Bumble Bee Species Detection and Occupancy in Northern Illinois: Recommendations for Bumble Bee Monitoring Efforts

Community monitoring of multiple bumble bee species makes it possible to determine if there are specific bumble bee assemblages associated with specific habitats or landscapes (e.g. urban, suburban, agricultural, natural), if declining species are associated with specific assemblages or experiencing niche replacement with a more common species, and helps parse pollinator-plant relationships and pollinator competition. Bumble bee species interact with one another as potential disease vectors, competitors for limited nesting habitat, and likely as competitors for limited floral resources, so multi-species monitoring efforts are logical for conservation purposes. Of the eleven bumble bee species known to occur in Illinois, Bombus affinis, B. fraternus, B. pensylvanicus, B. terricola, and B. vagans are thought to be declining throughout their range in eastern North America, with B. affinis being Federally protected. Insufficient survey effort can lead to inflated false-negative rates (present but not detected) for rare species. Thus it is crucial to understand how detection probabilities vary among bumble bee species based on survey-level covariates. We present the factors driving detection and occupancy for multiple bumble bee species based on multi-species occupancy models developed from data collected during 2019 surveys. We conducted surveys according to USFWS survey protocols for Endangered Species Act (ESA) implementation for B. affinis in northern Illinois at Glacial Park and Volo Bog. Our results provide recommendations for how to best allocate survey effort efficiently in terms of spatial and temporal replication for community monitoring when resources are limited. We also contribute to the current understanding of sufficient survey effort for ESA implementation connected to B. affinis.