Pipistrelles (Pipistrellus pygmaeus) swarming at dawn, before entering their roost. I have now had opportunity to film a longer video with a larger colony.
The video was recorded between about 04.10 and 05.00 on a morning when dawn was around 04.30. A colony count the evening before showed that 383 bats left the roost. I hand-netted two of them and both were lactating females, indicating that this is a maternity colony. When I filmed them it was too early in the maternity season for the young to be flying, but in just a few weeks there will probably be double this number of bats, as each young bat starts to follow it's mother out to feed at night.
The video shows up to fifty bats at a time swarming and there are close-ups of one of the roost entrances, showing how the bats "touch and go" at the entrance, without actually entering. At times, so many bats were attempting to do so that there was an aerial queue and the clattering on the wooden barge-board as they touched and pushed off again was audible some distance away.
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