Ravens often store extra food in hiding places called caches. In one study, researchers observed that ravens watched by another raven while hiding food often moved the food after the observer left. Ravens that had not been watched usually left their food where it was. The watched ravens were especially likely to move their food if the observer had previously stolen from caches. These findings suggest that ravens use past experiences to judge whether another bird may take their stored food.
According to the text, why were ravens especially likely to move food after another raven had watched them hide it?