Age Composition of Summer Colonies in the Japanese House-dwelling Bat, Pipistrellus abramus

Abstract

Age structure of summer colonies in P. abrumus was studied by banding and counting dental annuli. Females less than two years of age constituted the majority of the members in the relatively large-sized A and B colonies investigated by the banding-recapture method, whereas aider females, and males more than one year of age decreased rapidly. A similar age composition was found in the large C population and the small D colony, whose age structures were determined by counting incremental lines in dentine. The disappearance rate during the period from weaning to one year of age was E-29% in females and 85-96% in males. The low ratio in females is probably attributable to their remaining in the nursery colony even after weaning, and to their tolerance for scanty food and severe weather. The female disappearance rate from one to three years of age was relatively low, while that from four to five years of age was very high. After the first year of life, male mortality appears to be always higher than the female one. That the oldest age determined for P. abrumus was five years in females and three years in males, suggests that P. abramus is a fairly short-lived species in vespertilionid bats