Portland State University. Department of Biology
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Biology
1 online resource (xiv, 283 pages)
In this body of research, reproductive and adrenal hormones and behavior were used to evaluate individual and group responses to physiological, social, and environmental changes in zoo-housed Asian elephants, considering factors of sex, age, and life stage. Animals experience physiological, social, and environmental changes as part of their natural history and individual life experience. Measures of both positive and negative states are needed to assess the impact of these changes at the individual and group level. Such measures can help us better understand how animals cope with a changing environment, and can help inform management decisions. Through longitudinal analyses of more than 20 years of gonadal and adrenal hormone data (Chapters 2 and 3), we confirmed the presence of intrinsic glucocorticoid (GC) patterns associated with reproductive state in male and female Asian elephants, providing further evidence that GCs play a role in normal reproductive function. In females, circulating cortisol was higher in the follicular phase compared to the luteal phase of the ovarian cycle, and highest in lactational anestrous compared to all other reproductive states. In bulls, circulating cortisol covaried positively with testosterone and musth, as observed in previous studies of elephants and during the analogous condition of rut in other ungulates. Age-related changes in cortisol were observed in both sexes, and some individuals experienced higher rates of change in cortisol in one phase of their reproductive cycle versus another. In bulls, testosterone increased after puberty but decreased with advancing age. Concentrations of GCs covaried more consistently with physiological changes than with social changes in both sexes. Overall, the elephants in these studies showed adaptive adrenal responses to change, and they also exhibited substantial individuality in adrenal response to social life events. These findings reinforce the need to assess welfare on an individual basis and to consider factors influencing the impact of perceived stressors, such as social support, temperament, and life history. The study conducted to monitor an elephant herd through transition to a new habitat (Chapter 4) provided further insights on habitat features that help us meet the physiological, psychological and social needs of elephants under human care, and helped identify which of those features may be most beneficial for enhancing welfare. The complexity and flexibility of the new habitat was effective in improving overall health and welfare by encouraging activity and providing meaningful challenges and the opportunity to express more appetitive behaviors. The new habitat also offered increased control over environmental conditions and social interactions, and the space and resource distribution helped to support changing herd dynamics and greater social equity. Overall, these studies helped deepen our understanding of Asian elephant physiology, and highlight the importance of taking intrinsic patterns of hormone secretion into account when evaluating the impact of external changes. New insights into the welfare impact of habitat and husbandry factors help inform future housing and management decisions. Finally, a better understanding of the impact of social change and resiliency in response to real and perceived stressors allows us to improve social management to enhance welfare in both captive settings and free-ranging environments.
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Glaeser, Sharon Stuart, "Assessing Well-being of Asian Elephants (Elephas maximus) Through Major Events and Transitions, with Development and Aging, and Husbandry Changes" (2020). Dissertations and Theses. Paper 5545.
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