(Uploaded by Plazi for the Bat Literature Project) Although it is conjectured that diurnal capture may reduce the colony size of bats, little evidence is available. We monitored a maternity colony of cave-dwelling bats (Hipposideros armiger) both before and after casual diurnal disturbance and capture. Results from more than 40 days of monitoring after disturbance suggested that diurnal capture significantly reduced the colony size from more than 90 individuals to a few. Moreover, the trend for colony size after disturbance indicated that most bats may not return to the roost for the whole season. This study has implications for both bat researchers and wildlife managers.