Bioacoustics: How an audacious sonic survey could help revive damaged rainforests

Giacomo Delgado has lost his microphone. As we peer into the cloud forest of Costa Rica’s Barva volcano, a GPS device tells him it is somewhere nearby, but the only note he left when he placed the mic here is that it is attached to a moss-covered tree. That would be helpful, except it describes nearly every tree in the old forest. He squints. “I hate it when I don’t give myself good notes.”

For the past two months, Delgado, a doctoral researcher at ETH Zurich in Switzerland, and two other teams from Costa Rican universities have bounded across the country recording the soundscapes of its forests. The survey involves positioning microphones at more than 600 sites in every type of forest ecosystem in Costa Rica, making it, by some measures, the largest such “ecoacoustic” survey ever.

The survey is part of a shift in the way we monitor ecosystems. Cheaper audio recorders and improved methods of analysing complex acoustic data using machine learning have led to a boom in this field. And researchers are increasingly listening in to ecosystems to hear how they change and monitor their health.

In Costa Rica, by comparing the soundscapes of regenerating forests with those of forests with their biodiversity intact, the researchers aim to take the measure of ecosystems coming back to life across the country, in what could be some of the first evidence that large-scale forest restoration brings back the full diversity of ecosystems. But this has the…