Thusly, only group 1 males showed changes in minimum frequency and bandwidth in response to noise, and neither group 1 nor group 2 males changed their trill rates, which negatively affected their vocal performance. Only the group 1 males showed an increase in minimum frequency because they were at risk of having their songs masked by the background noise unlike the group 2 males who already had minimum frequency above background noise. Unexpectedly, group 2 males decreased minimum frequency with increasing vegetation, and group 1 males showed higher minimum frequency with increasing urban structure. As noise was not correlated with either urban or vegetative structure, the latter outcome is likely not due to the fact that more structured habitats are noisier. These results suggest that, based on individual variations in their songs, males generate novel spectral adjustments in response to anthropogenic noise. Additionally, peak frequency decreased with increasing urban structure for both groups, likely because lower frequency sounds don’t suffer as much from the effects of reverberation as high frequency sounds. Neither group adjusted their trill rates in response to urban structure, despite the fact that an increase in reflective surfaces causes trill notes to be slurred with one another, especially at high trill rates. Males also didn’t shorten their trills in order to minimise accumulation of reverberation over the song. Thus, since group 1 males in an urban setting narrowed their bandwidth but didn’t increase trill rate, they had poorer vocal performance. Similarly, since group 2 males in an urban setting didn’t lower their trill rates, they also suffered poorer vocal performance. As such, both groups of males, and especially group 2 males, could experience reduced mating success. It is possible that males cannot adjust trill rate or song length because of constraints imposed by female preference. Alternatively, males may benefit from sound reflections by picking perches which cause their signals to undergo constructive interference rather than destructive interference. That is, instead of reverberations causing the signals to become slurred and to cancel out, they would add up to increase in amplitude, thereby propagating the signal even further. In sum, it may be the case that chipping sparrows in structured environments choose their perches based on how well their song is amplified rather than by how little their song is degraded.
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