Date of Award

2016

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Bauer, Gordon

Area of Concentration

Biopsychology

Abstract

In their native habitat, gibbons produce complex vocalizations that are stereotyped by species in acoustic structure as well as in call frequency and timeframe. Gibbons’ vocalizations may be used as ritualistic territorial boundary defense and family unit advertisement, or as alarm calls in response to perceived threats. Within many artificial environments, external stimuli such as proximity to humans, proximity to vocalizing conspecifics, and altered weather conditions from those typical within their native habitat could influence the structure of vocalizations produced by captive gibbons. Previous research has indicated that separated, individual family units of same-species gibbons within zoo environments often overhear one another’s vocalization routines and invariably vocalize in synchrony. The current study analyzed the vocalization structure and routine of two different species of captive gibbons, Hylobates lar and Symphalangus syndactylus, to identify if their species-specific vocalization characteristics would be maintained or if there would be a more homogenized, collaborative vocalization structure and routine. Recordings were collected at Cleveland Amory Black Beauty Ranch from 7:00 AM to 5:00 PM for 31 days, then analyzed by vocalization duration, frequency, and timeframe. The results of these assessments indicate that the gibbons follow a vocalization schedule more like the wild, species-specific structure of S. syndactylus gibbons, average vocalization durations more like the wild, species-specific structure of H. lar gibbons, and a frequency that is significantly greater than that observed within either wild species’ populations, but aligns with vocalization frequency trends of captive gibbons. These results imply a potential framework in which the gibbons, although comprising two separate species and opposing family units, have formed a coalition against a third party threat, the humans, following a framework described as the “Dear Enemy” phenomenon (Getty, 1987).

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