DNA-based hair sampling to identify road crossings and estimate population size of black bears in Great Dismal Swamp National Wildlife Refuge, Virginia

The planned widening of U.S. Highway 17 along the east boundary of Great Dismal Swamp National Wildlife Refuge (GDSNWR) and a lack of knowledge about the refuge's bear population created the need to identify potential sites for wildlife crossings and estimate the size of the refuge's bear population. I collected black bear hair in order to collect DNA samples to estimate population size, density, and sex ratio, and determine road crossing locations for black bears (Ursus americanus) in GDSNWR in southeastern Virginia and northeastern North Carolina. I also investigated bear/vehicle collisions to determine patterns of road crossing.

Genetic analysis of 344 hair samples collected on 2 trapping grids identified 85 unique individuals which I used in a mark-recapture analysis. Estimated population size on the trapping grids was 105 bears (95% CI = 91-148) and average density was 0.56 bears/km². This density estimate projected over the entire Great Dismal Swamp ecosystem yielded a population estimate of 308 bears (550 km2 X 0.56 bears/km²). Similar population estimates generated by Hellgren (1988), Tredick (2005), and this study suggest a stable bear population in the Great Dismal Swamp ecosystem over a 20-year period.

I erected a 2.3-kilometer long strand of barbed wire along U. S. Highway 17 to monitor road crossing patterns near the Northwest River drainage. Genetic analysis identified 6 bears (4 males, 1 female, 1 unknown) that apparently crossed the highway in a 10-month period. Five of 6 bears deposited hair in a 171-m section which included the Northwest River corridor. The 6 bears detected crossed the road at least 11 times.

I investigated 10 reports of bear/vehicle collisions on the periphery of the refuge from June 2000 to May 2002. Six bears (4M:1F:1 unknown) were confirmed killed during this time period. Based on reported bear/vehicle collisions from Hellgren (1988), the Virginia Department of Game and Inland Fisheries database, and this study, a minimum of 4 to 5 bears are struck by vehicles each year on the periphery of the refuge. I identified 2 areas of multiple bear/vehicle collisions: highway 58 on the north side of the refuge near Hampton Airport and Highway 17 on the eastern side of the refuge in the vicinity of the Northwest River corridor.