A robust-design analysis to estimate American black bear population parameters in Utah
International Association for Bear Research and Management
We evaluated the efficiency of an extension of a single season capture–mark–recapture (CMR) population estimation method, a closed-capture robust-design model, to monitor trends in population size, apparent survival, and temporary emigration rates over a 5-year period for a low-density population of American black bears (Ursus americanus) in north central Utah, USA. We also used robust-design Pradel models to estimate finite rate of population change and recruitment. We identified individual bears through genetic analysis of tissue samples collected non-invasively at scent-lured sampling sites. Although the population was relatively small ( = 15–22), the Huggins robust-design model provided precise estimates of abundance (CV = 8–14%) and female apparent survival (CV = 9%). Apparent survival for females (ϕ = 0.80, SE = 0.07) was 2.2× higher than for males (ϕ = 0.36, SE = 0.12; P = 0.003). In contrast, temporary emigration was 40.8× higher for males (γ″ = 0.58, SE = 0.24) than for females (γ″ = 0.004, SE = 0.06; P = 0.024). Data were insufficient to estimate probability of staying for either sex. From the Pradel model, finite rate of population change was similar for males and females (λ = 1.05, SE = 0.12 for females; λ = 1.11, SE = 0.16 for males), but recruitment was 3.0× higher for males (f = 0.75, SE = 0.17) than for females (f = 0.25, SE = 0.10; P = 0.013). Population size appeared to be stable or slightly increasing over the 5-year period. This noninvasive CMR study provided relatively efficient, precise estimates of a low-density black bear population on a small study site. We recommend using robust-design closed-capture models if samples are taken over multiple years; in addition to population size, apparent survival, movement, recruitment, and finite population change can be estimated, providing timely insights into population trends and the mechanisms driving them.
Pederson, J. C., K. D. Bunnell, M. M. Conner, and C. R. Mclaughlin. 2012. A robust-design analysis to estimate American black bear population parameters in Utah. Ursus 23:104-116.