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To save the Amazon, scientists are listening to its rich sounds

  • An unprecedented study is analyzing biodiversity by listening to nearly 16,000 minutes of recordings made in Carajás National Forest, a protected region in the Brazilian Amazon.
  • Some 230 bird species have already been recognized in 7,000 minutes of recordings, in particular the white bellbird (Procnias albus) and the screaming piha (Lipaugus vociferans), the world’s two loudest birds; the next phase of the study will focus on identification of the mammals in the region.
  • The study has found that the sound samples from 14 distinct locations are similar, and that the rainforest doesn’t ever sleep, with many animals vocalizing at night.
  • The rainforest’s soundscape reveals information about its biodiversity, the ecosystem services it provides, and makes it possible to evaluate conservation and climate change mitigation measures.

The ear-piercing call of the screaming piha, a bird (Lipaugus vociferans) known locally as the cricrió, welcomes all who visit Carajás National Forest in the Brazilian Amazon state of Pará.

“The cricrió is quite commonly found in well-preserved rainforest because the species is very sensitive to disturbances,” says Leonardo Miranda, a researcher. “At times they are so numerous and sing so loudly that they block out the sound of other vocalizations.”

The screaming piha, or Lipaugus vociferans, is found throughout this region, which makes it “a very good example of what we refer to in the literature as a species that characterizes the place,” says Tereza Giannini, also a researcher. “When you arrive there, you know it: ‘Oh, OK, now I’m inside Carajás.’”

But there are times when another sound is more prominent: that of the white bellbird (Procnias albus), the most eloquent among the loudest animals ever studied. Reaching 125 decibels, this bird can sing louder than a rock ’n’ roll band or even a chainsaw. (The previous record holder, at 116 dB, is the screaming piha.) Researchers have even raised concerns about possible damage to the female bellbird’s hearing during the raucous mating season.

The songs of the screaming piha and white bellbird are prominent in the soundscape of Carajás and are favorites of Miranda, a biologist who worked on a study led by Giannini and published in 2020 on the region’s soundscape.

Aside from the fascination that communication between animals inspires — around the world, nearly 10,000 bird species, 7,000 frog species, 6,000 mammal species and an unknown number of fish and insect species are known to vocalize — understanding the sounds of the forest is one way to make its biodiversity heard and identify behavioral changes among its animals resulting from climate change, evaluate the effects of climate on ecosystem services, and create a basis for conservation programs.

These were the objectives of Giannini’s study that used recording devices installed in trees about 2 meters (6 feet) off the ground at 14 separate locations around the protected area. The researchers captured nearly 16,000 minutes of sound during their weeklong monitoring.

Soundscape analysis is one of the wildlife studies being carried out under the Carajás National Forest National Capital project, which analyzes the forest’s natural resources and their contribution to carbon absorption, climate regulation, water protection, and biodiversity itself.

A screaming piha (Lipaugus vociferans), once the loudest bird in the world. Image courtesy of Nereston de Camargo.

The music of the rainforest

More than 7,000 minutes of the sound files that the researchers gatheres has already been analyzed by the Emílio Goeldi Museum in Belém, Pará, which identified the songs of some 230 bird species. The mammal, amphibian and insect sounds caught in the recordings — beyond the ubiquitous sound of cicadas — will also be analyzed by February 2024.

In addition to the refined listening skills of experts, the researchers also plan to delve into existing sound collections and libraries of acoustic data on different species. These data will be compared with the new recordings by computer. One international network providing open access to biodiversity audio data is the Global Biodiversity Information Facility.

An interesting finding from the recordings from Carajás National Forest is that the Amazonian soundscape changes over the course of a day. Around midday, the volume is high, then goes down as the afternoon wears on. The rainforest, however, never sleeps. Each animal living there has its own circadian rhythm, and after the sound curve drops slightly at around 5 p.m., it picks right back up again, with the volume remaining loud into the night. “This doesn’t mean the forest is noisy, but many animals vocalize at night,” Giannini says.

Another interesting finding was that the 14 distinct sound sample locations revealed similar soundscapes. Even considering locations with different profiles — from seasonal dry areas to dense rainforest — the sounds produced in each spot seem to be homogeneous.

One nice surprise for the researchers was to hear the song of the vulturine parrot (Pyrilia vulturina), a bird endemic to the states of Pará, Maranhão and southern Amazonas that’s on Brazil’s list of threatened species. Aside from bird species, other animals identified in the recordings include the bush dog (Speothos venaticus), giant river otter (Pteronura brasiliensis), puma (Puma concolor), black-bearded saki (Chiropotes satanás) and red-handed howler monkey (Alouatta belzebul).

Conservation through listening

“Environmental changes resulting from human activities like environmental degradation, deforestation and exploitation of natural resources are happening at an accelerated pace. Our capacity for gaining information can lag behind,” says Miranda, a co-author on the 2020 study. “The new and innovative tools we have are advantageous for us to try and keep up with the changes happening in the environment.”

To collect the sounds of the forest, the researchers programmed their equipment to record for one minute every hour, around the clock. Miranda says the use of recording equipment is a safe, agile and economical resource, allowing for recording over long periods.

“For example, in order for us to cover 14 hours over 7 days simultaneously like we did in the study, I would have to leave 14 biologists in the field for 24 hours listening to the soundscapes and taking notes on which species they were hearing.”

Even though it was a simple solution, the use of sound recordings in the rainforest appears to be a rarity in research. “This may be one of the first times in Amazonia, especially in Eastern Amazonia,” Giannini says.

A white bellbird (Procnias albus) in Canaima National Park, Venezuela. Image by Brendan Ryan via Flickr (CC BY-NC-SA 2.0)

Other studies have shown that acoustic monitoring can be effective to evaluate Amazonian biodiversity, as was the case with a study published in the Proceedings of the National Academy of Sciences (PNAS) in April this year, which analyzed biodiversity in forests damaged by fires or logging.

“When we think about ways to preserve a forest like the Amazon, we also think about ways to preserve the ways in which the forest gives back to human beings,” says Giannini, who has researched the impacts of climate change on forests for 15 years. “We call these ecosystem services, and they include how much the forest regulates the climate, how much it protects the water, or how it captures carbon.”

“You can’t preserve what you don’t understand. To gain understanding, you need numerical data,” says Vera Lucia Imperatriz-Fonseca, a professor at the University of São Paulo who has carried out many studies in the Carajás region.

Experts say the biodiversity data being revealed in this study could be used to help conservation measures in many ways. One example is crossing the information with other studies already carried out in the region, like one that Miranda, Imperatriz-Fonseca and Giannini published in the journal PLOS ONE in 2019, which showed the environmental services provided by the birds in Carajás and a decline in species numbers by 2050 because of climate change.

“To think that in 30 years we could lose a good share of the rainforest’s services because of the climate … Biodiversity and climate are serious issues and meaningful biomonitoring can be carried out by listening to the soundscape,” Imperatriz-Fonseca says.

Banner image of a red-handed howler monkey (Alouatta belzebul). Image by Nick Athanas via Flickr (CC BY-NC-SA 2.0).

This story was reported by Mongabay’s Brazil team and first published here on our Brazil site on Oct. 17, 2022.


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