This is interesting – New Scientist has a story about how city-dwelling birds have evolved a different way of singing, so that they can be heard over cars and jackhammers and the rest of the urban din.
City birds’ songs are sung at 195 hz higher than their country-dwelling counterparts. Their contact calls (those made to communicate things like danger, or “there’s food here!”) were 90 hz higher. Furthermore, the city birds’ songs were slower, possibly because all the buildings around them cause echoes that make their songs harder to make out at faster speeds.
To be honest, I had not noticed this. Next time I’m in some rural setting, though, I’ll be sure to try to make out the faster, lower-pitched birds.
440hz 