Trapline foraging by bumble bees: VI. Behavioral alterations under speed–accuracy trade-offs

Abstract

Trapline foraging (repeated sequential visits to a series of feeding locations) has often been observed in animals collecting floral resources. Past experiments have shown that bumble bees cannot always develop accurate (i.e., repeatable) traplines to a sufficient level, despite their economic advantages in many situations. The bees' preference for short flights works against developing accurate traplines when plants or patches are distributed in zigzag fashion. How should bees cope with such situations in nature? We conducted laboratory experiments with artificial flowers to test 2 nonexclusive hypotheses: bees may travel faster to compensate for low traplining accuracy, and when local landmarks are available, bees may be able to develop traplines by remembering external spatial information in addition to the locations of flowers. As predicted, foragers on a zigzag-shaped floral array traveled faster, with lower route repeatability, than those on a triangular lattice where distance and angle could be chosen independently, suggesting that bees trade-off accuracy for speed when it is more feasible. In contrast, bees traveled more slowly with unchanged traplining accuracy when landmarks were added into both arrays, possibly because the landmarks caused information load or visual distraction. Finally, bees on the zigzag array with additional landmarks made a quicker decision to switch from accurate traplining to fast traveling. If landmarks helped the bees to grasp the overall array geometry in our experiments, they may also permit bees in nature to select a distribution of plants or patches that aids accurate traplining.