Topic: What we miss when we listen to bird song: the hearing side of avian communication.
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What we miss when we listen to bird song: the hearing side of avian communication
Dept of Biological Sciences
West Lafayette IN
Birders use spectrograms to help them understand bird song. When doing so, we implicitly assume that
birds are hearing what we see in the spectrogram. If so, then we’d expect that details of how birds hear
should match details of their song properties, and they often do. For example, tufted titmice use very
high frequency alarm calls and indeed have very good high frequency hearing. Similarly, birds with very
tonal song (e.g. titmice) are not very good at processing rapidly changing frequencies, but birds with
very rapid elements in their song (e.g. white-crowned sparrows) are better than you are at processing
rapid frequency changes (!).
Birds (and all other vertebrates) are also able to retune their auditory system across seasons.
Comparisons of their song with auditory performance suggest that they retune their auditory system in
the breeding season to extract song properties at enhanced levels. For example, Carolina chickadees
have a broad-band song that matches the upregulation of processing of a wide range of tones in the
breeding season. In contrast, white-breasted nuthatches have a song with maximum intensity at about
2 kHz, and their auditory system only gets better at 2 kHz during their breeding season.
We tested this further with 9 sparrow species that vary in habitat preference and song properties. The
song properties are not shared between related species, but they are strongly affected by habitat. Open
adapted species tend to have rapid, high frequency songs whereas closed-canopy species tend to have
low-frequency tonal songs. Oddly, there was no correlation between habitat and the range of
frequencies they hear well. Surprisingly, we found that song type (trill vs more complex notes)
correlated strongly with hearing properties – the implication is that the properties of trills are processed
very differently than the properties of more complex songs (say of song sparrows). These data on
sparrows suggest that the spectrogram does not tell the whole story. Which makes bird song all the