Blakiston's fish owl
| Blakiston's Fish Owl | |
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| At Kushiro Zoo, Japan | |
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| Genus: | Bubo (but see text)
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| Species: | B. blakistoni
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| Binomial name | |
| Bubo blakistoni Seebohm, 1884
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Blakiston's Fish Owl, Bubo blakistoni, is a fish owl, a sub-group of eagle owls who specialized in hunting riparian areas. 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 related species were previously placed in the genus Ketupa; mtDNA cytochrome b sequence data is equivocal on which genus name is applied for this species (Olsen et al. 2002). Its habitat is riparian forest, with large, old trees for nest-sites, near lakes, rivers, springs and shoals which don't freeze in winter.
Description
Blakiston's Fish Owl is possibly the largest species of owl at 60–71 cm (24–28 in long and weighing 2.7-4 kg (6-8.8 lb).[1] The wingspan is 150–205 cm (60–81 in). Superficially, this owl looks like the Eurasian Eagle-Owl, but is paler, and has broad, ragged ear tufts. The upperparts are buff-brown and heavily streaked. The underparts are pale buffish-brown. The throat is white. The iris is yellow (whereas the Eurasian Eagle-Owl has an orange iris). Vocalizations differ among the recognized subspecies. In the island subspecies, the male calls twice and the female responds with one note, whereas the mainland subspecies has a somewhat more elaborate, 4-note duet:"HOO-hoo, HOOO-hoooo" (here, the male call is in capital letters (HOO) and the female call in lower case (hoo)). This duet is so synchronized that those unfamiliar with the call often think it is only one bird calling. When an individual bird calls, it sounds like hoo-hooo. Juveniles have a characteristic shriek.
Subspecies
Of the following four subspecies described in the literature, only the first two (B. b. blakistoni & B. b. doerriesi) are accepted by science (Slaght and Surmach 2008). The other two (B. b. karafutonis and B. b. piscivorus) are now thought to be extinct and are present only for historical interest.
B. 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 buffy-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.
B. b. doerriesi (Seebohm, 1884). E. Siberia south to Vladivostok region and Korean border area. Larger than nominate with large white patch on top of the head; tail less marked and bars incomplete.
B. 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).
B. 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.
Feeding and Behavior
It feeds on a variety of aquatic prey. The main prey is fish, with common prey including pike, catfish, burbot, trout and salmon. Some fish these owls catch are quite large, weighing at least as much as the owl. In Russia, amphibians are taken in great quantity in spring, especially Dybowski's frog. 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. A wide variety of mammalian prey are described from Japan, including rodents and martens.[2] Fewer records are known of bird predation, but birds hunted are known to the size of hazel grouse (Slaght and Surmach 2008). 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 (Slaght and Surmach 2008).
These owls are primarily active at dusk and dawn. During the brood-rearing season, these owls are most often seen active during the day. For an owl, it spends unusual amounts of time on the ground. Early reports of concentrations of as many as 5-6 owls near rapids and non-freezing springs are dubious records, as these owls are highly territorial (Slaght and Surmach 2008).
Breeding and Status
This bird does not breed every year due to fluctuations in food supply and conditions. 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 (Takenaka 1998) and Russia (Slaght and Sumrach 2008). Reports of nesting on fallen tree trunks and on the forest floor are very rare occurrences at best, but possibly untrue. Other than nest cavities, there are very isolated records of nesting on cliff shelves and in old black kite nests (Takenaka 1998, Yamamoto 1999). Nest cavities have to be quite large in order to accommodate these birds. Clutch size is 1 to 3, usually 2 (Yamamoto 1999). In Russia, clutches are usually just one egg (Slaght and Surmach 2008). Eggs are 6.2 cm (2.5 in) long and 4.9 cm (1.9 in) wide. 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. Juveniles linger on their parents' territory for up to two years before dispersing to find their own territory. Once full-sized, these owls have few natural predators. There is one record of an adult fish owl being stalked and killed by a Eurasian lynx in Russia, while the owl hunted along a river bank (Yelsukov 2005, cited in Slaght and Surmach 2008).
The Blakiston's Fish Owl is endangered due to the widespread loss of riverine forest, increasing development along rivers and dam construction. The current population in Japan is approximately 100-150 birds (20 breeding pairs and unpaired individuals), whereas on mainland Asia the population is higher, variously estimated at several hundred or perhaps thousands of individuals (Slaght and Surmach 2008). In Russia, fish owls are killed by fur-trappers (see above), drown in nets set for salmon, and are shot by hunters (Slaght and Surmach 2008). In Japan, death by hunting is unlikely, but fish owls have been hit and killed by cars (Yanagawa 1993). Local conservation efforts in Japan have been undertaken including education and installation of large nest-boxes.
Henry Seebohm named this bird after the English naturalist Thomas Blakiston, who collected the original specimen in Hakodate on Hokkaidō, Japan in 1883.
Importance in Indigenous Cultures
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 currently considered a food source by the Evens people in northern Siberia and the northern Russian Far East.[3] Previously, fish owls were hunted as a food source by the Udege peoples in Primorye, but this practice has fallen out of favor in recent times (Slaght and Surmach 2008).
References
- Olsen, Jery; Wink, Michael; Sauer-Gürth, Heidi & Trost, Susan (2002): A new Ninox owl from Sumba, Indonesia. Emu 102(3): 223-231. doi:10.1071/MU02006 PDF fulltext
- Slaght, J.C. and S.G. Surmach. 2008. Biology and conservation of Blakiston’s fish owls in Russia: a review of the primary literature and assessment of the secondary literature. Journal of Raptor Research 42: 29-37. PDF fulltext
- "A Guide to the Owls of the World" by Claus Konig, Friedhelm Weick & Jan-Hendrik Becking. Yale University Press (1999), ISBN 0-300-07920-6.
- "Takenaka, T. 1998. Distribution, habitat environments, and reasons for reduction of the endangered Blakiston's fish owl in Hokkaido, Japan. Ph.D. dissertation, Hokkaido University, Sapporo, Japan."
- "Yanagawa, H. 1993. Causes of wild bird mortality in eastern Hokkaido. Strix 12:161-169"