A wide variety of mammalian prey are described from Japan and becomes most important to the diet during winter. Smaller mammals taken have included martens ("Martes" ssp.) and numerous rodents. Unidentified bats have turned up occasionally in Blakiston's fish owl pellets in the Russian Far East, although bats were much more prominent in the diet of Eurasian eagle-owls there (79 eagle-owl pellets and 10 fish owl pellets had bat remains, respectively). Large mammals are sometimes taken by this species, including hares ("Lepus" ssp.), rabbits, fox, cats ("Felis catus") and small dogs ("Canis lupus familiaris"). Fewer records are known of bird predation, but they are known to capture avian prey such as hazel grouse ("Tetrastes bonasia") and a variety of waterfowl species. A case where a black-crowned night heron ("Nycticorax nycticorax"), a rare species in Japan, was chased in flight by a male fish owl was observed but the heron managed to evade capture. A similar case of a fish owl chasing a grey heron ("Ardea cinerea") has also been reported.