Predictors of Bachman's Sparrow Occupancy at its Northern Range Limit

Peucaea aestivalis (Bachman's Sparrow), a songbird endemic to the southeastern US, has experienced long-term population declines and a northern range-boundary retraction. Habitat loss and degradation, largely related to fire suppression, are believed to be the major causes of population declines, but these relationships are less studied at the northern range-extent. Hence, we investigated habitat selection of Bachman's Sparrow on Fort Bragg Military Installation, where vegetation is characterized by extensive fire-maintained Pinus palustris (Longleaf Pine) uplands. We surveyed breeding male sparrows using repeat-visit point-counts. We visited 182 points 3 times from April to July during the 2014 and 2015 breeding seasons. We measured vegetation and distance to other habitat features (e.g., wildlife openings, streams) at each point. We recorded presence or absence of Bachman's Sparrows and fit encounter histories into a single-season occupancy model in program Unmarked, including a year effect on detection. Occupancy probability was 0.52 and increased with greater grass-cover and at intermediate distances from wildlife openings, and decreased with years-since-fire and with greater shrub height. Predictors of Bachman's Sparrow occupancy were similar to those reported for other portions of the range, supporting the importance of frequent prescribed fire to maintain herbaceous groundcover used by birds for nesting and foraging. However, our study indicated that other habitat features (e.g., canopy openings) provided critical cover within extensive upland Longleaf Pine-Aristida stricta (Wiregrass) forest.