Many birds, no road: what makes a soundscape feel full?

Some birdsong sounds like a whole hedge is awake. Some sounds like one bird with something stuck on repeat. A study published this year in People and Nature looked at where that difference comes from and found that the answer is partly in the listener’s ear.

The clips were built to hold the same number of birds

The research team, led by Konrad Uebel with colleagues at the universities of Surrey, East Anglia and Glasgow, assembled nine one-minute soundscapes from recordings of real British birds. They picked species that actually occur together in UK habitats, using national bird survey data, and left out gulls, whose calls some listeners find unpleasant.

The researchers kept one thing the same across all nine clips: each held three species and five individual birds. What they changed was the shape of the sound. Some clips were more or less complex from moment to moment, some had a bigger gap between the loudest and quietest parts of the birdsong range, and some spread their energy more evenly. Three standard acoustic measures tracked those differences.

Then some clips got a road. A “low” traffic layer was motorway noise alone, set quieter than the World Health Organization’s daytime guideline for road noise. A “high” layer added city sound to the motorway and was set louder.

Listeners: who took part and what they rated

Two groups took part. The main one was an online sample of 1,529 UK adults, chosen to match the country by age, gender and region. A smaller group of 62 undergraduate students repeated the task in a lab at a UK university.

People were advised to wear headphones and asked to close their eyes for each clip. After every clip they answered questionnaires about how restorative the soundscape seemed, how they felt, and one simple question: “About how many different types of birds would you say you can hear in these recordings?” The answer scale ran from none to four or more.

What the 2026 results showed

What changed	What happened to the ratings
More kinds of bird perceived	Higher ratings, in both groups
The acoustic measures themselves	No direct effect on the ratings
Low traffic (motorway only)	Ratings went down in most comparisons
High traffic (motorway plus city)	Ratings went down, most of all when the birdsong was loudest and busiest

Perceived variety mattered most. Every clip contained three species, but people’s estimates still varied a lot from clip to clip. The more kinds of bird people believed they could hear, the higher they scored the clip. The acoustic measures had no direct link to the ratings, though two of them did change how many birds people thought they heard. Clips of middling complexity tended to sound the most varied, more than the plainest or the busiest ones.

The road cost something even when it was quiet. Compared with birdsong on its own, both traffic layers were linked to lower ratings across most of the comparisons. The authors note that this held even at the lower level, which sat under the WHO daytime guideline.

Fuller soundscapes lost the most. The drop under heavy traffic was largest when the birdsong itself was louder and more complex. One explanation the authors offer is that there was simply too much sound energy in total: a full chorus and a busy road together may be more than a listener wants to take in.

Who was listening also mattered. Younger people, people who felt more connected to nature and people who knew more about birds tended to give higher scores.

Limits: where one-minute clips fall short of a park

The researchers are open about the limits. The soundscapes were assembled from separate recordings, so they call for the same work to be repeated with recordings of real natural places. The test used sound alone, with nothing to look at, even though what we see on a walk shapes what we hear. Each clip lasted one minute. And all the outcomes reported here were people’s own ratings on questionnaires, collected in the UK.

You can read the full paper at People and Nature or in the University of East Anglia’s open-access copy. This is a plain summary of one study, not health advice.

Listening for variety on your next walk

If you walk through a park or along a canal on your way somewhere, try counting voices rather than birds. A short whistle, a rattle, a long liquid phrase and a two-note call are four different textures, even if you can’t name a single species. This study suggests that the sense of “how many” is something listeners build themselves, and paying attention is part of how it gets built.

It also helps explain why one repeating call can feel thin. The study didn’t test a single bird on a loop, so this is an inference: if fullness depends on the variety a listener picks up, one voice saying the same thing gives the ear very little to count.

And it puts a name to what traffic does. A steady road hum doesn’t need to be loud to take something away, and in this study it took away most where there was the most to lose. If you play nature recordings in the background while you work, at home or in a mix of your own in moonMind, the pattern points toward several different voices and no road under them. Nobody has tested that as a mix, so let your own ears decide.

A soundscape feels full, it seems, not because of how much sound it holds but because of how many different voices you can pick out of it.

Sources

1. Uebel, K., Marselle, M., Buchan, C., Butler, S. J., Hanley, N., Higney, A., & Ratcliffe, E. (2026). “The influence of acoustic characteristics and anthropogenic noise on restorative perceptions of natural soundscapes.” People and Nature, 8(10), 3466–3480. https://doi.org/10.1002/pan3.70405 (open-access copy: https://ueaeprints.uea.ac.uk/id/eprint/104413/)