The sounds of a forest — from the guttural croaking of frogs to the chirpy trills of birdsong — can be used to track biodiversity recovery, according to a study published today in the journal Nature Communications. Paired with artificial intelligence, soundscapes can provide a low-cost way to measure the health of an ecosystem.
Researchers looked at reforestation projects in a part of Ecuador where 90% of the tropical forest had been lost to logging. “We could only describe that the trees [were] regrowing,” says Jörg Müller, a professor of animal ecology at the University of Würzburg in Germany and lead author of the study. “But what is happening to the animals?”
To answer that question, the study utilized bioacoustics — a branch of acoustics that quantifies all of the natural sounds humans can perceive. Researchers recorded the soundscapes of various plots in Ecuador at different stages of post-logging recovery, including both active agricultural pastures and forests on the mend. An AI model trained to recognize songs from more than 100 types of wildlife was then used to identify the species present on the recordings, with its identifications later backstopped by human experts.
They found that the more a plot of land had recovered from logging, the more its bioacoustics were alive with the warbles, buzzes and hums of its fauna. “We see communities which are already very close to old-growth communities,” says Müller.
The health of tropical forests is taking on new urgency because of climate change. Forests play a critical role in storing carbon, and forest preservation and restoration projects are increasingly used to backstop carbon credits designed to offset emissions, as well as biodiversity credits designed to offset the impacts of development on plant and animal species.
These projects, which are often geared at redeveloping forest ecosystems in abandoned agricultural spaces, can theoretically be used to mitigate carbon emissions and biodiversity loss. But both use cases have come under scrutiny in recent years due to poor monitoring and limited follow-through. Soundscapes could allow conservation managers to more effectively track how an ecosystem is bouncing back, according to the study.
“We want these rapid metrics of biodiversity to make sure that people are upholding what they’re saying they’re doing and preventing stuff like greenwashing,” says Rachel Buxton, a bioacoustics researcher who was not involved in the study. Buxton is an assistant professor at Carleton University’s Institute of Environmental and Interdisciplinary Sciences.
Traditional methods of tracking biodiversity include metabarcoding, a type of analysis that looks at short snippets of DNA to identify specific populations of species. The researchers found that bioacoustic monitoring led to similar findings as this more direct method but can be accomplished at a lower cost and with less intrusion on the environment.
“This is a totally passive method of sort of eavesdropping on an ecosystem that doesn’t involve having to trap anything, catch anything — you’re just listening,” says Buxton. “The idea that something more cost-effective like acoustic monitoring can reflect a similar metric of biodiversity is really exciting.”
In principle, Müller says, bioacoustic monitoring could be used anywhere. It doesn’t require an expert in the field, just someone to place the recording devices. But there are some limitations, including the training of AI models. “We have not enough experts and not enough money to identify all the sounds globally,” Müller says. “People have to make this effort to train these models to make this labeling data.”
Another drawback is that bioacoustics also capture noise from wildlife that may only be passing through, including migrating birds or mammals. That could skew takeaways around which species are permanent members of a rebounding ecosystem.
Still, bioacoustics could be a useful tool for understanding where a forest is on its path to recovery and could even capture human activity in an area, including poaching or illegal logging. Those needs will grow as more countries look to address declines in biodiversity.
“We are now in the times of global restoration of habitats,” Müller says. “With this data, we can present very well how communities of threatened species recover.”
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