How many bats in the belfry? Carrie Straight 05.03.01 During the day, many bats spend time together hanging in sheltered places called roosts. Bats use buildings, caves, trees, and other structures to hang out in. During the night, most bats hunt for insects or find some fruit to eat. The pipistrelle (Pipistrellus pipistrellus) of Europe is an insect eater and roosts in buildings. A lot of science is done by observation. It is difficult to find out information on a lot of animals because they are active only at night. So getting a good estimate of the number of individual bats is difficult. The easiest way to estimate how many bats there are, is to find out where the bats leave their roost and count them as they come whizzing out at night. Venables, a scientist, did just that. He was curious how many bats roosted in a church near his home. He visited the church once a week (except during the winter) in the evening and morning and counted the number of bats leaving and entering the roost for about 3 years. He also recorded the temperature and wind levels. The highest number of bats leaving the bell tower was 346. When it was windy, fewer bats came out. Venables, L.S.V. 1943. Observations at a pipstrelle bat roost. Journal of Animal Ecology 12(1): 19-26. ©2001 The Aurora Collection, Inc. All Rights Reserved. Site Development by: Interactive Multimedia. Inc.