These Scientists Are Using AI To Listen To Frogs

If you were a miner in California during the Gold Rush, you might have dined on a California red-legged frog. The largest native frog in the western United States, this Golden State denizen used to be found as far inland as the Sierra Nevada mountains and south, into Baja California. But today, they're listed as threatened https://www.fws.gov/species/california-red-legged-frog-rana-draytonii under the Endangered Species Act. Conservationists have worked to translocate new populations of the red-legged frog back to California in hopes that their numbers can be restored. But how do they monitor those populations' growth? Enter AI. Want to hear more stories about critters or conservation? Let us know at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:00Speaker 00

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• 0:18Speaker 01

  You're listening to Short Wave from NPR.

• 0:23Regina Barber?

  Hey, Short Wavers. Regina Barber here with just back from parental leave, science correspondent Nate Rot. Hey, Nate.

• 0:29Speaker 03

  Hey, Regina. I am overjoyed to be back, but mostly I am overjoyed to talk to you today about frogs and more specifically, an AI acoustic model to find them.

• 0:41Regina Barber?

  OK, you definitely had me at frogs and you lost me just a little with AI acoustic model.

• 0:46Speaker 03

  Yeah, that's fair. It's pretty technical speak. So let's start like this.

• 0:52Speaker 03

  So what you're hearing right now, Regina, is a recording from a pond outside San Diego in Southern California.

• 0:58Regina Barber?

  Wait, I think I heard a fair amount of frogs in that in that audio clip.

• 1:01Speaker 03

  Yeah. So unfortunately, in the words of Obi-Wan Kenobi, these are not the frogs you're looking for.

• 1:07Regina Barber?

  I think that was like, these aren't the droids you're looking for, but I appreciate the effort.

• 1:11Speaker 03

  Yeah, you know, any Star Wars reference I can squeeze in is great. So what you're hearing there are tree frogs. They're chorus frogs, your classic, you know, ribbit, ribbit, ribbit ones.

• 1:20Regina Barber?

  OK.

• 1:21Speaker 03

  But what scientists are trying to hear in these thousands of hours of recordings they've collected is the California red-legged frog, a federally threatened species. Here's Susan North, the Director of Stewardship for the Nature Conservancy in California.

• 1:35Speaker 04

  The California red-legged frog is the largest native frog in the Western United States, meaning it can grow up to a whopping five inches in size.

• 1:43Regina Barber?

  Five inches? OK, so that's like a little bigger than the palm of my hand. That's a big frog.

• 1:50Speaker 03

  Yeah, it's a big frog that used to have a really big range. So they used to be found up and down California, like as far inland as this here Nevada mountains, and down into Mexico on the Baja Peninsula. They were so prevalent, Regina, that they were used to be used as food for the miners during the gold rush.

• 2:07Speaker 04

  Unfortunately, over the last like 150 years, it has really declined and it's now occupying less than 70% of its range.

• 2:16Speaker 03

  But it wasn't just the miners and their voracious mining appetites. Non-native American bullfrogs share in the blame. They will also eat native frogs.

• 2:25Regina Barber?

  Got it.

• 2:26Speaker 03

  And there's other things, too.

• 2:28Speaker 04

  The biggest cause of decline in red-legged frog in California has been habitat loss.

• 2:33Speaker 03

  So wetlands turned into farming plots or parking lots, you know, ponds degraded by pollution. Susan says that's created this huge gap in the frog's range. So pretty much between like North Los Angeles and Central Baja, no frogs.

• 2:47Regina Barber?

  Wow.

• 2:47Speaker 04

  So that's a 260-mile gap in the range of the species, which is significant. And with a gap that size, you know, you're not going to have 5-inch frogs re-colonizing their range naturally.

• 2:59Speaker 03

  So Susan's group, the Nature Conservancy, and a whole host of other groups and federal agencies decided to try to bring these frogs back to, you guessed it.

• 3:12Regina Barber?

  OK, so these are the ponds we were hearing before?

• 3:15Speaker 03

  Exactly. So the challenge right now is that they're trying to figure out if this relocation effort is working. And the way to do that is by listening through recordings like this.

• 3:29Regina Barber?

  Today on the show, a border hopping effort to restore the California red-legged frog.

• 3:35Speaker 03

  And how new technology is helping scientists cut through a lot of unwanted noise.

• 3:40Regina Barber?

  You're listening to Short Wave, the science podcast from NPR.

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• 5:10Regina Barber?

  OK, Nate, so we have a threatened species, a frog, that has a bunch of groups deciding to like bring it back to Southern California. How did they do that?

• 5:18Speaker 03

  So this story is actually like kind of wild. And it starts down in Baja California, in Mexico.

• 5:23Speaker 05

  My name is Annie Peralta Garcia. I work at Fauna del Noroeste, a nonprofit in Ensenada.

