Sensors and sensibility

All kinds of new technology are being used to monitor the natural world

Smartphone components have made sensors cheaper, and machine learning can help analyse the resulting data

THE NEW FOREST CICADA had not been seen in seven years when it caught the attention of Alex Rogers, an ecologist and computer scientist at the University of Oxford. The insect is the only cicada native to the British Isles. It spends 7-8 years underground as a nymph, then emerges, reproduces and dies within six weeks. During its short adult life, it produces a high-pitched hiss that would make it easier to detect, were it not at the upper limit of human hearing. Its call is audible to children but not to most adults. It can, however, be picked up by smartphone microphones. This led to the invention of AudioMoth, an “acoustic logger” that can be set to listen for a particular sound and record it.

The device takes its name from the fact that moths can hear sounds across a wide frequency spectrum. It is roughly 60mm square and 15mm thick and includes a smartphone microphone, a memory card and a basic processing chip, powered by three AA batteries. Dr Rogers’s startup, Open Acoustic Devices, sells them for $60 through a group-purchasing scheme which helps keep costs low. At that price, “you can deploy many more devices, you can post them out to people and if they get lost or stolen, it doesn’t really matter,” says Dr Rogers. To date, some 30,000 AudioMoths have been scattered around the globe. A smaller version has just been launched and is being incorporated into an experiment to study how African carnivores are responding to warmer temperatures by monitoring the sounds they make, such as panting.

The AudioMoth is just one example of the explosion in the use of sensors to monitor ecosystems that has occurred in the past decade. Such devices are peppered across forests and…