Episode 04: Rescuing the Corroboree frogs with Michael McFadden
In Episode 4 of Amphibian Rescue, we travel to the Australian Alps to explore a successful and long-standing rescue effort to save the Southern and Northern Corroboree frogs.
Michael McFadden, Wildlife Conservation Officer at Taronga Conservation Society Australia, takes us inside more than two decades of work to prevent the extinction of these tiny, striking black-and-yellow species that have been pushed to the brink by chytrid fungus.
We explore how scientists and conservationists built insurance populations from eggs collected in the wild, learned how to breed a uniquely challenging species, and developed innovative strategies to return frogs to their habitat. From refrigerated shipping containers turned into frog facilities, to disease-free exclosures acting as bridges between captivity and the wild, to ultimately...yelling at frogs?
Along the way, we also look at the challenges that remain—from climate change and wildfires to the ongoing fight against chytrid—and the emerging genetics and biotech research that could help these frogs survive in the long term.
About our guest:
Michael McFadden BSc (Hons), PhD Candidate, is a Wildlife Conservation Officer at Taronga Conservation Society Australia and Supervisor of the Herpetofauna division at Taronga Zoo.
He has worked on amphibian conservation for over 20 years, focusing on conservation breeding, reintroduction biology, and population management for some of Australia’s most endangered frog species, including the Southern and Northern Corroboree frogs, Booroolong frog, and Yellow-spotted Bell frog.
Michael is co-convenor of the Zoo and Aquarium Association Amphibian TAG, contributes to multiple recovery teams, and has published more than 30 scientific articles and book chapters. Michael has also supported Amphibian Ark by helping deliver amphibian conservation training workshops across Australasia.
Documents referenced in the episode:
- Davidson, M. J., K. R.Zenger, J. S.Keogh, L.Berger, L. F.Skerratt, and T. A.Kosch. 2026. “Design and Application of a Genome-Wide SNP Array to Improve Conservation Outcomes in the Critically Endangered Southern Corroboree Frog.” Molecular Ecology Resources26, no. 3: e70080. https://doi.org/10.1111/1755-0998.70080.
- Davidson, M. J., L. Berger, A. Aquilina, M. Hernández-Poveda, D. Guinto, M. McFadden, D. Gilbert, D. Goodall, K. R. Zenger, L. F. Skerratt, and T. A. Kosch. 2025. “Exposure to low doses of Batrachochytrium dendrobatidis reveals variation in resistance in the Critically Endangered southern corroboree frog.” Global Ecology and Conservation 60: e03587. https://doi.org/10.1016/j.gecco.2025.e03587
Transcript
[00:00:00] Michael McFadden (MM): Without the ex situ colonies it is a species that I guess effectively would be gone from the wild now. It'd be certainly functionally extinct. It may have disappeared totally because, from about 2012, 2013, frogs were no longer kind of detected at non-translocation sites
[00:00:21] María Braeuner (MB): Welcome to Amphibian Rescue, the Amphibian Ark Podcast. Amphibian Ark's mission is to rescue amphibians in crisis, especially those that cannot currently be protected in the wild, with the ultimate goal of one day returning them to their safe and restored habitats. I'm your host, Maria Braeuner, and I invite you to join me as we share these inspiring stories of how ex situ conservation, collaboration, and science are already giving amphibians a second chance and a future back in the wild
You might recall from episode one that some of the first regions where the amphibian crisis raised alarm were Central America and Oceania, particularly Australia. Today, we're learning about an amphibian rescue story from Australia. By the time the global amphibian crisis was finally recognized, Australia had already lost at least six amphibian species, including the famous gastric-brooding frogs.
Now, you might have heard about these ones, two species of frogs with an extraordinary reproductive strategy where the female swallowed the fertilized eggs. She incubated them in her stomach for six to eight weeks through their entire tadpole stage, and eventually gave birth with what looked like vomiting tiny juvenile frogs.
This discovery stunned scientists. A vertebrate that could turn their stomach into a womb and completely stop digestion? It was strange, but also medically intriguing. And while researchers did get to some hints into how this works, research was interrupted by, well, their extinction. These two species were described in the mid-'70s, and by the mid-'80s they were already gone.
Since then, amphibian conservation efforts, including ex situ programs, have grown across Australia. And today, I have the pleasure to be talking with Michael McFadden, Wildlife Conservation Officer at Taronga Conservation Society of Australia at Taronga Zoo in Sydney. Michael has been working with amphibian ex situ conservation for over 20 years now, and in this episode, he tells us the rescue story of the corroboree frogs, two species that might not still exist today without conservation breeding programs.
Let's meet Michael.
