Liquid gold rush: Search strategies and trapline formation in nectar foraging bumblebees (Bombus terrestris) (#343)
Animals foraging for stationary, replenishing but ephemeral resources such as flowers are faced with a tricky optimisation dilemma. They must reach a trade-off between the efficient exploitation of previously discovered resources and the search for new ones. The first of these two problems, finding the optimal path between multiple locations, is not an easy task to solve. Known as the travelling salesman problem, with each point added to the path the number of potential routes that can be taken increases exponentially. Despite this, in both lab and field studies bumblebees have been demonstrated to converge upon optimal repeatable circuits (traplines) between forage sources using a set of simple learning heuristics (Lithorieu et al 2012). Using harmonic radar, my colleagues and I tracked the first 50 foraging bouts of bumblebee (Bombus terrestris) workers presented with 5 artificial nectar filled ‘flowers’ arranged in a trapezoidal array. The ‘flowers’ in the array are spaced so that bees following the behaviourally simplest nearest-neighbour rule would not be able to find the optimal route. Our study is the first to continuously track every consecutive foraging bout of a bumblebee as it discovers each of the five presented ‘flowers’ and develops a trapline through an array of resources. We found that foragers converge on more similar and efficient traplines over time, but never reached the optimal foraging route, or the shortest route available following the shortest neighbour rule. Preliminary analysis of forager tracks has found that bees deviated from the shortest path between known forage sources at semi-regular intervals. These deviations in flight behaviour appear to take forager bees over areas where artificial ‘flowers’ would be expected to be located based on her experience of the positions of the other 5 forage sources. We therefore suggest these deviations represent directed exploration flights based on foragers predicting the position of potential feeding locations based on the spatial pattern of the artificial 'flowers' provided.