If you watch a group of black-tailed prairie dogs for long enough, you’ll eventually see a delightful move called the “jump-yip”. One of these little ground squirrels lifts its front half off the ground, stretches its arms out, throws its head back, and makes a “wee-oo” sound.
The behaviour is contagious. Nearby prairie dogs do the same thing, and jump-yips cascade through the colony like a Mexican wave through a stadium.
People have seen this endearing behaviour since at least the 1920s, but no one has really understood its purpose. Prairie dogs will jump-yip in all sorts of situations: when they’ve been taken unawares; when keeping watch from their burrows; when defending their territories; when meeting other prairie dogs; or when a predator has left. In all cases, they’re less likely to run away after jump-yipping than immediately before, and the behaviour is most often interpreted as an “all-clear” sign. It means, supposedly, that danger has passed.
That can’t be right, according to James Hare from the University of Manitoba. “They are every bit as inclined to perform the display when predators were present as when they were absent,” he says. For example, he noticed that wild black-tailed prairie dogs would jump-yip while a coyote was visibly passing through their town. All was not clear, but they jump-yipped nonetheless.
Hare came to a different conclusion after two years of watching 14 prairie dog towns. (These rodents live in large colonies that can span hundreds of acres and include hundreds, thousands, or maybe even millions of individuals.)
He found that the critical thing isn’t what a jump-yipping prairie dog is doing at the time of its display, but how its neighbours react. Specifically, if more of its neighbours jump-yip too, and if the Mexican wave lasts longer, the instigator then spends more time foraging.
These results suggest that the jump-yips are a prairie dog’s way of quickly checking up on its neighbours, including how many there are and how alert they are. It’s the equivalent of a human soldier shouting, “Sound off!” A strong response means that the colony is being collectively vigilant, and the instigator can be a little more relaxed. This explains why the prairie dogs jump-yip in so many different contexts.
“There have been a variety of hypotheses for why prairie dogs perform jump-yips, with no firm answers,” says Con Slobodchikoff, who has been studying prairie dog communication for decades. “This study provides solid data that helps to explain why these animals use this form of communication.”
There are other examples of contagious displays that spread through a group. Yawning is an obvious one. If I yawn in public, chances are that nearby people (or even dogs) might start doing it too. You might be yawning just reading this.
Some scientists view contagious yawns as a sign of empathy—an indication that we’re tapping into the psychological states of our peers. After all, they’re more common in people who score more highly on tests of self-awareness and empathy, and we’re more likely to yawn contagiously when close friends and family yawn than when strangers do so. Perhaps it’s a way of doing a quick mental check on people around us, and boosting our collective attentiveness.
Hare thinks that the jump-yips of prairie dogs play a similar role. He wonders if these simple contagious behaviours are precursors to more advanced mental skills like “theory of mind”—the ability to know what others are feeling and thinking. After all, by responding to their neighbours’ reactions, a jump-yipping black-tailed prairie dog seems to have at least a rudimentary awareness of the mental states of its peers.
Reference: Hare, Campbell & Senkiw. 2013. Catch the wave: prairie dogs assess neighbours’ awareness using contagious displays. Proceedings of the Royal Society B http://dx.doi.org/10.1098/rspb.2013.2153