[00:02:49] MM: Uh, as, as a young child, I was very much always into reptiles and amphibians, uh, always chasing reptiles from a young kid. Uh, lizards, snakes. I remember bringing my first venomous snake home when I was 10 or 11 years old. I started working at Taronga Zoo when I was 21. So I did a zoology degree, and then I did my honors on a bird species, an endangered bird species, a Regent honeyeater. And, and at the university I was at, uh, there was one vertebrate zoologist, and she was an ornithologist, and she had a project ready to go on that species. Uh, even though I wasn't a bird person, I saw it as a conservation project, and I was really interested in conservation, so I'm like, "That sounds like a great opportunity. I'll do that." It was based at the zoo, and I kind of fell into the zoo through that avenue. Back then when I started, there, there wasn't a lot of conservation programs in zoos. There were small conservation programs, and there was a, a handful, not many for, for amphibian species in Australia. I met a mentor of mine, Dr.
Peter Harlow. He was the manager of the reptile and amphibian department at Taronga Zoo at the time, and I got to talking to him, and he encouraged me to apply for a job there as my honors research was wrapping up. And I did, even though that's not the direction I was looking at going to initially. I did really like the reptile and amphibian collection at the zoo, and I thought that might be a good job to do for a year or so, like I wasn't intending on staying and working at the zoo. I was interested in research and conservation. The reason I stayed on working at the zoo was because I guess I saw that, that there was scope for it. There was a need for it. In Australia we'd lost six species of amphibians at that point already, and we had another four or five I would say right on the brink of extinction and many others that were declining. So we lost those species, unfortunately, because there wasn't the scope to be able to, I guess, collect them, set them up in the insurance colonies. So- I guess starting at the zoo, seeing the Gold Frog, uh, program, also chatting to Peter Harlow, my manager, we decided there was a lot of scope there for us to do a lot of good with, with, uh, ex situ insurance colonies.
And at the time we didn't have a lot going, but we kind of really built upon it. So the Reptile and Amphibian Department alone at Taronga Zoo, there's seven species that are either critically endangered or extinct in the wild, and we have large, genetically broad insurance colonies of those species.
They're actively doing reintroductions of those species as well as a whole hell of a lot of conservation research. So it's quite ... I guess we can point to a lot of programs quite easily between a handful of zoos in Australia to demonstrate that there's a lot of species that would actually either be gone or just about to go without zoos and their breeding programs
[00:05:08] MB: And today we'll learn about two of these species, the southern corroboree frog, Pseudophryne corroboree, and the northern corroboree frog, Pseudophryne pengillei.
Both of these species live in Eastern Australia in the state of New South Wales in very specific but separate alpine habitats that Michael will tell us more about later on. These frogs are small, strikingly patterned in black and yellow, and unlike most frogs, they don't jump. They walk through their mossy environment with their tiny, tiny legs.
They are also highly territorial, which as we will learn soon, actually helps researchers find them in the wild. And they're also toxic. But unlike most famous poison frogs, like the poison dart frogs from Central and South America, who depend on their diet to produce their poison, the corroboree frogs can actually produce their own toxins.
This actually makes them a little bit less vulnerable to predation. But then, if they are relatively safe from predation and they for the most part live inside national parks, how did they become so endangered that they're now considered functionally extinct? Before we get back to Michael, let me explain this.
Functionally extinct means there may still be a few individuals left in the wild, but not enough to sustain a population. Either they can't find others to reproduce, or the numbers are so low that inbreeding becomes a serious problem. In other words, without intervention, the species would not survive in the wild.
So back to Michael. How did they get to this state?
[00:06:49] MM: Southern corroboree frog, Taronga started becoming involved in 2006, and by that stage the species was already in a lot of trouble. Unlike a lot of other threatened species, it's not impacted by, uh, invasive animals so much. It's not impacted by, um, land clearing or anything.
It's only found within a national park in Australia, in the, the highest elevation part of Australia, in Kosciuszko National Park, so our Snowy Mountains region. And by the mid-1980s, chytrid fungus had arrived in the Snowy Mountains and the species suffered a dramatic decline at that time. And one of the first researchers down there, Will Osborne, uh, Dr. Will Osborne from University of Canberra, noticed the declines in this species, and started trying to monitor the frog populations to try to work out what was going on. And then fortunately, back in the 1990s, late 1990s, another researcher, a young researcher at the time, Dr. David Hunter, started working on the species.
And Dr. Dave Hunter is still leading the charge for this species, kind of, I don't know, almost 30 years down the track. He's one of Australia's, I guess, greatest amphibian biologists, has done a amazing job with conservation management of these species. And he set up some, some eggs, uh, went to a place in Melbourne called the Amphibian Research Center.
And they were set up there to start establishing an insurance colony for the species. And that was from the late 1990s. Uh, and then zoos came on board really in the early 2000s. So that private facility started collecting eggs in the late '90s, and then by the, by the early 2000s, um, there was engagement with the zoo community.
