Flight durations in bumblebees under manipulation of feeding choices

Foraging bees spend less time flying between flowers of the same species than between individuals of different species. This time saving has been suggested as a possible advantage of flower-constant foraging. We hypothesized that the time required to switch flower type increases if (a) such switches are infrequent and (b) the bees need to decide whether to switch or not. Bumblebees were taught to forage on artificial feeders that were identical in morphology and reward schedule but differed in the color of their landing surface. In the first two experiments bees foraged alternatively between two feeders. In Experiment 1 the colors of the landing surfaces were switched every two or three visits, while in Experiment 2 they were switched every six or seven visits. In the third experiment, the bees were required to decide whether to make a color-constant or a color-shift flight. Intervisit time was defined as time elapsed between consecutive visits to feeders. When feeder colors were changed frequently (Experiment 1), we detected no difference between color-constant and color-shift intervisit times. When bees were repeatedly exposed to one color (Experiment 2), color shifts required a significantly longer time. When allowed to choose (Experiment 3), bees performed more color-constant flights than color-shift flights. Intervisit times were similar for color-constant and color-shift flights in this experiment. Intervisit times in Experiment 3 were significantly longer than in Experiment 2 and slightly but nonsignificantly longer than in Experiment 1. The results suggest that bees indeed save time though flower-constant foraging but that this time savings is a small (∼1 s/flower visit) under laboratory conditions, and appears only when switches between flower types are infrequent. The time saved may be more significant over long foraging trips, and when morphological differences between flower species are large, as often happens under natural conditions, providing a selective advantage to flower-constant foraging.