(AU ABC) Listening To The Planet: Understanding The Science Of Ecoacoustics

 ABC Science - Anna Salleh

From the symphony of nomadic birds on their journey across the continent, to the silencing of our forests by bushfires, ecoacoustics could help scientists track environmental change. (Supplied: David Rennie)

Imagine being able to hear the change of Earth's seasons, the effect of climate change on threatened birds, or the southward march of invasive cane toads. Like listening to the heartbeat of the planet, this is exactly the kind of thing researchers in the emerging field of ecoacoustics want to monitor.

Ecoacoustics is the study of sounds produced by the environment, ranging from animal calls to the wind and rain, and even human-made sounds like the hum of traffic.

But the study of biodiversity is a major focus, and Australia is leading the way here with a network of sound recorders planted across the continent, listening to our ecosystems.

Launched in 2019, the Australian Acoustic Observatory (A2O) has now planted hundreds of "ears" in the wild, from Cape York to the red centre, from the lush rivers of Tasmania to the dense forests of Queensland – and even on Cape Barren Island in Bass Strait.

The A2O recorders are solar powered and record onto a removable SD card – this site is in the Northern Territory . (Supplied: David Tucker)

Ecologist Lin Schwarzkopf from James Cook University, who helped design the acoustic observatory, says continent-wide recordings let scientists track all kinds of animals.

"We'll have a much better idea about the migratory routes of birds, how many birds are in these migrations, and where they stop to feed," she says.

"You could also detect the arrival of invasive species like cane toads."

This year, for Science Week, you too will get to listen to some of these sound clips collected by the A2O from across Australia.

Through the ABC's interactive, Hoot Detective, you will be able to help scientists identify owl calls, with the ultimate aim being to get a better idea of what species are where, and how well they're faring.

Experts need "citizen scientists" to help them process the endless hours of recordings being collected, says ornithologist Paul McDonald from the University of New England.

"You're faced with years and years and years of listening," Professor McDonald says.

"We can use the public to help look at a large amount of data in a relatively short amount of time."

Monitoring the environment 24/7  

Some of the acoustic sensors are near water, to capture the many animals that spend time in these areas. ( Tasmanian Land Conservancy Five Rivers Reserve: Matthew Newton) 

Ecoacoustics is particularly welcomed by biodiversity researchers who spend a lot of time on field trips to remote places to painstakingly count, trap and track animals — assuming floods and bushfires don't stop them.

"The beauty of this system is that we've got our recorders out there recording 24/7," Professor McDonald says.

"And they're picking up animals and events like rain that are occurring whether or not the researcher is there.

"It lets us monitor the whole country day in, day out, which is very exciting and something we haven't been able to do before."

Ecoacoustics could also help monitor the recovery of threatened species after events like bushfires, or the explosion in frogs after rain.

Frogs are another vocal animal that can be detected by acoustic sensors. (Wotjulum Frog/ Supplied WA Museum) 

"It's hard to express how little we know about some of these things," Professor Schwarzkopf says.

And while some scientists will focus on tracking individual species, others will be more interested in the overall 'soundscape', listening to the joyous turn of winter into spring — or something more sombre.

"We could possibly hear the end of the world as climate change increases, and it gets quieter as things go extinct."

Ecoacoustics is particularly useful for tracking animals that are hard to find, like the night parrot, koalas, and of course owls.

And storing sound collected over time will give scientists an acoustic "time machine" to explore historical changes to the environment, Professor McDonald says.

Evolution in the use of sound

Ecoacoustics is the latest stage in the evolution of the use of sound by ecologists and biologists.

Listen to Nature Track

Nature Track is a podcast that opens a window on the beautiful sounds of the Australian wilderness. Read more

"Every time there is a new advance in technology, biologists use it," Professor Schwarzkopf says.

It all started with researchers recording individual species, mainly to understand animal communication — a field often called 'bioacoustics'.

"People used to drag big old reel-to-reel recorders into swamps to record frogs," Professor Schwarzkopf says.

"Playback experiments" were next on the cards, where a researcher would, for example, play back a recording of a predator to test what effect this had on its prey.

But longer battery life, recorders that could be left outdoors, and eventually the advent of cheap storage for data, has all paved the way for ecoacoustics.

