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 chimpan- zees of 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.