Even Low-Level Traffic Noise Undercuts Birdsong's Stress-Relieving Effects, Study Finds

A new study from the University of Surrey has found that even low-level traffic noise can undercut the psychological benefits of birdsong, weakening one of the best-known ways nature helps people relax. The study, published in the journal People and Nature, examined how the acoustic qualities of natural soundscapes affect well-being, and whether nearby traffic noise interferes with those effects.

The researchers ran two studies using the same nine simulated soundscapes of birdsong and traffic noise at varying levels of acoustic complexity and volume. In the first, more than 1,500 participants rated how relaxed and restored they felt after listening. In the second, 63 participants listened to the same soundscapes in a laboratory while wearing a heart rate monitor.

Natural soundscapes containing birdsong improved psychological well-being regardless of their acoustic characteristics, but traffic noise reduced those benefits even at levels below World Health Organization guidelines for daytime traffic noise. Participants also showed significantly lower heart rate variability when traffic noise was present, a sign of greater physiological stress, and the negative effect was strongest when the soundscape itself was also loud or complex.

Although each soundscape contained only three bird species and five individual bird sounds, participants who perceived more species diversity reported greater well-being; the researchers say perceived diversity, not just actual diversity, may be key. Younger participants and those who reported greater knowledge of birds also reported higher well-being. Dr. Melissa Marselle and Dr. Eleanor Ratcliffe of the University of Surrey suggested that reducing speed limits near parks or increasing ground-level vegetation around park boundaries could help lessen traffic noise's effect on people enjoying green spaces.