The branch with the lowest priority is the Search For Target branch:

If no other branches can run then the Search For Target branch will run. This branch does not require any conditions in order to run. The first task that this branch runs is the Reset task. By running this task it ensures that all of the variables have been reset to their starting values. There is a small sub-branch which will trigger if the agent is near ammo: the Is Near Ammo task is reevaluated using a Both conditional abort. This means that if the Search For Target task is active the Is Near Ammo task can return success so the agent will abort searching for a target and instead Seek to the ammo location. As soon as the agent picks up ammo the Search For Target task will resume until it is aborted again by a higher priority branch.