Song Sparrow Song Varies with Urban Noise

In this study, Wood and Yezerinac (2006) studied whether male Song Sparrows changed their songs in response to anthropogenic noise. Most anthropogenic noise occurs in the lower frequency range of sparrows (1-2 kHz). Wood and Yezerinac predicted that males in areas with higher amplitudes of noise would modify their songs to have higher minimum frequencies, greater amplitudes for higher frequencies, and similar maximum frequencies well above the ambient noise.

To test these hypotheses, the researchers recorded the songs of 28 sparrows around the Portland, Oregon region. The songs were recorded for at least 3 minutes, and the ambient noise of the area was recorded immediately after the sparrows’ songs in the same location. Two songs from each sparrow’s recording were selected at random and analyzed. Measures were taken of the highest frequency, the lowest frequency, and the frequency of the greatest amplitude, duration, and number of notes. Additionally, they measured the average intensity of sound in either high frequency (4-9 kHz) or low frequency (1-4 kHz).

They found that Song Sparrows do change their song frequencies depending on the environmental noise. Sparrow songs had a higher minimum frequency and less energy in low-frequency notes in environments with louder, low-frequency background noise. There was no relationship between the maximum frequency notes and the background noise.

This study pertains directly to our class discussion on sound transmission. In class we learned how background noise can mask sounds and prevent them from reaching long distances. Animals that depend on communication to attract mates and defend territories should adapt their calls to find “open channels” in the environment noise. This study shows an example of how species can adapt and modify their sounds to adapt to the relatively recent changes human industrialization has brought to the environment noise. This adaptability allows sparrows to optimize their calls to the greatest distances.

Wood, W. & Yezerinac, S. (2006). Song sparrow (melospiza melodia) song varies with urban

noise. The Auk, 123, 650-659.