This video from Britain says about itself:
Nathusius pipistrelle bats advertising for mates
2 Nov 2012
Each autumn male Nathusius pipistrelle bats “sing” to attract mates. They often do this from mating roosts in buildings, trees and bat boxes. In this video you can see and hear one of these tiny bats advertising from underneath a roof tile. I’ve slowed and lowered the frequency of the call so you can hear the fabulous vocalisations that these amazing bats produce.
In 2012, 34 Nathusius pipistrelle bats were ringed in Blagdon in England.
Now, NOS TV in the Netherlands reports that one of these small bats was found in the Netherlands, late in 2013.
The pipistrelle was found dead at a farm in Franekeradeel local authority in Friesland province; about 500 meter from the sea coast.
Until now, it was not known that Nathusius pipistrelle bats were able to cross the North Sea. They are too small for attaching GPS gear to them.
See also here. And here.