Electronic Theses and Dissertations





Date of Award


Document Type


Degree Name

Doctor of Philosophy



Committee Member

Stephan Schoech

Committee Member

David Freeman

Committee Member

Duane McKenna


Presumably, a threatening encounter with a predator activates the hypothalamic-pituitary-adrenal (HPA) axis in free-living animals in what is commonly called a stress response, which may help mediate the lasting memory of the attack. However, these assumptions are based on experiments that do not resemble what free-living animals experience in nature, and typically involve laboratory models that can have considerably different physiological responses than their free-living counterparts. To address this gap in our understanding, I developed novel methods to examine the physiological stress response and its effects on learning and memory in ecologically relevant contexts. Specifically, I assessed the effect of witnessing a brief raptor attack on circulating levels of corticosterone (CORT; the primary steroid hormone that is released following HPA axis activation in birds) in European starlings (Sturnus vulgaris). Additionally, I adapted the laboratory based fear conditioning paradigm to analyze the relationship between stress induced CORT and the long lasting memory of free-living Florida scrub-jays (FSJs; Aphelocoma coerulecens). I also manipulated CORT in subjects to determine if CORT had a causal effect on memory consolidation. I found that starlings that witnessed a raptor attack as brief as 2 sec mounted a robust CORT response, which was similar to that following a standardized capture-and-restraint protocol. Also, FSJs were able to remember a threatening encounter with a novel predator for 2 years, and the consolidation of this memory was positively correlated with their stress-induced CORT response. Unexpectedly, moderate stress responders exhibited an exaggerated fear response with time, which may be explained by the affects of CORT upon reconsolidation or system consolidation. Further, FSJs that received a relatively high dose of exogenous CORT during memory consolidation did not exhibit subsequent fear responses, which suggest that CORT has an inverted U-shaped relationship with memory consolidation. This dissertation has revealed similarities and differences between free-living birds and models traditionally used in endocrinology and animal cognition. Some of these differences are surprisingly similar to symptoms observed in humans that suffer from post-traumatic stress disorder, and may have significant implications on an individual’s survival and the recovery of endangered species.


Data is provided by the student.

Library Comment

dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.