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Bubo blakistoniBlakiston's eagle-owl

By Erik Oien

Geographic Range

Blakiston's fish owls occur only in select areas of northeast Asia. The enigmatic birds are found in eastern Siberia, northern China, North Korea, and northern Japan. (Dinerstein, et al., 1994; Konig and Weick, 1999)

Habitat

Blakiston's fish owls require year-round open water to feed. They also need large trees for nesting cavities, and therefore are often found in riparian forests. Most of the surrounding woodlands are coniferous spruce and firs, or mixed deciduous forests with maple, ash and elm. (Hayashi, 1997; Konig and Weick, 1999; Slaght and Surmach, 2008)

Physical Description

Bubo blakistonii looks much like brown fish owls (Bubo zeylonensis) of Asia. It is also one of the largest owl species in the world. Blakiston's fish owls have partially flattened feathers surrounding their faces (a feature of all owls) also known as 'facial disks' that give them a flat-faced appearance. They also have large, full-feathered ear tufts. Facial plumage is tan with black stripes and the brow of the eye has a thin row of white feathers. The wings and tail are a dark brown with yellowish stripes and the underside plumage is light brown with thin vertical black stripes.

The bill is long and curved and color ranges from grayish-blue to brown. The large claws are black and the tarsis are feathered in front. The iris is yellow. Bubo blakistoni is a large owl with a length of 60 to 71 cm and a wingspan of up to 2 m. Its weight ranges from 2.7 to 4 kg, and the males are smaller than the females. (Burton, 1973; Konig and Weick, 1999; Slaght and Surmach, 2008; Slaght, 2009)

  • Sexual Dimorphism
  • female larger
  • Range mass
    2.7 to 4 kg
    5.95 to 8.81 lb
  • Range length
    60 to 71 cm
    23.62 to 27.95 in
  • Range wingspan
    2 (high) m
    6.56 (high) ft

Reproduction

Blakiston's fish owls tend to stay in pairs throughout the year. Male and female tend to be monogamous for many years. (Slaght, 2009)

Blakiston's fish owls do not breed every year; every two or three years is more typical. The young reach full size in 6 weeks and take up to 7 weeks to fledge. Fledgers still may remain in the area for up to a year and a half before they go off on their own. Once independent, the fish owl reaches sexual maturity at three years of age.

Blakiston's fish owls may select nest sites high up (2 to 18 m) in old-growth trees but have also been seen nesting on fallen trees on the forest floor. Laying begins in early spring and the pair typically has one to two eggs per two year interval. It takes about 35 days for eggs to hatch. (Burton, 1973; Konig and Weick, 1999; Slaght, 2009)

  • Breeding interval
    On average, Blakiston's fish owls breed once every two years.
  • Breeding season
    Blakiston's fish owls breed from early spring to summer.
  • Range eggs per season
    1 to 3
  • Average time to hatching
    35 days
  • Average fledging age
    50 weeks
  • Average time to independence
    1.5 years
  • Range age at sexual or reproductive maturity (female)
    2 to 3 years
  • Range age at sexual or reproductive maturity (male)
    2 to 3 years

In Blakiston's fish owls, females perform egg incubation while males hunt for food. After the chicks have hatched, the female begins to join the male in night foraging. Investment in the young is high for this species; parents care for offspring up to two months and even share territories with valuable river access with them for up to a year after they are independent. Harsh conditions of the habitat may be cause for such high attention to young. (Konig and Weick, 1999; Slaght and Surmach, 2008; Slaght, 2009)

  • Parental Investment
  • altricial
  • male parental care
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female
    • protecting
      • male
      • female
  • post-independence association with parents

Lifespan/Longevity

No numbers were found in the literature, however, lifespan is thought to be similar to other fish owls found in the wild in Asia, approximately eight to fifteen years. (Konig and Weick, 1999)

