Distinct yawns among gelada baboons send different social messages, scientists have found.
Male geladas tend to yawn during tense situations, whereas females tend to yawn during friendly encounters with other females, researchers said.
Gelada baboons, native to Ethiopia, are unique among yawning animals in that they have three distinct types of yawns that are easy to identify.
These types include yawns with covered teeth; yawns with uncovered teeth; and yawns with uncovered gums and head movements.
Researchers based at the University of Parma in Italy studied more than 5,900 yawns within two gelada colonies housed at NaturZoo in Rheine, Germany, noting the contexts in which the yawns occurred and the behaviours associated with each.
They found that yawns with covered teeth and yawns with uncovered teeth were most common among females, and were often accompanied by lip-smacking, which is a friendly behaviour.
"The most relaxed yawn types are generally performed by adult females and yawns by adult females are extremely frequent during social encounters," study co-author Elisabetta Palagi, a researcher at the National Research Council in Rome, told LiveScience.
"For example, we observed that when two different females approach, they often embrace and yawn together," Palagi said.
The more intense gum-bearing yawn, on the other hand, was more common with males, particularly those of high rank.
These yawns were often accompanied by some sort of vocalisation by the yawners, and often arose during periods of tension, such as directly before feeding. This suggests the display may be a form of intimidation.
Since yawns are generally involuntary, the team believes that, in most cases, the messages associated with gelada yawns are likely subconscious, Palagi said.
The team was published in the journal Scientific Reports.
