Phenotypic and behavioral plasticity may provide avenues for primates to adjust to new and changing environments, but there are clear limitations to such plasticity that become evident in captive settings. Despite variation in feeding programs across zoological institutions, captive gorillas widely exhibit metabolic and cardiovascular health issues including high cholesterol, hypertension, obesity, and diabetes, with cardiac disease as their leading cause of mortality. To investigate how altered nutrient availability, ingestive behavior, and energetic demands influence health outcomes in managed care, this dissertation examines the nutritional ecology, abnormal ingestive behavior, and energy expenditure of male western lowland gorillas housed in US zoos. Using dietary records, USDA FoodData Central profiles, manufacturer data, and laboratory analyses, I quantified nutrient composition of zoo diets across botanical categories and assessed intake across developmental stages and health statuses. Zoo diets were characterized by higher protein and lower fiber than wild diets, with browse items offering nutrient profiles more consistent with wild feeding ecology than cultivated fruits or manufactured foods. Gorillas with heart disease consumed diets higher in protein, and many foods exceeded sodium recommendations and optimal omega-6 to omega-3 ratios, underscoring potential dietary contributors to metabolic and cardiovascular risk.
I then examined male gorilla regurgitation and reingestion (R&R), a widely observed yet poorly understood abnormal ingestive behavior in zoo-housed apes. R&R was negatively correlated with time spent feeding, occurred more often in afternoons, and was frequently preceded by travel, feeding, and inactivity, suggesting links to satiety signaling or boredom. Certain food items, especially commercial feeds (e.g., chow), fruit juice, cabbage, nuts, and carrots, were disproportionately associated with R&R events. These results indicate that both behavioral context and dietary composition contribute to the expression of R&R and may reveal opportunities for refining feeding strategies and enrichment protocols.
Lastly, I quantified activity budgets and total energy expenditure (TEE) using instantaneous sampling and doubly labeled water in gorillas representing four demographic categories. Adolescent and pubescent males exhibited elevated TEE relative to their body mass, mirroring developmental energetic increases seen in humans and highlighting the metabolic demands of maturation. Adult males typically aligned with expectations of constrained energy expenditure, while individuals with cardiovascular disease occasionally showed elevated or irregular TEE, potentially reflecting compensatory physiological processes. These findings illuminate age- and health-related variation in great ape energetics and have direct implications for individualized nutritional and welfare management, including diet composition, energy density, enclosure design, and social group management.
Combined, these chapters provide a holistic evaluation of nutrition, ingestive behavior, and energetics in zoo-housed male gorillas, offering evidence-based strategies for improving captive ape health and contributing to broader discussions in primate nutritional ecology, biological anthropology, and animal welfare.
