Hearing the forest through the trees

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Since most of my work focuses on palm oil, which is a major driver of deforestation in the tropics, I get very excited about any tool that helps us understand how human activities such as land use change are affecting tropical forest organisms.

Audio recordings can be a great tool for assessing biodiversity. Experts can use audio recordings to identify the presence of certain species by their unique calls. But even without identifying individual species, the diversity of the acoustic frequencies used by animals in a forest and the patterns of the sounds that are occurring can tell you a lot about an ecosystem.

One way scientists have used acoustic data is to identify differences in animal species composition (or the types of animals that are occurring) by looking for differences in the “soundscapes” – or the patterns of sounds that are occurring – in different areas. Researchers have found that even in areas with similar numbers of species, landscapes with different types of animals will also have differences in the patterns of the sounds being used (Gasc et al 2013).

Here’s an illustration to help explain how differences in species composition can be detected by differences in the soundscapes.

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In both of these forests, the total number of animals is similar, but the composition of species is different. In the forest on the left, only red, orange and yellow animals occur. On the right, all the animals are blue, purple or green.

Since there are similar numbers of animals, you might expect these forests to be similarly noisy. However, since different species are occurring in each forest, they are also likely to make slightly different types of noises, at slightly different times of day.

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Even if the red birds in the first forest are very similar to the blue birds in the second forest, there will likely be differences in the frequencies and patterns of their calls. Yellow and green frogs will also likely have differences in their calls, as will the red and blue beetles. When you analyze all these sounds together in a soundscape, we can see that sites with different species compositions also have different soundscapes.

Acoustic data is relatively easy and inexpensive to collect, so soundscapes have a lot of potential as a tool to help us compare species composition between different forests or show how species composition is changing in one area over time.

Citation: Gasc, A., Sueur, J., Pavoine, S., Pellens, R., Grandcolas, P., 2013. Biodiversity Sampling Using a Global Acoustic Approach: Contrasting Sites with Microendemics in New Caledonia. PLoS ONE 8, e65311.

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