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Date of Graduation
5-12-2022
Semester of Graduation
Spring
Degree Name
Master of Science (MS)
Department
Department of Biology
Abstract
Urban environments are relatively recent on an evolutionary timescale, and, as such, they create novel selection pressures that may influence fitness and mate choice. Many ecologically significant factors change with increasing levels of urbanization, such as increasing anthropogenic noise, increasing impervious surface, and decreasing forest cover. There is growing empirical evidence that anthropogenic noise affects features of birdsong and, separately, that avian nesting success varies across an urban gradient, but rarely do studies examine both – a necessary step to elucidate the evolutionary potential of these novel pressures. I investigated song features, body morphometrics, and reproductive success in male gray catbirds across an urban gradient. Noise was included in best-fit models as a predictor for minimum and peak frequencies, with increases in noise level associated with increases in frequencies, which likely improves signal transmission in noisy habitats. For minimum frequency, male body size was also included in the best-fit model such that larger-bodied males sang with significantly lower minimum frequencies. Models of maximum frequency and frequency bandwidth both showed significant increases with increasing impervious surface and canopy cover. Nests were significantly more likely to fledge in areas of higher impervious surface, lower canopy cover, and less noise. Surprisingly, nests of males with slower song phrase rates were significantly more likely to fledge and contain more nestlings. Additionally, models revealed interactions between frequency measures and nesting success. In urban habitats, males that sang higher minimum frequencies were more likely to have successful nests, while males in suburban and rural habitats were more likely to fledge nests if they sang at lower minimum frequencies. Similarly, males in urban habitats had significantly more nestlings per nest as maximum frequency increased while their suburban and rural counterparts showed the inverse relationship. These results indicate urbanization not only influences song features, but also the nesting success of gray catbirds with certain song features, indicating a potential shift in selection occurring in urban environments. Future research should further expand this connection between sexual selection, reproductive success, and variation across an urban gradient to aid in urban development plans that will minimize negative impacts on migratory songbirds.
