Urban habitats impact the song and reproductive success of a migratory bird, the gray catbird (Dumetella carolinensis)
Faculty Advisor Name
Dana L. Moseley
Department
Department of Biology
Description
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 that alter habitats, such as increasing impervious (built-up) surface and decreasing forest cover. Urban areas also have higher levels of anthropogenic noise pollution – loud, low-frequency noise from traffic and industry. 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 populations of male gray catbirds (Dumetella carolinensis) across an urban gradient from the DC metro region to rural VA. Anthropogenic noise alone was a significant predictor of minimum and peak frequencies. Noise was also included in best-fit models as a predictor for these song features, with increases in noise level associated with increases in both minimum and peak frequencies, which likely increases signal transmission in noisy habitats. For minimum frequency, male body size was also included in the best-fit model such that large-bodied males sang with significantly lower minimum frequencies, while for peak frequency, larger beak sizes significantly predicted lower peak frequencies. Models of maximum frequency and frequency bandwidth each showed significant increases with increasing impervious surface and canopy cover. Nests were significantly more likely to successfully fledge and contain more nestlings in areas of higher impervious surface and less noise, as well as in areas of less canopy cover. Surprisingly nests of males with slower song phrase rates were significantly more likely to fledge and contain more nestlings. There was an interaction between habitat type and minimum frequency on 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 successful 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 being more or less advantageous in different environments, 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. Specifically, a study that measures fledgling survival would add important information to aid in future urban development plans that minimize negative impacts on migratory songbirds.
Urban habitats impact the song and reproductive success of a migratory bird, the gray catbird (Dumetella carolinensis)
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 that alter habitats, such as increasing impervious (built-up) surface and decreasing forest cover. Urban areas also have higher levels of anthropogenic noise pollution – loud, low-frequency noise from traffic and industry. 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 populations of male gray catbirds (Dumetella carolinensis) across an urban gradient from the DC metro region to rural VA. Anthropogenic noise alone was a significant predictor of minimum and peak frequencies. Noise was also included in best-fit models as a predictor for these song features, with increases in noise level associated with increases in both minimum and peak frequencies, which likely increases signal transmission in noisy habitats. For minimum frequency, male body size was also included in the best-fit model such that large-bodied males sang with significantly lower minimum frequencies, while for peak frequency, larger beak sizes significantly predicted lower peak frequencies. Models of maximum frequency and frequency bandwidth each showed significant increases with increasing impervious surface and canopy cover. Nests were significantly more likely to successfully fledge and contain more nestlings in areas of higher impervious surface and less noise, as well as in areas of less canopy cover. Surprisingly nests of males with slower song phrase rates were significantly more likely to fledge and contain more nestlings. There was an interaction between habitat type and minimum frequency on 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 successful 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 being more or less advantageous in different environments, 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. Specifically, a study that measures fledgling survival would add important information to aid in future urban development plans that minimize negative impacts on migratory songbirds.
