Vocalizations distinguish the prairie dog from all other rodents. At least ten different calls have been identified in the blacktail class of prairie dogs. Most of the calls—such as the challenge bark, defense bark, disputing “_churr_,” fighting snarl, fear scream, muffled bark, and tooth chattering—do not involve the entire community. Except for the fear scream, which is immediately noted by all members, these vocal signals are largely ignored by neighboring animals since they usually denote a local disturbance among the prairie dogs themselves. There are three warning calls, however, that are intended for the entire community; these constitute the bond that unites all the separate coteries of the town into a single social unit. At the sound of the _warning bark_, usually uttered by many animals at once and quickly relayed through the entire town, each prairie dog immediately rises to alert in an attempt to define the immediate danger. If the wave of alarms is particularly intense, the animals usually rush to burrow mounds, where they will await further developments. Usually only the prairie dogs in the immediate vicinity of an enemy will retire below ground. The remainder of the population continues to observe and sound the alarm. As an enemy approaches a particular burrow, the frequency and intensity of the occupant’s warning bark increases. Only at the last moment will the prairie dog cut short its tirade, capping it with an indignant _churk_ as it dives below ground. Another, more urgent, signal is the _hawk warning call_. The high-pitched, musical twin notes of this cry prompt an immediate dash for cover. Unlike the typical reaction to the warning bark, response to the hawk warning call is unhesitating. When this cry is given, seconds count, and visual confirmation of danger is not required to prompt a rush to safety. After danger has passed, the all-clear is sounded. Known as the _song bark_, this melodic whistle is always associated with a particular body posture. Rising up on its haunches, the prairie dog points its nose to the sky, gives the whistle, and promptly falls back on all fours. When learning to execute this call, pups usually topple over backwards. Once uttered, the call is repeated sporadically throughout the town. Communication is as important to the survival of the prairie dog society as is adequate food and shelter. Towns decimated by disease or poisoning soon vanish if the survivors are too few or scattered to communicate effectively. Deprived of an efficient warning system (and perhaps of the psychological need of social contact, as well), individual animals make easy targets for predators. Certainly they are too large and conspicuous to blend in well with their sparse surroundings. Unlike their small, well-camouflaged cousins, the thirteen-lined ground squirrels, prairie dogs cannot survive as individuals.