[00:00:00] Speaker A: Hey, everYone.
[00:00:00] Speaker B: Brooke here, your passionate rewilding host.
[00:00:04] Speaker C: Today. I have another mini soap for you. May 3 is Wild Koala Day, and I've had the pleasure of hosting a top koala expert, Danielle Claude, PhD, author of Koala a Natural History and an uncertain future.
In this episode, Danielle and I explore the facts and myths about koalas, like why they eat eucalyptus leaves when almost no other species does, how they obtain their microbiome, why they come to the ground, their brain size, and why they lounge around for many hours of the day.
After you're done listening to this snippet, I highly recommend scrolling through the archives and checking out episode 129 to learn more about koalas, including the top two conservation issues they're facing, fires and deforestation.
You can also find Danielle's book online everywhere. And trust me, as someone who read.
[00:01:01] Speaker B: The whole thing, it's a great book.
[00:01:04] Speaker C: All right, friends, please enjoy this koala fun fact episode with Danielle.
[00:01:12] Speaker B: One thing that your book taught me, and we can actually start to get into this right now, is there are so many misconceptions about koalas that I didn't even, I didn't even realize were misconceptions. I was just so ignorant and naive about the species just because that's just what we've always said about this is how Koalas live, this is how they are, this is their behavior, this is what they do. And your book definitely showed me otherwise. So could you talk a little bit more about that? Maybe give us, like, the Koala 101 about them, why they're unique. You even Went ThROUgh their natural history and their evolution and, and all kinds of stuff. But could you just almost spew on Us koalas and the 101 on them?
[00:02:01] Speaker D: Yeah. Well, I guess the perception that koalas are very simple and straightforward animals, and, I mean, koalas are one of the most well known and famous conservation species in the world in actual facts. So there is a lot of politics around koalas and that, you know, they receive a huge amount of Conservation money and, you know, they are iconic in the sense that, you know, a bit like being the poster child for Conservation in some ways for, you know, like a pAnda or polar bears or those sorts of iconic animals. So it is a really big issue in conservation. And, of course, it's confusing for a lot of biologists because biologists will say, well, koalas aren't, as a species, ANywhere near endangered.
They are actually exceedingly common in the southern forests of Australia, but they are endangered and seem to be going extinct in the east coast forest to the north, which is where people are worried about them. So there's this kind of complication around koalas.
And I guess I'm very wary of the stories we tell about species and actually any stories. It's part of the thing I like to do with my books is to really unpack what are the stories we tell? Why do we tell those stories? And what's the truth? What's real? What's it got an evidence base for it. So I'll often want to go back to the archives and double check everything.
But in the case of koalas, I had to use a real wide range of scientific evidence to try and unpack them. So that's, you know, I start the book in the fossil history because I think we see koalas as this singular species unlike anything else. I don't know, but it's always useful to know what their family history is. And if we go back into the fossil record, we find there's a whole range of different species that have things that koalas are related to. And we get a much better sense of what kind of an animal they are if you look at what their close relatives are.
So they're not as singular. I mean, they are still pretty singular, but they're not as isolated as we think of them. And it's important to try and get away from that idea. I mean, look at that idea about them being the last of their kind, because we have a tendency to blame animals for their own extinction. You know, we'll say, like the panda is, is stupid, maladapted has a really dumb diet and is going extinct because it can't breed properly.
And we have the same narrative with koalas in some ways, even though we, we can love it to death, we will still say it's, it's slow, it's stupid, it has a dumb diet. It, you know, it eats toxic leaves and it's doomed to extinction. So this idea of being doomed to extinction has been going on for as long as Europeans and settlers have been talking about koalas. And I don't think that's true at all because they're actually extremely resilient animals. They have bounced back from extinction at least twice. Near extinction, of course, at least twice that we know of, and once very recently with hunting of koalas in Australia, and before that, with the great megafauna extinction that wiped out a lot of the ice age animals. So koalas suffered from a huge extinction event, near extinction event then, too. So you know, they're really. So, they're a really resilient species and I think that was the interesting thing for me to look at, is how that came about.
