Warren surveys
All surveys were conducted in the morning before first light to maximise
the temperature differential between warren entrances and the
surrounding terrain. All sites were visually inspected for rabbit
warrens (active and inactive) on foot during the day and all identified
warrens were mapped with their GPS locations recorded. In Part 1 we
determined whether active rabbit warrens could be detected with a
thermal imager. We flew the drone with the Jenoptik imager directly to
the warren locations. In Part 2 we compared a professional imager (Vayu)
to a consumer imager (Zenmuse). We established parallel flight transects
to allow complete coverage of the area being investigated and to mimic
the actual survey method that should be employed to search for warrens.
We undertook visual counts of warrens and warren entrances in Part 2.
Visual counts were undertaken upon arrival and before the drone flights.
Parallel line transects approximately 10m apart were walked and all
warrens and associated entrances were recorded. Once imagery from the
drone flights was processed (see below), we undertook an additional
visual inspection on foot to confirm entrances identified from the
thermal imagery and to identify any false-positives or -negatives.