ESTIMATING POPULATION PARAMETERS OF THE LOUISIANA BLACK BEAR IN THE TENSAS RIVER BASIN, LOUISIANA, USING ROBUST DESIGN CAPTURE-MARK-RECAPTURE

The Louisiana black bear (Ursus americanus luteolus) is listed as a threatened species under the protection of the Endangered Species Act of 1973. The Louisiana Black Bear Recovery Plan calls for research regarding bear population viability and biology. From July 2006 to August 2008 I conducted a 3-year robust design capture-mark-recapture study of bears in the Tensas River Basin of northeast Louisiana. I used microsatellite genotypes from DNA extracted from hair samples to identify individual bears. Robust design encounter histories of bears were analyzed using Huggins full heterogeneity models in Program MARK. I ranked models using Akaike’s Information Criterion (AIC). I used model averaging to account for model selection uncertainty. Apparent survival rate, temporary emigration, the probability of an individual coming from 1 of 2 mixtures, and the probability of capture and recapture were estimated from encounter histories. Population abundance was a derived parameter. I used abundance estimates to calculate density, and population growth. Apparent survival did not differ by gender or year and was 0.91 (95% CI = 0.62–0.98). There was no temporary emigration. Models in which capture probabilities varied by mixtures were favored over models lacking mixtures. For both genders and across all years, >80% of individuals were in a mixture with capture probabilities ranging from 0.02 to 0.03 for males and 0.07 to 0.08 for females. Estimates for recapture were higher than capture indicating a positive behavioral response to being captured for females. Model-averaged estimates of abundance for females were 143 (95% CI = 113–204), 106 (95% CI = 83–151), and 133 (95% CI = 100–195) and for males were 198 (95% CI = 117–360), 116 (95% CI = 69–209), and 185 (95% CI = 112–323) during 2006, 2007 and 2008, respectively. Mean population size for both genders averaged across years was 294 (SE = 31) and density was 0.66 bears/km2 (SE = 0.07). Video and photographic evidence suggested that adult males were less likely to be sampled while visiting hair snares. I offer suggestions to reduce this heterogeneity bias.