Birds exposed to artificial traffic noise were observed to change their tune to compete with the urban noise.
"[F]indings suggest that birds must make difficult trade-offs in urban areas and places where traffic and industrial noises threaten to drown them out. Either they sing less appealing songs or tones in an effort to rise above the din, or they sing the songs that make them sound appealing at the risk of not being heard at all.
'If females can hear all song types equally well, they will go for the sexy ones, but if they cannot hear the sexy ones well anymore, then they might just go for the songs they can still hear,' said Wouter Halfwerk, a behavioral ecologist at Leiden University in the Netherlands. 'It could very well be that noise pollution is interfering with reproductive decisions by females.'"