Although Blakiston’s fish owl was formerly widespread throughout Hokkaido, it now occurs only in very restricted areas and has a population estimated at no more than 40 breeding pairs. The primary cause of population decline is thought to be the loss of suitable habitat and a reduction in the availability of their prey (fish). Since 1986, the government has supplied fish by means of artificially stocked ponds in some habitats under the conservation programs. I have been carrying out a long-term study of the life history of Blakiston’s fish owl since 1987, based on continuous observation of marked individuals of a single family.

Breeding attempts were observed in all the years between 1987 and 2011, but some of the clutches did not hatch in eleven out of 23 years. Clutch size was two (13 of 23 years) or one (10 of 23 years). Incubation was performed entirely by females for 34-42 days before hatching. Seventeen of 20 nestlings, hatched from 1989 to 2011 fledged successfully at 48-60 days of old. During the nestling period, fishes from the stocked fishery accounted for 90% of all prey mass parents brought to the chicks. Extremely high breeding attempt rates (100%) high fledging success (85.0%) must be supported with their stable and plentiful food supply by artificially feeding.

I also report the potential adverse effects on the owls of amateur photographers invasion to the vicinity of the nest.