They say “walls have ears”, but what about trees? Hundreds of trees across forests in France have had microphones installed in a bid to monitor the biodiversity and animal populations of the areas.
The project is called Sonosylva. It was launched by French scientific research centre the CNRS in 2024, is in collaboration with the biodiversity office l’Office français de la biodiversité (OFB) and the Muséum national d’Histoire naturelle (MNH).
The groups state that their aims are to:
Monitor the biodiversity of forest environments in mainland France using eco-acoustics, “a rapidly growing discipline”
Provide a regular and accurate picture of biodiversity across the country, “in particular by estimating population trends and working on the links between anthropogenic [human activity] pressures and the responses of biodiversity”
Tree criteria
Trees chosen to have microphones installed were selected based on precise criteria in 103 forest areas. The trees must be in locations that are a minimum of 50 hectares in size and be at least 400 metres from any edge of the area.
They are also typically in protected forests (meaning those that have been identified as particularly precious to the ecosystem or biodiversity, and could otherwise be under threat from noise pollution or other human activity).
The trees must also be at least 25 cm in diameter (for the trunks), and at least 1.5 metres tall.
A map of the forests included in the study so farSonosylva.cnrs.fr
The microphones capture one minute of noise every quarter of an hour, day and night.
"First of all, we try to get as far away as possible from sources of noise, so away from the road and also from the hiking trails. Then we point [the device] in the opposite direction to the prevailing winds,” said Mathieu Bernard, forestry technician and member of the Île-de-France Est agency at the Office national des forêts (ONF), to TF1.
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“It shouldn't be too low because animals such as does or stags, for example, could move it or knock it over,” he said.
“Even a well-protected forest is not immune to pollution from aircraft or the presence of a road, which can affect all the flora and fauna,” said Jérôme Sueur, teacher-researcher and eco-acoustician at the MNH.
Crucial forest evidence
In a single season, the scientists will collect nearly a million audio files, amounting to more than 18,000 hours of recording.
The microphones enable researchers to:
Draw up a list of the species present in the area
Compile “a more global vision, like a landscape, of all the sounds that are produced by both animals and human beings”, said Nicolas Hette-Tronquart, research officer at the OFB
Many animals use sound to communicate, and any interference can hamper their ability to find food, find a mate, or escape predators. Excess noise can even reduce birds’ ability to combat illnesses. Plants can also be affected by excess noise vibration, or a lack of pollinators (if the latter die off or leave the area).
The research has already revealed some interesting trends: in Landes, cicadas have been recorded, while a surprise owl was captured in the middle of the night in Savoie.
This owl, identified as a boreal owl, gave researchers new and concrete evidence of how the bird is managing to deal with climate change, said Mr Sueur.
Without the microphones, this crucial evidence would not have been picked up.
Yet, the project is expected to run for at least two years before any definite conclusions can be drawn, with the first real analyses set to begin in late 2025. Further analysis will continue in 2026, with official publications of the results also expected then.
It follows in the footsteps of a similar “mapping system” that was set up in Germany nine years ago, which successfully enabled researchers to better understand old forests versus new ones.
