Bumblebee Foraging Behavior: Changes in Departure Decisions as a Function of Experimental Nectar Manipulations

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Abstract
The nectar-gathering foraging behavior of bumblebees (Bombus flavifrons and B. bifarius) was observed on control and nectar-enriched inflorescences of three Rocky Mountain herbs, Aconitum columbianum, Delphinium nelsonii and D. barbeyi, to determine whether bumblebees actually forage in a manner consistent with the learning mechanism proposed by Ollason. When gathering nectar from two of the three species, bumblebees encountering a series of enriched plants initially increased the number of flowers per inflorescence that they visited relative to control inflorescences. After the blossoms from a small number of enriched racemes were probed, the average number of flowers visited per plant returned to control levels. These results are consistent with the predictions made by Ollason and suggest that foragers'' assessment of habitat quality is modified during a foraging bout. These results are used to estimate the extent of bumblebees'' memories of previously encountered nectar rewards. the small estimated size of bumblebee memories may be adaptive under spatially heterogeneous reward schedules.