D3527: Conservation tools for PNW bumble bee species: Models and field studies

Bombus franklini has one of the smallest habitat ranges of bumble bees in the world, limited to a small portion of Northern California and Southern Oregon. Following a sharp population decline since the late 1990s, the U.S. Fish & Wildlife Service (USFWS), with the help of volunteers, has annually monitored and tracked bumble bee diversity on Mt. Ashland, OR– the last documented locality of B. franklini. This summer, we supplemented our visual surveys by collecting eDNA samples from flowering plants to increase our bumble bee species detection rates. We also created species distribution models (SDMs) for several bumble bee species using historic records as well as climate and landscape data. These SDMs were designed to aid the USFWS in the search for B. franklini, inform future status reports, and highlight areas for future monitoring. Recognizing that shifts in the broader bumble bee community may influence B. franklini’s persistence, we developed a mark-recapture pilot study to monitor the population size of the most common bumble bee species at Mt. Ashland, B. vosnesenskii. The mark–recapture pilot allowed us to estimate the total population size of B. vosnesenskii at Mt. Ashland, which we found this year to be an estimated 7,393. The USFWS has anecdotally noted an increase in this species over the years, and our study provides a framework to document population changes over time. Because B. vosnesenskii is a generalist, tracking its population trends may reveal whether it is outcompeting other bumble bee species in the area.