Prey taken by Long-eared Owl Asio otus in the breeding season in Hokkaido

Abstract

Long-eared Owl pellets were collected and analyzed during the breeding season of 1973 in the shelterbelts at Ishikari plain, Hokkaido. The shelterbelts consist of natural broad-leaved wood (Ulmus davidiana, Fraxinus mandshurica, Alnus japonica etc.) and planted trees (Populus nigra and Robinia Pseudo-acacia). The bush layer is thin but sasa-grass covers the ground densely.The prey taken were five species of Rodentia, one species of Insectivora and small sized birds. The main food of the owl was the Red-backed Vole Clethrionomys rufocanus, which was the most abundant species of small rodents in the shelterbelt (Table 1). The proportions of prey which appeared in the pellets roughly reflect the abundance of mammalian prey species which live in the shelterbelt and it seems that the owl was opportunistic concerning its predatory behavior. The average number of prey items per pellet was 2.6.The monthly age composition of Red-backed Voles which appeared in the pellets was similar to that of voles captured by snaptraps in a shelterbelt (Table 2. Fig. 2).