And Taronga Zoo in 2006 received our first, um, it is a shipping container facility, so a frozen food storage container that was converted to a frog conservation facility, with refrigeration which we need because this species is only found in our snowy mountains where it gets quite cold in the winter.
So during the winter it's like a fridge down there. They live under a layer of snow during the winter, so we have to cool our facility down to three or four degrees Celsius during the winter period to give them a kind of a, replicate what's happening in the wild. So in 2006 the facility was being built. That was when I met Dr. Dave Hunter. I, I went down to Kosciuszko for the first time in, in January 2006. So I'd say that's just over 20 years ago now. Uh, and that's where I, I met Dave. I, I, um, took a week off from the zoo on leave and drove down to the Snowy Mountains and spent a week up in the mountains with him surveying corroboree frogs.
And they were still at a number of sites back then. The, the population was still very low. The decline was kind of at the tail end, but there was still corroboree frogs at a number of sites throughout the mountains. And it was, I guess, interesting going back each year in 2007, 2008, 2009, and each year seeing kind of 50% of the sites had gone, and then the next year you go back and there might've been 20 sites, and now there's 10, and then the next year there's like seven or eight, and then it just declined and declined and declined.
And unfortunately by 2012, um, that was around the last year I think we had eggs at sites that weren't translocation sites. So here's a species that really, without the ex situ colonies, is a species that I guess effectively would be gone from the wild now. It'd be certainly functionally extinct or may have disappeared totally because, uh, from the, about 2012, 2013, frogs were no longer detected at non-translocation sites. So it's a species in a lot of trouble. Like in, in the wild at the moment, there's probably about under 50 adults remaining, uh, at non-fence sites. And I'll talk about the fences in a moment, what we're, what we're doing out there. But yeah, for the corroboree frog, they're a species only found in our Snowy Mountains.
And yeah, we, we got engaged in 2006. Uh, we built a facility back then. Um, uh, soon after, Melbourne Zoo started to increase the colony as well. Um, and then later down the track, Healesville Sanctuary came on board. But in 2006, breeding of the species still hadn't been established, and there was a clutch here or there, but that was about it.
And then I guess by 2010, we had our first mature frogs, and even then our, our breeding success was quite low initially. And then over the course of 2011, 2012, we really started to work out how to start breeding this species. They're very, I guess, an unusual species, a difficult species to breed. They're not your, your typical frog that is found in... that lays their eggs in a water body, uh, like they amplex and they sit in the water and lay their eggs in the water and so forth. This is a, this is a species that lays its little nests in moist terrestrial nests. So it lays its eggs above the water level, uh, in moist nest areas. And just there's a lot of things to get right to breed a species like this one. So it took a few years to work it out, but fortunately within a few-- within a number of years we started to work out the breeding success for this species and were able to start producing large numbers of this species that can be used for conservation purposes.
[00:11:01] MB: Before going into how they got to reproduce them ex situ, I had to ask, how does a corroboree frog nest look like?
Well, these little guys live in Sphagnum moss. They get under a layer of moss, and the males sort of push around the moss aside to create a little hole or a cavity that is big enough for himself, but also for females to be able to get in and lay the eggs.
[00:11:27] MM: And sometimes I guess he needs to make it a little bit bigger throughout the breeding season, 'cause there has been times...
They only lay about 35 eggs in a clutch, and there's been times where we've gone to look at eggs and there's been up to 200 eggs in a certain male's nest. So he's been a very lucky male, and he's got U- up to 10 females lay eggs in his nest, so he's obviously got a great call. He's a good singer, uh, and he's got... he's picked a nice little, um, I guess, real estate location. Uh, and the females like that site, so they've laid eggs in there and it's a... Sometimes there's a lot of eggs, so he would've had to create, like, a larger cavity, like, keep kind of pushing out, pushing out the area around his nest to, to make space for more eggs and-
[00:12:01] MB: For me as a person from a tropical country, I'm just fascinated that they live in the snow.
I think, you know, if... You know, the- we, we know the frogs in Canada kind of have this gellification process to, to not crystallize and not have the ice r- kill them or break their cells. How is this for the corroboree frogs? Is there something similar? How do they live in such an environment, and they tolerate the snow and freezing temperatures?
And why do they reproduce in, in winter or autumn?
[00:12:31] MM: It's a great question. Yeah, no, uh, with southern corroboree frogs, we actually don't know if they freeze , but they, they are really well-adapted to that cold climate. Uh, and they're only found up in that snowy mountains country, where it does get snow throughout the winter.
During the summer, it's quite warm. It's quite nice during the summer. It's not, it's not tropical by any means. Um, but 25-degree Celsius days are, are quite common. So it's, like, it's sunny, it's hot kind of thing. You, you're certainly getting around in a shirt. Um, and that's the time of year they breed.
