Echolocation calls were recorded in 1998 and 1999 between May and October with the exception of the grey long-eared bat and Nathusius' pipistrelle. Some recordings were taken outside known roosts as the bat flew towards the microphone. Other recordings were taken on release from the hand after capture by harp-trap or mist-net as far from the release point as possible.

The equipment used was either an UltraSound Advice S-25 bat detector was linked to a USA portable ultrasonic processor and recorded onto a Sony WD6 Professional Walkman or an UltraSound Advice S-25 bat detector linked to a National Instruments PCMCIA format analogue-to-digital conversion board.

See Parsons & Jones (2000) for the full method used.