Gorilla, behavior, cortisol, stress, space restriction


The concept of quantifying animal welfare has received much discussion, in various industries such as agriculture, laboratory, and zoological facilities. Behavioral, physical, and physiological indicators of welfare have previously been used to assess animal welfare; each having advantages and disadvantages, ranging from the practicality of data collection, to the validity of the data and how it is interpreted. Concurrent assessment of multiple measures is a more robust way to examine animal welfare, which utilizes the advantages of each measure, and provides additional information on which to base conclusions and animal care management decisions. This study used measures of behavior and urinary cortisol to examine the potential stress response of a captive gorilla group to short-term space restriction associated with temporary confinement to indoor housing facilities. The study duration was three months; one month of baseline data collection, one month of indoor restriction, and one month of monitoring post-restriction. All-occurrences of selected behaviors were collected, with an emphasis on social and stress-related behaviors, and urine samples were collected daily from a sub-set of the group. A urinary cortisol metabolite enzyme immunoassay was validated and used to monitor adrenal activity in gorillas. Measured cortisol increases in response to a known stressor (medical illness) provided a physical validation of the cortisol EIA and established biological relevance of the assay system. No significant differences in social behaviors (aggression, affiliation) or stereotypic behaviors were observed. Significant (p<0.05) increases in cortisol concentration were measured, suggesting that the gorillas were responding to a stressor during the study period. The observed cortisol increase was not likely to have been caused exclusively by the temporary indoor confinement. Potential additional causes of increased adrenal activity during the study included: presence of the observer and novelty of re-landscaped outdoor enclosure. While the increases in cortisol concentration demonstrate an observed stress response, the magnitude of this stressor, and thus the degree of the stress response, was minor. The stress experienced was not significant enough to alter the normal biological function of the gorillas, and thus, can be considered negligible. The gorillas' ability to effectively deal with this expected stressor may have been enhanced by the additional enrichment provided to the gorillas during their indoor confinement. Gorillas were provided with additional browse, more enrichment items, additional training sessions, and increased keeper interaction while they remained indoors. These animal care and management techniques may have buffered the predicted negative impact on animal welfare due to increases in stress by providing stimulating novelty in the gorillas' indoor environment.


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Graduation Date





Waterman, Jane


Master of Science (M.S.)


College of Arts and Sciences



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Masters Thesis (Open Access)

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Biology Commons