Preliminary Estimation of Population Density of the Siberian Flying Squirrel (Pteromys Volans Orii) in Natural Forest of Hokkaido, Japan

Abstract

The Siberian flying squirrel Pteromys volans is widely distributed from northern Finland east to Chukotka of Russia; south to the eastern Baltic shore and across the southern Ural Mountains and Altai Mountains of Russia to Mongolia, northern China, Korea, Sakhalin Island of Russia, and Hokkaido Island of Japan (Nowak 1991; Wilson and Reeder 2005). This squirrel is arboreal and inhabits the boreal evergreen forests of the Eurasian Continent (e.g., Nowak 1991). It nests in tree cavities (Yanagawa 1999; Yanagawa and Muraki 2006; Asari and Yanagawa 2008; Asari et al. 2009; Nakama and Yanagawa 2009). Pteromys volans orii, a subspecies endemic to Hokkaido Island, Japan, is common from lowlands to mountainous areas (Kuroda 1921; Ishii 2005; Oshida 2009). Ecological characteristics of this subspecies in fragmented forests, small forests, and windbreak forests in urban or agricultural areas are already reported (Yamaguchi and Yanagawa 1995; Yanagawa 1999; Asari et al. 2008, 2009; Tojo and Yanagawa 2008). We, however, doubt these characteristics are original. They may have been influenced by human activities in these semi-artificial environments. To understand the original ecological characteristics of P. volans orii, we need to investigate this subspecies in its original habitats, such as the natural and mountainous forests in Hokkaido. There are only a few reports on the ecological characteristics of P. volans orii in mountainous natural forests (Nakano et al. 1991; Masuda 2003). The vegetation of Hokkaido’s natural forests mainly consists of Abies sachalinensis, Picea jezoensis, Quercus mongolica, Betula spp., and Tilia japonica (Tatewaki 1958; Horikawa 1972; Okitsu 2002). This is quite different from forests of northern Eurasia where P. volans occurs. Of these tree species, Abies sachalinensis is confined to Hokkaido Island, southern parts of Sakhalin Island, and the Kuril Islands (Satake 1989), but is most abundant in Hokkaido’s natural forests. We expected to find an ecological association between P. volans orii and A. sachalinensis. As a first step understanding the ecological characteristics of P. volans orii, we selected a large A. sachalinensis-dominated mixed forest for preliminary examination of the population density of this subspecies by capture-mark-recapture methods using wooden nest boxes. Nest boxes are often used in ecological studies of flying squirrels in the Holarctic region (e.g., Raymond and Layne 1988; Layne and Raymond 1994; Hanski et al. 2000; Taulman and Smith 2004). Because the animals are not strongly attracted by bait, nest boxes are more suitable for estimating the population density of those arboreal small mammals (Fokidis and Risch 2005). Here, we discuss preliminary population density estimates for P. volans orii in the natural forest of Hokkaido.