Abstract
The change in distribution of Blakiston's Fish Owls Ketupa blakistoni was investigated by using primarily obtained specimens from museums and supplemented with information from the literature and Ainu legends. Sixtynine of 104 specimens found in Japan (including discarded) contain some information about their collection sites. Here I present historical evidence for the occurrence of fish owls in even the southern-most part of Hokkaido in the 19th century. However, habitat loss caused a reduction of population size and the owls disappeared from the southern and northern parts of Hokkaido in 1950's and from the Ishikari plain in the early 1980's. Their distribution in Hokkaido is now restricted to the eastern part of the island. Between 1954 and 1995 the causes of death were known for 31 fish owls. All deaths were caused by humans. Drowning in the fish-stocked ponds was the main cause (36.8%) followed by traffic accidents (21.1%) and electrocution (13.2%). In order to conserve the owl species, population changes should be monitored continuously and their habitats should be preserved and restored.
