We radio-tracked 24 Myotis daubentonii and 35 Myotis nattereri during the swarming season to determine the catchment area of a swarming site and to study habitat preferences of the bats so that important foraging habitats within the catchment area could be identified. Sixty-one percent of individuals were relocated and 39 day roosts were found for 31 bats. Maximum range from the swarming site was 26.7 km for M. daubentonii and 24.8 km for M. nattereri. Minimum convex polygons depicting the minimum catchment area of the swarming site measured 254 km2 for M. daubentonii and 497 km2 for M. nattereri. Including recoveries of ringed bats increases the area enclosed by the maximum range to at least 4118 km2. Compositional analysis of habitat used in relation to that available suggested selection of mixed agricultural areas by M. nattereri. Broad-leaved woodland was preferred for foraging. Parkland, woodland and open-water habitats were common around roosts of M. daubentonii. Such habitats should be conserved and enhanced to protect these species. Some individuals of both sexes returned to the swarming site of capture, but none visited another swarming site. Bats may be faithful to only one site and may be inflexible should that site be destroyed. Because the catchment area of swarming sites is large, such sites are probably important centres of outbreeding. Protection of these mating sites should be a conservation priority, and key habitats should be protected over a large area around swarming sites.