Hey you welcome to Stuff to Blow Your Mind. My name is Robert.
Lamb and I am Joe McCormick, and today we're bringing you an episode from the vault. This is part two of our series on the reptiles of the Galapagos. This was originally published December tenth, twenty twenty two.
Enjoy Welcome to Stuff to Blow Your Mind, production of iHeartRadio.
Hey, welcome to Stuff to Blow your Mind. My name is Robert.
Lamb and I'm Joe McCormick, and we're back with part two of our series on the reptiles of the Galapagos Islands. Now, in the previous episode, we focused mainly on the marine iguana, or as they were often referred to early on, those hideous creatures, those stupid, awful, sluggish lizards. We mounted a defense of the marine iguana. But today we are here to talk about the Galapagos tortoise. And I wanted to kick things off by reading a passage from Charles Darwin
in the Voyage of the Beagle. Darwin, of course, was not just a great scientist, but a really wonderful writer, and I think this will help set the scene. So are you ready to hear about Darwin's first vision of San Cristobal Island. Then then what they called Chatham Island.
Yeah, let's let's hear from from old Charles.
And this is part of a narrative of when he slept ashore one night on the island. So off the boat, Darwin writes. The entire surface of this part of the island seems to have been permeated like a sieve by the subterranean vapors. Here and there the lava, whilstsoft, has been blown into great bubbles, and in other parts the tops of caverns similarly formed have fallen in, leaving circular pits with steep sides. From the regular form of the
many craters. They gave to the country an artificial appearance which vividly reminded me of those parts of Staffordshire, where the great iron foundries are most numerous. The day was growing hot, and the scrambling over the rough surface and through the intricate thickets was very fatiguing, but I was well repaid by the strange Cyclopean scene. As I was walking along, I met two large tortoises, each of which
must have weighed at least two hundred pounds. One was eating a piece of cactus, and as I approached, it stared at me and slowly walked away.
The other gave a.
Deep hiss and drew in its head. These huge reptiles, surrounded by the black lava, the leafless shrubs and large cacti seemed to my fancy like some Antediluvian animals. The few dull colored birds cared no more for me than they did for the great tortoises. So Darwin transported to a time from before Noah's flood by the vision of these bizarre, gigantic tortoises crawling around on the on the lava.
Yes, this is the great sceni paints here and and yeah. As I mentioned in the first episode, I was. I was fortunate enough to get to travel to the Galapagos Islands just a couple of months ago. In San Cristobo Island was one of the islands that I got to visit, and this was pretty much the the experience I had with my family walking through one of the the areas
they had set aside for these magnificent tortoises. They're just they just they walk around as if yeah, if you don't matter, unless you get a little too close for their liking, in which case there'll often be this hiss and this retraction of their head. I mean, their heads don't retract in the same way that say, a box turtle does, but they're able to sort of pull their head in a bit. But that the hissing that Darwin is describing here, it does have a very, I don't know,
pneumatic kind of quality to it. It feels it sounds like some sort of machinery. And indeed, that's that's kind of more what it is, as opposed to like the hiss you might hear from a house cat or something. And one of the things that I kept thinking about while encountering them is that they already move with this kind of herky jerky kind of locomotion. They already move like they are elaborate mechanical creatures created for practical effects
for a nineteen nineties science fiction feature. And then they also make this hissing sound to move part of their anatomy. So it almost creates this feeling of am I seeing
real animals or is this an elaborate hoax these animatronics? Yeah, yeah, yeah, they feel almost like animatronics, but of course they're they're they're they're quite alive, and they're quite, but that's part of their strangeness, and they just the awe of watching these giant creatures walk arou around, slowly, eat, and occasionally have some startling interactions.
Now I'm greatly envious of the opportunity you got to see these animals in person, but I trust that you did not do what Darwin did upon encountering these beasts and try to ride them.
Absolutely not, no, no. The only time the times we were forced to get uncomfortably close in one of these situations of the area that we were walking through had a path and you're supposed to stay on the path and keep your distance from the tortoises. Sometimes though the tortoises will just get on the path. You have to find your way around them, and they don't necessarily like that.
But we kept our distance, and you want to keep your distance because, yeah, if you get a little too close, they're going to stop interacting with their environment for a little bit. And if you don't want to watch that, you want to watch them eat and rampage around and occasionally have these fabulous stare downs between two males which I don't know, we may describe this later, So maybe I shouldn't get into that just yet.
