Document Type


Date of Degree Completion

Spring 2020

Degree Name

Master of Science (MS)


Primate Behavior

Committee Chair

Jessica Mayhew

Second Committee Member

Sofia Blue

Third Committee Member

Andrew Piacsek


Post-release monitoring is vital to the rehabilitation process. Gibbons offer a unique challenge, as they are notoriously difficult to follow through the forest, but their duets offer a non-invasive window into their lives. The aim of this project is to create a method that will evaluate the health of rehabilitated and released gibbons through acoustic analyses. Gibbon duets are in part genetically determined, but learning may play a role in song development. Additionally, songs may indicate resource holding potential, and are vital to acquiring mates and producing offspring. Captive-raised gibbons are often denied the experience of co-singing with their parents, and are generally less fit than their wild counterparts due to living in confined spaces. The female great call is a primary holder of information during a song bout, and will be the focus of this study. To explore how captivity could impact singing, we recorded the great calls of six individuals from three Nomascus species of rehabilitated gibbons at the Endangered Primate Rescue Center (EPRC) in Cuc Phuong National Park, Vietnam. The first song bout from each day was used for analysis. We extracted 23 parameters from 102 great call recordings (n = 10-25/gibbon). A Principal Component Analysis revealed that the first three components accounted for 71.81% of the variance in the data. PCI focused on the bark phrase, PCII focused on the Oo phrase, and PCIII focused mainly on temporal parameters. We then ran correlations to explore how these principal components related to age and weight. This study provides preliminary evidence to support a non-invasive way to monitor behavior and rehabilitation using acoustic markers. Our results suggest that genetics, age, and weight impact the production of female Nomascus spp. great calls. The significance of acoustic markers in rehabilitation practices is generally overlooked in the literature and merits further investigation. Future studies should implement acoustic markers to monitor individuals in captivity to better inform rehabilitation and release practices.