The risk-sensitive foraging behavior of carpenter bees (Xylocopa micans)

In the stochastic world of nectar foragers, the volumes and concentrations of the nectar found within flowers are variable. Nectarivores may respond to alternative plant species, based in part on differences in the variabilities of the plants\u27 nectar supplies. This response has been termed risk-sensitive foraging, where risk results from random variation. In the laboratory, the foraging situation for carpenter bees (Xylocopa micans were experimentally simplified by offering the bees a choice between either low variance or high variance artificial flowers. Forager preference under these conditions was found to be unaffected by energy budget, contrary to the predictions of the Energy Budget (z-score) Model of risk-sensitivity. Behavior was also unaffected by whether the bees chose between individual flowers or patches of flowers. Individual carpenter bees were found to be indifferent to variability in both nectar sugar concentration and nectar volume when none of the flowers was empty. Bees showed decided risk-aversion, however, when variability in nectar volume resulted from the presence of completely empty flowers. This important finding suggests that apparent risk-sensitivity reported for other nectarivores may have resulted from a learning constraint mechanism and may resolve the apparent conflict in the literature between these and earlier studies of nectarivore risk-sensitivity