The Blakiston's fish owl is endangered, and is perhaps the largest owl in the world. There are thought to be less than 1000 pairs of these birds remaining in the wild, with very few individuals held in captivity. Found only in northeast Asia, this secretive species has a fragmented distribution in the remote forests of northern Japan, the Russian Far East, and northeastern China. In Russia this aquatic prey specialist manages to persist year-round in a climate frozen for months on end. Critical issues for its conservation include management of riparian habitat outside protected areas and education of local populations about the species.
Population and Distribution:
Blakiston's fish owls have a fragmented distribution in the Russian Far East, northern Japan, and northeastern China. There are two generally-recognized subspecies, an island subspecies, which occurs on Hokkaido Island, Japan, and Kunashir and Shikotan Islands of the southern Kuril Islands, Russia, and a more broadly-distributed mainland subspecies, which ranges across Russia from Magadan in the north to Primorye in the south. The species may occur in North Korea, but political tensions have prevented recent survey attempts there.
Surveys suggest that the fish owl population in the southern Russian Far East (encompassing all of Primorsky Krai and Khabarovsky Krai south from the Amur River) is approximately 100-130 pairs. With extrapolation to the entire fish owl range, the population could be more than 800 pairs. Recent surveys estimate one pair of Blakiston's fish owls every 3.8 river km along the Samarga River in northern Primorye, possibly the highest natural concentration of this species globally. Concentrations of breeding pairs in suitable habitat are generally described as one pair every 6-12 river km.
Blakiston's fish owls can form pair bonds as early as their second year, and reach sexual maturity by age 3. Pairs do not breed every year. Courtship occurs from January-February, with a clutch of one or two eggs laid in March. Young fledge up to 50 days post-hatching. Data on breeding success are scant: on Kunashir Island during a 6-year period breeding success was 24%; with six fledglings resulting from 25 eggs. Juveniles remain on their natal territory into their second year, apparently dispersing as late as July the following year.
A fish owl chick and egg. Photo by Jon Slaght.
Blakiston's fish owls require cavernous old-growth tree cavities in riparian habitat for suitable nest sites and stretches of productive rivers that remain at least partially unfrozen in winter.
The fish owl prey base is quite diverse, but even in winter, small fish are a primary target. In addition to fish, Blakiston's fish owls also prey on a variety of waterfowl species, small mammals, and amphibians. Reliance on certain prey species is seasonal: for example, in spring, frogs are particularly important and taken in great abundance.
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Two cases of predation (one by an Asiatic black bear, the other by a Eurasian lynx) are the only known sources of Blakiston’s fish owl mortality not directly tied to human activity. Unlike Amur tigers, which are poached for commercial gain, most fish owls die needlessly when they become entangled and drown in fishing nets, are captured in hunters’ snares, or are simply shot for sport. Additionally, given their high fat content (particularly in the months leading up to winter), Blakiston’s fish owls were once prized as a food source by the indigenous Udege peoples, but this practice seems to be less common now.
Habitat loss due to logging in old-growth riverine forest (much of it illegal) is a significant threat. Although a resident pair of Blakiston’s fish owls seems to occupy no more than 10 km2 as a home range, fish owls have very specific habitat requirements. Most known Blakiston’s fish owl nests have been found in natural tree cavities, and many fish owl territories have only a handful of such old-growth trees large enough to support a nest. If these few trees are removed, the owls will not breed. Furthermore, fish owls need productive stretches of river that remains unfrozen throughout the year to provide hunting habitat – not a simple requirement given the Russian Far East’s harsh winter climate. Thus, Blakiston’s fish owls are often tied to stretches of river where warm upflowings keep waters unfrozen in winter.
Blakiston’s fish owls have been recorded in several of Primorsky Krai’s protected areas, but nearly all known nest territories (>95%) fall outside the borders of existing protected areas. Therefore, management of habitat outside protected areas is critical for Blakiston’s fish owl conservation, and any such plans must include the land-use needs of local communities. Education of local populations about the species will also greatly aid Blakiston’s fish owl conservation, as most causes of mortality are human-related and easily avoided.