Due to noise pollution, some birds are forced to sing at higher frequencies making them less attractive. Noise pollution from roads, industries and other sources forces some birds to sing at higher frequencies. Since the male birds are having to change their tunes, they become less attractive to females. (I know some men in real life who are like this.)
A new study shows that when bombarded by noise pollution, some male birds begin to sing higher tunes, rendering them less attractive to females. Data from study suggests that birds must make difficult trade-offs in urban areas and areas where loud noises threaten to drown them out. In order to rise about the norm in an area surrounded by noise, they sing less appealing songs or tones, or sing the songs that make them sound appealing at the risk of not being heard at all.
It will be interesting to see what happens over the next few years with these birds.