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Function of Onset Timing in White-handed Gibbon (Hylobates lar) Communication

Azniv Khaligian, Jaime Utter, Joy Layton, and Dr. Angela Dassow, Biology Department, Carthage College, 2001 Alford Park Drive, Kenosha WI 53140

White-handed gibbons (Hylobates lar) possess a diverse vocal repertoire that occurs in a variety of contexts including play and territorial display. The vocalizations that occur during territorial display, such as duet songs, have been well-studied. However, play vocalizations have not. This study aims to compare the play bleat onset time to call onset time in duet songs in captive gibbons. The significance of response time is important in understanding the contextual function of these vocalizations. Bleats, or play vocalizations, are produced in response to tactile and visual stimuli during play. Comparing this gestural stimuli to a vocal stimuli, such as the hoo note, which is a precursor to duetting, may lead to a better understanding of the correlations between stimuli type and response time. Audio from a pair of adult captive gibbons was collected from the Racine Zoo in Racine, WI. Audio files were filtered and analyzed using Adobe Audition. Bleat onset, or the time between the first second of gestural play to the start of the first bleat, was measured. Call onset was measured at the start time from the first hoo note to a change in vocal unit type. A two-sample t-test assuming unequal variances was done comparing call onset and bleat onset. Results showed one and two tail p-values at less than 0.01, indicating that there is a longer response time to a vocal stimuli compared to a gestural stimuli. This supports the hypothesis that bleats act as a functionally distinct category of sound in white-handed gibbon communication. Future studies will aim to compare play bleat onset and duet call bout onset between wild and captive white-handed gibbons.

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