Abundance of Black-backed Woodpeckers and other birds in relation to disturbance and forest structure in the Black Hills and Bear Lodge Mountains of South Dakota and Wyoming
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Black-backed Woodpeckers (Picoides arcticus) are rare residents of northern conifer forests and are almost always associated with disturbances, such as fire and beetle infestation. The Black Hills population of Black-backed Woodpeckers has been petitioned to be considered a Distinct Population Segment under the Endangered Species Act and more information on their population size in the region is needed. Our objective was to map abundance of Black-backed Woodpeckers in the Black Hills and Bear Lodge Mountains of South Dakota and Wyoming and provide a population estimate for Black-backed Woodpeckers in the region. We located 124 and 115 transects, containing 1,232 and 1,138 sampling points, in 2015 and 2016, respectively. We conducted 5-minute point count surveys from late-March to late-June and visited each point three times to estimate detection probability. We characterized vegetation around each point using GIS derived landscape variables that included: percent cover of green trees, beetle killed trees, dead trees, and year since wildfire. We detected 362 Black-backed Woodpeckers across both years. We fit three-level hierarchical time-removal models that simultaneously estimated abundance, availability, and detection probability in R package "unmarked" using gmultmix and ranked models using Akaike Information Criterion. The global abundance model received the most support. Abundance was negatively related to percent cover of dead trees and green trees and a positively related to percent cover of beetle killed trees, and percent area of 1- to 2-, 3-, and 4- to 5-year-old wildfires. Abundance of Black-backed Woodpeckers varied the greatest across present cover of beetle killed trees and wildfires that had burned within the last five years. Mean density was 0.00528 birds/ha in 2015 and 0.00626 birds /ha in 2016. An estimated 2,920 (LCL: 1,449; UCL: 5,917) and 3,439 (LCL: 1,739; UCL: 6,908) individual Black-backed Woodpeckers, which is equivalent to 1,460 and 1,720 pairs of Black-backed Woodpeckers, in the Black Hills in 2015 and 2016, respectively. Our study is the most extensive survey of Blackbacked Woodpecker abundance in the region and sets the stage for future analyses of the species population viability in the region.