As urbanization spreads, understanding its impact on wildlife is increasingly urgent. By comparing the traits and fitness of individuals within the same species found in both urban and rural habitats (urban adapters), we can better understand the behavioral and physiological coping mechanisms wild birds employ in the face of rapid environmental change. For my dissertation, I investigated the physiological, behavioral, and fitness differences between urban and rural living song sparrows (Melospiza melodia) to explore how song sparrows are adjusting to urban environments. In my first chapter, I investigated urban birds' termination of the glucocorticoid stress response by looking at their ability to reduce circulating levels of glucocorticoid 'stress' hormones and the relative abundance of receptors that provide negative feedback in the hippocampus and hypothalamus. I found that urban males have a lower relative abundance of glucocorticoid receptors and the enzyme 11β-HSD2 in the hippocampus compered too rural, though we found no difference in negative feedback at the periphery, as both urban and rural song sparrows responded similarly to a challenge with synthetic glucocorticoid (dexamethasone). In chapter 2, I asked if increased aggression, which has been rigorously documented in urban males, is also expressed by females, and whether this aggressive signaling is constraining other reproductive behaviors such as maternal care. Indeed, female song sparrows, like males, expressed increased aggressive signaling compared to rural, suggesting urban habitats may favor a more aggressive phenotype. Finally, in Chapter 3, I investigated the consequences of increased male aggression on their social partners and offspring by measuring parental care and nestling outcomes across urban and rural habits. I was unable to establish a trade-off between parental care and aggression in either sex, suggesting this increased aggression is not constraining other reproductive behaviors. In fact, the more aggressive urban males visited the nest significantly more frequently, a trend also seen in urban females during the daylight hours, though the relationship was not significant over a 24-hour period. Additionally, urban birds had significantly higher reproductive metrics compared to rural, though they also had the added cost of increase brood parasitism by brown-headed cowbirds (Molothrus ater) compared to rural. Overall increased urban aggression was associated with higher reproductive success without any reduction in paternal care. Additionally, we found physiological differences in the glucocorticoid stress response system associated with the differences in habitat but whether theses differences represent mechanisms of acclimation or potential costs of living in urban habitats is not yet clear. / Doctor of Philosophy / As urbanization spreads, understanding its impacts on wild bird conservation is increasingly urgent. By comparing the behaviors and reproductive success of animals living in urban and rural habitats (urban adapters), we can better understand the coping mechanisms wild birds' employ in the face of this form of rapid environmental change. In my dissertation, I compared the physiology, behavior, and reproductive success of urban and rural song sparrows (Melospiza melodia) to explore the changes song sparrows make to survive and reproduce in urban environments. In my first chapter, I investigated how urban birds terminate their stress response by looking at their ability to reduce circulating levels of stress hormones and the relative abundance of "shut down" targets in the brain. In chapter 2, I asked if increased aggression, regularly document in urban males, is also expressed by females, and whether this aggression is constraining other reproductive behaviors. Finally, in Chapter 3, I investigated the consequences of increased male aggression on their social partners and offspring by measuring parental care and nestling outcomes across urban and rural habits. I found that urban males have a lower relative abundance of one type of "shut down" target, and a lower abundance of a potentially protective enzyme in the hippocampus, though we found no difference in how quickly urban and rural birds cleared stress hormone from their blood. Female song sparrows, like males, expressed increased aggressive signaling compared to rural, suggesting urban habitats may favor a more aggressive pattern of behavior. However, I was unable to establish a trade-off between parental care and aggression in either sex, suggesting increased aggression is not constraining other reproductive behaviors. In fact, the more aggressive urban males visited the nest significantly more often, a trend also seen in urban females during the daylight hours, though the relationship was not significant over a 24-hour period. Additionally, urban birds had significantly higher reproductive metrics compared to rural, though they also had the added energetic cost of increased brood parasitism by brown-headed cowbirds (Molothrus ater), compared to rural. Collectively, my results suggest that individuals of this species, the song sparrow, may benefit from livening in low intensity urban habitats and that living in such altered environments favors or permits higher aggression.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/111832 |
| Date | 14 September 2022 |
| Creators | Lane, Samuel Joseph |
| Contributors | Biological Sciences, Sewall, Kendra, Hopkins, William A., Moore, Ignacio T., McGlothlin, Joel W. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution 4.0 International, http://creativecommons.org/licenses/by/4.0/ |
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