Maliau gibbon project (proposal)

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Vocalization: Signals of Intention and Subsequent Behavior in Hylobates muelleri

Abigail Schoenberg



Primate vocalizations are at the center of a debate concerning whether or not human language is an evolved version of non-human primate communicatory systems. While one could imagine that primate vocalizations are the ancestors of human speech, others believe that human communication only resembles non-human primate communication in non-verbal ways. For instance: "Given that language is inseparably bound up with human cognition, the most promising place to look for the antecedents of language is in primate cognitive abilities. We are more likely to find hints about language origins by studying how primates use their minds than by studying how they communicate" (Burling 1993).

However, defenders of non-human-primate vocalizations as an ancestor of human speech necessitate further study of non-human-primate vocalization. The Mullerian Gibbons of Sabah, Malaysia provide a mode of such study.

Arguably the most important division of gibbon vocalizations are their songs – that is, the behavioral vocalizations that “emphasise a role in territorial advertisement, mate attraction and maintenance of pair and family bonds” ( These songs have been well studied in many different cases.

However, few studies have been conducted on the more informal vocalizations of gibbons, such as warning calls to family members, reflexive sounds produced when startled, etc.

Such studies have been conducted on macaques. In one study, the grunts and girneys of female rhesus macaques were analyzed to determine whether they have evolved into signals encoding information about the caller's intention or subsequent behavior; studies suggested that they had not (Whitman 2007). The Mullerian Gibbons of Sabah may provide different results.


Are gibbon vocalizations signals encoding information about the caller's intent and/or subsequent behavior?

I hypothesize that the data I collect will reflect the fact that vocalizations do encode information about intent and subsequent behavior, in that all or nearly all calls will be specific signals followed by the appropriate physical response (for example, territorial calls will be followed by displays, warning calls to family members will be followed by flight, etc.).

I rationalize that this will be so because, unlike macaques, gibbons live in small, monogamous family groups. Therefore, there may be little to no unintentional chatter, and any vocalization will be directed at a specific receiver.


I will be collecting data from gibbon encounters on the mornings of July 13-18. I will be walking in the field, on and off trail, with Harbin, a Maliau Basin guide. Once a gibbon or group is encountered, I will watch and videotape the behavior. I will then record the following details:

  • Minute-by-minute analyses of the behavior of each gibbon present, including:
    • Pre-Vocalization Behavior
    • Vocalization
    • Post-Vocalization Behavior
  • Apparent Stimulus for Vocalization
  • Time of Day
  • Weather
  • Number of Gibbons present
  • Miscellaneous information


Each instance of gibbon vocalization will be classified into one of two categories:

  • Yes, the vocalization was followed by the appropriate subsequent behavior.
  • No, the vocalization was not followed by the appropriate subsequent behavior; it was random.

My hypothesis is that there will be little to no instances in the latter category. If there is a significant proportion in that category, however, my hypothesis will be proven incorrect.