Comparing urban and wildland bear densities with a DNA-based capture-mark-recapture approach

Abstract

California’s black bear (Ursus americanus) population has tripled over the last 3 decades, causing an increased incidence of human–bear conflicts, many of which now occur in urban areas. Consequently, it is imperative that bear managers have the ability to monitor population parameters in both wildland and urban environments to help manage bears. Capture-mark-recapture (CMR) methods using uniquely typed genetic samples (DNA) collected via hair-snares have been widely used to monitor bears in wildland areas. However, we are unaware of researchers applying this technique to bears occupying urban areas. We implemented a multi-year DNA-based CMR study to compare bear densities between an urban area and a nearby wildland area. We deployed hair-snares for 6 weekly capture occasions during June and July, 2011 and 2012. We uniquely typed DNA from snared hair follicles using 14 microsatellite loci and 2 sexing loci. We coupled unique identification with robust-design closed-capture models and model averaging in Program MARK to estimate abundance. We identified 41 and 62 individual bears on the urban and wildland study areas, with average densities of 3.8 and 1.8 bears/10 km2,respectively. Our data support the hypothesis that bears can occur at greater densities in urban areas. Based on these results, we recommend using DNA-based CMR methods to monitor populations of bears in urban areas, but we suggest increasing the density of sampling locations to account for greater bear densities. Furthermore, we contend that DNA-based CMR can also estimate survival, recruitment, rate of population change (λ), and identify movement patterns by incorporating additional survey years.

Keywords

• american black bear
• california
• dna-based capture-mark-recapture
• hair-snare
• population estimate
• robust design
• urban bear
• ursus americanus