Now, researchers at the University of Manitoba in Winnipeg say they have the answer, claiming the prairie dogs use it as a method of testing how reliable their neighbours are at keeping watch for predators.
Black-tailed prairie dogs use a move called the jump-yip, in which they jolt upright, jerking their heads back and forelimbs up. They also emit a "wee-oo" sound, lead author James Hare said.
Published in the journal Proceedings of the Royal Society B, the researchers recorded 173 jump-yip bouts in 16 distinct prairie dog towns over the course of a year.
They eliminated bouts where predators appeared, where there were any vocalisations other than the wee-oo sound and where the animals were grazing or chewing at the time of the wave.
Findings showed that bout instigators increased their proportionate allocation of time to foraging in response to how many prairie dogs responded to their wave.
"Moreover, bout instigators are undoubtedly constrained to devote time to vigilance so as to assess bout response characteristics prior to adjusting their foraging–vigilance trade-off accordingly ... Jump–yip displays thus function to promote the accrual of information regarding collective vigilance within the group, clarifying earlier speculation regarding the function of these displays," the authors conclude.
The researchers say that by testing the responsiveness of their neighbours, prairie dogs are able to adjust their behaviour according to how well they can trust their vigilance to protect them from predators.
Hare said: "This fits beautifully with work on primates, including humans, which suggests that contagious displays – like yawning – provide a window into the mind of others, suggesting of course, that species probing the minds of others are aware that they are distinct from those individuals. That is to say, they are consciously aware.
"Prairie dogs foraged less when individuals were less responsive to their jump-yip display, suggesting they use jump-yips to actively probe the awareness of their neighbours."