Behavior

Blakiston's fish owls are excellent hunters of the fish in rivers and lakes. With extraordinary vision they primarily hunt at dusk and night, but it is not uncommon for them to hunt in the day as well. Sometimes they swoop down from a tree along the bank to snatch fish if the water is not iced over. Blakiston's fish owls are known to spend a good deal of time on the ground, and during winter, tread over snow to hunt ice pockets. Some birds have even been observed wading in shallow water to catch crayfish and amphibians. (Burton, 1973; Slaght and Surmach, 2008)

  • Average territory size
    2.6 km^2

Home Range

While research is being conducted to better understand the range distribution of this species, observation has shown that a pair of fish owls usually only occupies an area of about 2.6 square kilometers, so long as there is access to water. Due to harsh winter conditions, Blakiston's fish owls may seasonally relocate for a more suitable hunting environment. (Slaght and Surmach, 2008)

Communication and Perception

Calls by adults are identified by a ‘boo-boo uoo’ or ‘foo-foroo’. Adults perform duets, where males and females call in quick succession. The pattern changes across populations but for those on the mainland, males contribute the first and third notes and females contribute the second and fourth. Occasionally the order is reversed with the female initiating the duet, but this occurs only when the pair is agitated.

Like all owls, Blakiston's fish owls rely heavily on visual and auditory stimuli, and feature unique physical adaptations. The facial disk feather arrangement serves to gather sounds and increase accuracy when detecting prey movement. Large, immobile eyes allow the owls to capture enough light to hunt prey at night. (Konig and Weick, 1999; Slaght and Surmach, 2008)

  • Other Communication Modes
  • duets

Food Habits

Bubo blakistonii mainly feeds on fish, and depends on open water or holes in the ice where it may fly down and make use of its powerful claws. It also hunts on the ground and in shallow water for crayfish and frogs. Mammals and waterfowl may occasionally be consumed in icy winters when water has frozen completely. (Burton, 1973; Konig and Weick, 1999; Slaght and Surmach, 2008)

  • Animal Foods
  • birds
  • mammals
  • amphibians
  • fish
  • aquatic crustaceans

Predation

No known predators were found in the literature.

Ecosystem Roles

Blakiston's fish owls impact the populations of fish, small vertebrate, and other organisms they feed on.

Economic Importance for Humans: Positive

The regions where Blakiston's fish owls are found are largely unpopulated by humans and there are no direct links reported between this species and humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Blakiston's fish owls on humans.

Conservation Status

IUCN Red List recognizes this species as a rare and endangered bird. Despite not living among humans, this species occurs in timber rich areas that are valued for their natural resources, primarily in Japan and Russia. As such, habitat destruction by the logging industry is a concern for this species. Poachers have been known to kill Blakiston's fish owls. With an estimated 5,000 individuals remaining in the wild, saving every bit of forest and enforcing species management is of dire importance. (Hayashi, 1997; Konig and Weick, 1999; Slaght, 2009)

Contributors

Erik Oien (author), Florida State University, Emily DuVal (editor), Florida State University.

Glossary

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

duets

to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

piscivore

an animal that mainly eats fish

riparian

Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

References

Burton, P. 1973. Owls of the World: Their evolution, structure and ecology. New York: Dutton&Co.

Dinerstein, E. K. O. W. 1994. An Emergency Plan to Rescue Russia's Biological Diversity. Conservation Biology, Vol. 8 no. 4: 934-939.

Hayashi, Y. 1997. Home range, habitat use and natural dispersal of Blakiston fish owl. Raptor Research, Vol. 31: 283-285.

Konig, C., B. Weick. 1999. A Guide to the Owls of the World.. New Haven: Yale University Press.

Slaght, J. 2009. Chasing a Giant. Wildlife Conservation, March/April: 10-15.

Slaght, J., S. Surmach. 2008. Biology and Conservation of Blakiston's fish owls. Raptor Research, Vol. 40: 29-37.

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