Mhm bats... Some years ago when doing more ornithology and similar we were catching bats for ringing them and I remember the little blighters were very smart. Most were able to sonar-detect quite fine nets if there was even the slightest wind and simply evade them in a right-angle maneuver that would tear an F16 to pieces ;-)
How about rigging up the detector to the video, in such a way you could simply search for the peaks in sound track when they fly in/out of the hole? They must use sonar when flying in/out, don't they... Frantisek