So they do breed while it's warmer , they breed typically in the middle of summertime, so kind of mid-January through to mid-February for us, which is, in the Southern Hemisphere, that's kind of the peak of our summer period. And the little male sets up a little nest area on, around the edge of a pool, whether or not it has water or not, sometimes there are ephemeral pools that have no water. And he'll set up a little nest chamber, and he'll get in there, and he'll start calling away for females. Um, and then if a female likes his call and likes where he set up his nest, she'll go in there, lay her eggs. He'll stay in there. He'll keep calling, hopefully, and he'll get more females as they come through.
Sometimes they could have five, six, even more females come through and lay eggs in the nest. Uh, it's during that time of year that we survey for corroboree frogs too. Uh, something that's a little bit, uh... a technique that's a little bit unusual. When we survey for corroboree frogs, we're not actually spotting them because y- you don't see them.
They're, they're under the sphagnum moss. They're deep in the moss. Uh, we actually yell at them, uh, and they yell back at us. So we walk around throughout the, the bog systems where they are, and we yell at them. Yell out, "Yeah," or, "Yeah, frog," or something along those lines. And this little frog thinks you're another corroboree frog, and he starts kind of barking back at you with his territorial call, to say, "This is, this is my pond. These are my ladies. Go away." Uh, and that's how we work out numbers of corroboree frogs calling. We can actually hear them calling. We don't disturb them at that time of year because if we do, if we disrupt the nests during the middle of the breeding season, it could impact their breeding success that year.
So we typically mark the nests up, so a little bit of surveyor's tape or something like that, and we don't touch the nest. Then we come back at the end of the breeding season to, to check on breeding success Um, but they, they lay their eggs in those nests and then they rely on either autumn rains or early snow melt, uh, to flood the pools and inundate those nests.
By that time, the male's already gone and the eggs are in the nest. And as soon as the, the, the eggs get inundated, and then they hatch. So they could be an egg for a couple of months, but as soon as they get flooded or wet, they hatch and they enter these little ponds. And they exist in the ponds throughout the winter period.
And so the, the tadpoles don't freeze solid. The pools stay at maybe one or two degrees Celsius. So they stay, they stay really cool, but they don't freeze solid. The frogs on the other hand, throughout that winter period, they bunker down. So whether it's deep in the moss or the vegetation or under things like logs in the forest, they bunker down, and when the snow falls, it falls over their habitat and it creates, I guess, an insulating layer. So the frogs don't get right into the low minuses. Uh, the data loggers out there indicate the temperature stays between zero degrees Celsius and kind of two degrees Celsius. So it's, it gets very cold, but tends not to freeze.
[00:15:19] MB: In this respect for breeding them ex situ. When the ex situ program began, was this already known?
[00:15:27] MM: It was a challenge. So it was known how they breed, it was known where they lay eggs and Dr. Dave Hunter had lots of data on the nest and he, he's, uh, he's a professional in that area. And fortunately, before we started breeding them, I've had a chance to do a few breeding seasons in the wild with Dave and check out the nests and where they lay so that we could try to replicate that at the zoo.
Now, there's a lot of critical things, I guess, to get them breeding. One of the things is for the Corroboree frogs, they breed in the same weeks of the year every year. So regardless of temperature, regardless of rainfall. In a really dry year, you might get less calling or less breeding, but it's still the same time of year. So it's not like tied to rainfall, for example. Um, so on, on all our Corroboree frog facilities, for example, we have a light sensitivity switch. When it gets light in the morning, it turns the lights on in the facility, and as it gets, uh, dark in the evening, it turns the lights off. So every day coming into summertime, your days get a couple of minutes longer. So it's following natural photo period, longer days in summer to shorter days in winter, 'cause that would be a key trigger we think for reproduction. Um, other than that too is temperature. So we wanted to mimic the wild environment, cool the container right down to four or five degrees Celsius at least during the winter period. And they overwinter, they bunker down in their moss and we don't see a frog, we don't feed a frog for kind of four months of the year while they bunker right down. And that was set up from the start, giving them good UV light and, uh, um, planting. But then some of the fine tweaking came into the nest site selection.
So we had sphagnum moss sitting on, on the aquarium gravel, and we had hit and miss breeding. We had some success breeding, uh, sometimes not so much success breeding, so we had to kind of alter how the moss meets the gravel. But some of the other things that were tricky too is, uh, initially we had just males and females in the breeding tank to start with, and we did have some breeding success. It was a little bit scattered. Um, and then we started making sure we had the sexes separate outside the breeding season. And we started introducing the males into the breeding tanks, um, about a month before the females. So that way they had a full month of time to, to get in there, scope it all out, set up their nests, really, really get it all prepared and start calling away.
