PHYSIOLOGICAL INTEGRATION OF SEASONAL AND DAILY CUES IN THE NORTH AMERICAN BROWN BEAR
Ware, Jasmine Victoria
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Timekeeping enables organisms to accurately and reliably perform functions integral to survival, such as reproduction, migration, and hibernation. The grizzly bear (Ursos arctos horribilis) is a highly adaptable species that must cope with changing seasonal conditions, food resources, and human disturbance. Despite these pressures, the North American population of grizzly bears is currently expanding into human inhabited landscapes and humans are encroaching on grizzly habitat. Together, these events require a better understanding of the proximal and ultimate factors shaping the grizzly's activity and physiology. In the current series of studies, I evaluated the role of light, food, and hormonal signals on modulating daily and seasonal activity in a captive grizzly bear population at the Washington State University Bear Research, Education and Conservation Center. The results of these studies reveal that the grizzly bears respond to photic and non-photic cues in a seasonally dependent manner. Specifically, light serves as a strong entraining agent when food is absent (during hibernation) but when food was present, its role usurped that of the light:dark cycle. Furthermore, circulating hormone concentrations were observed to fluctuate with seasons, but their manipulation did not dramatically affect activity patterns, suggesting a less prominent role in modulating behavior patterns. Taken together, the results of these experiments indicate that the brown bear is a behaviorally flexible species that has likely evolved specific adaptations to cope with annual changes in food availability and, more recently, human pressure.