Silencing the symphony of one of the most biodiverse rainforests on the planet

A new study measuring biological sounds reveals how palm oil and teakwood industries contribute to deforestation and threaten wildlife in Costa Rica.

A recording captured in one of Costa Rica's expansive rainforests floods my ears: the steady drip of humidity from verdant plants, the caws of vibrant toucans, the signature screeches from howler monkeys that can be heard from miles away; if I close my eyes, I can nearly feel the swoosh of air from these creatures as they soar and swing in lush trees above.

These are the sounds from one of the most biodiverse rainforests on the planet located in Osa Peninsula, Costa Rica, which are captured by scientists in order to measure the quantity and variety of wildlife species in a given area. The next audio, however, is anything but blissful.

Crickets. What was once a grand chorus of life becomes a graveyard of the sounds that used to fill it. This audio was collected from one of the many plantations that are built by tearing down vast portions of the rainforest. Researcher Dr. Jenna Lawson from Imperial College London's Department of Life Sciences witnessed firsthand the ghostly silence and undeniable dearth of wildlife on these plantations.

Dr. Lawson is studying the impact of rainforests in Costa Rica being increasingly converted into palm and teak plantations. Palm plantations produce palm oil, which is used in countless everyday products from makeup to chocolate, while teak tree plantations harvest wood that is used predominantly in furniture.

In defense of their industries, some of these companies claim that there is plenty of wildlife and biodiversity on their plantations. But these assertions didn't align with Dr. Lawson's observations during her time there. "I noticed that we were facing a serious issue in this region," Dr. Lawson explains. "You can see all these animals living on the border of the plantations, but many of them just can't get across."

Noticing the stark contrast in wildlife abundance between natural rainforests and human-built plantations resting just meters apart, Dr. Lawson devoted her research to discovering the true impact of these plantations on biodiversity.

Measuring biodiversity

How can we measure biodiversity? While it can be difficult to measure species diversity and abundance directly, we can learn a lot about the health of a rainforest by listening to its bioacoustic activity, or the individual sounds produced by the living organisms in a given ecosystem. One way to do this is by using passive acoustic monitoring (PAM). PAM continually records the noises produced by wildlife at different points of the day and can distinguish noises produced by different species.

Dr. Lawson and her team set up 120 of these recorders at various locations throughout the natural rainforest as well as in the teak and palm plantations. The devices captured audio recordings day and night for 7 days.

In a natural rainforest, there are peaks of biotic noise in the morning and at night. These dusk and dawn choruses include birdsong, which is a critical form of communication required for mating, egg laying, and other behaviors required for survival. The data collected by PAM recorders in natural parts of the rainforest reflected these patterns, indicating a healthy ecosystem.

The sound samples collected in the teak and palm plantations located in the middle of these rainforests, however, tell a much different story.

In teak plantations, the typical peaks of acoustic activity observed at dusk and dawn were significantly reduced. There was a small spike in wildlife noise in the mornings, but it did not begin at natural dawn—the morning chorus began much earlier than usual compared to natural rainforests, likely due to artificial light and sound produced by human activity that disturbs the animals' natural rhythms. Already, the complex communication systems of various animal species are considerably impaired on these plantations.

If the volume was only turned down in teak plantations, then it was nearly silenced in palm plantations.

The audio clips collected from the palm plantations are nothing short of haunting: the characteristic morning and evening choruses are entirely abolished. If you imagine the wildlife recordings as a heart monitor, the "heartbeat" of the rainforest flatlines on palm plantations. "It's awful to go from one area where it's beautiful and full of wildlife everywhere and then go to another area where it's just gone," Dr. Lawson shares.

Species communication is strongly linked to species survival, so this disruption in communication is a threat to the survival of numerous animals inhabiting Costa Rica's rainforests. Spider monkeys, jaguars, great green macaws, and several more species are already in danger of extinction.

Calls for sustainable farming

Biodiversity is vital to the health and survival of our planet. "It's the building blocks for everything," Lawson stresses. "If we don't have biodiversity, all the ecosystems that we rely on for our survival fall apart, from the air we breathe to the water we drink."

Luckily, there is a path forward in tackling this issue. And eliminating palm oil and teak wood altogether isn't necessarily the solution. "Palm oil isn't inherently bad," Dr. Lawson explains. "But we need to think about how and where we put these plantations." Rather than placing them in the middle of large rainforests, which prevents animals from crossing and leaves them isolated in patches, they could instead be grown on the edges of the rainforest. Small farmers with smaller plantations tend to make more biodiverse and sustainable palm plantations, but they often can't afford to compete with large palm plantations. Lawson stresses that moving forward palm and teak planters need to focus on building more sustainable farms and stop dividing rainforests in a way that leaves animals vulnerable to extinction.

Home to 250,000 animal species and 4,000 plant species, the Osa Peninsula plays a fundamental role in our planet's health, and the growing silence from this region is truly a cry for change.

Provided by Imperial College London