Landsat to monitor an endangered beetle population and its habitat: addressing annual life history and imperfect detection
Habitat-based conservation is a priority for the endangered American burying beetle (Nicrophorus americanus Olivier), but its annual life history, dispersal ability, and low detectability contribute to difficulties explaining its decline, identifying manageable habitat characteristics, and mapping its distribution. Objectives of this study were to (i) assess factors affecting detection of beetles with baited pitfall traps, (ii) identify important habitat characteristics, and (iii) map spatio-temporal patterns of habitat quality and beetle abundance. At a military installation in western Arkansas with one of the largest remaining N. americanus populations, 257 sites were surveyed over 5 years using three nights of baited pitfall trapping at each site. Geographic information systems (GIS)-based habitat assessments included three site radii (100, 800, and 1600 m). Year-specific vegetation condition was quantified using satellite images and other GIS data. N-mixture models were used to account for imperfect detection and to assess competing models of beetle abundance and detection. Detection rates (mean = 20%) were dependent on overnight temperature, dew point, and wind speed with upper and lower temperature thresholds beyond which detection was reduced. Habitat assessments were most effective within 800 m site radii, consistent with previous estimates of N. americanus trap sample range. Beetle abundance was associated with grasslands and open-canopy woodlands with rolling topography, sandy loam soils, and moderate patchy disturbances from wildfire. Landsat, unlike vegetation maps, quantified year-specific habitat quality and allowed spatio-temporal population dynamics to be mapped at a yearly time-step for this annual species.