Analysis of night-spotlighting counts for white-tailed deer: Indiana Dunes National Lakeshore, 1991-2006

Underwood, H.; Knutson, Randy

We analyzed 13 years of night-spotlighting surveys for white-tailed deer (Odocoileus virginianus) conducted on the Indiana Dunes National Lakeshore (INDU). An approximately 30 km survey route was established in 1991 and was traversed for five nights in mid-February. Surveys were conducted in 1991, and then from 1995-2006. Data from 1992-93 could not be used. No survey was conducted in 1994. Perpendicular distances from the transect line of all detected deer were either estimated or measured using a hand-held laser-rangefinder. Deer density was calculated using the distance sampling methodology, which combines three independent variance components: detection probability, encounter rate, and cluster size. Because road segments often divided two different Deer Management Units (DMUs), we adapted density formulations to accommodate one- and two-sided transects (i.e., road segments). Deer density was estimated for 10 DMUs across INDU. The highest deer density (>77 deer/km2) was recorded in the Beverly Shores DMU during 2000. In 2006, deer densities across INDU ranged from about 19 deer/km2 to just under 58 deer/km2. An analysis of effective strip half-widths (ESWs) showed that nearly two-thirds of all deer go undetected during surveys, and the probability of detection varies substantially among DMUs and sometimes from one side of the road segment to the other. Estimating perpendicular distance works fine in DMUs with ESWs ≤50m, but where long-range detections are possible, distances are invariably underestimated and sometimes substantially. Improved definition of what constitutes a deer cluster seems to have resulted in lower variation in that component. Precision around estimated density is variable, owing mostly to low effort (roadway driven) in some DMUs. More survey replication or additional road segments are required to increase precision. Specific recommendations for improving the deer population monitoring protocol are discussed.

Analysis of night-spotlighting counts for white-tailed deer: Indiana Dunes National Lakeshore, 1991-2006

Products