Some of the A2O recorders are located in places where owls live, like in this Tasmanian Land Conservancy’s Five Rivers Reserve. (Tasmanian Land Conservancy's Five Rivers Reserve: Matthew Newton) 

Computer engineer Paul Roe from the Queensland University of Technology, who leads the A2O, is naturally enthusiastic about this use of sound to monitor the environment.

He says that while remote sensing with satellites and drones is a good way to keep an eye on vegetation, recording sound is the most effective and "non-invasive" way of monitoring animals, especially over large areas.

"Acoustics' time has come," he says.

But scientists will have their work cut out for them making sense of the massive amount of data they're collecting.

With its initial five-year funding, the A2O will collect 2,000 years' worth of data, which amounts to 2,000 terabytes that will need massive cloud storage and powerful computer processing.

"We've translated the problem of in-the-field observation into one of data analysis," Professor Roe says.

"We still need to analyse the data to see what's going on.

"We're trying to make ecology a big data science."

A20 researchers Paul Roe and David Tucker checking on a recorder in the field. (Supplied: David Tucker)

Enter citizen scientists … and artificial intelligence

This is where citizen scientists come into play.

Through projects like Hoot Detective, scientists are recruiting anyone with a connected digital device to help them pick out animal calls from sounds they've collected.

A tool known as the spectrogram is used here — it's a graph that plots frequency against time, and gives a visual representation of a sound clip.

As humans identify sounds in the spectrogram and feed what they've discovered back, that information can be used to train computer programs to automatically recognise calls.

This the sound of a young boobook owl trilling as seen in a spectrogram. (Supplied: Australian Acoustic Observatory) 

These "automatic recognisers" use the same sort of complex machine-learning algorithms involved in face recognition, which need lots of examples to learn from.

"If you want to scale ecological monitoring, you need to find a way to automate it," Professor Roe says.

But while finding individual species in lots of data for humans or computers can be likened to finding "a needle in a haystack", ecoacoustics also involves "zooming out" to "understand the haystack" itself.

For this, researchers can use what's called a "false colour spectrogram", which summarises the information so it fits on your computer screen and codes different sounds in different colours.

"So you can look at a whole night of data in one picture," Professor Roe says.

While you can still zoom in like you do on Google Maps to the level of individual species, zooming out is useful for other things.

"You may not know what you're looking for. You might be just trying to find patterns of change," Professor Roe says.

These false colour spectrograms show different soundscapes over a 24-hour-period – in site 1 you can only hear the wind, whereas in site 2 (a shrubland) there are lots of calls. (Supplied: Marina Scarpellil)

Getting the big picture

Marina Scarpelli is one ecoacoustics researcher who wants to zoom out and get the big picture.

"I am interested in how different ecosystems have different sounds," says Ms Scarpelli, who is doing a PhD at the Queensland University of Technology.

She planted small sound recorders close together in different vegetation types on a semi-arid property in Queensland.

After that she created colour-coded spectrograms using mathematical filters called "acoustic indices," tuned to different sounds in the recording, from birdsong to wind.

"Acoustic indices give you a fingerprint of the sound or the environment," says Professor Roe, one of her supervisors.

"So you can use that a bit like a bar code to characterise the environment and how it's changing."

Marina Scarpelli attaches a small sound recorder to a tree as part of her early research. (Supplied: Marina Scarpelli) 

Early results from Ms Scarpelli's analysis show the shrubland had more birds than the woodland, while areas without vegetation were so quiet, all that could be heard was the sound of the wind that whipped up during the day.

"We could clearly hear the differences and we can also see the differences in the spectrograms," Ms Scarpelli says.

She says the findings were expected because most of the birds in the shrublands are insect-eaters, and insects prefer shrubs to trees.

"Everything ended up making good ecological sense."

Now she has developed a reliable method, Ms Scarpelli will be using A2O data to analyse the acoustic "barcodes" of everything from tropical forests to deserts.

She hopes work like hers helps give us a better idea of our impact on the Earth.

“We know humans are changing the environment really fast, and not for the best in most cases," she says.

"Sound can be a good way to measure how the changes are happening."

Many A2O recorders are on protected properties like this. (Bush Heritage Australia: Tom O'Hara)

Links

• Using ecoacoustic methods to survey the impacts of climate change on biodiversity (pdf)
• Climate Change Music: From Environmental Aesthetics to Ecoacoustics
• Climate change is breaking Earth’s beat
• Ecoacoustics: The Ecological Role of Sounds
• The Australian Acoustic Observatory (pdf)
• Confronting Climate Change Through Sound