Imaging bats as they exit maternity caves during the summer offers the possibility of being an objective and precise (repeatable) technique that can easily be performed by field biologists. If cameras are positioned correctly and have the right field of view, all exiting bats will be recorded in the imagery. A night vision camera system is required since emergences occur under low light conditions and illumination in the visible band alters the bats’ behavior. For small caves (those with no more than a few thousand bats) it is possible for an observer to manually count the exiting bats by replaying the imagery. Above this number it becomes difficult to impossible for a human observer to get reliable counts, and other counting methods are required. Digital image processing (IP) techniques have been shown to be effective at detecting and estimating bat emergences. ERDC’s Environmental Laboratory (ERDC-EL) is developing image processing techniques that actually count all bats emerging from a cave. This is based on using a change detection procedure to detect and track bats flying through the camera’s field of view and then evaluating the tracked pattern to count bats exiting and returning to the cave. The procedure can be used on imagery collected with thermal infrared cameras, which take “heat pictures” without any illumination. ERDC-EL is also testing the use of illuminated near-infrared cameras, which illuminate the field of view in the near-infrared waveband outside of the spectral sensitivity of bats. |
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