Traffic Noise Weakens Birdsong’s Mental Health Benefits, New Study Shows

Sitting in a park and listening to birds sing feels good, and that feeling is easy to take for granted. A new study is putting hard science behind it, and what researchers found about traffic noise may change how cities think about green spaces.

A research team, publishing in the journal People and Nature, set out to understand exactly what makes natural soundscapes mentally restorative, focusing on birdsong and the role of road traffic noise. Even traffic noise below the World Health Organization’s recommended level for daytime roads was enough to measurably undercut the mental health benefits of listening to birds. And when the birdsong was louder or more acoustically rich, traffic noise interfered even more with its restorative effect.

That faint hum of cars in the background may matter more than it seems. Even at its lower, quieter setting, it chipped away at the sense of restoration people reported from listening to birds, one of the most accessible forms of mental reset that nature offers.

Why Birdsong Helps, and What Traffic Noise Gets in the Way Of

Researchers have long known that natural environments support mental health. Most of that research has focused on what people see, such as trees, parks, and open green spaces. Far less attention has gone to what people hear. This study set out to fill that gap by focusing on sound.

Two separate studies were conducted. First, a large online study recruited 1,529 UK residents, sampled to be representative of the UK population by age, gender, and region. Second, a smaller lab-based study brought 62 undergraduate students into a controlled setting where researchers measured heart rate variability, the subtle changes in timing between one heartbeat and the next that can signal how relaxed or tense the body is.

Both groups listened to nine carefully constructed birdsong recordings. Each soundscape was built from actual bird calls downloaded from a citizen science database and assembled to vary in how layered and loud the natural sounds were. Researchers then layered traffic noise, either below or well above WHO daytime guidelines, over some of those soundscapes. After listening, participants reported how restored and relaxed they felt.

What People Think They Hear Matters More Than What’s Actually There

One of the most surprising findings had nothing to do with traffic. Every soundscape in the study contained the exact same number of birds: five individual birds representing three species. Despite that fixed reality, participants consistently guessed different numbers of species when asked how many types of birds they could hear. Those who believed they were hearing more types of birds reported higher scores on the study’s well-being and restoration measures.

With the actual number of bird species held constant across every recording, perception tracked how good listeners felt, not the real count of birds. Soundscapes with a moderate level of layering, not too sparse and not overwhelmingly busy, were the most likely to make listeners feel like they were hearing a wider mix of birds.

Psychology and music theory both describe an inverse-U pattern, where a moderate amount of variety is preferred over too little or too much. Too little becomes monotonous. Too much becomes chaotic. Natural sound environments seem most beneficial between those two extremes.

Even a Little Traffic Noise Does Real Damage to Birdsong’s Benefits

Across both studies, traffic noise consistently lowered participants’ sense of restoration and well-being. Soundscapes with no traffic noise scored best. Low traffic noise, set below the WHO daytime guideline, still pulled scores down compared to pure birdsong. High traffic noise, set well above the guideline at a volume meant to feel roughly twice as loud, produced the worst outcomes by a wide margin.

Traffic noise did the most harm when the natural soundscape was already louder and more layered. Researchers suggest this may be a kind of sensory overload effect, where too much combined sound energy, both natural and artificial, overwhelms the listener rather than restoring them.

Physiological data from the lab study lined up with those self-reports. For two of the three soundscape types tested, listeners’ heart rate variability shifted toward a less relaxed state when traffic noise was present than when they heard only natural sounds. Researchers caution that the measurement windows lasted only one minute, so these particular results should be read carefully.

Certain personal characteristics also shaped how people responded. Participants who reported a stronger connection to nature rated the soundscapes as more restorative overall. Those with more knowledge about birds also reported higher well-being and were more likely to perceive greater bird diversity in the recordings. People who described themselves as more sensitive to noise reported lower well-being across the board, particularly when traffic sounds were present. Younger participants tended to score higher on well-being measures than older ones, though researchers note this is somewhat puzzling given that other studies have found the opposite.

A Walk in the Park Isn’t as Simple as It Sounds

Parks, nature reserves, and green spaces are frequently promoted as tools for improving public mental health. Cities invest in them. Doctors increasingly recommend spending time in them. But if traffic noise is allowed to bleed into those spaces, even at volumes considered officially safe, the benefit those spaces are meant to provide is being quietly eroded.

Researchers note that strategies like reducing speed limits on streets near parks, promoting public transportation, or planting dense vegetation along park edges to buffer sound could help protect these acoustic environments. Researchers put these forward as directions for park planning, not as options this study tested. As noise pollution rises globally, treating the absence of traffic noise as a public health resource worth protecting may be exactly the kind of policy shift that urban planners need to take seriously.

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