Traffic noise may be changing the songs of Malaysia’s gibbons

In a healthy tropical forest, morning is anything but quiet. Birds call, insects hum and, if you are lucky, the long, elaborate songs of gibbons can be heard carrying through the canopy.

But researchers from Universiti Sains Malaysia (USM) studying gibbons have found that groups living near noisy roads appear to call far less often than those in quieter surroundings, raising questions about how traffic and development may alter the soundscape of a forest even when the trees remain standing.

According to a recent report by The Guardian, research led by USM doctoral student Benjamin Galea compared the morning calls of white-handed gibbons at three Malaysian sites with different levels of human disturbance.

The research, which has yet to be peer reviewed, involved recordings taken during the wet and dry seasons in 2023 and 2024.

The results were striking: gibbons living close to a highway called in just 36% of recordings, compared with 71.4% at a quieter seaside location and 84.6% near a hiking trail. Within individual sites, the likelihood of calling also fell as background noise increased.

“Gibbons’ songs are not just background noise or a way of announcing their presence,” research supervisor Nadine Ruppert told The Guardian, explaining that their calls can travel for close to 1km through dense vegetation.

“They are important for communication between groups, territorial interactions and social bonds. So when we introduce persistent human-generated noise into their habitat, we are potentially interfering with a very important part of their lives.”

This matters because sound is central to how these animals interact over distance. If traffic begins to mask their calls, the experts want to know whether it could affect anything from territory defence and pair coordination to warning others of potential danger.

There may even be consequences beyond the gibbons themselves. Ulrich H Reichard, a professor of anthropology at Southern Illinois University Carbondale who was not involved in the local research, noted that birds and squirrels appear to recognise and respond to gibbon alarm calls.

In that sense, a gibbon’s voice is not simply part of the forest soundtrack; it may contribute to a broader network of communication among animals sharing the same habitat.

So, are roads actually silencing them?

Not necessarily, and this is where the findings become more nuanced. One possibility is that heavy traffic simply makes calling less effective because the sound is masked.

Another is that the highway gibbons may be adapting their behaviour by singing earlier, before the monitoring devices began recording at 6am. On some mornings, the researchers found that the animals were already partway through their songs when recording started.

Singing earlier could help them avoid peak traffic noise, although Galea noted that such a change might in turn interfere with resting, feeding or communication with neighbouring groups that are not active at the same time.

The hiking-trail group complicates the picture further. Despite regular human activity, these gibbons called most frequently, possibly because they lived closer to another gibbon group and therefore had greater reason to defend their territory acoustically.

Galea also found evidence that they may adjust how they vocalise when vehicle noise becomes more significant, suggesting that gibbons are not simply passive victims of a changing soundscape.

Even so, plenty remains unknown. As Reichard put it: “One important question that we have to ask is how much calling is necessary for successful communication.”

A forest is more than its trees

What the research does highlight is a form of habitat change that is much harder to see than deforestation. Conservation often focuses on how much forest remains, whether trees are being cleared, and whether animals still have enough physical space in which to survive.

Yet wildlife also experiences its surroundings through sensory cues – which means a forest can remain visibly intact while becoming less suitable in ways humans may barely notice.

A patch of forest may still look green on a map, but if it is hemmed in by roads, housing or industry, its acoustic environment can change substantially. Conservation, therefore, should consider not only how much forest remains, but what animals experience while living within it.

White-handed gibbons are already classified as endangered: their population is believed to have declined by more than 50% over the past 45 years owing to habitat destruction, hunting, capture and other causes.

And while noise pollution is unlikely to be their greatest threat, the USM research suggests it could represent another, less visible pressure on animals already living in increasingly fragmented landscapes.

That makes the study interesting not because it proves traffic is silencing Malaysia’s gibbons, but because it raises a broader question about what makes a habitat truly habitable.

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