Preferred Name
Shannon Eppert
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Date of Graduation
8-6-2021
Semester of Graduation
Summer
Degree Name
Master of Science (MS)
Department
Department of Biology
Abstract
Increasing urbanization has increased anthropogenic noise levels near developed areas. Urban noise is high amplitude and low-frequency, and these frequencies can overlap with the signals animals use to communicate, including bird songs. Many urban birds sing higher minimum frequencies in urban areas, which avoids some masking by noise, but the mechanism behind this difference is not well understood. Immediate flexibility is the ability to alter song in real-time in the presence of sudden noise, allowing for avoidance of masking and better signal transmission. I investigated if male catbirds increased signal transmission in the presence of anthropogenic versus high-frequency noise playback compared to pre-playback. I conducted this experiment along an urban gradient from Virginia to the Washington D.C. metro region with 17 male gray catbirds (Dumetella carolinensis). I then measured song minimum frequencies using two sampling methods; one using the peak frequency contour (PFC) tool in Raven Pro to measure all elements, and second, the peak amplitude threshold (PAT) method in Signal 5 to measure the very lowest minimum frequency. The PFC analysis showed significantly greater average minimum frequencies during urban low-frequency noise playback relative to pre-playback minimum frequencies, but the effect size was small at only 73.3 Hz, opening the question of whether this shift would allow songs to avoid noise masking. Catbirds also showed flexibility of their maximum frequencies during masking high-frequency noise, decreasing roughly 260.9 Hz. In contrast, there was no significant difference between pre-noise and during low-frequency noise in the PAT method, which measured the very lowest frequency of each 10-second song clip. The results provide no clear evidence of immediate flexibility in catbirds, because the effect size of the minimum frequency shift of all catbird notes was not greater than the frequency resolution of Raven Pro. Moreover, this small shift of minimum frequencies did not reach the effect size observed in other species of birds such as Parids and may be suggestive of a by-product from the Lombard effect rather than an overall shift of minimum frequency.
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