January 11, 2013
Birds Sing Louder At Higher Frequencies
Alan McStravick for redOrbit.com — Your Universe Online
Have you ever been to oh, let´s say, New York City or Chicago? Maybe Philadelphia or even downtown Fort Worth? If you have and you are, like me, a lover of city life and city residents, you will have noticed that the inhabitants of these cities move a little faster, have a little less patience and talk quite a bit louder. Is it the environment that drives these actions and behaviors? Does the city just attract these specific types of individuals, like moths to a bright light, to reside in the hustle and bustle? It may just be that a subject of one of my favorite Beatles songs, a blackbird, will help us to perhaps learn a little more about ourselves.
This is because we are learning how animals are, in order to deal with the increase in noise pollution in their habitats, developing several different strategies. Previous studies have shown that urban dwelling birds will sing their songs at a higher pitch in an attempt to counteract the low-frequency drone of road traffic. But this is just half the story. According to researchers at the Max Planck Institute for Ornithology, the use of pitch modulation as a counter-balance to lower frequencies is just a side effect of the primary use of an elevated pitch. As they claim, songs at a higher pitch are also songs that are louder. This allows the birds to make themselves far better at being heard across greater distances and amongst the din of city noise simply by the increase in volume rather than by raising its frequency.
The researchers, based in Seewiesen and Radolfzell, engaged in an interesting comparative study of urban blackbirds in Vienna and their country cousins in the nearby Vienna Woods. A control colony of blackbirds was also raised by hand in a laboratory setting at the institute. The purpose of their study was to investigate the correlations between frequency and amplitude of the blackbirds´ song under controlled conditions. What the researchers learned was that these birds were able to produce higher tones at higher amplitudes. Thus, blackbirds in the city tended to sing at these higher frequencies so that they might produce a song that was far louder, allowing for them to be heard at greater distances.
If we can look back to previous studies we see that researchers have had an interest in the motivations behind the increased pitch of these songbirds, albeit for different reasons and reaching alternate, though related conclusions. For example, researchers at the University of Copenhagen and the University of Aberystwhth contend that the constant and steady noise of the city is but one factor that plays a role in the louder singing of the sparrow, blackbird and great tit. They believe, also, that the physical structure of a city is an important factor, altering the birds´ songs.
"Urban architecture is a crucial determinant of how urban birds sing," stated Professor Torben Dabelsteen of the University of Copenhagen and one of the authors of the previous study. He believes the explanation solely that the birds are singing out to combat the ceaseless city noise they are surrounded by is an explanation that is, itself, incomplete.
Of course, there have been researchers all along that never really accepted the idea that the noises of the urban jungle alone were the cause for birds in cities to sing at higher frequencies.
"Now, with the help of controlled sound recordings, we have shown that the higher frequencies in urban birds' songs are also transmitted across cities when there isn't any noise from traffic. This shows that the physical structure of cities must play a considerable role in the heightened frequencies," explains Dabelsteen.
From buildings to open spaces to tight alleyways, the layout of, and structures within a city are important factors in the song of the urban birds. Each of these components of a city work to both reflect and distort noise in differing ways. This audible distortion is important to wildlife and is a necessary consideration that the city birds must take into account. In the urban environment, one bird can see another far more easily than in a rustic environment. Even still, the city dwellers must affect any stratagem they can in order to reduce echoes from structures and streets in order to effectively communicate with one another.
By comparison, the birds outside of the city didn´t require an adaptation that would require them to sing at such impressive volume. Even though the trees that are the environment of the rural birds can act to distort sound, as well, they also obstruct clear lines of sight, unlike the open spaces of the city. These rural distortions are used to the advantage of the inhabitant birds in locating one another and in judging distances.
Though living in a city setting seems like it might have too many drawbacks for birds, not the least of which would be the possibility of laryngitis, there are several reasons we have seen the colonization of the urban setting by wild animals. While humans, noise and light pollution are ever-present in an urban environment, the advantages for these animals are apparently too good to pass up. When you factor in the increased and readily available supply of food combined with new breeding options, we see just why and how it is that many of these wild animals have undergone an astonishing adaptation to city life.
For example, the robin that chooses a metropolis as its home will sing in the latter part of the evening as the city´s traffic noise is on the decline after the evening rush. The robin chooses this time of day to sing in order to attract their potential mating partners. It is also the time of day they have opted for to defend their territories.
There are a few competing and complementary theories out there on why it is the urban bird will project their song. Whether factoring for city noise or city structure, the data definitely shows that the metropolitan bird is far more boisterous than his counterpart in the country. Erwin Nemeth, lead author of the Max Planck study stated, “The higher volume of the higher-pitched song is more effective than the higher frequency. 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 at the Max Planck Institute added, “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.”
One thing is certain, however. On my next visit to a city center I will find it difficult not to keep an ear out for these avian belters of the avenues and boulevards. And I, like the researchers cited in this article, will wonder if they are singing so loudly due to their spatial or auditory environment.