- Scientists have deployed acoustic monitoring techniques to measure the success of a forest protection mechanism in Costa Rica.
- Using more than 16,000 hours of audio data, scientists found that the payments for ecosystem services (PES) initiative in Costa Rica has helped recover biodiversity in naturally regenerated forests.
- On comparing the soundscapes, scientists found that naturally regenerated forests sound more similar to protected forests than to pastures.
Can listening to forests help us understand if the life inside them is thriving? Apparently, yes.
Giacomo Delgado likens it to a doctor examining heart health.
“A doctor has listened to many people’s hearts, and knows what healthy hearts sound like,” Delgado, a doctoral researcher in the Department of Environmental Systems Science at ETH Zürich, told Mongabay in a video interview. “She then starts to compare your heart to other heart sounds to see if you have a healthy heart.”
A team of researchers, led by Delgado, has used the same logic to assess the success of a forest protection and restoration mechanism in Costa Rica. Using more than 16,000 hours of audio recordings of the forest, they found that biodiversity was restored in naturally regenerated forests. These forests were also found to sound similar to forests that have been protected for years.
In 1950, half of Costa Rica was forested; by 1995, forest cover had been reduced to 25%, driven in part by cattle ranching and agriculture expansion in the 1970s and 1980s. Since then, however, Costa Rica became something of a pioneer in the payment for ecosystem services (PES) system, a mechanism where landowners and local communities are financially compensated for protecting and preserving forests. The country’s PES initiative, launched in 1997, is one of the first national-level programs of its kind in the world, and to date has covered more than 1.3 million hectares (3.2 million acres).
“Costa Rica’s PES program is notable not only for its longevity and scale, but also for the institutional framework built around it,” Laura Villalobos, assistant professor of economics and environmental studies at Salisbury University in the U.S., told Mongabay in an email interview. “The program has progressively incorporated scientific evidence to prioritize areas facing higher risks of deforestation,” said Villalobos, who wasn’t involved in Delgado’s study.
While satellite data have shown an increase in forest cover, it’s been more challenging to assess whether the recovered forests have life thriving within them. More often than not, forest cover regeneration is considered the key metric of success in PES programs. Biodiversity assessments, however, are more difficult and expensive to implement over large areas. As a result, “biodiversity restoration is still measured predominantly through changes in forest cover, often used as a proxy for biodiversity outcomes,” Villalobos said. “This doesn’t capture the quality of biodiversity, species diversity and ecosystem functioning.”
Enter bioacoustics. For years, scientists have used this noninvasive technology — essentially placing microphones throughout the forest to record animal sounds — to conduct large-scale biodiversity assessments over wide swaths of forests. It’s also used to understand the behavior and communication patterns of animals.
To determine if regenerated forests are functioning as viable habitats, Delgado sought answers to a wide range of questions. When are the big bursts of sounds happening? What species are making these choruses of sounds, and at what times? Is there a high diversity of sounds? Is the sound distributed through all sorts of pitches?
“We have listened to healthy forests and made designations on sound profiles of healthy forests,” Delgado said. “We used those to see how close recovering forests sound to the healthy baseline.”
Delgado and his team captured close to 16,658 hours of audio data from 119 sites across the Nicoya Peninsula in northwestern Costa Rica. They placed their audio recorders in protected areas, forests recovering under the PES program, monoculture plantations, and pastures, and retrieved them a week later. The sites that were sampled include 50 forests that were allowed to regrow naturally without any human intervention. These forests have been recovering after being abandoned for cattle ranching and farming for anywhere between 25 and 42 years.
After analyzing the data, they found that the sound profile of naturally regenerated forests under the PES program was very similar to that of protected forests. These patches were found to be “1.4 times more acoustically similar” to protected forests than they were to pastures. “Healthy forests have strong peaks of acoustic activity right when the sun is coming up and going down,” Delgado said. “Whereas in pastures, these are much less pronounced and the biggest peak is in the middle of the day when humans are active there.”
Biodiversity in monoculture timber plantations was also found to be recovering, but not as strongly as in naturally regenerated forests. “You hear and feel a lot less in monoculture plantations where things are sometimes very quiet, almost eerily so,” Delgado said.
Villalobos said using sound to measure the success of PES programs goes beyond determining whether the forest is still standing. It also allows researchers to determine whether the recovered forests are functioning as healthy habitats. However, she said, since the study compares areas with PES against reference protected forests without PES, some questions remain unresolved: What would have happened to the PES areas had they not received the incentive? Would PES areas sound different in the absence of the payments?
“Even so, the methodology is valuable because it moves beyond forest cover as a proxy and begins to measure ecological quality more directly,” she said.
Delgado and his team are planning to continue their work. They’re now expanding their research across the entire country, having already collected 16 years’ worth of audio data from 600 forests. This time, in addition to assessing whether the forests are recovering, they’re also planning to identify what other factors correlate to forest recovery.
“We want to find out which variables, whether it’s climate or forest cover or socioeconomic factors, are the biggest drivers of this recovery and what’s causing the biodiversity to return,” he said. “That’s really the point of doing ecosystem restoration: bringing back these natural communities of living beings that can thrive together.”
Banner image: A forest in Costa Rica. The country is considered a pioneer in a forest protection mechanism that has helped drastically reverse deforestation. Image by Rhett Butler/Mongabay.
Abhishyant Kidangoor is a staff writer at Mongabay. Find him on 𝕏 @AbhishyantPK.
Citation:
Delgado, G. L., Van den Hoogen, J., Dent, D. H., Bradfer‐Lawrence, T., Werden, L. K., Cole, R., … Crowther, T. W. (2026). Large‐scale forest restoration accompanied by biodiversity recovery in Costa Rica’s redistributive payment for ecosystem service program. Global Change Biology, 32(2), e70730. doi:10.1111/gcb.70730
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