Date of Award

Spring 4-11-2022

Degree Type


Degree Name

Master of Science in Integrative Biology (MSIB)



Committee Chair/First Advisor

Dr. Todd Pierson

Major Professor

Dr. Sarah Guindre-Parker

Second Committee Member

Dr. Kristen Navara


The Trivers-Willard hypothesis states that mothers can adjust their offspring sex ratios according to their own condition and the environmental conditions they face during breeding. Past tests of this hypothesis in avian species have focused on how natural variation shapes sex allocation trade-offs. However, urbanization also influences individual condition and presents animals with novel challenges in optimizing their brood sex ratio. One likely mediator of the relationship between environmental conditions, parental condition, and sex ratios is corticosterone (CORT), the primary glucocorticoid in birds. However, no research has examined the links between urbanization, individual condition, CORT, and adaptive sex allocation within the same study. Furthermore, research that has examined CORT’s influence on sex ratios focused solely on maternal CORT, but in species with bi-parental care, paternal CORT or the similarity of maternal and paternal CORT levels may also influence the brood sex ratio. In Chapter One, I introduce the foundations for this research, including sex allocation theory and the impacts of urbanization on wildlife. Chapter Two reviews the state of prior work on the relationships between urbanization, individual condition, parental hormones, and sex ratio allocation. Using a field-collected dataset, Chapter Three explores whether sex allocation in European starlings (Sturnus vulgaris) differs for animals in urban versus rural habitats and is related to parental CORT or condition. Finally, in Chapter Four, I discuss future considerations for how global change may alter sex allocation in animals and offer suggestions for future work to expand on my findings.