Locating nests of endangered bumble bees: Lessons from field trials in northern Germany

Abstract Several bee species are threatened by the loss of food and nesting resources associated with agricultural intensification. To identify these threats and inform conservation decision‐making, it is crucial to fill remaining knowledge gaps, regarding, for example the nesting sites of some rare bumble bee species. Here, we discuss different strategies of locating nests of the rare and threatened above‐ground nesting bumble bee species Bombus muscorum in difficult‐to‐access grassland habitats in Northwest Germany. Different methods of hunting for nests (searching vegetation structures potentially used for nesting and infrared detection) and tracking bumble bees back to their nests (using different markers and radio trackers) were tested and optimized during the five‐year project. Methods used to hunt for nests were unsuccessful due to the limited number, size and cryptic nature of nests. Tracking methods were difficult due to the bumble bee's ability to fly quickly and their limited ability to carry the additional weight of the tags. While no nests could be located, tracking individuals using paper strips glued to their thorax was identified as most suitable, with tracking times of up to 2 h and distances of up to 800 m, and only eventually losing sight due to the difficult terrain. Our recorded distances are well over 55 m, which were previously stated as the average foraging distance of Bombus muscorum . We suggest that other researchers use the presented methodology as a straightforward technique for tracking bees over long distances, assessing foraging ranges and locating inconspicuous bumble bee nests.