Abstract
I conducted bat-capture surveys for seven consecutive years (2004 - 2010) in a forest located in the south of Sapporo, Hokkaido. A total of 285 bats of six species, including Murina ussuriensis and Myotis ikonnikovi, were captured in 194 capture nights. Distinct sexual size dimorphism was observed in the body mass and forearm length of M. ussuriensis ; females were larger than males. Distinct sexual size dimorphism was also observed in the body mass of M. ikonnikovi ; however, the direction was opposite: males were larger than females. The body mass of female M. ussuriensis showed noticeable seasonal changes. It indicated that at the study site the parturition and nursing young occurred during July and that the young of the year began flying at the beginning of August. It also suggested the possibility that mother bats remarkably reduce body mass during the latter part of nursing period.
