Even Low Levels of Traffic Noise Can Diminish the Stress-Relieving Benefits of Birdsong

A new study from the University of Surrey has found that traffic noise can interfere with the psychological benefits of birdsong and other natural sounds, even when the noise remains below recommended daytime exposure limits.

Published in People and Nature, the research examined how different acoustic features of natural soundscapes influence people's psychological well-being and whether the presence of traffic noise changes those effects.

Natural sounds, particularly birdsong, have been associated with lower stress, improved mood, and a greater sense of mental restoration. In contrast, road traffic noise is known to increase stress and irritation. The researchers say their findings highlight the importance of protecting the acoustic environment of parks and other green spaces.

"Being in nature and listening to its sounds is a natural way of improving well-being," said Dr. Melissa Marselle, a lecturer in environmental psychology at the University of Surrey. She noted that researchers still need to better understand which characteristics of natural soundscapes—such as volume, complexity, variety, and the number of bird species—produce the strongest psychological benefits.

How the researchers conducted the study

The team carried out two complementary experiments. More than 1,500 people participated in the first, listening to nine simulated soundscapes combining natural sounds and varying levels of traffic noise. The soundscapes also differed in acoustic complexity and volume. After each recording, participants assessed how relaxed and mentally restored they felt.

A second study involved 63 participants in a laboratory setting. They listened to the same nine soundscapes while wearing heart-rate monitors, allowing researchers to measure physiological responses in addition to reported feelings.

Traffic noise weakens nature's restorative effect

The researchers found that natural soundscapes featuring birdsong improved participants' psychological well-being across different acoustic conditions. However, adding traffic noise significantly reduced these benefits.

Importantly, the negative effect was observed even when traffic noise was below World Health Organization guidelines for daytime road traffic exposure. Participants exposed to natural sounds mixed with traffic noise also showed lower heart rate variability, suggesting a stronger physiological stress response.

The researchers found that higher levels of traffic noise were particularly disruptive when the natural soundscape itself was acoustically intense or complex. They suggest that the combination may lead to sensory overstimulation, reducing people's sense of calm and restoration.

Dr. Eleanor Ratcliffe, an associate professor of environmental psychology at the University of Surrey, said the findings were particularly relevant as cities expand their networks of parks and other green spaces. She suggested that reducing speed limits on roads near parks or increasing vegetation along park boundaries could help limit traffic noise and allow people to benefit more fully from natural environments.

Perceived bird diversity also matters

The study revealed another interesting connection: participants reported greater well-being when they perceived a greater variety of bird species in the soundscapes. Although the recordings contained sounds from only three bird species and five individual bird calls, people's perception of greater bird diversity was associated with stronger positive effects.

The researchers believe that the perceived richness of birdlife may be an important factor in determining how restorative natural soundscapes feel.

Age also appeared to influence the results. Younger participants reported greater well-being than older participants. One possible explanation is that younger people generally have better hearing and may therefore have experienced the soundscapes more clearly.

Participants who said they knew more about birds also tended to report greater well-being and perceived a higher diversity of bird species.

The researchers conclude that protecting natural soundscapes from traffic noise could be an important part of urban planning, helping people gain greater psychological and physiological benefits from time spent in green spaces.

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