The mating system of European bats is often reported as ‘resource-defence polygyny’ where the resource is a male roost and its adjacent territory. With a large amount of field data we tested predictions of that model on the spatial dispersal of males in a resident population of a migratory species, Pipistrellus nathusii, well known for its complex vocal advertising by males during the mating season. The study was conducted in southern Bohemia throughout nine seasons (1999–2007) and revealed that (i) pronounced aggregations of male roosts and vocalization sites were affected by the vicinity of the breeding colony, and (ii) dyadic or triadic aggregations were observed in 65% of resident males that shared a common vocalization site. Dyadic or triadic groups were often quite stable over time (for up to seven successive years). No direct agonistic behaviour was observed between group members in contrast to regularly observed synchronization in their activity patterns and advertisement vocalizations. The busy vocalization sites were also visited by alien males that also produced advertisement vocalization and by non-vocalizing males that may have acted as sneaks. All these phenomena suggest considerable diversity in male strategies, suggesting that the mating system does not correspond entirely to ‘resource-defence polygyny’ nor can it be regarded as a lek mating system to which it corresponds in other characteristics (e.g., aggregations of males and the essential role of female choice). We expect that the broad diversity in mating tactics that characterises the species under study may also reveal features relevant to the mating systems of other temperate bats.