Taking eight GPS-tracked flocks of five birds each, they clock-shifted either the whole flock, none of the birds, or only the lead bird. In those where the whole flock was on the same, wrong page, they tended to deviate away from their homeward path. When just the leader was confused, however, the rest of the birds course-corrected, despite the leader's incorrect path. The head bird spent less time at the top, and lost more followers when the rest of the flock knew what was up.