Warren and entrance detections by thermal imager

Thermal imaging technology is a developing field in wildlife
management.  Most thermal imaging work in wildlife science has
been limited to larger ungulates and surface-dwelling mammals. 
Little work has been undertaken on the use of thermal imagers to detect
fossorial animals and/or their burrows.  Survey methods such as
white-light spotlighting can fail to detect the presence of burrows (and
therefore the animals within), particularly in areas where vegetation
obscures burrows.  Thermal imagers offer opportunity to detect
the radiant heat from these burrows, and therefore the presence of the
animal, particularly in vegetated areas.  Thermal imaging
technology has become increasingly available through the provision of
smaller, more cost-effective units. Their integration with drone
technology provides opportunities for researchers and land managers to
utilise this technology in their research/management
practices.   We investigated the ability of both
consumer (<AUD$20,000) and professional imagers
(>AUD$65,000) mounted on drones to detect rabbit burrows (warrens)
and entrances in the landscape as compared to visual assessment. 
Thermal imagery and visual inspection detected active rabbit warrens when
vegetation was scarce. The presence of vegetation was a significant factor
in detecting entrances (P<0.001, α=0.05).  The consumer
imager did not detect as many warren entrances as either the professional
imager or visual inspection (P=0.009, α=0.05).   Active
warren entrances obscured by vegetation could not be accurately identified
on exported imagery from the consumer imager and several false-positive
detections occurred when reviewing this footage.  We suggest that
the exportable frame rate (Hz)was the key factor in image quality and
subsequent false positive detections.  This feature should be
considered when selecting imagers and suggest that a minimum export rate
of 30Hz is required. Thermal imagers are a useful additional tool to aid
in identification of entrances for active warrens and professional imagers
detected more warrens and entrances than either consumer imagers or visual
inspection.