From 2001 to 2003 we radio tracked 23 Pipistrellus pipistrellus and 23 Pipistrellus pygmaeus to investigate whether there are any differences in foraging behaviour between the two cryptic species during the summer, and to consider whether any differences between these species are important for their conservation planning. There were significant differences between the two species in relation to flying time, mean maximum distances travelled from the roost, numbers of foraging bouts made and span of home ranges. The results suggest that P. pipistrellus makes more flights to a greater number of foraging locations (and possibly) feeding habitats than P. pygmaeus, although these foraging areas are likely to be closer to the roosts. This behaviour is particularly marked during lactation. In contrast, P. pygmaeus spends less time flying, makes fewer foraging bouts but travels further distances, suggesting that this species is selecting specific foraging habitats. These differences in foraging behaviour support the hypothesis that these species occupy different ecological niches, and conservation planners should be aware of these differences when considering the requirements of pipistrelles in the UK.