The rainforests are alive with the sound of animals. Besides the pleasure of the din, it is also useful to ecologists. If you want to measure the biodiversity of a piece of land, listening out for animal calls is mucher than grubbing about in the undergrowth looking for tracks or spoor. But such “bioacoustic analysis” is still time-consuming, and it requires an expert pair of ears.

In a paper published on October 17th in Nature Communications, a group of researchers led by Jörg Müller, an ecologist at the University of Würzburg, describe a better way: have a computer do the job. Smartphone apps already exist that will identify birds, bats or mammals simply by listening to the sounds they make. Their idea was to apply the principle to conservation work.

The researchers took recordings from across 43 sites in the Ecuadorean rainforest. Some sites were relatively pristine, old-growth forest. Others were areas that had recently been cleared for pasture or cacao planting. And some had been cleared but then abandoned, allowing the forest to regrow.

Sound recordings were taken four times every hour, over two weeks. The various calls were