SUBMISSIVE PANT–GRUNT GREETING OF FEMALE CHIMPANZEES IN MAHALE MOUNTAINS NATIONAL PARK, TANZANIA

Abstract

One of the unique greeting behaviors of chimpanzees (Pan troglodytes) is pant–grunt vocalization, which is given only by lower-ranking individuals toward a more dominant group member. It is a typical social behavior performed when adult females encounter adult males. Previous studies have proposed some social functions of pant–grunts, such as signaling submission, signaling appeasement, expressing support, and checking tolerance. To evaluate the social variables driving pant–grunts, I investigated pant–grunts by adult female chimpanzeesof the M group in Mahale Mountains National Park, Tanzania. I found that pant–grunts functioned as a submissive signal between adult males and females, but did not always occur during encounters of adult females with adult males. Whether the pant–grunt functions as an appeasement signal remains unclear, but adult females performed pant–grunts as a reaction to the aggression of other individuals. Adult females did not express their support for a particular male by pant–grunting during the study period, probably because the dominance rank among adult males was stable. Rather than checking tolerance at the time, maintaining relations with adult males by pant–grunting was more essential for adult females. Whether adult females performed pant–grunts during encounters with adult males depended on the individuals present, the social power balance, and the current social interactions.