In comparison with Pipistrellus pipistrellus, very little is known about the mating behaviour and hibernation of P. pygmaeus. The phenology of display and swarming behaviour were studied using bat detectors and mist nettings in the ruins of Nový Hrádek castle (southwestern Moravia, Czech Republic), where P. pipistrellus and P. pygmaeus hibernate in mixed-species clusters. We hypothesize that if both pipistrelle species share the same swarming site and hibernaculum they can compete with each other and their mating and courtship activity can be separate over time. The highest songflight activity was found between mid-August and mid-September. At the beginning of the mating period, songflights of both species were recorded in the second third of the night, whereas from the end of September, the peak of display activity moved to the first third of the night. We did not find clear evidence for temporal niche partitioning between species during autumn mating behaviour at locality of study. Proportion of P. pygmaeus observed in the hibernaculum was significantly higher than its observed in acoustic recordings and in mist-netted bats. It may show different mating behaviour between both pipistrelle species. Males of P. pipistrellus produced display calls close to hibernacula, whereas males of P. pygmaeus probably mate elsewhere, likely before any long autumnal migration near nursery colonies.