On Costa Rica's Nicoya Peninsula, researchers armed with audio recorders and a counterintuitive idea set out to answer a question that satellites could not: whether a bold experiment in paying landowners to restore forests had actually brought biodiversity back to life.
For three decades, from 1960 to 1980, Costa Rica's rich forests fell to chainsaws and cattle pastures. But in 1996, the country made a historic wager—establishing the world's first Payment for Ecosystem Services program, which paid landowners directly to help restore forests rather than exploit them. The gamble was rooted in a simple insight: ecological destruction is often rooted in economic desperation, so why not address both at once?
Three decades into the program, satellite imagery showed that canopy cover had returned. But canopy alone doesn't tell you if the birds have come back, if the insects are thriving, if the intricate web of life has truly reknitted itself. Enter Giacomo Delgado from the Institute of Integrative Biology in Zurich and his team, who realized that nature's own sounds might be the truest measure of recovery.
The researchers set up 119 audio recorders across the Nicoya Peninsula and let them roll through 16,658 hours of recordings—capturing the dawn chorus at 5:00 and 6:30 a.m., the vibrant soundscapes of midday, and the dusk chorus when nocturnal life stirs to life. They compared the acoustic signatures of naturally regenerating forests enrolled in the PES program for at least ten years against mature reference forests, monoculture timber plantations, and degraded pastures. The results, published in Global Change Biology, were striking.
The naturally regenerating PES forests were acoustically far more similar to mature reference forests than to the degraded pastures they had once been. At certain times and sites, regenerated forests were four times more similar to mature forests than to pastures—a measure of biodiversity recovery that no satellite could have captured. During the dusk chorus in particular, the acoustic overlap was nearly complete, with similarity values regularly exceeding 0.90. Even timber plantations, which had at least some tree cover, registered as merely 1.24 times more similar to reference forests than regenerated sites were.
The dawn chorus told a subtly different story—a reminder that ecological recovery is not instantaneous. During early morning hours, regenerated forests still echoed more like pastures than mature forests, suggesting that certain species have slower recovery timelines. But across the full day, the signal was unmistakable: paying landowners to let forests grow back worked. Life had returned.
Beyond the data, the study reveals something deeper about the relationship between human welfare and environmental health. The PES program was never just an environmental intervention—it was a statement that conservation requires justice, that you cannot restore forests while impoverishing the people who live among them. By channeling resources to local land stewards, Costa Rica demonstrated that efforts to help people can simultaneously help the planet. Today, the program protects over 200,000 hectares, and as the study's authors note, it stands as "a model program and an integral part of Costa Rica's progress in protecting its natural heritage." The symphony of a recovering forest, captured in sound, offers hope that such models can work.