In situations with redundant or competing sensory information, humans have been shown to perform cue integration, weighting different cues according to their certainty in a quantifiably optimal manner. Ants have been shown to merge the directional information available from their path integration (PI) and visual memory, but as yet it is not clear that they do so in a way that reflects the relative certainty of the cues. In this study, we manipulate the variance of the PI home vector by allowing ants (Cataglyphis velox) to run different distances and testing their directional choice when the PI vector direction is put in competition with visual memory. Ants show progressively stronger weighting of their PI direction as PI length increases. The weighting is quantitatively predicted by modelling the expected directional variance of home vectors of different lengths and assuming optimal cue integration. However, a subsequent experiment suggests ants may not actually compute an internal estimate of the PI certainty, but are using the PI home vector length as a proxy.

SUMMARYIndividual foraging ants are known to rely on views of their surroundings for route learning and for pinpointing goals. Different strategies have been proposed to explain how ants might process visual information for navigation, but little is known about the actual development and nature of the view-based strategies used by ants in complex natural environments. Here, we constrained the knowledge of Melophorus bagoti ants to either the nest vicinity or a curved route (length 10m) and analysed their initial direction when released at both novel and familiar locations. In parallel, we used 360deg pictures of the scene as a basis for modelling different navigational strategies. We propose here a new hypothesis based on skyline height comparison to explain how ants home from novel locations. Interestingly, this strategy succeeded well at novel locations but failed on familiar terrain. By contrast, the use of a visual compass strategy failed at novel locations but could explain the results on familiar routes. We suggest that ants might switch between skyline height comparison and a visual compass strategy, depending on whether they are on familiar terrain or not. How ants could switch between strategies and how their memories develop are discussed in turn.