These Scientists Are Using AI To Listen To Frogs

Summary

Short Wave: These Scientists Are Using AI To Listen To Frogs

Released on July 18, 2025, by NPR’s Short Wave, this episode delves into the innovative use of artificial intelligence (AI) in conservation efforts to revive the California red-legged frog, a federally threatened species.

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Introduction

Hosted by Regina Barber, the episode introduces science correspondent Nate Rott, who brings attention to a unique conservation project involving frogs and AI technology.

Regina Barber [00:29]: “Hey, Nate.”

Nate Rott [00:29]: “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.”

---

The California Red-Legged Frog

The episode centers around the California red-legged frog, the largest native frog in the western United States, which can grow up to five inches. Historically widespread from the Sierra Nevada Mountains to the Baja Peninsula in Mexico, the species has seen a dramatic decline over the past 150 years, now occupying less than 70% of its original range.

Susan North, Director of Stewardship for the Nature Conservancy in California [01:34]: “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.”

Nate Rott [02:06]: “But it wasn't just the miners and their voracious mining appetites. Non Native American bullfrogs sharing the blame. They will also eat native frogs. Got it. And there's other things, too.”

The primary cause of this decline has been habitat loss, with wetlands being converted into agricultural lands, parking lots, and polluted ponds, creating a substantial 260-mile gap in the frog's habitat between North Los Angeles and Central Baja. This fragmentation prevents natural recolonization of frogs across these regions.

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The Reintroduction Effort

In response to the decline, various groups, including the Nature Conservancy and federal agencies, initiated efforts to reintroduce the red-legged frog to Southern California. The project involves relocating frogs from Baja, Mexico, to restored habitats in San Diego and Riverside counties.

Regina Barber [05:03]: “So this story is actually kind of wild. And it starts down in Baja, California in Mexico.”

Annie Peralta Garcia, Fauna del Noroeste [05:08]: “My name is Annie Peralta Garcia. I work at Fauna del Noroeste, a non-profit in Ensenada.”

Annie Peralta Garcia, a biologist with a longstanding commitment to the red-legged frog, spearheaded the founding of Fauna del Noroeste to focus on research and habitat restoration. Genetic testing revealed that the remaining frogs in Southern California more closely resembled those in Baja, making the translocation from Mexico a viable conservation strategy.

Robert Fisher, U.S. Geological Survey [06:28]: “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.”

In 2020, two sites in Southern California were approved for receiving relocated frogs. Despite logistical challenges posed by the COVID-19 pandemic, the relocation was successfully executed using helicopters to transport egg masses from Baja to the U.S. border and subsequently to the designated sites.

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Challenges in Monitoring Frog Populations

Post-translocation, the critical question was whether these efforts were yielding positive results. Monitoring the success of the reintroduction required determining if the frogs were breeding and establishing stable populations. Traditional methods of manually listening for frog calls in thousands of hours of nighttime recordings were impractical due to the volume of data and background noise.

Susan North [07:56]: “A really important measure of success comes kind of at about 5 years of age. That's when they should start breeding. So the first Translocation was in 2020. We're now in 2025.”

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AI Acoustic Models: A Solution

To address the monitoring challenges, scientists partnered with software engineers to develop custom machine learning models capable of identifying the specific calls of the California red-legged frog amidst a myriad of other sounds, including other frog species, wildlife, and anthropogenic noise.

Nate Rott [10:24]: “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.”

Bennett Hardy, San Diego Natural History Museum [10:47]: “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 moss is incredible. It's, it's systematic monitoring of two species.”

The implementation of AI drastically reduced the time required to process audio data, enabling researchers to efficiently identify the presence and breeding activities of the red-legged frogs.

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Success and Future Plans

The collaboration bore fruit when, in the previous winter, the AI models successfully detected the distinct mating calls of the California red-legged frog in Southern California for the first time in 25 years. This breakthrough was confirmed by discovering new egg masses near the detection points, indicating successful breeding.

Nate Rott [11:57]: “Well, they were at least trying to breed. Right? That's what the sound suggests.”

Clark Winchell [12:10]: “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.”

Moving forward, the team plans to continue translocating frogs to further areas within the significant habitat gap, with the ultimate goal of establishing self-sustaining populations that could potentially lead to the species being removed from the endangered list.

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Importance of Conservation

The episode underscores the broader significance of conserving species like the California red-legged frog. Beyond their intrinsic value, these frogs play a crucial role in controlling mosquito populations and mitigating the spread of diseases such as Zika, dengue, and West Nile virus.

Bennett Hardy [13:43]: “He has a line. A good tinkerer 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, 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.”

This analogy highlights the interconnectedness of ecosystems, emphasizing that the loss of one species can have unforeseen and detrimental impacts on the entire environment.

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Conclusion

Nate Rott and Regina Barber conclude the episode on a hopeful note, celebrating the successful integration of AI in conservation efforts and the promising future of the California red-legged frog.

