Takahisa Matsusaka

When does play panting occur during social play in wild chimpanzees

To clarify the social functions of play panting in chimpanzees, I investigated when they emitted play panting in social play and how the interactions were affected by the occurrence of play panting. The subjects were the M-group chimpanzees living in Mahale, Tanzania. The following observations were made: (1) chimpanzees emitted play panting when they were tickled or chased but rarely did so when they tickled or chased others. Chimpanzee play panting does not have the function of a play signal communicating that these “aggressive” actions are performed not as aggression but as play. (2) Chimpanzees emitted play panting more often when they received “aggressive” actions that supposedly elicited higher arousal. (3) A chimpanzee tended to continue to perform “aggressive” actions when the target emitted play panting. Play panting activates the interaction of social play by encouraging the performer to continue tickling or chasing. These results can be summarized as showing that chimpanzee play panting serves as positive feedback to the play partner for continuing somewhat fragile interactions, which may contain the risk of excessive arousal and the risk of confusing “defensive” actions by the target of the “aggressive” actions with real efforts to escape the situation.

Sniffing behaviors in Mahale chimpanzees

Although it is difficult for observers to determine how non-human primates use olfaction in a natural environment, sniffing is one clue. In this study, the sniffing behaviors of wild chimpanzees were divided into six categories, and sex differences were found in most categories. Males sniffed more frequently than females in sexual and social situations, while females sniffed more often during feeding and self-checking. Chimpanzees sniffed more frequently during the dry season than during the wet season, presumably due to the low humidity. This suggests that the environment affects olfactory use by chimpanzees and that chimpanzees easily gather new information from the ground via sniffing.

Study Sites of Chimpanzees and Bonobos

Local names of the major study-sites referred in the Glossary are listed below with main reference sources. Shorter-term study sites such as Bai Hokou, Beni, Campo, Filabanga, Kabogo, Kanka-Sili, Kasakati, Moukalaba, Ndoki, Odzala, Petit Loango, and Tongo are described in the glossary.

Prevalence of muzzle-rubbing and hand-rubbing behavior in wild chimpanzees in Mahale Mountains National Park, Tanzania

In 1998, four chimpanzees in the Mahale Mountains National Park, Tanzania, were observed wiping their mouths with non-detached leaves or stalks of grass, or rubbing their mouths with a tree trunk or branch, especially while eating lemons. The number of mouth-wiping/rubbing individuals increased to 18 in 1999. By 2005, 29 chimpanzees were documented wiping/rubbing their muzzles in this way. Although it is difficult to determine whether the chimpanzees acquired this behavior as a result of trial and error or social learning, the fact that chimpanzees at other sites perform this behavior with detached leaves or leafy twigs much more often than with intact items suggests the possibility that cleaning with intact plant parts at Mahale spread via social learning.