The first experiment is a dummy coyote placed in amongst a colony of prarie dogs. Using the car and camouflaged tents to hide behind, all the scientists disappear from view, so when the predator is revealed, it is the only thing the prairie dogs are concerned about. The dummy coyote seems to do the trick, the prairie dogs are certainly being vocal. Other individuals are also calling, just in response to the initial calls - they don't have to see the stimulus in order to know there's a coyote nearby. Every call recorded is subsequently anaylsed by the researchers, allowing them to see the differences in time and frequency between the different calls. What the scientists believe is that each individual Prairie dog has it's own unique voice, with it's own particular tonal quality. Although each voice print is different, they all have a common call for a coyote. They can probably distinguish between individuals making the call, and still understand the message of danger.