Road to recovery? Occupancy trends and counts of an endangered bumble bee provide conflicting evidence

There is growing interest in integrating community science data with structured monitoring data to estimate changes in distribution patterns of imperiled species, including pollinators. However, significant challenges remain in determining how unstructured community science data should be incorporated into formal analyses of species distributions. We developed a dynamic framework for combining community science and structured monitoring data of bumble bees to estimate changes in occupancy of rusty-patched bumble bees, Bombus affinis, a federally endangered species in the United States. Our analysis applies traditional metapopulation theory and accounts for imperfect detection to estimate site-specific extirpation risk and colonization rates across the known distribution of B. affinis in the Upper Midwest. Despite a 144% increase in presence-only detections from 2017 to 2022, our analysis revealed that occupancy probabilities and the estimated number of occupied sites have remained static or declined slightly across a four-state region during this period. Furthermore, our analysis provides preliminary evidence the probability of local extirpation risk of B. affinis increased in response to drought, but that effect was tempered by having a high number of neighboring patches occupied by B. affinis (i.e., rescue effect). Our study provides a framework that can be used by managers for tracking population recovery goals for B. affinis and other bumble bees of conservation concern. In addition, our study highlights the importance of accounting for imperfect detection and addressing spatial sampling biases in bumble bee monitoring efforts, particularly those where a portion of the monitoring data are generated from community science projects.