Trapline foraging by bumble bees: effects of experience and priority on competitive perfomance

Background/Question/Methods Animals collecting resources that are fixed in space but replenish over time, such as floral nectar and pollen, often establish small foraging areas to which they return faithfully. Some repeatedly visit a set of patches in a significantly predictable sequence (so-called "trapline foraging"), which may allow them to focus on more profitable patches in their foraging areas. The functional significance of trapline foraging itself, however, has not been empirically demonstrated, especially in competitive situations. We conducted laboratory experiments with artificial flowers to test whether and how accumulated foraging experience in bumble bees affects their movement patterns and foraging performance in the presence of competition.

Results/Conclusions Experienced bees with prior access to flowers achieved higher rates of nectar intake than did later arrivals, because they traveled faster between flowers and returned to flowers at more regular intervals. These behavioral skills improved foraging performance in competitive situations in two ways: nectar accumulated in flowers could be harvested before its replenishment rate slowed down, and nectar could be taken before the arrival of a competitor. In each foraging trip, however, bees traveled more slowly as they followed more repeatable routes. Despite this tradeoff between speed and accuracy in traplining, bees constantly upgraded both skills as they gained experience in a habitat. This upgrading still occurred in the absence of a competitor. Foraging-area fidelity thus allowed bumble bees to establish long-term spatial memory required for fast movements and accurate traplining and, in turn, increased their foraging performance in competition with less experienced individuals.