Pant-hoot

The pant-hoot is a loud, structurally complex vocalization of chimpanzees. The call is generally divided into four distinct, successive phases: introduction, build-up, climax and let-down. This introductory phase begins with soft, breathy, low-frequency 'hoo's' that transition into the build-up phase; a series of increasingly rapid, low-frequency in-and-out pants. Following the build-up phase, the call quickly builds into the climax, consisting of loud, high-frequency screams that eventually slow into the let-down phase, similar in structure to the build-up, but with decreasing amplitude and pace until the call is complete. Both male and female chimpanzees produce these unique vocalizations, with high-ranking adult males predominantly and more frequently emitting the pant-hoot. The pant-hoot is most often produced jointly with other males, in a complementary behaviour known as chorusing, as opposed to producing the calls individually. These loud, long-distance vocalizations are produced for numerous purposes in a variety of different circumstances and situations. Pant-hoot chorusing can be used to aid in the formation of social groups or parties amongst male chimpanzees, and used to display the dominance and strength of their party to conspecifics. Pant-hoots are also produced upon the arrival of fruit trees to indicate the location of abundant resources and when joining and greeting other members of their social group. Calls are produced to indicate the spatial location of the individuals in a party, facilitating the maintenance and unity of the social group by providing a means of communication between members while travelling, often listening to the distant calls made by other chimpanzees and responding to them. Also, pant-hoots are used to identify and distinguish between members of a social group, as each individual upholds some variation in their specific calls. Additionally, the level of pant-hooting in chimps vary based upon their individual dominance rank within a party. There are also levels of variation observed within the structure and expression of pant-hoot calls within this range of circumstances, which serve to separate populations, social parties and individuals from one another, allowing coherence between the members in all situations, as well as the establishment of individual identities among each chimp. Grunting is made in situations like feeding and greeting. Submissive individuals make "pant-grunts" towards their superiors.

Social bonding (affiliation)

Pant-hoot chorusing in chimpanzees is a facilitative method of social bonding between males in a population and can be indicative of the level of affiliation between members in a party. A social affiliation between male chimpanzees can be recognized by observable behaviours such as reciprocal grooming, non-vocal displays and the support of a member during conflicts with conspecifics. The display of these behaviours between two male chimpanzees or an entire group suggest that these individuals are highly affiliated with strong social bonds. The production of pant-hoots between members is also reflective upon this observation, in which individuals are more likely to engage in chorusing behaviours with their long-term affiliative social partners, as opposed to other neutral males in which they are not affiliated. However, male chimpanzees have been found to occasionally chorus with neutral males in situations where their preferred social partner is unavailable, forming short-term social bonds, and essentially displaying the three behaviours indicative of social bonding; grooming, support and non-vocal displays during days when they pant-hoot chorus with these neutral males. This illustrates how joint pant-hoot chorusing can facilitate the formation of social bonding activities between male chimpanzees. The establishment of this bond can be indicated to each member of the party as the joint chorus and response to the initial caller illustrates the commitment and attention that the correspondent has devoted to the caller, and subsequently, the formation of the social bond between them. The formation of social groups among male chimpanzees can be beneficial in both short-term and long-term scenarios. The formation of short-term social bonds between males in absence of their preferred social partner can serve as an alternate mechanism for coalition, providing temporary support and protection while separated from their long-term partners. In the formation of long-term bonds, members of a chimpanzee party will display their pant-hoot chorusing behaviour as an indication of their socially affiliative strength to third-party males, suggesting their support of one another, combined dominance and the overall strength of their territorial defence.

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