In Europe, where natural quiet no longer exists, except possibly in some far northern regions of countries such as Finland and Norway, entire populations of birds are adapting their songs to be heard above the din of noise pollution. The New Scientist (December 2006) reported that in urban areas birdsongs were losing lower notes and shifting to higher pitches that were less masked by traffic noise.

Gordon Hempton, John Grossmann, One Square Inch of Silence-…, loc. 941