Data from: Higher songs of city birds may not be an individual response to noise

It has been observed in many songbird species that populations in noisy
urban areas sing with a higher minimum frequency than do matched
populations in quieter, less developed areas. However, why and how this
divergence occurs is not yet understood. We experimentally tested whether
chronic noise exposure during vocal learning results in songs with higher
minimum frequencies in great tits (Parus major), the first species for
which a correlation between anthropogenic noise and song frequency was
observed. We also tested vocal plasticity of adult great tits in response
to changing background noise levels by measuring song frequency and
amplitude as we changed noise conditions. We show that noise exposure
during ontogeny did not result in songs with higher minimum frequencies.
In addition, we found that adult birds did not make any frequency or song
usage adjustments when their background noise conditions were changed
after song crystallization. These results challenge the common view of
vocal adjustments by city birds, as they suggest that either noise itself
is not the causal force driving the divergence of song frequency between
urban and forest populations, or that noise induces population-wide
changes over a time scale of several generations rather than causing
changes in individual behaviour.