Roost switching and activity pattern of the soprano pipistrellePipistrellus pygmaeus revealed by radio-tracking

Our data show that it is extremely difficult to determine the actual size of a P. pygmaeus colony in central Europe because females use more than one roost simultaneously. By contrast, numerous pipistrelle colonies in England do not switch roosts for most of the reproductive season (e.g. Davidson-Watts & Jones 2006). This fact is very important especially in view of long-term monitoring programmes in which the size of maternal colonies is considered a basic index of population dynamics. After lactation began, some females visited roosts occupied by vocalizing male P. pygmaeus and in one case simultaneously with male P. nathusii. Four lactating females visited sites where we recorded songflight calls of P. pygmaeus. We concluded that they might have been uttered by a male flying along the same flight route (Barlow & Jones 1997) although male advertisement calls were registered later, after weaning the young. Lactating females must be able to invest some of their stored energy in visits to male territories even during lactation, a period of highest energetic cost.