Clamorous City Blackbirds
Max Planck Institute for Ornithology
First posted on 01-11-2013
Birds can sing louder at higher frequencies and thereby make themselves heard in traffic noise
Despite the unfavorable environmental conditions they encounter in town, many wild animals have colonized cities as a new habitat. In cities they must deal with greater numbers of humans along with more light and noise pollution than they encounter in rural settings. However, the urban habitat also offers certain advantages. For example a more abundant supply of food and new breeding options. Many animals have thus adapted surprisingly well to city life.
To attract mating partners and defend their territories, urban robins sing later in the night, once traffic noises decrease after the evening rush. Many other bird species, including blackbirds, sing in urban environments at a higher pitch, so that their song is easier to distinguish in the lower-frequency traffic noise.
However, as a group of scientists from the Max Planck Institute for Ornithology has discovered, this is just half of the story. They studied urban blackbirds in the city and in rural settings. Additionally, they raised birds by hand at the Max Planck Institute and investigated the correlations between the frequency and amplitude of their song under controlled conditions. Their research indicated that the animals were able to produce higher tones at higher amplitudes. In the city, blackbirds prefer to sing at these high frequencies, which they can also produce at a high volume.
The researchers also examined which effect is better suited to avoiding the acoustic masking of traffic noise: the higher frequency or the higher amplitude that results from it.
“The higher volume of the higher-pitched song is more effective than the higher frequency,” says Erwin Nemeth, first author of the study. “So we assume that the increased volume is the main cause of the higher frequency singing by city birds.” Henrik Brumm, the leader of the research team, adds: “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.”