And what we do is wait for the males to hit their kind of peak craziness for calling to get to the point where you're in the facility and you can hear males calling everywhere, and we figure that's the time that's good to put the females in. And that's where we enter the females into the tank. And we found that provided the best breeding success, and it al- also allowed us to have all our clutches in a shorter period of time, so that way all the eggs are around the same stage of development for when we want to hatch them or if we wanna release them to the wild So it has taken a lot of tinkering, a lot of tinkering to get it right.
A lot of even diet and, uh, multivitamins and so forth. And, and also even plant growing. Like, for us to, to get the Corroboree frog breeding habitat going really well, we need the moss and that in the tanks to actually be thriving as well. So it's not just keeping the frogs alive, it's keeping, I guess, the environment and the tank alive, too.
[00:18:11] MB: It's so much work that goes into it and so much knowledge from, from the biology of the species, the ecology of the species. And talking about the, the ecology, and you were mentioning at the beginning also a lot about collecting eggs. And in many rescue programs, we read about people looking for the adults to reproduce them.
And with the Corroboree- Mm-hmm ... there's a lot on the papers about collecting only eggs. Can you tell us a little bit about this part also? Why only the eggs?
[00:18:39] MM: Um, yeah. So for, for the Corroboree frog species, to set up the ex situ colonies, we, we, we only collected eggs. Uh, and there's a couple of reasons for that.
One is, I guess the species was already in such a state of trouble and, and low numbers, that collecting adult frogs is really gonna... it could have an impact on those remaining populations. And, and really for us to collect enough, I guess, genetics and enough individuals, we would have an impact on the populations. By collecting eggs, we can just collect a certain proportion of eggs from each nest, uh, and we're able to start the ex situ colony by that. We're able to find the eggs quite readily. So unlike some frog species that might breed in a pond or a river, it might be difficult to access eggs, we could find the eggs quite readily.
Um, so by collecting eggs, we could collect a portion of eggs from nests right throughout the range of the species, and we did it over a number of years. And that way it's having, I guess, minimum impact on the existing population, um, and also allowing us to collect enough, enough founders.
It's not always the case. With some frog species you certainly do need to collect adults. And we've done rescues of other frog species, more recently the Booroolong frog, where we've had to go in and do a, actually a salvage operation before they disappeared, and so we collected adults there. But for the Corroboree frog, fortunately their biology allows for us to, to locate nests, collect eggs, and have minimal impact on the population.
Uh, one of the benefit is, um, that we've never had chytrid fungus come through on an egg because it's a, a jelly capsule that chytrid doesn't grow on. Um, but the, the cons of a species like this that's a, a subalpine species or a cool climate species, is that sexual maturity takes a long time. Um, they take almost a full year to go through from egg through their tadpole stage to metamorphosis.
And then the frog, for this frog, it's usually about four or five years before they're sexually mature. So by the time you've collected an egg, it can be five or six years before that frog's ready to breed. So it is a bit of a, it is a bit of a slow process for the Corroboree frog to, to get them through.
So collecting eggs does take a while to, to really kick up with the ex situ colony. Um, but fortunately through good husbandry we know we have really good success with eggs. So from an egg stage through to metamorphosis, we have at least 85 to 95% success, um, from eggs surviving through to metamorphosis in the frog. And, and throughout the early life stages.
[00:20:44] MB: So egg collection gave the team a way to establish insurance populations with minimal impact on the frogs that were still there in the wild. And like Michael mentioned, the eggs are not susceptible to chytrid. You might remember that chytrid affects amphibians through their skin, specifically going after the keratin, like the keratin that you and I have in our hair or nails.
But amphibian eggs do not yet contain keratin, making them less susceptible to infection by chytrid. This makes eggs a valuable strategy to establish insurance populations. However, chytrid remains one of the biggest threats for the Corroboree frogs in the wild And unfortunately, it's not the only one.
Climate change is adding new pressures. In recent years, wildfires have increased in intensity and frequency across Australia, including in these alpine habitats of the corroboree frogs. Here again, insurance populations play a crucial role because they also make it possible to rebuild populations after wildfires.
At the same time, conservationists both in situ and ex situ are working to reduce these risks directly in the field. So let's get back to Michael and hear how that works.
[00:21:57] MM: For this program, it's really fortunate it's, well, I guess we've got really good collaborations between ex situ and in situ. So what we have at the moment, each year the breeding programs produce eggs. Last week I was down in Kosciuszko National Park getting out to some of the sites, actually reintroducing eggs to the wild. And when we do that, we do that to some wild sites, we do it to some wild sites that have had artificial pools created in it. In some sites, Dave has set up artificial tubs that allow us to be able to reintroduce eggs- we'll put eggs into the tubs, which allows what you alluded to a second ago with wildfires and drought, uh, sometimes in really drought years when, when wildfires can occur and so forth, the pools can dry up, and if a pool dries up while there's tadpoles in it, they all, they all die. So we have artificial pools set up at some sites in the field, so that way we know they're gonna retain water throughout that period to allow us to metamorphose successfully.