Regina Barber [14:31]: “Wow. Okay, so they are mating, they are making babies.”

Nate Rott [14:22]: “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.”

The episode serves as an inspiring example of how technological innovation can aid in preserving endangered species and restoring ecological balance.

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Produced by Hanich, created by showrunner Rebecca Ramirez, and fact-checked by Tyler Jones, this episode of Short Wave showcases the vital intersection of technology and environmental conservation.

Transcript

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[Regina Barber]

You're listening to Short Wave from npr. Hey, short wavers. Regina Barber here with just back from parental leave, science correspondent Nate Rott. Hey, Nate.

[Nate Rott]

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.

[Regina Barber]

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

[Nate Rott]

Yeah, that's fair. It's pretty technical speak, so let's start like this. So what you're hearing right now, Regina, is a recording from a pond outside San Diego in Southern California.

[Regina Barber]

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

[Nate Rott]

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

[Regina Barber]

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

[Nate Rott]

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.

[Regina Barber]

Okay.

[Nate Rott]

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.

[Susan North]

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.

[Regina Barber]

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

[Nate Rott]

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 the Sierra Nevada Mountains and. And down into Mexico on the Baja Peninsula. They were so prevalent, Regina. They used to be used as food for the miners during the gold rush.

[Susan North]

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

[Nate Rott]

But it wasn't just the miners and their voracious mining appetites. Non Native American bullfrogs sharing the blame. They will also eat native frogs. Got it. And there's other things, too.

[Susan North]

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

[Nate Rott]

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.

[Susan North]

Wow. 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 recolonizing their range naturally.

[Nate Rott]

So Susan's, 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.

[Regina Barber]

Okay, so these are the ponds we were hearing before.

[Nate Rott]

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.

[Regina Barber]

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

[Nate Rott]

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

[Regina Barber]

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

[Annie Peralta Garcia]

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[Regina Barber]

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

[Nate Rott]

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

[Robert Fisher]

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

[Nate Rott]

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.

[Robert Fisher]

2010S, 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, but at.

[Regina Barber]

Least there were like some. Unlike that, like Gap we were talking about in Southern California, where there's none at all.

[Nate Rott]

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

[Regina Barber]

Shout out to the less charismatic species out there.

[Nate Rott]

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.

[Bennett Hardy]

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.

[Regina Barber]

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

[Nate Rott]

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, and the COVID 19 pandemic is just beginning to start.

[Bennett Hardy]

It was like planes, trains, and automobiles.

[Nate Rott]

It was just a lot of different moving parts. So Hanny'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, and I'm sorry, Regina. They did not use planes and trains, but they did use a helicopter.

[Regina Barber]

Okay, close.

[Nate Rott]

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

[Regina Barber]

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

[Nate Rott]

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

[Regina 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, yeah.

[Nate Rott]

So again, here's Susan north, who helped coordinate this effort at the Nature Conservancy.

[Susan North]

A really important measure of success comes kind of at about 5 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.

[Regina Barber]

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

[Nate Rott]

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.

[Clark Winchell]

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.

[Nate Rott]

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

[Clark Winchell]

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

[Regina Barber]

Okay. So there are these microphones surrounding these ponds, recording every night for like weeks, weeks.

[Clark Winchell]

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.

[Regina Barber]

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

[Nate Rott]

And to make it even like more complicated, it. 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. They've recorded songbirds, ducks and wild turkeys. And they've even heard a screech owl and a great horned owl.

[Regina Barber]

What?

[Nate Rott]

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.

[Clark Winchell]

AI tool set that's been trained on the red legged frog specifically. So it can pick that out pretty well in our data.

[Nate Rott]

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 U.S. fish and Wildlife Service, this whole thing is mind blowing.

[Bennett Hardy]

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, what they've done with AI on this project and those audio moss is incredible. It's, it's systematic monitoring of two species.

[Nate Rott]

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.

[Regina 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?

[Nate Rott]

Good news, Regina. They have.

[Regina Barber]

Excellent.

[Nate Rott]

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?

[Regina Barber]

Yeah, as soon as you said that. Yes.

[Nate Rott]

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.

[Regina Barber]

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

[Nate Rott]

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.

[Clark Winchell]

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.

[Regina Barber]

Wow. Okay, so now what is going to happen? Like are they going to keep moving these red legged frogs over the border?

[Nate Rott]

Yeah. So they're planning to keep doing translocations. They're going to 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.

[Regina Barber]

Yeah, that, 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 of just preventing this frog's extinction.

[Nate Rott]

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.

[Bennett Hardy]

He has a line. A good tinkerer 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, 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.

[Regina Barber]

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

[Nate Rott]

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

[Regina Barber]

Nate Rott, 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.

[Nate Rott]

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

[Regina Barber]

This episode was produced by Hanich, created by showrunner 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 short wave from NPR.

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