I'll give them a few minutes to clear out. IF they don't, like is likely to happen in an oak flat I'll finally clear my throat or something. If that doesn't work I've actually thrown a water bottle or something down to make thunk. If that doesn't get them nervous enough to move on I break out a light and shine it on them and wave it around. That usually sends them off... usually not in a panic.. but a high stepping "something isn't right" mode.