How flexible is the systematic search behaviour of desert ants?

Foraging desert ants, Cataglyphis fortis, rely on path integration for navigation. If the path integrator has not led them to the exact position of the point of departure, the nest entrance, they start a systematic search for the nest. Previous studies have shown that the longer the preceding outbound run has been the less confidence an ant has in its path integrator. This lower confidence is expressed by wider search loops. In this study, we investigated whether additional cues influence the systematic search patterns of desert ants. We captured ants that were trained to a feeder, either at different points during their inbound journeys or when they were about to enter the nest. They were then transferred to an unfamiliar test area, within which their paths were recorded. Most of the ants captured along their inbound path reeled off the remaining part of their runs and then commenced their nest search, whereas those captured at the nest entrance started searching for the nest entrance immediately. The latter group of ants had far narrower search patterns than ants that were captured during their inbound runs, irrespective of search path length (20, 40 or 50 m). This indicates that the ants' systematic search behaviour is more flexible than assumed hitherto. We compare the results with two previous studies and discuss different potential cues that ants could use to adapt their search patterns.