• 5:30Speaker 03

  So Annie's been in the red-legged frog game since like her undergrad. She got her PhD surveying every stream in the northern part of the Baja Peninsula for the frogs in the mid-2010s.

• 5:40Speaker 05

  It was pretty fun, especially for my husband, that he loves the fieldwork. And, you know, we found out that they were only found in 10 sites in the southern part of the range. And even though they were there, they were not in high numbers.

• 5:55Regina Barber?

  But at least there were like some, unlike that like gap we were talking about in Southern California, where there's none at all?

• 6:02Speaker 03

  Yeah, exactly. So like post-graduation, Annie started this nonprofit to do research and habitat restoration for those red-legged frogs in Baja's like other less charismatic species.

• 6:12Regina Barber?

  Oh, a shout out to the less charismatic species out there.

• 6:16Speaker 03

  Yeah, no doubt, right? They need love too. So Annie's team has helped raise and stabilize the populations of those frogs at some of those sites, which is really important to the rest of this story because genetic testing of the last known red-legged frogs in Southern California showed that they more closely resembled Baja's frogs than the red-leggeds that still exist further up in like Northern and Central California. Here's Robert Fisher, a biologist with the U.S. Geological Survey.

• 6:44Speaker 06

  And thinking about, you know, reintroducing frogs and bringing them back and restoring these ecosystems, it became clear we needed to use a Mexican source for the frogs.

• 6:54Regina Barber?

  Okay, I love this. I love this like international cooperation that's gonna happen here.

• 6:58Speaker 03

  Yeah, so Robert says in 2020, these two sites in Southern California were approved to receive relocated frogs. They've been cleaned out of predatory bullfrogs, the paperwork and permitting nightmare had been navigated.

• 7:10Regina Barber?

  Okay.

• 7:10Speaker 03

  And the COVID-19 pandemic is just beginning to start.

• 7:14Speaker 06

  It was like planes, trains, and automobiles. It was just a lot of different moving parts.

• 7:19Speaker 03

  So Annie's team and others collected parts of an egg mass from one of the sites in Baja, put it in a cooler, transported it by car.

• 7:27Regina Barber?

  Cool.

• 7:28Speaker 03

  I'm sorry, Regina, they did not use planes and trains, but they did use a helicopter.

• 7:32Regina Barber?

  Okay, close.

• 7:34Speaker 03

  So that's like the actual sound of the helicopter from a video that the team shared. They moved it to the U.S. border and eventually to Robert's team, which brings them to these prepared sites in San Diego and Riverside Counties.

• 7:47Regina Barber?

  I mean, it sounds super like fascinating, but also like a logistical nightmare.

• 7:54Speaker 03

  Yeah, Robert described this whole thing as like an impossible dream that he's gotten to see happen.

• 7:59Regina Barber?

  Okay, so these frogs have been like translocated back to Southern California. Do we know that it's working? Like if the populations are stable?

• 8:07Speaker 03

  Yeah, so again, here's Susan North, who helped coordinate this effort at the Nature Conservancy.

• 8:11Speaker 04

  A really important measure of success comes. Kind of at about five years of age, that's when they should start breeding. So the first translocation was in 2020. We're now in 2025. And that's really why we were on the edge of our seats, waiting to see if we were going to find egg masses or hear frogs calling, which means that they're attempting to breed.

• 8:31Regina Barber?

  Ah, okay. Hear them calling. This is where that fancy like AI acoustic model comes in.

• 8:36Speaker 03

  Yes. So like in order to know if they're successful, you need to know if these frogs are trying to mate. And if you're an amphibian-loving scientist like Bennett Hardy is, who works at the San Diego Natural History Museum.

• 8:48Speaker 07

  I'd love to be out there every night at these ponds and with my tent and camping and being up every night and trying to listen for them, but it's just not feasible.

• 8:57Speaker 03

  So instead, they set up a series of microphones at both of their restoration sites.

• 9:02Speaker 07

  And the idea is that these are then recording the sounds of the night that we're not able to be there for.

• 9:09Regina Barber?

  Okay, so there are these microphones surrounding these ponds, recording every night for like weeks?

• 9:14Speaker 03

  Weeks.

• 9:16Speaker 07

  And then we have thousands and thousands of hours of files from these devices. And now we need thousands of hours of ears to be able to sort through all these files, find where the frogs are, when they are, if they are, and get through all of that data, which is a huge task.

• 9:34Regina Barber?

  Oh, my gosh. Yeah, like this is an audio producer's nightmare. So much tape, so many sounds.

• 9:41Speaker 03

  It's horrible. And to make it even like more complicated, it's not like you can just pop one of these sound files into an audio program and like look for spikes in the sound waves, because there are so many other sounds. So Bennett shared audio clips they've recorded of coyotes.

• 10:01Speaker 03

  They've recorded songbirds, ducks, and wild turkeys.

• 10:07Speaker 03

  And they've even heard a screech owl and a great horned owl.

• 10:11Regina Barber?

  What?

• 10:16Speaker 03

  And of course, there's still the many chorus frogs and bugs and cars that you'd expect to hear in Southern California. So to find those needles in this sound haystack, Bennett says their group partnered with software engineers to create custom machine learning models.

• 10:31Speaker 07

  AI toolset that's been trained on the red-legged frog specifically, so it can pick that out pretty well in our data.

• 10:39Speaker 03

  Bennett says it can sort through the data in like tens of minutes. So they even created another model, like another AI model to identify the calls of those non-native bullfrogs so they can get ahead of any new threats. And for like Clark Winchell, who describes himself as a mud boot biologist, who helped prep these relocation sites for the US Fish and Wildlife Service, this whole thing is mind blowing.

• 11:02Speaker 08

  I spent countless hours by myself in a kayak all night long, listening for bullfrogs. It's not the most efficient use of time. What they've done with AI on this project and those audio masts is incredible. It's systematic monitoring of two species.

• 11:22Speaker 03

  And as anyone who's worked in wildlife conservation or heard about it knows, like monitoring species takes a lot of time, effort, and money, and this helps them save on all of that.

• 11:32Regina Barber?

  Yeah, so let's get to the most important question, though, of this story that I've been thinking about. Have they actually heard any of these California red-legged frogs?

• 11:41Speaker 03

  Good news, Regina, they have.

• 11:44Regina Barber?

  Excellent.

• 11:48Speaker 03

  So this is from last winter, and can you kind of hear that grunting sound like a finger rubbing on a balloon beneath the sound of those tree frogs?

• 11:56Regina Barber?

  Yeah, as soon as you said that, yes.

• 11:59Speaker 03

  So that is the sound of the California red-legged frog, and this is the first time it has been heard in these parts of Southern California in 25 years.

• 12:09Regina Barber?

  Wow. So they are mating, they are making babies.

• 12:13Speaker 03

  Well, they were at least trying to, right? That's what the sound suggests. So after they heard this, the team sent out folks to survey near the microphone where they picked up this sound, and they did find a new egg mass. So here's Bennett again.

• 12:25Speaker 07

  We knew right then and there that, hey, this whole thing is successful. It's working, all of our hard work over the last six years and beyond for this species in this region is starting to pay off.

• 12:38Regina Barber?

  Wow, okay, so now what is gonna happen? Like, are they gonna keep moving these red-legged frogs over the border?

• 12:45Speaker 03

  Yeah, so they're planning to keep doing translocations. They're gonna keep on monitoring the populations they've moved. And the hope is that when these populations become self-sustaining, they'll be able to start like translocating egg masses from these Southern California sites to new ones to keep seeding new populations in that big gap we talked about. They're hoping for some natural dispersal, some of the frogs just to move on their own to new areas. And eventually, maybe, the hope is they'll be able to get off of the endangered species list.

• 13:13Regina Barber?

  Yeah, that would be great. And like Nate, we all love hearing like a happy wildlife conservation story. I don't think anybody wants to hear about, obviously, an animal going extinct, but stepping back, is there benefits to all this work outside of just preventing this frog's extinction?

• 13:30Speaker 03

  I mean, so, nobody wants to see an animal go extinct, but also, nobody likes mosquitoes, right? And the frogs help with that, especially with diseases like Zika and dengue and West Nile virus showing up in Southern California. But you know, I like always ask biologists this question, like, you know, why should somebody who doesn't know anything about this frog care? And Clark Winchell had maybe the best answer I've ever heard. So he quoted the famed naturalist Aldo Leopold talking about ecosystems.

• 13:59Speaker 08

  He has a line, "A good tinker keeps all the parts." And I will just say, in my day of rebuilding carburetors on old trucks, when you got them done and there's one screw laying on a table...

• 14:13Speaker 08

  You knew you were screwed. I don't think any scientist has an answer on that. But it is important to maintain biodiversity as best we can moving forward.

• 14:25Regina Barber?

  I really, really like that analogy. Being compared to a carburetor and pieces left over. I love it.

• 14:31Speaker 03

  Yeah, gearheads everywhere rejoice. Yeah, it'll definitely stick with me every time I think about why we should care about species going extinct.

• 14:38Regina Barber?

  Nate Rot, thank you so much for bringing this story to us. Now I want to listen for like red-legged frogs like the next time I go visit my family in California.

• 14:46Speaker 03

  Heck, yeah. Let me know when you do it and we'll camp out, inefficient as it may be.

• 14:53Regina Barber?

  This episode was produced by Hannah Chen, edited by Shorerunner Rebecca Ramirez, and fact-checked by Tyler Jones. Robert Rodriguez was the audio engineer. Beth Donovan is our senior director and Colin Campbell is our senior vice president of podcasting strategy. I'm Regina Barber. Thank you for listening to Shorewave from NPR.

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