Thomas J. O'Shea 1980 The tiny (3.1–3.8 g) vespcrtilionid bat <i>Pipistrellus nanus</i> was studied in Kenya palm-thatched roofs from May 1973 to July 1974. Roosting social organization and related activities and behavior are described. ♂♂ held diurnal roosting territories where ♀♀ gathered in small and compositionally labile groups, attracted to the most vocal ♂♂. Annual variation in population-wide aspects of social organization follows predictable seasonal changes in climate and predator abundance. Variability between individuals follows a common mammalian pattern: high male competition for ♀, variance in presumed male reproductive success, and a mating system resembling one based on resource defense polygyny. Social organization in this population contrasts with that known from studies of other <i>P. nanus</i> populations. application/pdf 10.1111/j.1439-0310.1980.tb01048.x en Blackwell Wissenschafts-Verlag Roosting, social organization and the annual cycle in a Kenya population of the bat <i>Pipistrellus nanus</i> article