Date of Award:

5-2019

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Wildland Resources

Committee Chair(s)

Eric M. Gese

Committee

Eric M. Gese

Committee

Susannah S. French

Committee

Craig M. Thompson

Committee

David N. Koons

Abstract

Fishers (Pekania pennanti) are a species of concern in the Sierra Nevada Mountains of California. Cortisol is a glucocorticoid hormone released to mobilize energy in response to stress and has been used as an indication of an individual’s physiological response to its environment. By collecting samples of fisher hair and measuring an individual’s cortisol, we examined the physiological stress response of the animals to human disturbances (housing density, road density, habitat type, and silvicultural treatements) and drought (tree mortality) in their home ranges. Using AICc model selection, we found that levels of tree mortality within a fisher’s home range significantly influenced cortisol levels. Various human disturbances had a smaller effect on cortisol levels. Furthermore, we examined the relationship between cortisol and fitness through the metrics of body condition, female kit counts, and survival. We found that females with low cortisol had significantly higher survival rates than females with medium and high cortisol. With the recent drought, bark beetle infestation and subsequent tree mortality being >80% in some areas of our study, cortisol levels could continue to increase, potentially leading to further decreased fitness within this fisher population. We also examined the difference in habitat selection between the core and entirety of the home ranges and found that fishers prefer late-successional forest in the core of their home ranges.

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