So some go into those sites. But in more recent years, Dave's worked really closely with the National Parks and Wildlife Service of New South Wales to set up these big disease-free exclosures. And these exclosures are quite large. They're big fenced areas, probably about half the size of a football field, so quite large exclosures. And within the fenced areas, corroboree frog habitat has been created, and they're in really remote parts of Kosciuszko National Park. And the purpose of them is to exclude chytrid fungus. And up in Kosciuszko, the southern corroboree frog lives sympatrically with another species called the common eastern froglet, or Crinia signifera, and that species, unfortunately... well, fortunately for that species, uh, unfortunately for the corroboree frog, they can carry chytrid fungus. So about 90%, if not more, are infected with chytrid, but it doesn't affect them in any way. They don't die, they don't become sick. But in effect, they act as reservoir host species, so they're constantly shedding spores of chytrid fungus, which means unfortunately wherever they occur up in Kosciuszko, chytrid is present in the wild and will remain present in the wild. So these big enclosures have been designed to keep that species out.
Fortunately, we haven't got a lot of tree frogs up there, and fortunately, unlike I guess the rainforests throughout Central America and those kind of regions where we know chytrid can be carried on rainfall and, and in the mist and, and, and that kind of thing, up in Kosciuszko National Park, we don't have frogs up in the, the air. There's, there's no kind of chytrid up in the trees. The chance of getting chytrid into these enclosures is quite low. So effectively they act as, I guess, as an extra ex situ colony, but in the field. So within the range of the species. So they experience snowfall, they experience natural UV, natural diet, um, natural climatic conditions. It's more resource efficient, but it's higher risk as well. If chytrid fungus ever gets into one of them, it could, it could cause devastation really quickly, or if a wildfire comes through. And we had that back in 2019/20. Southeastern Australia had some of the worst wildfires ever and unfortunately two of our enclosure sites got heavily impacted by the wildfires.
They went through, they burnt through the enclosures. We lost a lot of frogs during those wildfires, which is a significant problem. So wildfires is a problem that, uh, unfortunately with the way climate change is going, will probably become a bigger problem into the future, an ongoing problem. So for us, it's more about making the populations more robust and making the enclosures more robust. And, and that's, that's been done since the last wildfires. Uh, Dave has set up, in the field, fire suppression systems. So we've got large tanks of water that can be satellite controlled, 'cause out in the remote parts of Kosciuszko we don't have internet access or anything like that, but can be satellite controlled, so they can be wet down significantly before any fires come through, which will help protect all the existing infrastructure in the field. I think if we can get them past the disease in the short term, we'll be able to return to populations in the, in the thousands, if not the tens of thousands again. It's just a matter of finding that silver bullet to make it more resistant to chytrid fungus in the long term.
[00:25:37] MB: And when you say in the, in the long term, climate change might have two different impacts here, right? Like, the increased wildfires, but also reduced snowfall that is necessary for their hatching, right?
Is this also something that, that- Yeah ... worries you?
[00:25:52] MM: No, it does. Definitely reduced precipitation is not a good thing. And, and throughout the 2000s, so from 2000 and maybe '03 or '04, we had something, uh, down in southeastern Australia called the millennial drought. And during the millennial drought, that, that was when we had a prolonged period of drought. And during that time, there would've been very little recruitment in the wild for corroboree frogs because the, the persistent drought meant that a lot of the ephemeral pools just didn't fill with water. So in those times you would get fewer recruitment for, for years at a time. So it is a problem long term.
There is still habitat, and there's still habitat where pools form reliably, but in the long term, climate change definitely could be a problem for this species. For now, we're still persisting as if hopefully climate change can be addressed. It's a big uphill battle there. I, I believe, chytrid fungus is by far the worst driver of extinction in species at the moment. That's the reason that we're not able to reestablish populations and, and that kind of thing, and that's, that's something we're really, we're addressing first. And we're really getting into that at the moment. Over the last number of years, we've done a, a fair bit of research on, on chytrid. A whole range of research collaborations with James Cook University and now University of Melbourne, looking at immunity to chytrid fungus.
And, and more recently, um, with University of Melbourne, a PhD student, Mikaela Davidson, uh, did some great work on corroboree frog, looking at immunity and differences of immunity, uh, a- and their genes within the population of corroboree frogs to determine whether or not some corroboree frogs from the populations are more resilient than others to chytrid fungus, trying to identify which frogs and which family groups are more resilient than others to chytrid, and try to work out which genes may be responsible for making them more resistant than others. And through that research, uh, Miki was able to kind of identify genes or complexes of genes that, that may afford more resistance and kind of come up with a strategy to selectively breed for resistance to chytrid. So that's something that's, that will be looked at in years to come. I'm quietly optimistic that in years to come we will have solutions to be able to make them more resilient to, to chytrid fungus.
