has a surprisingly sophisticated system of alarm calls, scientists say. The results of a new study reveal that depending on the predator a bird spots, it will utter one of many variations of the chick-a-dee call to let other chickadees in the area know what sort of danger is afoot. For instance, the sighting of small raptors--which are better than their large counterparts at hunting the tiny chickadees--elicited longer calls, which prompted the chickadees form larger groups that then mobbed the enemy. Calls signaling less danger led to the formation of smaller mobbing parties. The findings appear in the current issue of Science.