In my Animal Communications class we are studying chimpanzee vocalizations. The study and analysis of the vocalizations of Gombe Chimpanzees (Pan troglodytes) from (1971-193) by Jane Goodall provided us with sufficient data to help determine which male chimpanzee would fulfill the top position of the dominance hierarchy. We organized and separated the data in a way in which allowed us to find a correlation between frequency of pant hoots and dominance. Our predictions of relative social-rank were based on vocalizations such as pant-hoots, pant-grunts, and waa-barks, as well as other factors including the individual’s age, and response from group members.
Chimpanzees (Pan troglodytes) are our closest living relatives, sharing more than 95 percent of our DNA and are amongst the most intelligent animals on the planet (Britten 2002). They travel in fission-fusion social groups, meaning that the troops in which chimps function in, are constantly fluctuating. This occurs dynamically as new members may join the troop, while existing members may wander off and join a different troop or start one of their own. These Sub-Saharan primates have evolved to incorporate a dominance hierarchy within these groups to establish social order.
The dominance hierarchy among male chimpanzees is fairly linear, ranging from the most submissive male in the group to the most dominant alpha male. Although female chimps have their own, more complex social hierarchy, a male chimp always retains dominance over a female (regardless of the female’s social ranking). In addition to determining social-standing, the male-dominance hierarchy is used to settle disputes and to determine possession of females as mates. By adhering to the social order in-stated by the dominance hierarchy, male chimps are often able to resolve conflicts with the use of vocalizations and gestures rather than resorting to physical violence.
Several factors play a key-role in determining which male will fulfill the top position of the dominance hierarchy, including physical strength, aggressiveness, intelligence, and age (Sapolsky 2005). The alpha-male of a troop typically falls within a range of 20 to 26 years of age. Male chimps assert their dominance through a variety of social interactions, such as vocalizations, facial expressions, body gestures, and actions (Arcadi 2000).
One of the most commonly used vocal signals among chimpanzees is the pant-hoot, a four-part call used by both males and females. Pant-hoots are used in a wide variety of situations, including expressing excitement, food-enjoyment, and announcing arrival. Because each chimpanzee has its own distinct pant-hoot, this call can be used to determine an individual’s identity. As a result of cultural evolution, pant-hoots generally vary between geographic populations and individuals (Whiten & Boesch 1999). This is very similar to human accents and our ability to recognize each individual voice.
Another important vocalization is the pant-grunt, which also serves as an indicator of dominance ranking. The pant-grunt is a unidirectional call, expressed as a sign of submission from a lower-ranking chimp to a higher-ranking individual, therefore the direction of this call can be used to discern the social hierarchy.