And if we're able to get them past chytrid —and we have populations like that— they can live for a long time, so they can live out short periods of drought like that, like I guess they always have for many, many generations in the past. Hopefully we can build up a resilient enough population that they can kind of withstand climate change for the meantime.
But getting them past chytrid's our initial goal, just building that resilience. But for a species that takes so long to become sexually mature and lay so few eggs, doing it on their own- evolution's a slow process in a species like that. So hopefully, we can give them enough assistance to get them past this kind of existential problem, that hopefully we'll, we'll be able to see them back up in great numbers again.
[00:28:23] MB: Up to now, we've been talking about the southern corroboree frog, but there's another species, the northern corroboree frog. They look very similar, and Michael tells me that their behavior is pretty similar as well. They also walk in their substrate with their tiny chunky legs. They're also very territorial, and they also build nests in a similar way than the southern corroboree frogs.
But their status, the threats, and their ex situ rescue story can be a little bit different.
[00:28:52] MM: Similar to the southerns, chytrid fungus is by far the main threat impacting that species. They do have other threats too. There's things like blackberry incursion, so weed incursion. Uh, there's also, uh, feral pests, so things like horses and deer and pigs, uh, cause issues for northern corroboree frogs. They do for southerns, but only to a lesser extent. For northern corroboree frogs, they're more of a problem. And climate change, of course, too, uh, similar to southern corroboree frogs. But for northern corroboree frogs, some habitats, climate change can probably be even worse, 'cause they're found in some drier... they're found in the same kind of sphagnum bogs as southerns, but there's populations in, in drier habitat too. In those drier habitats, I guess you can get years of no... like failed recruitment, so the pond's not actually getting any water in them, in which case the eggs die, or get a little bit of water, the eggs hatch, but then it dries out and tadpoles die. So climate change can be a problem there too.
Unlike a southern, which is kind of functionally extinct in the wild, the northern corroboree frog still has probably a couple of thousand adults remaining in the wild. And, uh, as you know, a couple of thousand frogs isn't, isn't a great deal of frogs, especially with the populations that go up and down the way they do.
And for the northern corroboree frog at Taronga Zoo, we have a little over 1,000 specimens And for southern corroboree frog we have about 450 specimens. So we have quite large populations. They're all genetically managed quite intensively. Uh, every, every one of those thousand northern corroboree frogs we can tell apart.
Uh, they're all individually identified by their color pattern. Every thousand of those corroboree frogs we have has, has their photos, their back and belly photos in our identification book, and we can, we can work out who's who. And we do the same when, when we release them. We, we take photos of the back and belly of every one of those northern corroboree frogs that we release.
Um, unlike the southern corroboree frog though, the northern corroboree frog, our translocations have actually had a little bit more, a little bit more success. And the reason being, the habitat being a bit drier, chytrid's there, chytrid's causing an issue, but in dry years it's not as bad. And, um, for northern corroboree frogs, we've been releasing frogs, so since... it's been a while now, since 2014 we've been putting out, um... Well, since 2010 or '11 we started putting out eggs, but 2014 we started releasing some frogs. And we've been playing around with a whole range of different strategies.
[00:30:59] MB: Before we hear more about the releases, let me clarify two terms. The IUCN defines translocations as the human-mediated movement of living organisms from one area, which can include a captive environment, with release in another area.
Reintroduction is the intentional movement and release of an organism inside its indigenous range from which it has disappeared. So reintroductions are a type of translocation, but not the only one. As we now know, some of the translocations of the corroboree frogs are going out into this chytrid-proof exclosures.
But what has to happen to get to this point?
[00:31:43] MM: So we usually have an idea of what translocation we wanna do. For southern corroboree frogs, we've really focused on eggs in recent years. So what we'll do is collect eggs from the nests at the zoo. We usually take any eggs that we can produce, we take out for release to the different disease free exclosures, to the different sites that we're trialing. And every year we're trialing new things too, trying to establish them at different new sites, and everything we learn, adapt for that for coming years. For the frogs themselves though, if we're gonna do a frog release at any stage, whether it's into the exclosures or, uh, for southern corroboree frogs for example, we, we'll plan it out usually a couple of years in advance depending on when, what age we want them to be. Because it takes a full year to get them through to a metamorph frog, if we wanna put out frogs that are kind of one year or two year of age, we need to start planning for that three years in advance to get the cohort through to our age for release. So usually we will produce, um, I guess a, a number of frogs and get them to that... we'll know what we wanna produce, and we'll hold back that number of eggs for that purpose, and the rest of them will be released as eggs.
