L. Chittka et al., FORAGING DYNAMICS OF BUMBLE BEES - CORRELATES OF MOVEMENTS WITHIN ANDBETWEEN PLANT-SPECIES, Behavioral ecology, 8(3), 1997, pp. 239-249
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.