Wild bumblebees use both absolute and relative evaluation when foraging

Foraging theory assumes that animals assess value based on objective
payoffs, however, animals often evaluate rewards comparatively, forming
expectations based on recent experience. This form of evaluation may be
particularly relevant for nectar foragers such as bumblebees, where
individuals can visit thousands of flowers daily that vary in nectar
quality. While many animals, including bees, demonstrate reference-based
evaluation in experimental contexts, it is unclear whether this occurs in
the wild. Here we asked how daily experience with wildflower nectar
influenced wild bumblebees’ reward evaluation. We measured the daily
nectar concentration of bee-visited wildflowers (Penstemon spp.), before
presenting foragers with conspecific flowers filled with a range of
artificial nectar concentrations. We recorded bees’ acceptance of
artificial nectar, probability of subsequent visits to flowers on the same
plant, and residence time. While bees had a minimum threshold of nectar
acceptability that was unaffected by experience, when there was
higher-concentration environmental nectar, they were less likely to accept
lower-quality rewards on manipulated plants. Bees also visited more
flowers and stayed longer on plants with higher-concentration nectar. This
study shows evidence for both absolute and reference-based evaluation in
wild bees and points towards differences between bees’ behavior in lab-
and wild-foraging contexts.