: As a first step in understanding structure and dynamics of white‐tailed deer (Odocoileus virginianus) populations, managers require knowledge of population size. Spotlight counts are widely used to index deer abundance; however, detection probabilities using spotlights have not been formally estimated. Using a closed mark—recapture design, we explored the efficiency of spotlights for detecting deer by operating thermal imagers and spotlights simultaneously. Spotlights detected only 50.6% of the deer detected by thermal imagers. Relative to the thermal imager, spotlights failed to detect 44.2% of deer groups (≥1 deer). Detection probabilities for spotlight observers varied between and within observers, ranging from 0.30 (SE = 0.053) to 0.66 (SE = 0.058). Managers commonly assume that although road counts based on convenience sampling designs are imperfect, observers can gather population‐trend information from repeated counts along the same survey route. Our results indicate detection rate varied between and within observers and surveyed transects. If detection probabilities are substantially affected by many variables, and if transect selection is not based on appropriate sampling designs, it may be impractical to correct road spotlight counts for detection probabilities to garner unbiased estimates of population size.

Many monitoring programs for white‐tailed deer (Odocoileus virginianus) on both private and public lands across the United States have long relied on the use of road‐based spotlight surveys for monitoring population size and trends. Research has suggested spotlight surveys are ineffective and that road‐based surveys for deer are biased because of highly variable detection rates. To evaluate variability in detection rates relative to the assumption that repeated surveys along roads will provide reliable trend data for use in calculating deer density estimates, we collected 5 years of thermal‐imager and spotlight survey data using a multiple‐observer, closed‐capture approach. Using a Huggin's closed capture model, data bootstrapping, and variance components analyses, our results suggest that density estimates for white‐tailed deer generated from data collected during road‐based spotlight surveys are likely not reflective of the standing deer population. Detection probabilities during individual spotlight surveys ranged from 0.00 to 0.80 (median = 0.45) across all surveys, and differed by observer, survey, management unit, and survey transect replicate. Mean spotlight detection probability (0.41) and process standard deviation (0.12) estimates indicated considerable variability across surveys, observers, transects, and years, which precludes the generation of a correction factor or use of spotlight data to evaluate long‐term trends at any scale. Although recommended by many state, federal, and non‐governmental agencies, our results suggest that the benefit of spotlight survey data for monitoring deer populations is limited and likely represents a waste of resources with no appreciable management information gained. © 2012 The Wildlife Society.

Capture of neonatal white‐tailed deer (Odocoileus virginianus) often is hampered by inherent difficulties in locating study animals. A variety of techniques have been described for location and capture of fawns, including foot searches, female behavioral cues, spotlighting, and vaginal transmitter implants. However, each technique has certain limitations imposed by such factors as habitat structure or logistical difficulties. We describe a new technique for locating deer fawns in which thermal imaging technology was employed. Only 3.3 person‐hours were required per fawn located and 9.4 person‐hours required per fawn captured. We suggest that this technique is equally or more efficient than other reported capture techniques for neonatal white‐tailed deer.