Bumble bees are known to possess high learning abilities and use their skills to become more efficient at foraging tasks, such as handling complex flowers. They are also known to develop preferences for the most rewarding flowers and continue utilizing those flowers as long as they are rewarding. Thus, bumble bee foragers should become more efficient at returning resources to the colony with foraging experience. Although much is known about task efficiency in bumble bees under laboratory conditions, the measureable impact of learning on resource return rates under field conditions is much less studied. We quantified foraging trip duration and resource return rates for individual bumble bees during their first eight days of foraging from an observation bumble bee colony free flying in an open habitat. We tracked trip duration using RFID technology and estimated the weight of resources returned to the colony by observing the weight of each bee on an analytical balance as the bee exited and entered the colony. We tracked a total of 20 individual bees on 308 foraging trips over 15 days.
Results/Conclusions
Weight of resources returned per trip increased nearly 4-fold over the first four foraging days before reaching a plateau for the subsequent four days. Similarly, resource return efficiency (resources returned per time spent foraging) also increased over the first four foraging days. Thus, it appears that the ability to learn how to handle flowers in the landscape and/or find the most rewarding flower patches in the landscape greatly increases the ability of bumble bees to return food to the colony. Although larger bees are theoretically capable of carrying more resources, and thus justifying the added expense of producing their larger size, surprisingly, we did not find a significant increase in resource return (as either resources per trip or as efficiency) with increasing body size. We did see a trend toward the largest return amount being related to body size, thus confirming the theoretical prediction, but bees frequently returned fewer resources than they were capable of carrying.