Investigating vocal plasticity in song sparrows (Melospizia melodia) as a mechanism to avoid masking noise in urban environments
- WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
- Karen Mitsuko Inouye (Creator)
- Institution
- Western Carolina University (WCU )
- Web Site: http://library.wcu.edu/
- Advisor
- Barbara Ballentine
Abstract: Animals that successfully colonize urban areas must be tolerant of anthropogenic disturbance including noise. Chronic anthropogenic noise may be difficult for animals that use acoustic signals to overcome if it disrupts communication. Most anthropogenic noise is below 1.5 kHz but can spread into higher frequency ranges overlapping with acoustic signals used in animal communication. Songbird species are common urban colonizers that use acoustic signals that are critical for reproductive success. To avoid the masking effects of loud anthropogenic noise, many songbird species that occupy noisy urban areas have been observed to use songs and calls with higher minimum frequencies compared to rural counterparts. Precise mechanisms for the observed frequency shifts are not well understood but can be accomplished through natural selection, cultural selection, and vocal plasticity. In this study, I test whether male song sparrows (Melospiza melodia) can use vocal plasticity to avoid masking noise when exposed to experimental noise. Song sparrows that occupy noisy urban habitats are observed to have songs with an increased minimum frequency when compared to song sparrows in quieter areas. However, it is unclear how urban song sparrows can increase minimum frequency because song sparrows do not naturally use frequency shifting during singing but rather use a repertoire of crystallized songs with fixed frequency characteristics. I tested the response of 46 males on the campus of Western Carolina University with two experimental noise treatments. Noise treatments differ in whether the frequency of the noise overlaps with song sparrow songs (2.5-4.0 kHz, masking) or does not overlap (0.5-1.5 kHz, non-masking). All males were exposed to both treatments but on different days. During trials, I recorded singing before, during, and after each treatment. I used Raven Pro to measure minimum and maximum frequency, frequency bandwidth, and song length for up to 10 songs from each period of the trials and calculated means to use in statistical analysis. I found an increase in minimum frequency for songs during the masking noise but not during non-masking noise. There was no difference in maximum frequency between treatments, thus bandwidth was significantly narrower during the masking treatment. I found no significant difference in how males changed perches, song types, or variants in response to either noise treatment. However, I found that when males switched to a new song type or variant when the noise started, that they switched to a type or variant that significantly increased the minimum frequency during masking noise. My results suggest that male song sparrows use vocal plasticity to immediately avoid the negative effects of masking noise. My results do not rule out the possibility of cultural or natural selection on frequency shifts observed in urban song sparrows. However, vocal plasticity is a flexible strategy that may allow adopters to both increase detectability in masking noise but also minimize the potential negative impacts of frequency adjustments on song function. Future studies should focus on how vocal plasticity in song sparrows impacts detectability and discrimination of song in anthropogenic noise.
Investigating vocal plasticity in song sparrows (Melospizia melodia) as a mechanism to avoid masking noise in urban environments
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Created on 6/1/2023
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Additional Information
- Publication
- Thesis
- Language: English
- Date: 2023
- Subjects
- Song sparrow
- Noise pollution
- Birdsongs
- City noise
- Audio frequency