Biologists from Boise State Universityhave been making noise in the forests of the western American state of Idaho.They are making noise to study the value of quiet in nature.They want to know how people and animals react to noise pollution.The researchers placed outdoor speakerson the side of a half-kilometer-long part of a road in the Boise National Forest.For two years, they played the sounds of passing cars through the speakers.Professor Jesse Barber of Boise State University saysthey found the sounds caused migratory birds to flee.The birds also failed to gain weight.Recently, researchers played sounds of machinesthat are used to remove natural gas from the ground.（Sound）That sound is heard in natural gas fields throughout the American West.Professor Barber says these experiments are designedto help researchers learn the effects of noise pollutionon birds, insects, bats, plants and people."We are testing the idea that these things are coupled-- that as the soundscape gets louder, wildlife suffers.But that also feeds back on to how much people get out of that experience,how much they value it,and thus how much they are willing to protect that same place."The research team also studied a group of volunteers who watch birds for fun.Mitch Levenhagen is a graduate student in the research team.He measured how much the artificial noiselessened the ability of the birdwatchers to identify recorded bird songs.He recorded eight songs in the noise condition and eight songs in the quiet.He then repeated the experiment without the artificial noise.The birdwatchers were happy when the noise machine was shut off.The birdwatchers said the artificial noise affected their abilityto identify bird sounds more than they thought it would.Birdwatcher Jim Lyons said the experiment caused him to value quiet more."The whole thing has been ear-opening, shall we say.To be part of this is very stimulating, very interesting.I am going to think about it from now on."Volunteer Janice Engle said she, too, likes the quiet."I moved out of the city to a little place in the country where I wanted it to be quiet.I greatly value that.It is hard to find those places more and more.There are lots of ways to mitigate sound.But it is trade-off. There is always a cost.And it comes down to people's values. What do we value more."The National Park Service is paying for some noise pollution research.The federal agency is also examining other ways to reduce noise.They include putting new surfaces on roads.And they are creating quiet areas with signs telling visitorsto turn off their mobile phones.Next year, Mr. Levenhagen and Professor Barberwill go to Northern California to ask visitors at Muir Woods National Monumentand other parks how they feel about noise.