It's been known for a while that birds increase their singing volume to make themselves heard in the big city, but recent studies show that the city birds might even be evolving into a new species.
"Silvereyes are common native Australian songbirds found in both town and country. "Their natural sounds would be masked by urban noise," says Potvin. Such noise, generated mostly by road and air traffic, is at pitches between 1 and 4 kilohertz – bad news for silvereyes, which sing in the 2 to 6-kilohertz range."
The results of the study showed that City Birds sing in a much higher pitch (about 195Hz higher) and in a slower manner. The higher pitch makes the songs possible to recognize from all the city noise, while the slow singing could be to counter the sound-reflecting effect of the buildings, as longer pauses between their 'syllables' make them easier to understand.
I just wonder when they change their color to match a certain other Urban Bird.