Esther A. Leung (Biology) University of Texas at Arlington: Caitlin Kight (Biology) College of William and Mary
Urbanization affects the life of birds in many ways. One of the influences is the masking of bird songs by noise caused by human activities, which makes it difficult for birds to communicate. Acoustic communication is important in birds in defending their territory and attracting mates. (Slabbekoorn 2007) Research has shown that birds adapt to the background noise in their habitat by adjusting the design of their songs. The song amplitude of Nightingales is individually regulated according to the level of masking background noise. (Brumm 2004) Frequencies of Little Greenbul songs are shown to differ between habitats due to the level of ambient noise. (Slabbekoorn 2002) An evolutionary change is suggested to be taking place, in which birds adapt the designs of their songs to overcome acoustic difficulties. (Slabbekoorn 2007) Aiming to see how the ambient noise affects Eastern Bluebirds around Williamsburg, Virginia, we recorded male songs at different bird-box locations. We played a Bluebird song with speakers to elicit the birds' response. When analyzing songs from twelve of the sites with the software Raven, we focused on comparing the high frequency and the max power of the songs to those of the ambient noise. In other words, we wanted to see how the ambient noise in Bluebirds habitat affects their song, in terms of both frequency and amplitude. Based on previous literature, we expected the frequency and amplitude of the birds would increase with the ambient noise. We found that there is no significant relationship between the high frequency and max power of songs and the ambient noise. This may be due to the possibility that the birds adjust lower frequencies, instead of the high frequencies. It might also be possible that the broad range of ambient frequency minimized the differences in frequencies among the sites. In other words, the sites selected had similar ambient frequencies. As for the amplitude, the sites we looked at might not have been of a great enough variety of noise levels, and the birds might already be singing at their loudest. In addition to having a more diverged site selection, analyzing specific song syllables that overlap in frequencies and amplitude with those of the ambient noise, or being able to control those acoustic features of the ambient noise, would yield a better comparison.
For additional documentation Esther Leung provided a PowerPoint Presentation entitled "The Affect of Ambient Noise on Bluebird Songs " provided here in PDF form.