And in the process of unpacking that, of course, I unpacked a whole heap of really amazing information around how koalas are so well adapted for the trees they live in specifically. So the co evolution of eucalypts and koalas is a really incredible story and I think that really, really helps us to understand exactly what's going on with them. Why they're difficult to breed, why they need so much space, all of those sorts of things.
[00:06:20] Speaker B: Yeah. I was not aware just how PiCKY they are. And you went into fantastic depth about their microbiomes and how specific they are and having to get.
[00:06:37] Speaker D: What did you.
[00:06:38] Speaker B: Call it, that special, almost like poo formula that babies need from their mother to get the biome to be able to even digest these leaves.
[00:06:47] Speaker D: But, yeah, for maybe those of us.
[00:06:49] Speaker B: That don't know much about eucalyptus, the family that these, that these koalas love to eat, could you maybe explain a little bit more about them? And why are they so difficult to eat? And why is the koala like pretty much one of the only species that feeds almost exclusively on them?
[00:07:06] Speaker D: Yeah, yeah. So TYPICALLY when we think about eucalyptus trees, we think of them as just a singular tree, you know, singular type of tree, the eucalyptus. But of course, they're a really large and diverse family of tree or group of trees. There's almost 900 species and subspecies of eucalypts. Most of them are from Australia. So they're very, very specific to Australia, although of course, everybody's familiar with them because they've been one of the most.
They're sort of a reverse colonizer. We've actually sent eucalypts off into the world and they are one of the most widespread planted trees now, elsewhere, hardwood, certainly, in the world. So, you know, so most people are familiar with them in America, in China, in Europe, all those sorts of places. And, you know, they are very characteristic and we have some.
And I raced outside this morning to go and grab some leaves off the trees because I'm surrounded by eucalypts. And that's the interesting thing, of course, that, you know, we think of eucalypts as being something strange and unusual. But in Australia they are the dominant forest. So, so our great forest estate is nearly always dominated by eucalypts. So they're a really, really common type of tree, but they do have these very tough. These are actually regrowth. So they're a little bit softer than many of them are, but they're quite leathery, hard leaves.
And if you crush them, they've got a very powerful smell because they're full of the eucalypt oils.
So eating them takes quite a bit. It's quite of a struggle to eat them. They're very fibrous. And mammals can't digest cellulose and lignin in plant matter themselves. So most herbivores have really complex stomachs in order to digest this very fibrous plant material. So that's whether they're eating grass or leaves or whatever it is they're eating.
So koalas don't have really complex stomachs, but what they do have is a really large, it's called a caecum, and it's the equivalent of the appendix in humans. So while our appendix is very residual and it's only about the size of your thumb, the koala caecum is almost 2 meters long. So it's a huge THIng for a small animal to have. And it's like, basically what it is is like a pouch. So a big pocket in the digestive system that's full of a microbial soup. And it's the microbes that herbivores use to digest the cellulosa and lignin in the leaves and in grass as well. So the koala chews up all the leaves. There's fine particles diverted into the cecum, into this soup, where they'll stay for several days a week to have all the nutrients digested and be broken down by the bacteria and other microbes. And the large particles will be swept through the normal digestive system and popped out the other end.
So that's the basic thing. But then, of course, there are the toxins that are in the leaves. So koalas have to have a way of dealing with those toxins. And a lot of the toxins in eucalypts actually make mammals feel nauseous, so they create nausea in the animals, so they'll eat a little bit of it and then they'll say, no more of that. Thank you. So koalas deal with this in part with their Liver. They have a Supercharged Liver that's quite large and complex in its structure. And it seems to have a double dose of genes for removing toxins from eucalypts. And they're so good at removing toxins that they're actually also really good at removing things like medicine from their system. So it's really hard to treat koalas for diseases, because not only do they have this Liver that removes all the toxins, but of course, also some of those medicines will also really disrupt their Microbial System, which ends up meaning that they don't eat. So a good example of that is the treatment of chlamydia, which koalas suffer from quite a lot, particularly on the east coast. And a normal dose for chlamydia in Humans would be a three Day dose of antibiotics in Koalas. That will be a 30 Day dose to clear up that disease. So, you know, that just gives you an idea of how powerful that Liver is. So, yeah, getting hold of all those nutrients in leaves is a really tight struggle. They've got really complex proteins that are really Hard to extract. And this is something that was a real struggle for me to come to grips with. It's not my area of expertise. But, you know, the. That sometimes they can actually, when they eat some of the leaves on some species of eucalypts, they can eat the leaves and actually end up with less nutrition than they started with. So it's so hard for the leaves are so complex and resist being processed so much that they actually extract nutrients out of the koala rather than the other way around. So it's really, really important that the koala gets it right, which ones they eat.
