Do Orangutans Really Laugh? An Investigation into the Existence of Tickle-Induced Play Vocalizations among Pongo pygmaeus at the Orangutan Care Centre and Quarantine in Kalimantan, Indonesia

Laughter is a physiological process and a fundamentally social phenomenon with physical, biological, psychological, philosophical and social dimensions. Laughter is ubiquitous among human populations but its evolutionary history has not been thoroughly examined. Although laugh-like play vocalizations have been reasonably well-established among chimpanzees, little is known about its existence in other species. It has been suggested from anecdotal reports on bonobos and gorillas, in addition to the handful of studies on chimpanzees, that play faces and play vocalizations are usually produced during rough and tumble social play and tickling. While there is a general consensus on the existence and characteristic features of great ape play faces, data on great ape play vocalizations and their relationship with play faces is scant. In addition, this limited evidence for laughter in great ape species does not extend beyond chimpanzees, and there has only been one other study conducted on orangutans thus far. This study tries to fill this void and investigates the existence of laughter in wild-born, ex-captive orangutans housed at the Orangutan Care Centre and Quarantine in Kalimantan, Central Borneo, Indonesia. Forty-one orangutan (24 males, 17 females) were tickled by familiar caregivers and their facial and vocal responses recorded. First, I analyzed the presence and frequency with which four play face variants co-occurred with vocalizations among the full sample. I then examined whether the reactions were influenced by sex, age, and time spent in rehabilitation. The analyses indicated that when tickled, orangutans exhibit play faces significantly more often than non-play faces and silent play faces more frequently than vocalized play faces. Sex, age, and time in rehabilitation did not affect these findings. Lastly, while some orangutans emitted vocalizations when exhibiting play faces, the rate at which the two behaviours co-occurred in the sample was lower than the level required to fulfill the definition of laughter used in this study. Therefore, the hypothesis that orangutans laugh could not be supported. Limitations of this study and future directions are discussed.