Unobtrusive videotaping of bats at night can be accomplished in two ways.

One way is to record activity in infrared wavelengths that lie just beyond the visible spectrum. I have an old Sony Handycam, and these early video recorders had excellent night vision capabilities (so much so that they supposedly could 'see' through clothing, and as a result this feature was subsequently constrained by Sony in later models). Used in combination with infrared spot lights allows for the unobtrusive recording of Big Brown Bats (Eptesicus fuscus) as they leave their day roost.

Alternatively, nighttime activity can be recorded using a thermal camera, which can sense much longer wavelengths. I've used a Therm-App thermal imaging camera to record the bats as they awake from daily torpor.
A Big Brown Bat grooms itself before the evening's first flight. Taken with a Sony Handycam in Night Shot infrared mode.

Another videoof a Big Brown Bat grooming itself before flight.

Thermal video of a Big Brown Bat taken with a Therm-App HZ camera coupled with a 3x inframetrics telescopic lens and the ThermAppPlus Android app.
Thermal video of a Big Brown Bat about to take off from its day roost. Captured using a 3x Inframetrics telescope lens mounted in front of a Therm-App HZ camera. Video was recorded using the ThermAppPlus app.
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