Bumblebees retrieve only the ordinal ranking of foraging options when comparing memories obtained in distinct settings

Are animals’ preferences determined by absolute memories for options (e.g., reward sizes) or by their remembered ranking (better/worse)? The only studies examining this question suggest humans and starlings utilize memories for both absolute and relative information. We show that bumblebees make decisions using only memories of ordinal comparisons. After learning to discriminate pairs of different flowers by sucrose concentration, bumblebees preferred flowers (in novel pairings) with 1) higher ranking over equal absolute reward, 2) higher ranking over higher absolute reward, and 3) identical qualitative ranking but different quantitative ranking equally. Despite these suboptimal choices, bumblebees found the optimal option in an ecologically relevant foraging task. Our results illuminate a divergent mechanism of learned preferences that may have arisen from adaptations to bumblebees’ natural environment.