Nathusius' pipistrelle bats (Pipistrellus nathusii, Keyserling & Blasius 1839) breeding in Ireland

We describe the most westerly known maternity colony of Nathusius' pipistrelle bats (Pipistrellus nathusii). The bats were identified by using morphometric measurements and analysis of time-expanded echolocation and social calls. The roost, containing approximately 150 individuals, was located in a mid 19th century farm stable block and store house situated in parkland in County Antrim, Northern Ireland. The roost was visited on 30 April, 1 May and 22 June 1997. Over this period, 11 bats were caught: one adult male, five pregnant females, four lactating females and a juvenile male. Direct observation of behaviour patterns suggests that mating groups of P. nathusii may occur in Ireland as late as May. The migratory nature of this species is discussed.