UPDATE: As of November 6, 2015, a colony of prairie dogs is about to be exterminated in Colorado. Please sign a petition to say NO! Your signature is your voice.
Professor Slobodchikoff has long studied the vocal repertoire of Gunnison's prairie dog.
With a single bark, he says, a prairie dog may warn about the type and direction of an encroaching predator, and even describe its colour.
If confirmed, that means the chattering rodents communicate in a more complex way than even monkeys or dolphins. LISTEN TO THE SOUNDS where you can also read the full article.
Lewis and Clark, while on their famous 1804 journey across North America, noted that this "wild dog of the prairie...appears here in infinite numbers." At that time, an estimated five billion prairie dogs lived throughout the continent's vast prairie! source: http://nationalzoo.si.edu
Here's another good link for more information: