Biology professor Mitch Aide uses his ears to learn about the frogs, birds and insects that are all around him. This scientist at the University of Puerto Rico is trying to track how animal populations are affected by a world that's under increasing pressure from human activities.

Aide says, "We would like to have five, 10, 20 years of data of how populations are changing."

In recent years, Aide and his colleagues have been putting recorders in the field so they can listen around the clock to the species they are studying. For example, they staked out a marsh where someone recently discovered a new species of frog.

"That is a recording from Sabana Seca. It is a wetland on the north coast of Puerto Rico, and this is where we put the original permanent recording station," Aide says.

The solar-powered station makes a one-minute recording every 10 minutes; 144 recordings a day, every day. It's a great way to keep an ear out for the newly discovered species as well as a half dozen other amphibians in the area. But there's a catch.

"You can save time in the field, but in the end you have to invest a lot of time in the laboratory listening to these recordings," Aide says. "It's torture."

So Aide recruited help from the University of Puerto Rico's computer scientists. As they report in the journal PeerJ, they've developed an automated system, called the Automated Remote Biodiversity Monitoring Network, to go through all those recordings and pick out the sounds of the species they're studying.

"The way it works is that the biologist who knows the calls gives the computer examples," he says.

The computer then looks for a match — kind of like the way the Shazam or SoundHound apps can listen to a song playing on the radio and tell you what it is.

Aide is encouraging field biologists everywhere to use his open-access system on the project's website to help build up a library of sound-recognition patterns that researchers can share.

"Right now, anybody who has an Internet connection can listen and view over a million recordings that we've collected from the different projects," he says.

What's especially appealing about this is he's gradually building a permanent repository of field recordings.

"One of the things I really like about this technology is that each recording is like a museum specimen. Anybody in 10, 15, 20 years can go back with new technology, with new ideas, and listen and analyze those recordings again," he says.

The sounds of the humpback whale change between seasons, years and populations.

Aide's project is just one example of computerized sound recognition in biology. Cornell University has another project focused on monitoring the world's oceans using bioacoustics.

"We have networks of recording devices around the world listening for fishes and whales as far north as the Arctic Circle, down to the tropics in the Atlantic and Pacific Oceans," says Cornell's Aaron Rice.

Rice says that means they are also swamped with recordings.

"In our lab group, we have years of data that no mere mortal could ever listen to in a single lifetime," Rice says.

So he, too, is working to automate this process by developing computer programs to sift through all that sound to identify animals and track them as they move through the world's oceans. Rice says the same idea is also taking hold across the parched lands of Australia.

"They have a string of recorders going from north to south across Australia and their goal there is to identify the spread of invasive bird species," he says.

That project illustrates one of the challenges of these computerized systems. It turns out one of the most aggressive invasive species is the European starling. And, as this recording from Cornell's Macaulay Library shows, starlings like to mimic other species.

It's not easy to teach a computer to recognize those ambiguous sounds. And the task at hand is much larger — the scientists would ultimately like computer programs to identify every animal sound that appears in a recording, so they can track the fate of the world's species.

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