- 動物学雑誌 (ISSN:00445118)
- vol.73, no.7, pp.189-195, 1964-07-15
The present paper deals with the distribution and breeding season of Smith's red-backed vole (Eothenomys smithi) in the subalpine forest zone (Tsuga diversiforia-Abies Mariesii forest zone, alt. 1,300-2,400m)on Mt. Yatsugatake in Honshu, Japan. By using snap traps, a survey was made every August in 1957, 1959, 1960 and 1961, and every month from April 1962 to March 1964. 1. In the subalpine forest zone, Anderson's red-backed vole (Clethrionomys adersoni) and the wood mouse (Apodemus argenteus) were the most abundant species. E. smithi is distributed widely in this area, but the population density was in general low, although in some localities it was high, as in areas with haevy undergrowth. E. smithi occurred with Clethrionomys andersoni and there was not observable habitat segregation between them. 2. The average tail length and hind foot length was 43.09mm and 16.32mm, respectively. 3. Pregnant females were found from May to October, and the maximum monthly pregnancy rate was attained in July. The yearly average number of embryoes was 2.3. Out of 32 females examined, 6(18.7%)had three pairs of mammae and 26 (81.3%) had two pairs of mammae. The monthly average testicle sizes increased quickly in spring and attained a maximum in June, after which their size was quickly reduced. 4. It is known that E. smithi occurs in forested regions on Honshu, Shikoku and Kyushu in Japan, but recently Imaizumi (1957) distinguished a new variety E. smithi occurring in the northern part of Honshu (including Mt. yatsugatake) from those in the southern part of Honshu, Shikoku and Kyushu, and he named the former E. kageus. He suggested that E. kageus has two pairs of mammae and that E. smithi has three pairs. The present results, however, show that the color, body measurements and habitat of E. kageus are very close to those of E. smithi, and further that the specimens having both types of mammae are found in the same area on Mt. yatsugatake. Thus the difference in the number of mammae betwwn E. kageus and E. smithi may be due only to individual variation.