Data cleaning and statistical analysis
We downloaded the footage from the thermal imagers to an external hard drive and reviewed the footage from this drive using VLC media player 3.0.8. We recorded observations in a custom-built Microsoft Excel (Microsoft Corporation 2018) workbook which utilised the drone’s tracklog to georeference observation locations. This file was then exported as a KML file and viewed in Google Earth Pro (Google Earth Pro 2019) to aid in comparison between thermal imager and visual inspection detections.
Where transect imagery overlapped, double observations of warren entrances were removed. If a warren complex was identified on one transect, and additional warren entrances were identified on the immediate next transect in the same location, then a determination was made on whether these entrances belonged to the same warren or constituted a new warren. This ensured warren counts were not over-estimated.
Warrens were classified by the amount of vegetation present that was likely to obscure entrances. Warrens with no vegetation present were classified as “open”, warrens obscured by vegetation (e.g. entrances were beneath shrubs) were classified as “vegetated” and warrens that had entrances in the open and obscured by vegetation were classified as “mixed”. These classifications also applied to the entrances associated with that warren for analysis (i.e. individual entrances in “mixed” warrens were not further classified into “open” or “vegetated” categories for analysis).