A comparison between two ways to measure minimum frequency and an experimental test of vocal plasticity in red-winged blackbirds in response to noise

In: Behaviour
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  • 1 Department of Evolution and Ecology, University of California, Davis, CA, USA
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We examined whether red-winged blackbirds modulate their vocalizations in response to experimental highway noise, alternating between ambient-control and noise-playback periods. Our measures of song duration were shorter, and with a lower value of freq5% (a measure of energy distribution), during noise-playback; however, we interpret these results as noise-induced artefacts. This apparent lack of vocal plasticity should be taken cautiously because we had a small sample size and most birds produced only one song type: song type-related vocal plasticity was unlikely to be found. We found no evidence of a shift in minimum frequency with noise when this was measured with a threshold method on power spectra, but it seemed to increase when measured by eye from spectrograms. Our results suggest that the by-eye practice can lead to bias, which is problematic as several previous studies have used this procedure. Use of the threshold method, over the by-eye practice, is encouraged.

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