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Scientists learn to listen when it comes to assessing rainforest health

  • Scientists with The Nature Conservancy are using acoustic sampling recorders to help them assess how effective local land use planning efforts are at conserving wild species.
  • “You would expect the soundscape to be really full in an intact forest, with something occupying a lot of the different frequencies.”
  • Two types of recorders are used to capture a range of forest sounds beyond what the human ear can hear alone.

In the fight to protect the extraordinary biodiversity of Papua New Guinea’s rainforests, some conservationists are collecting a unique set of data: the sounds of the forest.

Scientists with The Nature Conservancy (TNC) and Princeton University are using acoustic sampling recorders in the Adelbert Mountains, a remote range on Papua New Guinea’s north coast, to help them assess how effective their local land use planning efforts have been at protecting the region’s wildlife.

Subsistence agriculture is a major driver of deforestation in Papua New Guinea, so TNC has worked with communities in the Adelbert Mountains for the past decade and a half to help allocate different areas of land for development, hunting, gardening, forest use and conservation, TNC’s Justine Hausheer said in a blog post.

Anecdotal evidence suggested that the system was working, Hausheer explains, but TNC scientists wanted harder evidence that the conservation areas were large enough to sustain key species like birds-of-paradise and the bandicoot.

But the bioacoustic data they are collecting is not just to monitor specific species. Taken together, all of the sounds of the forest over a 24-hour period, from insects buzzing and birds chirping at sunrise to frogs croaking and mammals grunting as they go about their day, can be used to monitor overall forest health.

“All of the animals we are hearing are vocalizing at slightly different frequencies or with distinct acoustic patterns,” Eddie Game, TNC’s lead scientist for the Asia Pacific Region, said in a blog post. “They all have their own niche to communicate with each other.”

The richer the soundscape, the healthier the ecosystem, Game says. “You would expect the soundscape to be really full in an intact forest, with something occupying a lot of the different frequencies. In a degraded forest you might have a lot of sound, but not occupying as much of the spectrum.”

Game and his team have worked with computer scientists at the Queensland University of Technology in Australia to develop an algorithm that can analyze the bioacoustic data they’re collecting. It’s no exaggeration to say bioacoustics can be used to paint a picture of what’s going on in a forest:

A false-color spectrogram of data from the Musiamunat conservation area. Spectrogram © Michael Towsey and Anthony Truskinger, Queensland University of Technology.

The team is using two types of recorders, acoustic and ultrasonic, to capture the full range of the audio spectrum needed to perform a proper analysis on a forest soundscape.

The acoustic recorders basically capture the range of sounds audible to humans, those between 1 and 24 kilohertz, which is also the range birds, frogs, mammals and most insects vocalize in. The ultrasonic recorders pick up sounds up to 96 kilohertz, allowing the scientists to gather data on bats and insects that the unaided human ear could not hear.

And from that data set, Game said he hopes to get an accurate picture of how well current land use allocations are doing at protecting biodiversity in the region at far less expense and much more quickly than more traditional methods might allow.

“This is a terrific way to gather scientific evidence and look at the impact of our work in a way that doesn’t require a huge team of taxonomic specialists to be in the field for weeks on end.”

Kumul Lodge, Mt Hagen, Western Highlands Province, Papua New Guinea. Male. New Guinea endemic Bird-of-Paradise.
King of Saxony Bird of Paradise (Pteridophora alberti) Varirata National Park, Port Moresby, Papua New Guinea. Photo by David Cook.
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