In the verdant and melodious depths of the eastern Democratic Republic of Congo, where the songs of birds match the murmur of leaves, several Indigenous people affirm the results of research that emerged in July. Biodiversity scientists, intrigued by the human perception of nature, launched a study titled, “Perceived biodiversity: Is what we measure also what we see and hear?”

The idea behind it was simple: In one phase, participants were asked to listen to sounds recorded in forests with varying levels of diversity, and in another phase, participants were shown images of natural environments. The goal? To find out what people perceive when they see or hear different levels of biodiversity and to what extent actual biodiversity and perceived biodiversity are consistent. Intriguing, isn’t it?

To unravel this mystery, the researchers studied 48 participants in each group who were exposed to visual cues (57 photos taken in forests with varying levels of biodiversity) or audio cues (16 10-second recordings from natural environments) and then categorized the images and sounds based on the amount of biodiversity they perceived.

Kevin Rozario, one of the authors, explained in a voice message to Mongabay: “We simply told them, ‘Look at these images, listen to these sounds. Tell us what you see and what you hear.’ And they began to compare freely, using their memories and experiences.”

The results showed that people’s perceptions were closely aligned with actual biological diversity. The sounds of the forest, the cries of animals, the rustling of leaves: All of this forms a language that participants understood. The researchers went so far as using mathematical indices to quantify these perceptions based on visual and acoustic stimuli.

“The perceived visual and acoustic diversity was significantly correlated with the actual visual and acoustic diversity, respectively,” Rozario said.

But beyond the laboratories, it is also in the stories and experiences of community elders that the forest reveals its deepest secrets.

Back in the DRC, far from the noise of vehicles and factories, on the peaceful and green island of Idjwi, Rwankumkumba Kamanzi Athanase, a 70-year-old farmer and pastor from the village of Bwiru, not involved in the study, shared his testimony with Mongabay via a phone call: “In our Nyamusisi forest, we were so used to the monkeys that even without seeing them, when we heard their cries, we knew what was happening in the bush. Some lived in holes and caves, and when there was or would be a landslide or a natural disaster, we knew it because we could hear it in their alarming cries.”

He continued, saying that this situation has dramatically changed since Rwandan refugees fled war and genocide in 1994: “They cut down the trees for wood and to build houses. … But before, the cries of the birds changed according to the hours: Morning, noon, evening — and that helped us to know what time it was without having watches on our hands.”

For some Indigenous people, the forest speaks, dances and breathes. When the leaves rustle, they know that animals are present and carrying a message. In the dry season, the animals hide in the rocks and approach water courses at times.

In 2015, Kambale Nganga, chief of the Kamandi village in the Lubero territory of North Kivu, journeyed to the city of Goma, moving along the winding and tiered road of the Virunga chain known as Kabasha in Virunga National Park. Recalling the story, he recounted that sensory perception was key to his understanding of the landscape. “On this mountain chain, it was easy for me to spot the presence of the Semliki River, thanks to the very green vegetation that was visible from far away on its banks. This color indicated the health of the vegetation surrounding the river just by looking at it,” he said during a call with Mongabay. “And often, where there is a very green forest like that, it is also easy to find birds and animals that come there to drink water and others even to hunt in the dry season. There, then, from afar, it is the sound that comes out that helps to know if there are animals or not,” he added.

Batundi Hangi Vicar, national coordinator of FDAPID, a development center in South and North Kivu that works with Indigenous communities and people in need, said to Mongabay via email that Indigenous people are recognized as exceptional trackers and that their perceptions in the bush make them very good field experts.

“Thanks to the pungent smells carried by the wind passing through the forest, a few kilometers away, the Pygmies are able to know if someone has cut down a tree in the bush,” Batundi said. “And the temperature they naturally feel under a canopy, they are able to say if it will rain or not during the day. In addition, by lying down and putting their ears to the ground in the bush, a few kilometers (1 or 2) away, they are able to listen for the presence of animals, especially when they are in large masses like gorillas, elephants, buffaloes and even some antelopes.”

These experiences, and the research results, are part of a growing body of evidence on human perceptions of biodiversity — and their links to mental health. “Biodiversity is crucial for human health and well-being,” the study authors write, and “perceived biodiversity — people’s subjective experience of biodiversity — seems to be particularly relevant for mental well-being.”

Far away, in the southern part of America, in the capital city of Georgetown in Guyana, another study published in 2021, utilizing different research methods, underscored these findings, not only by highlighting the importance of biodiversity perception but also emphasizing the significance of biodiversity for human mental well-being. “We assess the accuracy of these site perceptions with objective measures of sound (using a bioacoustic sound index), bird species richness, and percent coverage of vegetation, water, and impervious surfaces,” the authors wrote. “Results showed that if sites were perceived as species rich, containing natural sounds like birdsong, natural rather than artificial, and safe, they were perceived as more restorative, resulting in improved wellbeing.”

It is worth noting that each person’s sensory stimuli are varied depending on their experiences. The positive impact of perceived biodiversity on mental health could be a valuable, though often overlooked, tool for raising awareness for nature conservation.

“In this study, we present visual indices and several acoustic diversity indices that quantify aspects of perceived and actual diversity. These indices can serve as cost-effective tools for managing and planning green spaces to promote biodiversity and mental well-being,” Rozario added.

Banner image: A male olive-backed euphonia (Euphonia gouldi) singing at full voice in the rainforest of Costa Rica. Researchers studied people’s perceptions of biodiversity based on what they see in images and hear in natural recordings. Image by Andy Morffew via Wikimedia Commons (CC BY 2.0).

Citations:

Rozario, K., Shaw, T., Marselle, M., Oh, R.R.Y., Schröger, E., Botero, M.G., … Bonn, A. (2025). Perceived biodiversity: Is what we measure also what we see and hear? People and Nature, 7(8). doi:10.1002/pan3.70087

Fisher, J.C., Irvine, K.N., Bicknell, J.E., Hayes, W.M., Fernandes, D., Mistry, J., & Davies, Z.G. (2021). Perceived biodiversity, sound, naturalness and safety enhance the restorative quality and wellbeing benefits of green and blue space in a neotropical city. ScienceDirect, 755(2). doi:10.1016/j.scitotenv.2020.143095