AboutZoos, Since 2008


Cap­tive Rhino health influ­enced by urban noise?

pub­lished 02 Novem­ber 2014 | mod­i­fied 02 Novem­ber 2014

Texas researchers have made a first step in look­ing for clues to improve rhino repro­duc­tion in cap­tiv­ity by inves­ti­gat­ing noises present in zoo habitats.

The sound­track to a wild rhi­noc­eros’ life is wind pass­ing through the savan­nah grass, birds chirp­ing, and dis­tant ani­mals mov­ing across the plains. But a rhi­noc­eros in a zoo lis­tens to chil­dren scream­ing, cars pass­ing, and the per­sis­tent hum of urban life.

White rhinos at Madrid ZooA group of researchers from Texas believes that this dis­crep­ancy in sound­scape may be con­tribut­ing to rhi­nos’ dif­fi­cul­ties thriv­ing and repro­duc­ing in cap­tiv­ity. Dur­ing the 168th Meet­ing of the Acousti­cal Soci­ety of Amer­ica (ASA), which is held 2731 Octo­ber at the Indi­anapo­lis Mar­riott Down­town Hotel, they will present their acousti­cal analy­sis of a cap­tive south­ern white rhi­noc­eros habi­tat, a first step towards under­stand­ing the impact of noise on these endan­gered animals.

Though zool­o­gists have stud­ied the impact of fac­tors like diet and hygiene on rhino repro­duc­tive health, sound has been largely ignored. How­ever, rhi­noc­er­oses have some of the keen­est senses of hear­ing in the ani­mal king­dom, able to per­ceive infra­sonic sounds below the fre­quency range of human range of hear­ing. In the wild, they can sense preda­tors com­ing from miles away by the vibra­tions their foot­steps send through the ground. Because rhi­nos are so sen­si­tive, noise that humans don’t notice – or can’t even hear – could be dis­tress­ing and dis­rup­tive to them, neg­a­tively impact­ing their health, said Suzi Wise­man, a bioa­cousti­cian at Texas State University.

Wise­man and col­leagues at Uni­ver­sity of Texas at Austin and Bay­lor Uni­ver­sity used sound detec­tors strate­gi­cally placed around the rhi­noc­eros enclo­sure at Fos­sil Rim Wildlife Cen­ter near Glen Rose, Texas to record dif­fer­ent fre­quen­cies of sound that the ani­mals encoun­tered over the course of a week.

You go there and it feels really quiet, and most peo­ple aren’t aware of the noises
Suzi Wise­man, Envi­ron­men­tal Geog­ra­phy, Texas State University-​San Mar­cos, Waco, Texas, US »

The about 700 hectare con­ser­va­tion park, located about an hour and a half drive from Dal­las, is fur­ther removed from urban life than most zoos. “But when you start record­ing [the noises], you start to notice them on all sides. You’re really show­ing up with a con­stant infra­sound the whole time,” added Wiseman.

Much of the noise recorded at Fos­sil Rim was nat­ural in ori­gin – wind, birds, and other ani­mals at the site. How­ever, the researchers also iden­ti­fied noises from a nearby road, jet planes pass­ing over­head, and park staff and vis­i­tors. Infra­sonic noise was per­sis­tent across all record­ings, though its sources have not yet been fully identified.

So far, the researchers have only analysed one sound­scape and so can­not con­clude the spe­cific impact it might have on the rhi­noc­er­oses. How­ever, they plan to record sounds from more zoos and parks, look­ing for a con­nec­tion between par­tic­u­lar types of noise and ani­mal health. It is likely that urban zoos would have more noise from human ori­gins than the rel­a­tively remote facil­i­ties that have tra­di­tion­ally had the great­est suc­cess in breed­ing cap­tive rhi­nos, Wise­man said.

One of my ques­tions is if there’s a con­tin­uum – from nat­ural sound­scape on one end to com­pletely urban, com­pletely anthro­phonic – then is there some­where along that con­tin­uum where an ani­mal, par­tic­u­larly a rhi­noc­eros, stops being healthy?” said Wiseman.

Zoos’ noise chal­lenges
The researchers hope their work will help zoos develop opti­mal habi­tats for ani­mals, often a chal­lenge given tight space and lim­ited bud­gets.

Still, Wise­man said, there are sim­ple steps zoos can take to reduce ambi­ent noise and improve qual­ity of life for their inhab­i­tants. For exam­ple, plac­ing sound-​absorbing bar­ri­ers around enclo­sures and replac­ing noisy zoo vehi­cles with qui­eter elec­tric ones both make a big dif­fer­ence at a rel­a­tively small cost. Zoos plan­ning major ren­o­va­tions could con­sider more ambi­tious strate­gies, such as choos­ing to house large, sound-​sensitive ani­mals in more rural loca­tions, where ani­mals would have more space and less expo­sure to city noise.

The abstract of ASA meet­ing pre­sen­ta­tion “What com­prises a healthy sound­scape for the cap­tive South­ern White Rhi­noc­eros (Cer­a­totherium simum simum)?” by Suzi Wise­man, Pre­ston S. Wil­son and Frank Sepulveda:

Many crea­tures, includ­ing the myopic rhi­noc­eros, depend upon hear­ing and smell to deter­mine their envi­ron­ment. Nature is dom­i­nated by mean­ing­ful bio­phonic and geo­phonic infor­ma­tion quickly absorbed by soil and veg­e­ta­tion, while anthro­phonic urban sound­scapes exhibit vastly dif­fer­ent phys­i­cal and seman­tic char­ac­ter­is­tics, sound repeat­edly reflect­ing off hard geo­met­ric sur­faces, dis­tort­ing and rever­ber­at­ing, and becom­ing noise. Noise dam­ages humans phys­i­o­log­i­cally, includ­ing repro­duc­tively, and likely dam­ages other mam­mals. Rhi­nos vocal­ize son­i­cally and infra­son­i­cally but audio­grams are unavail­able. They gen­er­ally breed poorly in urban zoos, where infra­sonic noise can be chronic. Bio­log­i­cal and social fac­tors are stud­ied but lit­tle atten­tion if any is paid to sound­scape. We present a method­ol­ogy to analyse the sound­scapes of cap­tive ani­mals accord­ing to their hear­ing range. Sound met­rics deter­mined from record­ings at var­i­ous insti­tu­tions can then be com­pared and cor­re­la­tions with the health and well­be­ing of their ani­mals can be sought. To develop this method­ol­ogy we stud­ied the sonic, infra­sonic and seis­mic sound­scape expe­ri­enced by the white rhi­nos at Fos­sil Rim Wildlife Cen­ter, one of the few U.S. facil­i­ties to suc­cess­fully breed this species in recent years. Future analy­sis can seek par­tic­u­lar para­me­ters known to be inju­ri­ous to human mam­mals, plus para­me­ters known to invoke response in animals.

(Source: Acousti­cal Soci­ety of Amer­ica meet­ing press release via News­wise, 24.10.2014)

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