresent breeding sites. In national forests embracing most of
Blakiston's Fish Owl breeding grounds, efforts have been started torestore their nesting habitat of broad-leaved and coniferous mixed
forests by reserving broad-leaved trees (Hayashi 2009a). However,
the targeted habitats comprise no more than an extremely small
portion of their range. More efforts should be put into the habitat
restoration of "Kotankoro-kamui" (Ainu name of Blakiston's FishOwl) which used to be an icon of primeval forests of Hokkaido forthe native Ainu people.
The fatality of young birds due to accidents in human environments
also keeps a curb on the population increase and range expansion(Hayashi 1999, Saito 2002). In addition to measures to prevent theirroad accidents and electrocution on power lines, the restoration of
riparian forests to help secure their dispersal from the natal site
contributes to reducing their accidental deaths. It is also instrumental
in the range expansion to release birds that have recovered frominjuries into a habitat with a single bird or a former range (Hayashi
2009 b). The reintroduction of Blakiston's Fish Owls requires a longterm strategy including the use of captive-raised birds in a zoo.
Along with habitat restoration, the reintroduction of captive birds tothe wild would be urgently needed for the conservation ofBlakiston's Fish Owls.

Literature
Collar N.J. (ed.). 2001. Threatened birds of Asia: the BirdLife International red
data book. BirdLife International, Cambridge, U.K.
Hayashi Y. 1999. Past and present distribution of Blakiston's Fish Owl (Ketupablakistoni) in Hokkaido, Japan - Based upon museum specimens. J. Yamashina
Inst. Ornithol. 31:45-61. [J+E]
Hayashi Y. 2009. Close inbreeding in Blakiston’s Fish-owls (Ketupa blakistoni). J.
Raptor Res. 43:145-148.
Hayashi Y. 2009a. The habitat maintenance is the most important, is it
not? :conservation of the Blakiston's Fish Owl. "Conservation of rare birds ofJapan." (Satoshi Yamagishi ed.) Pp.75-98, Kyoto University Pub., Kyoto. [J]Hayashi Y. 2009b. Translocation of a Blakiston's Fish Owl in northern Hokkaido.
Japanese Journal of Conservation Ecology 14:249-261. [J+E]
IUCN Species Survival Commission. 2008. The IUCN Red List of Threatened
Species 2008. http://www.iucnredlist.org
Wildlife Division of Nature Conservation Bureau, The Ministry of theEnvironment. 2002. Revised edition Red List of Threatened Birds of Japan 2.
Birds. Japan Wildlife Research Center, Tokyo. [J]Saito K. 2002. Traffic accident of the Blakiston's Fish Owl (Ketupa blakistoni) - anexamination of wildlife medicine -. The 1st Wildlife and Traffic Research
Symposium: 27-30. [J]Slaght J.C. & Surmach S.G. 2008. Biology and conservation of Blakiston’s FishOwls (Ketupa blakistoni) in Russia: a review of the primary literature and anassessment of the secondary literature. J. Raptor Res. 42:29-37.
Takenaka K. 1999. The Blakiston's Fish Owl. "Shiretoko Library (1) Birds inShiretoko". (Shari Town Shiretoko museum, ed.) Pp.78-125, Hokkaido
Shimbunsha, Sapporo. [J]Yamamoto S. 1999. The Blakiston's Fish Owl. Hokkaido Shimbunsha, Sapporo. [J]Languages of literature cited other than English: [J] in Japanese, [J+E] in Japanesewith English summary.

AuthorYuko HAYASHI Law Department of Sapporo University
I spent one and a half years in New Zealand
far away from Hokkaido, northern Japan, but
my affection for Blakiston's Fish Owls wasso strong that I could not help coming home
to see them as many as three times whilestaying there. I feel my happiness incontinuing to serve them in my love without
reward.
hayashiy@sapporo-u.ac.jp

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