In the mountains of Ethiopia, the BBC’s Steve Backshall and his Deadly 60 team track a group of graminivorous (grass-eating) gelada baboons to observe their amazing, lion-sized, canine teeth, which are central to the primates’ social communications. From Mary Bates at Wired’s Zoologic blog:
The gum-bearing yawn was most common with males, especially high-ranking ones. This kind of yawn exposed the gelada’s impressive canine teeth, which stood out against the reddish-pink color of their gums and the inside of their mouths. It was often accompanied by a loud call, and the researchers believe the yawn functions as a long-distance display. Males used this yawn during periods of tension, such as the time right before feeding, suggesting it may serve to intimidate other geladas.
The other two less intense types of yawns were seen most in females during friendly interactions. The researchers found these yawns to be more contagious, and observed females mirroring the intensity of other females’ yawns. They believe these yawns are part of a complex communication system between geladas that often engage in friendly interactions. The contagiousness of the yawns in these contexts suggests the behavior might play a role in synchronizing the activity between two geladas, strengthening the emotional connection between them, or signaling the quality of their relationship.
Gelada males and females might use yawns differently, but all three types of yawn contribute to the smooth workings of gelada society; they function to let everyone know who’s in charge and which geladas are friends.