So for that reason, koalas only eat about 70 species of eucalypts across Australia. And any one koala will only eat between four and ten species that are found in their area. And it's quite probable that their microbiome is specifically adapted to those individual species that it's familiar with. And as you mentioned, they get those microbes, they're not BORn with the microbes, they don't have them in their gut when they're young, when they're milk feeding. But at some point, as they're developing, the mother will actually evacuate her cecum, so she'll empty the big dose of the microbial soup from her cecum and it comes out as this runny green pap. And the baby koala laps that up. Absolutely loves it. It's a big, disgusting mess when this happens, but that inoculates koala, that baby, the joey, with the right microbiome for its forest, the forest that it lives in. So it means that as soon as it gets that, it can start eating gum leaves, which before it doesn't eat them at all, it have a bit of a chew and a play with them, but it won't eat them. So it's a really fascinating system. This way, the mother inoculates the baby with exactly the right biome. And you might think that's a strange and disgusting thing to do. In actual fact, we're increasingly understanding that microbiomes are really important for our own health, for probably most animals health. And even in humans, there's an element of fetal contamination during the birth process that gives us our gut biome as well. So we do a very similar thing. And humans that have lost their gut biome through massive antibiotic courses and things are also inoculated in, not in the same way, but they do the same thing in hospitals. They don't like talking about it very much, but the same process is used in humans as well.
[00:14:27] Speaker B: Yeah, I come from a family of all ladies, and so the whole childbirth process, you know, I'm very used to that. And, you know, having a vaginal birth versus a c section, they've come to show that there are consequences for the baby. So, yeah, I'm not surprised that this is how a baby Joey would get the proper microbiome to the ecosystem that it lives in, because how else would it get it? How else are those, that very special soup, essentially, that is the species that will break down the leaves that they eat. How are they going to get that? So it just makes sense that it would come from the mother in an interesting waY. I'm sure you've seen it and I'm sure it's very interesting to see. Yeah, I think so. This starts to dabble on their behavior, and you did, again, a wonderful job just breaking myths about their behavior, that they're this just slow, lazy species. And that's not the, that's not actually the true story, you know, so could you talk a little bit about that, maybe? Why did they get that, that reputation? And I guess, is it true? You know, what, what is the, maybe a normal day of a koala like, and, yeah, how should we look at them and what they do?
[00:15:46] Speaker D: Yeah, I guess, I guess the interesting thing about koalas is that there's quite a lot of quite pervasive underlying myths that we tell about Koalas. Obviously, we get the sort of Reddit end stream of the story where, you know, people will say they're stoned on the eucalypt movies, that they know they're drugged out because it's true. They are slightly sleepy and they generally are slow moving so that they sleep up to 90% of their time. A KOALas daY, active day could be not much more than half an hour. So they pack everything into a short timeframe. So that is true. But I guess that's also led to this idea that they sleep a lot because of the food they eat. So there's this prevailing thought that they sleep a lot and they're slow because their food is low nutrition. They're not getting very much nutrition out of their food supply. Therefore they have to reduce their energy consumption, therefore they sleep a lot. And this has also led to the belief that they have a small brain, that this brain has actually shrunk because of the low level of nutrition in their food. Now, when I was thinking about this story, I was thinking, that doesn't really make sense to me. You know, we have a lot of animals that sleep a lot. I've got a cat, and it spends 90 of its day asleep.
