FORAGING DYNAMICS OF BUMBLE BEES - CORRELATES OF MOVEMENTS WITHIN ANDBETWEEN PLANT-SPECIES

What rules determine whether bumble bees continue exploiting plants of the species just visited or switch to another species? To tackle this question, we recorded handling times and flight times from bees forag ing in a natural meadow containing five plant species. Inter- and intr a-specific plant distances were quantified. The bee-subjective colors of the five species were determined; two of these species had similar colors and structures, while three species were distinct from all othe rs. The following rules were identified: (1) The decision to switch sp ecies was correlated with previous flower handling time, which we assu me is a function of the reward amount received at the flower. After sh ort handling times, the probability of switching to another species in creased, whereas it decreased after long handling times. This differen ce became even greater if the bee bad had a run of several short or se veral long handling times. (2) Constant flights (those between flowers of the same species) and transition flights (those between flowers of different species) followed stereotyped temporal patterns independent of the distances between flowers. Constant flights within five plant species consistently had median durations of about 2 seconds, whereas median transition times between species took 3-6 seconds. (3) This tem poral rule broke down, however, if the flowers of two case transition flights had equal dynamics as constant flights. (4) Bees switched more frequently from rare than from common species but even more frequentl y between similar species. We conclude that the bees' choices were det ermined by a set of rules that guided them to stay with the current pl ant species as long as flowers were rewarding and available within clo se distance but to switch to another species if flowers offered low re wards encountered at close range.