Aerial vertical‐looking infrared imagery to evaluate bias of distance sampling techniques for white‐tailed deer

Abstract

Population monitoring requires techniques that produce estimates with low bias and adequate precision. Distance sampling using ground-based thermal infrared imaging (ground imaging) and spotlight surveys is commonly used to estimate population densities of white-tailed deer (Odocoileus virginianus). These surveys are often conducted along roads, which may violate assumptions of distance sampling and result in density estimates that are biased high. Aerial vertical-looking infrared imaging (aerial imaging) is not restricted to roads and therefore enables random sampling and detection. We compared estimates of population density and precision, and evaluated potential sources of bias for these 3 techniques for deer on Arnold Air Force Base in Tennessee, USA, during January-February 2010. Using data from aerial imaging conducted along systematic strip transects, we found that deer were distributed close to roads and deer responded to the landscape along the road edge or to observers driving along roads. As a result of these distributional patterns, estimated deer density based on ground imaging and spotlighting from road-based surveys was 3.0-7.6 times greater than density estimated from strip transects using aerial imaging. Ground imaging did not produce better estimates than spotlighting. Observers on the ground counting all deer seen at test plots with hand-held thermal imagers saw fewer deer than were seen on aerial images, suggesting high detection of deer by aerial imaging. Despite its higher cost (US$10,000) over spotlight surveys, we recommend aerial imaging instead of road-based ground surveys for monitoring populations of deer and discourage the continued use of non-random road-based surveys as a method for estimating white-tailed deer populations. Ó 2014 The Wildlife Society.

Using spotlight observations to predict resource selection and abundance for white‐tailed deer

“…Detection probability in our study was estimated to be <1, which is consistent with other spotlighting efforts (Collier et al 2007, McShea et al 2011). LaRue et al (2007 and Beaver et al (2014) reported that distance sampling overestimated density for deer using spotlight observations in comparison with other survey designs, which is consistent with our results. Similarly, accounting models rely heavily on estimates for various population parameters and outputs may be sensitive to the initial population size used to parameterize models for deer (Grund and Woolf 2004).…”

“…First, spotlight surveys are most often conducted at local scales (e.g., a forest or park property) along non‐linear road‐based transects (Naugle et al , Focardi et al , Roberts et al , Stapp and Guttilla , Collier et al ). The use of non‐linear roads may violate assumptions for random or systematic sampling in distance sampling studies, and may further bias detection rates and density estimates if roads follow landscape features that structure animal populations (McShea et al , Beaver et al ) or animals select for or against features created by road openings (e.g., in highly forested landscapes; McCaffery and Creed , Ward et al ). Second, observation rates for deer across landscapes are rarely constant and may vary according to factors (e.g., observer, topography, land cover type; Corlatti et al ).…”

Capture—recapture of white‐tailed deer using DNA from fecal pellet groups

“…However, using roadbased ground surveys, Beaver et al (2014) found densities were 3.0 -7.6 times greater. Deer density was assumed to be higher in the security area than the management units of AAFB.…”

“…Our estimates of deer density (5.8 deer km Ϫ2 ) were similar to values from Beaver et al (2014;4.0 -6.6 deer km Ϫ2 ) using aerial vertical-looking infrared imagery for a security area of AAFB where hunting was not allowed. However, using roadbased ground surveys, Beaver et al (2014) found densities were 3.0 -7.6 times greater.…”

Confirmation of Coyote Predation on Adult Female White-Tailed Deer in the Southeastern United States

“…For example, track counts and fecal pellet counts have been abandoned largely because they are not reliable methods for estimating population size (reviewed by DeYoung 2011). Similarly, spotlight surveys are rife with detectability issues (Collier et al 2007(Collier et al , 2013, and more technologically advanced approaches like infrared thermal imagery do not fare much better (Beaver et al 2014), as background temperature and forest cover characteristics can result in poor accuracy and precision (DeYoung 2011). Aerial survey techniques are most useful in open areas lacking canopy (precluding use in much of the eastern United States) and still require consideration of detectability biases (DeYoung 2011).…”