Document Type


Date of Degree Completion

Fall 2017

Degree Name

Master of Science (MS)


Primate Behavior

Committee Chair

Lori K. Sheeran

Second Committee Member

Kara Gabriel

Third Committee Member

Karen Lewis


Enrichment is an aspect of captive husbandry that has been shown to positively impact animals’ well-being and can be designed to encourage species-typical behaviors, such as foraging and arboreality. Enrichment can include housing together multiple compatible species. Orangutans are sympatric with siamangs and agile and Bornean gibbons, so several zoos house these four Asian ape species in the same enclosure, in part, as social enrichment. In my study, I observed enrichment use and social interactions in a mixed-species enclosure at the Oregon Zoo, which housed two Sumatran (Pongo abelii) and two Bornean (P. pygmaeus) orangutans with two Northern white-cheeked gibbons (Nomascus leucogenys). The study subjects were Bornean orangutans Kitra and Bob, Sumatran orangutans Kumar and Inji, and gibbons Phyllis and Duffy. From August 4-September 4, 2015, I conducted scan sampling every 30 seconds for 15-minute time blocks, totaling 82.5 hours and 9,911 scans. Using proportion tests, I tested whether each ape was equally likely to use arboreal and terrestrial enrichment. I predicted subjects would be more likely to use arboreal enrichment because of their arboreal natural histories. All individuals used arboreal enrichment significantly more than terrestrial enrichment. During my study, the two Sumatran orangutans and the two gibbons were housed together. I predicted that conspecifics would be more likely to interact than heterospecifics. Chi square tests supported this prediction. An additional component of my second hypothesis, which was conducted through descriptive statistics, was that interactions between conspecifics and heterospecifics would be more affiliative than aggressive. I found that heterospecifics and conspecifics had more affiliative instances (n = 1,750) than aggressive ones (n = 65).