Research Ecologist US Geological Survey West Glacier, Montana
When sampling, it is common to fail to detect a species even when it is present. I will share recent work where we accounted for detection using occupancy models for the western bumble bee (Bombus occidentalis). Although, once common throughout western North America, it is now a species of concern and will be considered for listing by the U.S. Fish and Wildlife Service (USFWS) under the Endangered Species Act (ESA). We attempt to improve alignment of data collection and research with USFWS needs to consider redundancy, resiliency, and representation in the upcoming species status assessment. We reviewed existing data and literature on B. occidentalis, highlighting information gaps and priority topics for research. We modeled the overall trend in occupancy from 1998 to 2018 of B. occidentalis within the continental United States using existing data. The probability of local occupancy declined by 93% over 21 years from 0.81 (95% CRI = 0.43, 0.98) in 1998 to 0.06 (95% CRI = 0.02, 0.16) in 2018. The decline in occupancy varied spatially by landcover and other environmental factors. Detection rates vary in both space and time, but peak detection across the continental U.S. occurs in mid-July. We found considerable spatial gaps in recent sampling, with limited sampling in many regions, including most of Alaska, northwestern Canada, and the southwestern U.S. We therefore propose a sampling design to address these gaps to best inform the ESA species status assessment through improved assessment of how the spatial distribution of stressors influences occupancy changes.
