Use of thermal infrared sensing to estimate density of white-tailed deer

We estimated density of white-tailed deer (Odocoileus virginianus) using spotlight surveys and aerial surveys with an infrared (IR) sensing system at Sand Lake National Wildlife Refuge in South Dakota. Thermal IR sensing detected 88.2% of deer counted by ground personnel. In 1993, density estimates (17.0, 15.8, 16.6 deer/km²) were calculated using 3 sets of non- overlapping transects to reduce biases (i.e., double-counting, deer movement, and deviation from transect) associated with overlapping transects. Variation in density estimates obtained from aerial surveys using IR conducted in February 1994 with uniform snow depth and May after snow melt was low (CV = 10.3%). Spotlight counts associated with IR sensing flights underestimated deer density by 38%. High detection rates and increased estimates from IR sensing indicated that IR sensing was a more reliable density estimator than spotlight surveys. Although cost of IR sensing in 1993 ($99/km²) was about 4-fold higher than cost of visual aerial transect sampling, in areas where current methods of estimating density are questionable, estimating density by IR sensing is justifiable.