Stand outside in any natural environment, close your eyes, and listen. You’ll hear birds calling, or crickets chirping, or frogs croaking. Those sounds of the natural world are bioacoustics, and they’re more than just a nice soundtrack — they’re valuable data for scientists and conservationists.
What’s Going On?
The sounds of any natural place are inherently unique and can reveal important information about the health of that location. Vocalizations from frogs, birds, bats, mammals, and insects form what scientists call the biophony — sounds from living things.
Combined with anthropophony (noise generated by people) and geophany (noise from natural phenomenon like wind and rain) these three elements of sound form the characteristic sound of a place, called the soundscape.
Acoustic data have traditionally been used to identify the presence of individual species or to assess the diversity of species groups, like birds. An emerging field of research is now using the entire scope of data, often called the soundscape, as a rough measure of biodiversity.
“Animal voices in many habitats evolved so that they can stay of the acoustic turf of others,” writes Bernie Krause in his 2012 book The Great Animal Orchestra.
Known as the acoustic niche hypothesis, Krause’s theory maintains that species that need to communicate via vocalization have evolved to communicate in particular frequency ranges and in particular acoustic patterns. That partitioning allows animals to communicate with other members of their species over the cacophony of other noise.
Places with more vocalizing species have greater acoustic diversity, and by inference greater biodiversity. (Camp out in the Amazon Basin and you’ll have difficulty sleeping.) A healthy, intact habitat should have a complex and well-defined soundscape, with most acoustic frequencies occupied. As a habitat is degraded and species disappear, the soundscape becomes less rich and less well-organized.
What the Science Says
Studying bioacoustics at the soundscape level is emerging as a useful tool for conservationists to assess ecosystem health.
Scientists from France’s Muséum National d’Histoire Naturelle tested acoustic samplings’ ability to highlight differences in three locations in New Caledonia, a cluster of islands about 1,200 kilometers off the eastern coast of Australia.
Their results showed that acoustic sampling was sensitive enough to reveal differences between the three sites that had similar habitats and species richness. They write that acoustic sampling “has the potential of revealing compositional differences between sites and could therefore help in conservation management.”
A second study from researchers at Michigan State University and the Queensland University of Technology successfully used acoustic sampling to assess the health of fragmented eucalypt forests around Brisbane, Australia. By comparing the soundscape to traditional ecological data — number of trees, native species richness — they found that patch size and connectivity were significant drivers of acoustic change.
These and other studies demonstrate that changes in the heath of a habitat affect the soundscape, and that acoustic analysis can detect those changes.
Why It’s Important
By functioning as a rough measure of biodiversity and ecosystem health, acoustic sampling can help conservationists gather evidence to see if conservation efforts are working.
The Nature Conservancy is currently using acoustic sampling to measure the impact of its conservation land-use planning efforts in Papua New Guinea’s Adelbert Mountains. Agriculture is a substantial cause of forest loss in New Guinea, and the Conservancy has worked with 11 communities to allocate specific parcels of their land for village development, agriculture and gardening, hunting, general forest use, and conservation.
Both the provincial and national governments are eager to expand these efforts to other parts of the country.
“But we have this issue that we don’t have really good evidence yet of how big these forest conservation patches need to be to sustain the sort of species that these communities are interested in conserving,” says Eddie Game, Conservancy lead scientist for the Asia Pacific region.
To help solve that problem, Game and his colleagues deployed both acoustic and ultrasonic acoustic sampling recorders in three Adelbert communities in July 2015.
“We hope the conservation areas will have really intact biophonies, really intact frequency ranges,” says Game, “and we are going to see how that compares to the other land uses, like gardening and forest use.”
Krause, one of the first scientists to recognize soundscapes as a separate and important element of any natural ecosystem, advocates for the value of soundscapes in their own right, aside from their value to conservationists.
“The pristine natural soundscapes are reserves and resources as much as unimpeded sight lines,” he writes, “and are just as critical to our enjoyment and awareness of the natural wild world.”
The Bottom Line
Each natural landscape has a corresponding and unique biophony, created by vocalizing frogs, birds, bats, insects, and mammals. Conservationists can use this biophony as a rough measure of biodiversity, allowing them to assess the health of a location and measure changes in the acoustic community over time. The Conservancy is using acoustic sampling to measure the impact and effectiveness of their land-use planning efforts in Papua New Guinea.