Foraging dynamics of bumble bees: Correlates of movements within and between 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 foraging in a natural meadow containing five plant species. Inter- and intra-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 others. The following rules were identified: (1) The decision to switch species was correlated with previous flower handling time, which we assume is a function of the reward amount received at the flower. After short handling times, the probability of switching to another species increased, whereas it decreased after long handling times. This difference became even greater if the bee bad had a run of several short or several 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 temporal 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 frequently between similar species. We conclude that the bees' choices were determined by a set of rules that guided them to stay with the current plant species as long as flowers were rewarding and available within close distance but to switch to another species if flowers offered low rewards encountered at close range.