Variation in reflective flow and forager navigation, but not traffic rate, explain speed of obstruction circumnavigation on Atta colombica foraging trails

abstract: Many species follow networked roads. When roads are blocked, the obstruction must be circumnavigated, or traffic rerouted. We obstructed trails of the leaf-cutting ant Atta colombica and compared individual- and group-level circumnavigation as well as trail reuse following obstruction removal. Groups that circumnavigated the obstruction fastest were also the first to return to the original trail once the obstruction was removed. Also, nestward ants returned to using the original trail more quickly than outbound ants. Traffic rate was not related to speed of obstacle solving. The magnitude of reflective flow (reversing direction) explained much of the variation in obstacle-solving time, both comparing nestward versus outbound ants and variation across obstacles. Two other factors explaining variation in obstacle circumnavigation times were percentage of nestward ants carrying leaves and whether ants searched in the appropriate direction for the trail beyond the obstruction, possibly due to variation in the availability of navigation cues or motivation. Reflective flow allows highly-networked leafcutter trails to respond to blockages by using alternative cleared routes, with strength of navigation cues and motivation linked to foraging costs and benefits likely determining the effort expended to “solve” the obstacle versus give up