When Rachel Carson wrote the environmental classic Silent Spring in 1962, she warned that unchecked human impacts might create a silent future.
Forty years later, biologists uncovered a striking effect of noise pollution on songbirds. They found that low-pitched traffic noise in European cities forced birds to sing at higher pitches. Songbirds in a noisy park beneath the Eiffel Tower sang at a pitch of 400 Hz higher than those in quiet forests outside Paris.