You know, dogs spend a lot of time asleep. Typically, the type of animals that spend a lot of time asleep have a high nutrient diet. So they sleep because they can. They, you know, they get their food and they just chill out for the rest of the time. So I thOught, well, if this is a low nutrient problem, why is the animal not eating more?
Now, it's true, it could be because of the amount of time it takes to digest the food. But nonetheless, when I looked into it, I realized that koalas consume pretty much the same biomass of leaves as any other low nutrient herbivore does, like the same body size. Goat or sheep will eat about the same amount of food. So I couldn't. And I also thought, well, if it's something to do with digestion, you'd end up with a bigger animal, so that it's got more capacity to still leave. Psychologically and evolutionarily, it just didn't make sense to me that they would sleep because they're low in nutrients and they do seem to get exactly the same nutrient value out of what they eat as any other animal.
The gum leaves are low nutrient, but so is grasS. You know, it's no better or worse, not as TOxIC, but it's probably even harder to digest.
So it made me realize that what's going on with the Koalas is that they're sleeping.
They're sleeping because they can. They get up, they find an appropriate tree that's got lots of food for them, they climb up the tree, they settle in, they eat their fill, and then they sit around and digest. So why wouldn'T you have a sleep? I guess the thing I wanted to think about then was, well, why do other herbivores not sleep? Of course, herbivores on the ground are vulnerable to predation, and their response to predation is to run away. So THEY have to be awake and alert to watch for predators. So koalas have a different predator strategy. Their predator strategy is to sit quietly and inconspicuously in the trees and hope no one notices them. And they actually are really hard to spot in trees. And they have predators, but they're not quite AS exposed to predators as animals ARe on the ground. So koalas are vulnerable to predators on the ground when they come down from their trees. So dogs are ONE of their major predators, but once they're up the tree, they're pretty safe. So they're basically chilling out because they can and relaxing so that, I think, unpacks a lot of those things. The other issue about their brain size is also a myth. I think that what happened was people were doing brain measurements on pickled specimens and the tissue had shrunk.
And koala brains do shrink when they're preserved. If we look at recent specimens, the brain is pretty much completely normal for their body size. And there's also been MRI scans done now on living animals. And the brain is just a normal sized brain. Might have a slightly more cerebral fluid around the brain, possibly as a protection from falling, but. And they do have quite sturdy skulls. I've got one here, actually.
So this is. This is the koala skull. Oh, how cool.
And it. And it is quite. It's quite a solid, solid little skull, but it is absolutely normal sized for its body size, and the brain cavity is as well. So. So, yeah, there's. There's nothing that unusual about that. So. But that myth actually is not just in popular commentary. It actually does pop up in. In the scientific literature as well.
[00:20:42] Speaker B: Oh, really?
[00:20:43] Speaker D: So it's just something. People haven't given a great deal of comparative thinking to it. To think, why do animals sleep? What makes sense in terms of evolution? And I think that's worth having a closer look at because it does impact on our concept of, you know, koalas. The other thing. Koalas are being stupid. Right. I think, you know, I'm really wary about quick comments about intelligence in animals, because usually, as humans, when we're looking at, we talk about intelligence, we're usually thinking about things like us.
We're the sort of the gold standard for intelligence in our own perceptions. And so we're unlikely to appreciate the cognitive strategies that other animals use in their environment. And to me, intelligence isn't about our kind of language, communication, problem solving, creativity, any of those things. It's more about flexibility, cognitive flexibility, the ability to come up with new strategies and behaviours in response to changing environments.
And although koalas might be slow and they might not do a lot in a day, they're not very busy. So it takes a long time for you to collect data on koala behaviour. They are very flExible, and we know that because everywhere we look at KOALAS in different parts of the countRy, they behave differently.
So they're actually doing different things in different Places. And I think that's really interesting. We don't really know how KOALAS find their way through a forest. How do KOALAS know which trees to go to, which trees to go back to, which trees to avoid? They have the huge range. It takes one koala needs actually a forest the size of an average sports field to support it. So that's a single koala per that large area. And so they're traveling across big distances and there's lots of questions about how they navigate that, you know, are they really moving randomly through the environment? I don't think so. I think that would be quite unusual for an animal to do that. But maybe, maybe they are. But those are the sorts of questions I think are worth looking at more in terms of koalas, rather than just assuming theyre stupid and operating by chance.
