Forest Elephants Passive Acoustic Monitoring

In partnership with

Forest Elephants Passive Acoustic Monitoring

Finding forest elephants — and poachers — by sound, across Central Africa's rainforest.

60% lost in a decade

50 microphones

24/7 listening

Source code Try the demo Bio AcousticsPassive Acoustic MonitoringMachine Learning Live

Forest elephants are vanishing: more than 60% have been lost in the past decade, and over 12,000 are killed each year for their ivory. The hardest part of protecting them is simply knowing where they are. In the vast, dense rainforests of Central Africa they are nearly impossible to see — so instead of watching for them, we listen.

Working with the Elephant Listening Project and the Cornell Lab of Ornithology, we built open-source tools that scan terabytes of forest audio to automatically detect and localize elephant rumbles — turning sound into the population and anti-poaching data that conservation has been missing.

Our vision is to conserve the tropical forests of Africa through acoustic monitoring, sound science, and education, focusing on forest elephants.

– The Elephant Listening Project

From a rumble to a located elephant — the acoustic monitoring pipeline Microphones across the forest record around the clock, a model finds rumbles in the audio, and the array pinpoints where each call came from.

A forest elephant in the rainforest undergrowth A forest elephant melts into the dense undergrowth — exactly why they are so hard to see, and why listening works where watching can’t.

Why forest elephants matter

Forest elephants are ecosystem engineers: the rainforest is shaped by their daily lives, and unravels without them.

Forest gardeners

They eat fruit and spread seeds across huge distances, and their movement opens clearings and trails — keeping the forest diverse, regenerating, and in balance.

Climate & water engineers

By promoting forest growth they help these forests store carbon, and by digging for water in dry riverbeds they create water holes that sustain other species through the dry season.

Biodiversity backbone

Their nutrient-rich dung fertilises the soil and feeds insects and fungi, while the dynamic habitats they maintain let countless plants and animals thrive.

Under pressure

Forest elephants face pressure from every side — and their slow reproductive rate means losses are hard to recover from. Tap each pressure to learn more.

Forest-elephant ivory is prized for its hardness and rose-coloured tint, driving targeted killing — more than 12,000 elephants a year. It is hard to detect in dense, poorly-protected forest.

Hunting elephants for meat has grown into an international business, threatening animals of all ages, including calves, as human populations grow.

Logging, mining and oil extraction are the most pervasive industry pressure, reshaping the forest elephants depend on.

Roads cut for extraction open once-remote forest interiors to hunters and settlement, multiplying the threat to elephants deep in the range.

Forest elephants breed slowly, so populations recover far more slowly than they are being lost — compounding every other pressure.

A basket of rhino horns beside burning elephant ivory, Kenya 2016 A basket of rhino horns next to a pyre of burning elephant ivory in Kenya, 2016. Photo: Ben Curtis, AP.

We have lost 60% of all forest elephants in the past decade.

– The Elephant Listening Project

What a rumble is

Rumbles are the low-frequency calls elephants use to communicate. Much of a rumble sits in the infrasound range — below 20 Hz, often beneath the threshold of human hearing.

Spectrogram of elephant rumbles A spectrogram of elephant rumbles — the low-frequency energy that carries across the forest.

Because their wavelength is so long, rumbles travel several kilometres and pass through dense forest, letting elephants stay in contact across vast areas they cannot see across. They use them to coordinate and bond as a herd, to signal readiness to mate, to raise the alarm at danger, and to keep mothers and calves together. That same far-carrying signal is what makes the forest listenable: if we can reliably pick rumbles out of the noise, we can find elephants.

Detecting rumbles at scale

Fifty microphones are arranged in a grid across the tropical forest, recording continuously. The challenge is the sheer volume of audio — and the answer is a model that finds rumbles in a spectrogram the way an object detector finds objects in a photo.

How the model turns a spectrogram into detected rumbles Each chunk of audio becomes a spectrogram; the model boxes every rumble and scores it.

The open-source tools process audio in batch across all available CPU and GPU cores, so a 24-hour recording is scanned in around 20 seconds. At that speed, a full month of audio from all 50 recorders — roughly 1 TB — is analysed in about 8 hours rather than weeks of manual review.

Spectrogram	Detected rumbles

Analyzing months of audio recordings can now be done in a matter of hours, not weeks.

We cover how the detector was built and run in the companion post on analyzing elephant rumbles at scale.

Conclusion

Listening turns the hardest part of forest-elephant conservation — finding animals that can’t be seen — into continuous, non-invasive data. Around-the-clock acoustic monitoring reveals where elephants are over time, surfaces signs of poaching, and gives rangers and researchers the evidence they need to act, at a scale and cost that field surveys never could.