City-dwelling blackbirds typically produce more high-pitched songs than their country counterparts, and researchers say the urban birds prefer shrill sounds to make their voices heard over road traffic.
For their study, scientists from the Max Planck Institute for Ornithology in Germany looked at urban blackbirds in Vienna and country blackbirds in the nearby Vienna Woods, as well as captive birds.
An analysis of the frequency and amplitude of the birds' songs show that the animals were able to produce higher tones at higher amplitudes — meaning the higher pitched the song, the louder it could be, which could explain the blackbirds' preference.
"By actively selecting high-frequency sounds, the city birds can increase their capacity to sing loudly and in this way counteract the acoustic masking of their song by the ambient noise," researcher Henrik Brumm said in a statement.
The birds' tactic is just one example of the strategies animals adapt to live effectively alongside noisy humans. Some urban robins wait to sing latter in the night after traffic dies down, the researchers note.
But even far away from cities, noise from humans can be a serious problem for other animals. Of marine mammals, whales have the greatest acoustic sensitivity at low frequencies, and their songs — which are crucial for mating and finding their companions — can be drowned out by the undersea noise of shipping traffic and energy exploration. A 2010 study found that North American right whales increase the volume of their calls as environmental noise increases.
The new study was detailed last week in the journal Proceedings of the Royal Society B.