From MSNBC:
Nuthatches appear to have learned to understand a foreign language — chickadee. It’s not unusual for one animal to react to the alarm call of another, but nuthatches seem to go beyond that — interpreting the type of alarm and what sort of predator poses a threat. When a chickadee sees a predator, it issues warning call — a soft “seet” for a flying hawk, owl or falcon, or a loud “chick-a-dee-dee-dee” for a perched predator.
The “chick-a-dee” call can have 10 to 15 “dees” at the end and varies in sound to encode information on the type of predator. It also calls in other small birds to mob the predator, Christopher Templeton of the University of Washington said in a telephone interview. “In this case the nuthatch is able to discriminate the information in this call,” said Templeton, a doctoral candidate.
More here.