Deep in the mountains of Arunachal Pradesh, where the mighty Siang river carves its way through the Himalayan wall, nestled the Adi hamlet of Tuting, surrounded by a sea of green—overgrown fields, verdant mountains, the river itself deep green. The very moonlight seemed green as it shone on the ghostly mist rising from the gorge. Eighteen years ago, a search for India's last Takin—that strange-looking, mysterious kin of the musk-oxen—had led me (and colleagues from the Wildlife Institute of India) to this remote village, amid dense rainforests that we'd only read about, us kids of the concrete jungle. We were wide-eyed with wonder.
Talom Yaying, an Adi hunter from Tuting took us to look for takin in the mountains, where he hunted regularly—living the "simple, good" life of harmony with nature? Maybe...! He offered us his cave for the night, in the heart of the rainforest, high up on a ridge overlooking the great gorge. Such wonderful, magical country—and so hopeless my attempts to capture its rapturous beauty on a few square centimeters of celluloid! Put that camera away!
On our way back, Talom told me he felt compelled to spend a few nights every week in his cave—away from his village home and family. For in the village, the only sounds to awaken him at dawn were chicken and dogs and pigs. But up in his cave, he was serenaded by the songs of wild birds and other animals! Even in Tuting, a village completely surrounded by the rainforest, he missed the sounds of the forest! Unlike us city-bred wildlifers, he knew exactly what he missed and where to find it. We don't even understand what we've lost, when or where. Growing up amid the steady din of city life, most of us don’t even recognize those other natural sounds, the warbling of birds, the croaking of frogs, the chirrupping of crickets. How, then, can we hope to recover what we don’t even know we’ve lost?
All these years later, many spent studying songbirds in the wild and amidst human habitats, I share Talom’s sense of loss more keenly as I contemplate how all the noise we make adds another, barely recognized, dimension to the loss of biodiversity that all of us bemoan. We recognize, of course, the many overt ways in which our cities displace (if not outright kill) wildlife species by destroying and transforming their habitats. But we are only just beginning to understand the less visble impacts, such as the steady and growing hum of traffic and industry, which alter the behavior and diversity of animals in / near our cities.
Like us, many animals rely on sound to communicate with their mates, relatives, competitors, even enemies—and birdsongs offer the best studied examples. Birds use a variety of sounds to communicate, from simple tweets / whistles to elaborate songs rivaling the finest tunes coming from your FM radio. The more complex songs are used by males to attract mates and to warn rivals for territories. In general, males with bigger repertoires and more complex songs are more successful in courting females and fathering young compared to those that can hum but a few bars of one tune. What’s more, avian pop charts can also vary from station to local station, resulting in regional dialects of song. Some of us (the subspecies of humans known as birdwatchers) can identify different bird species by their voices, even among the duller look-alike warblers (the little brown/green jobs)—while keener ears can learn to tell apart the Greenish Warblers that spend their winter in Maharashtra / Andhra Pradesh from their cousins who prefer to settle in Tamil Nadu or Kerala for the winter!
How well sound waves carry your message depends, of course, on the medium they travel through—and background noise can seriously interfere with audio communication. As you know if you’ve tried to make a phonecall while stuck in traffic, or to sustain that philosophical discussion during a dinner party, the noisier the background, the harder it is to convey your message or understand what the other party is saying! Birds have the same problems: male birds are unable to show off the full extent of their vocal repertoire, especially the subtle vocal modulations, if their habitat is too noisy; and females suffer too because they cannot find the best males, thereby losing the chance to produce attractive sons who will in turn produce the most grandchildren (for that, indeed, is what the evolutionary game is all about when you get right down to it). A recent study found that Australian Zebra Finch females, given the choice between several different male songs (in the laboratory where they listened to recordings) were quite discriminating when the background was quiet, but became rather poor in distinguishing between songs when traffic noise was broadcast along with the same songs! Isn’t the audience always quieter—and more touchy about any noise—at a classical than at a pop music concert?
One way birds can cope with all the noise we make is by singing louder when it gets noisy—and this so called cocktail party effect has been observed in some species. Urban noise, especially traffic, also tends to be generally low-pitched, so an alternative is for birds to get shriller, sing at a higher pitch–exactly what Great Tits have been observed to be doing in Europe. A more subtle effect is for birds to simplify their songs, cutting out some of the fantastic frequency modulations, harmonics, and other vocal gymnastics they are capable of—not unlike how maestros of classical music may be forced to stoop to Bollywood tunes or advertising jingles to make a living! If those tricks don’t work, one has to find relatively quieter times during the busy urban day to sing one’s melodies—which may be why that annoying Magpie Robin keeps waking you up at 4 in the morning, well before dawn!
Of course, not many species are flexible enough to make these adjustments and continue living in the city. Those that cannot cope likely go extinct locally, leaving behind a poorer urban bird community. Chalk up another reason why cities worldwide are occupied mostly by the depressingly familiar contingent of pigeons and starlings and crows—the usual suspects in the homogenization of urban wildlife that seems part and parcel of the globalization package. In the long run, if our cities keep growing, and we keep finding more ways to make noise, we will chase away most of our more discriminating feathered singing friends, while those that remain will sing an impoverished urban dialect. And we all lose the symphony of biodiversity to the homogeneous urban cacaphony. We must all share Talom Yaying’s sense of loss—even though some of us just don’t know it yet!
Katti, M. (2001). Vocal communication and territoriality during the non-breeding season in a migrant warbler Current Science, 80 (3), 419-423 PDF
Warren, P., Katti, M., Ermann, M., & Brazel, A. (2006). Urban bioacoustics: it's not just noise Animal Behaviour, 71 (3), 491-502 DOI: 10.1016/j.anbehav.2005.07.014
Swaddle, J., & Page, L. (2007). High levels of environmental noise erode pair preferences in zebra finches: implications for noise pollution Animal Behaviour, 74 (3), 363-368 DOI: 10.1016/j.anbehav.2007.01.004
Slabbekoorn, H., & Peet, M. (2003). Birds sing at a higher pitch in urban noise Nature, 424 (6946), 267-267 DOI: 10.1038/424267a
Fuller, R., Warren, P., & Gaston, K. (2007). Daytime noise predicts nocturnal singing in urban robins Biology Letters, 3 (4), 368-370 DOI: 10.1098/rsbl.2007.0134