Ur­ban Wildlife

The con­stant thrum of life in the city is harm­ing many ur­ban­ized species, in­clud­ing hu­mans

Canadian Wildlife - - NEWS - By Matthew Church

The con­stant thrum of life in the city is harm­ing many ur­ban­ized species, in­clud­ing hu­mans

Cities are noisy. At its worst, the street-level ex­pe­ri­ence can be lit­er­ally deaf­en­ing, with wail­ing sirens, pound­ing jack­ham­mers, and in­con­sid­er­ate car and mo­tor­cy­cle own­ers show­ing off their barely le­gal ex­haust sys­tems. Some cities, like my home­town, even have ad­ver­tis­ing trucks driv­ing around with ro­tat­ing bill­boards and blar­ing sounds — gra­tu­itous air, light and noise pol­lu­tion on wheels.

Even cities at their most quiet — on an early sum­mer Sun­day morn­ing, or a cold mid­win­ter Tues­day night — emit a con­stant buzzy hum. Like a city’s other forms of pol­lu­tion, noise de­grades ur­ban en­vi­ron­ments and neg­a­tively af­fects our lives. Con­sis­tently, stud­ies con­firm what most of us al­ready know in­tu­itively: that be­ing ex­posed to per­sis­tent, loud, un­wanted noise causes el­e­vated blood pres­sure, loss of sleep, in­creased heart rate and other car­dio­vas­cu­lar ef­fects, and changes in brain chem­istry. There is a cost to these ef­fects. Ac­cord­ing to the World Health Or­ga­ni­za­tion, these health ef­fects lead to “so­cial hand­i­cap, re­duced pro­duc­tiv­ity, de­creased per­for­mance in learn­ing, ab­sen­teeism in the work­place and school, in­creased drug use, and ac­ci­dents.”

Of course, na­ture can be noisy too. And that’s why most species have adapted and evolved to be aware of, re­spon­sive to and even in­ter­ac­tive with the sonic land­scape in the wild. An­i­mals process sounds in ways that some­time sur­prise hu­mans: frogs’ low rum­bles com­mu­ni­cate lo­ca­tion, affin­ity and al­lure to friends and foes alike; squir­rels lis­ten in on the com­mu­ni­ca­tion calls of op­por­tunis­tic blue jays, as­sess­ing any risk of in­va­sion to their cache while they are out and about. Such be­hav­iours are what keep them alive, whether they are prey in the in­stance, or preda­tor.

For ur­ban wildlife too, sonic over­load has ter­ri­ble health ef­fects. Af­ter all, per­sis­tent noise will in­ter­fere with an an­i­mal’s ca­pac­ity not just to com­mu­ni­cate, but to pro­tect it­self, to pro­cre­ate and raise its young, even to nav­i­gate. A re­cent study iden­ti­fied per­ma­nent dam­age to mice DNA re­sult­ing from acous­tic over­load, as well as el­e­vated mor­tal­ity rates among ev­ery­thing from rats to sea­horses.

While the ef­fects may be sub­tle, they can be last­ing and pro­found. For fish in busy ur­ban har­bours, pro­longed ex­po­sure to noise will even­tu­ally dam­age their swim blad­ders, which serve as their “ears”; blad­ders also con­trol buoy­ancy, so ef­fects can be dev­as­tat­ing. Duck, chicken and quail em­bryos, among oth­ers, fa­cil­i­tate “hatch­ing syn­chrony” with other eggs in a nest through a kind of vi­bra­tion-de­tec­tion/hear­ing re­sponse. It is a use­ful trait that eases the bur­den on the adults car­ing for them, im­prov­ing the odds of sur­vival for all in­volved. But with too much an­thro­pogenic am­bi­ent noise, the mes­sages are un­heard, lead­ing to fledglings with nutri­tional deficits and de­vel­op­men­tal prob­lems in­ca­pable of com­pet­ing and sur­viv­ing. The flock suf­fers.

Food gathering is also af­fected. Many species’ ca­pac­ity to iden­tify their next meal re­lies on their highly evolved au­di­tory acu­ity, which is ren­dered use­less by the ur­ban acous­tic over­lay. Owls and bats are two city-dwelling an­i­mals, both highly ef­fec­tive noc­tur­nal hunters, that rely on low-fre­quency sound lo­cal­iza­tion to iden­tify, lo­cate and cap­ture their prey. The par­tic­u­lar wave fre­quency of road traf­fic sounds in­ter­feres with their for­ag­ing ef­fi­ciency by mask­ing prey move­ment sound. As a re­sult, pop­u­la­tions dwin­dle, and the ef­fects re­ver­ber­ate through the lo­cal bio­sphere as it is thrown out of bal­ance. Some but not all species of bat can switch to sonar-based echolo­ca­tion and some­what less ef­fec­tively home in on their prey that way.

When it comes to com­mu­ni­ca­tions in the wild, there are two types: the de­lib­er­ate and the in­ad­ver­tent. In the for­mer, where the an­i­mal is at­tempt­ing to com­mu­ni­cate, many species are adapt­ing to city sound­scapes by mod­i­fy­ing their calls’ tim­ing, in­creas­ing rep­e­ti­tion, al­ter­ing tone and rais­ing vol­ume to over­come the buzz’s mask­ing ef­fect. You can hear the changes in bird chicks’ beg­ging, in squir­rels’ alarm sig­nals, in the echolo­ca­tion cries of bats and in the mat­ing com­mu­ni­ca­tion sig­nals in birds. What’s not heard are the in­ad­ver­tent sig­nals: the bee­tle’s rus­tle on a leaf, the splash of a leap­ing fish or greedy blue jays chirp­ing as they cir­cle an unat­tended cache. With­out these sonic cues, the pre­cise phys­i­cal and be­havioural adap­ta­tions of vir­tu­ally ev­ery species that are so cen­tral to stay­ing alive are ren­dered use­less. Sur­vival be­comes that much harder.

For many Cana­dian ur­ban­ites, the noise of the city is a con­stant, to the point that it is a com­fort even as it makes us sick. For ur­ban wildlife too, the ur­ban sound­scape presents life-threat­en­ing chal­lenges. For those that can adapt, the re­wards are con­sid­er­able. But for those whose es­sen­tial daily func­tions are im­peded or even nul­li­fied by the ur­ban ca­coph­ony, life in the city is hard and get­ting harder.

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