For northern corroboree frogs- In recent years, because we know that the metamorphs are actually, the young frogs are surviving quite well when we release them, we focus rather than releasing eggs 'cause from egg release, I think we had about a 4 to 5% survival rate that returned back to nests. Releasing the juvenile frogs, we had about a 30% survival rate. We actually had less success releasing them as adults than we did as juvenile frogs. So that was, I guess, for me, that's a great thing, because if we had higher success from the adult release, then we'd probably have to rear more cohorts through three or four years of age to release. The fact they go out earlier is really good, because it allows us to put out a lot more frogs. Uh, so it uses less space in the facility year on year. We can put out a lot more frogs that way, which is, which is great.
[00:33:22] MB: And once those frogs are released, they know exactly what to do.
[00:33:26] MM: The good thing about frogs, as opposed to, I guess, birds and mammals, that have a lot of learnt behaviors and, and learning from, from their adults, that the juvenile frogs are pretty well adapted to just trying to eat anything that moves. A juvenile corroboree frog feeds predominantly on ants in the wild. Um, but when we've released them in the past, one year we took them out there in March. I released them out of a takeaway container, had, like, 10 frogs in a container, released them out of the container, and, and the whole, this whole bunch of frogs had gone about maybe 5 or 10 steps and just stopped and started picking off all these little springtails that were present, uh, like wild ones in the container. Like, these things have been packed up in the morning, driven six and a half hours, been in the car down a bumpy fire trail, get out there, put them out in the whole, this whole new, novel, massive environment, and these frogs are taking 10 steps and just stopping to feed. So they're pretty hardwired, I think, to know how to survive. They see something run past the front of it, and they, they eat it.
As a result of some of that research that we've been doing, it's allowed us to fine-tune our translocation technique. And just over the last couple of years now, we've really ramped up the number of frogs that we've released. And only a few weeks ago, we released 842 northern corroboree frogs to the Brindabella National Park. With that kind of translocation, I'm optimistic that that's enough to bolster those populations, that they can stay persistent for at least another 10 years or more. And then we can top up and do further translocations as required to augment the population. And really, it's just a holding game, trying to keep them persistent out in the wild long enough for them to either build natural resistance to chytrid fungus, which we are seeing in some frog species in Australia, we've seen a number of species that crashed dramatically back in the '80s. Some of those species are actually bouncing back now, and it gives us some hope that over time, the corroboree frog might do that. So we're hoping we can keep populations persistent out there.
[00:35:05] MB: Now, my favorite part. Michael actually already mentioned this at the beginning of the episode, but I just had to ask again.
Once they are back into the wild and they have to go back year after year to monitor how they're doing, how do they do this?
[00:35:20] MM: After we release the corroboree frogs, every year monitoring is undertaken. Dr. Dave Hunter does it all for the southern corroboree frogs and for a good chunk of the northern corroboree frogs.
For the northern Brindabella population of northern corroboree frogs, I'll go out there throughout February- March and drive down there and spend the day yelling at frogs effectively. Um, uh, I would probably look like a crazy person. Not, not that I don't any- anyway, but I'd probably walk around, uh, um, looking like a crazy person, 'cause we're walking around the bogs yelling at frogs. Yeah, yelling out, "Yeah," or, "Yeah, frog." They think you're another male calling, and they give off their little territorial call, which is pretty much a, a, "Go away, this is my nest. These are the female frogs in my area." Yeah, frog
[00:36:06] MB: So if you ever feel like going into the mountains and yell at frogs, you might want to give Michael a call. And now you will know that behind that moment, behind a tiny frog yelling back from the moss, there are over 20 years of studies and work and learning how they behave and learning how to breed them and how to release them and how to rescue a species in crisis.
These frogs lived in protected national parks, yet chytrid changed the rules, and the climate change is not helping. But Michael reminds us that there are many reasons for hope, especially thanks to all the partners involved in studying and rescuing the tiny Corroboree frogs, who will hopefully one day, completely on their own, yell back at us.
This podcast is brought to you by Amphibian Ark, hosted by me, Maria Braeuner, with original music by Pablo Bolaños of Biota Specimens, and made possible by supporters like yourself who believe amphibians are worth saving. You can help us bring this important message to more people by subscribing wherever you listen to podcasts.
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Until next time
About the podcast
Amphibian Rescue is produced and hosted by María Braeuner, with original music by Pablo Bolaños | Biota Specimens.
Episodes are reviewed and fact-checked by the Amphibian Ark team of experts: Luis Carrillo, Devin Edmonds, Renata Ibelli Vaz, Jonathan Wilcken, Cybele Lisboa, Elizabeth Townsend, María José Chang, and Beatriz Velásquez.
Trailer video footage by © Jaime Culebras; additional clips via © Canva.com by Leo Lee, Black Box, Atelopus | Getty Images, Daniel Bahrmann | Pixabay.
Other photos and videos used in Episode 4 © Michael McFadden & Taronga Conservation Society Australia.
The podcast is made possible thanks to the continued support of Amphibian Ark donors and partners around the world.
Together, we can continue rescuing amphibians in crisis.
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