[00:23:07] Speaker B: Yeah, that is the perfect example. So I just returned from Tanzania where I had a wonderful two week long safari. Also met up with Martinez over there. So I work in conservation tourism. Thats what I do professionally. And the difference in behavior was incredible, just like you said. I mean, I watched firsthand multiple herbivores get eaten and by big cats with big teeth. Not just cats, but also, you know, hyenas and all kinds of stuff that their whole goal is to feed themselves. So the difference in behavior, that makes total sense. And as you were saying that, that I had an immediate conservation question that came into mind.
How often are they coming onto the ground? And when they do, is that when they are the most vulnerable? And if that is, is that happening now at a higher rate? I'm assuming that deforestation and habitat loss is probably just as big of an issue as it is in Australia as it is most parts of the world right now. So is that one of the biggest threats that's happening with koalas or what have you seen with maybe coming down to the ground?
And how has that translated into the risk that they are putting themselves into?
[00:24:30] Speaker D: Yeah, that's definitely.
They are definitely at their most vulnerable on the ground and they probably. That's always been their greatest predation risk. I mean, they are taken by powerful owls, the big owls that we get in australian forest.
[00:24:47] Speaker B: I love owls.
[00:24:51] Speaker D: I'm sure wedge tailed eagles, well, they're known to be taken by wedge tailed eagles. We have quite a lot of big, big predatory birds, but their major threat is almost certainly when they're on the ground, and particularly mothers with Joey's on their back are extremely vulnerable. So. And if you think about it, that's probably one of the biggest impacts on population is, is the breeding rate for koalas. So if you have a predation that's targeting mothers on the ground when they're moving between trees, that's going to have a significant impact on controlling populations or limiting populations.
So that's a really interesting feature. And yes, you're right, changes in habitat are also having a big impact. So we've got increasing deforestation, increasing habitat fragmentation. So koalas have to travel between patches of forests at times or be restricted to a single forest, or the forests are also being degraded. So it's quite common to get clearance through the forest, you know, removal of the understory, those sorts of things, all of which forestry changes, so the types of trees change. All those sorts of things are resulting in koalas being on the ground more, having to travel longer, distances that are unsafe. Of course, one of those major fracturing factors in their habitat are roads and cars are a huge mortality impact on koalas. We get a lot of koalas being hit by cars because they're trying to cross the roads and the freeways, and we keep putting our roads across their roads, so the paths they need to follow are being cut off and then we've got development. Koalas like to live in similar areas to humans, so. Or vice versa, really. So humans are moving into those fertile river valleys, forested river valleys, cutting down the trees and building houses. And we get a lot of real estate developments that don't take into account the needs of the local koala population very often advertised the properties as being, you know, you get koalas in the trees. Isn't it LOVELY? Oh, whoops. Down all the trees, there's no more koalas. So, you know, it's really important that we look at those particular things we're doing and target those as strategies, you know, not removing any remaining native forest. Logging. Native forest logging and clearing is meant to have been stopped in Australia decades ago, and yet it's still happening because there's too many exemptions and there's not enough you know, checking and regulation on what's actually going on and also making sure that development happens in an appropriate way, that key koala habitats are protected, that feed trees are protected, all of those sorts of things. And particularly protecting forests along river systems is really important because the trees that koalas feed on best, and probably the trees they need to breed, are the ones that are long river systems where the trees are very lush. They're not producing as many toxins, so they're much better for the animals to reproduce with.
[00:28:09] Speaker A: Thank you for joining me on this wild adventure today. I hope you've been inspired by the incredible stories, insights and knowledge shared in this episode. To learn more about what you heard, be sure to check out the show
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[00:28:41] Speaker B: Mean the world to me.
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[00:29:44] Speaker B: Today, this is Brooke signing off.
[00:29:47] Speaker A: Remember, together we will rewild the planet.