Yeah, yeah, we can talk about the mock fights later on. So the Galapagos tortoise is I think you would say, originally the dominant land herbivore of the Galapagos Islands, which makes them kind of unique because there's pretty much nowhere else on Earth now where the dominant land herbivore is a reptile. So these are very unique and beautiful creatures, and the Glapagos tortoise stands out so much among the endemic fauna that it's actually the origin of the archipelago's
name in one way or another. There's a little bit of nitpicking on that, but basically it goes like this. By the fifteen seventies, these islands had already appeared on at least a couple of European maps. The one I saw named was by a Flemish cartographer named Abraham Ortelius, and it named the islands Insulae de los galapago or meaning Islands of the Tortoises. Now, the nitpicking about the terminology I've read is what exactly the word galapago or
Galapagos originally meant. According to a book that I'm going to reference multiple times in this episode, Galapagos and Natural History, second Edition by John Creecher and Kevin Laughlin from Princeton University Press. That editions out just twenty twenty two. They write that the origin of the name of the islands is an old Spanish word, galapago, which was a name for a specific type of saddle. So there's like, you know, a saddle you'd use on a horse. I guess that
has a kind of upturned front. That was a galapago. And some, but not all, of the Galapagos tortoises have saddle shaped shells. Others have a more straightforward dome. And we can talk about the evolutionary reasons for those differences later on. But when Tamas de Berlanga landed on the islands in fifteen thirty five, a story we talked about
in the previous episode. After this, he wrote a letter to the king in which he observed describing the animals of the island, he observed mucos lobos marinos meaning many sea lions, tortugas meaning sea turtles, iguanas, and Galapagos, and the authors write that this is probably a reference to the tortoises and their saddle shaped shells rather than to literal saddles being on the island.
This is a solid observation that thankfully still holds true today. Mucos lobos marinos and tortugas, iguanas and tortoises. Yes, yeah, the sea lion, I mean the mucco lobos marinos. That was probably the most astounding of all when you're near the coast, because they're everywhere and sometimes laying. There'll be like a male that's come up and he's like laying in the street, or they they love park benches. There are a lot of fun to wide.
Well.
The difference in the Spanish name. I guess if it's lobo marino that would mean see wolf, not sea lion, right, But that that heightens the kind of implicit comedy of naming these animals after what you would think of as a more actively voracious land predator, whereas you know, I guess when they're on the land, they're not quite so threatening as maybe a wolf for a lion would seem.
Yeah, I mean, well, on one hand, yeah, you have some of the little tiny islands are at least one that's named for the wolves for the lobos, and of course that's why, because sea lions are hanging out there and yeah, on the on the on the beach. They're often quite docile and you see people getting way too
close to them in some cases. But the big males, of course, are very territorial about hanging on to their bit of property and their and their females, you know, their their their beach real estate, and so there of course always they're continuously loudly sending the alarm and occasionally chasing off other males. So there's there's a lot of drama if you just sit back and watch the sea lions. And I imagine that listeners from other parts of the world can to this as well.
Yes, yes, keep your distance, folks, I mean, observe, but there's no reason to get in the sea lion space.
Though sometimes in my experience, sea lion will come for your space. I was just seated away from sea lions and then here comes this female and she's just howling about something and insists on taking my spot on a log, and I'm like, it's yours at yours, and then she just hangs out on the log for a few minutes and then leaves it. I don't know, She's just trying to make a point.
So if you have never seen the Galopagos tortoises before, you can easily find lots of pictures of them. But to briefly describe the adults, there are many different species scattered across the different islands. Maybe we can get into the exact numbers on that in a bit, but generally what they all have in common is that they're very large.
They have large shells, some species with rounded dome tops, others with the saddle shape that Burlonga probably observed, which are typically turned up in the front to have a kind of big notch above the animal's head and neck. They have long, dry, wrinkly necks which are surprisingly slim, almost I dare say snake like in a way. They have blunt, round snouts and a beak like mouth with no teeth, and everywhere you can see their their skin.
In between the shell parts there is typically a lot of leathery, wrinkly flesh, which just makes them look like old people.
Yeah, they they have this kind of appearance of a of acute shriveled old person.
Vase.
Uh. They're they're very They're very sweet to look at it's it's it's kind of hard to to not anthropomorphize them as such even and and that can, of course, can become complicated when you start considering like the full range of their of their lifestyle and the way that they they live and reproduce and so forth. Uh, it never pays to anthropomorphize creatures too much.
Yeah.
Now, no one thing many of us today might not appreciate, even if you go to the Galapagos today or if you see Good Nature documentary footage from there, is how many tortoises there were when people first arrive, Before the animals had any natural predators other than the threat post to hatchlings by the Galapagos Hulk, this place was swarming with tortoises. And to try to get a picture of that, I wanted to cite some basically math work that Creature
and Laughlin do in their book. So they're talking about the reproductive rates of these tortoises. So they say, if a female tortoise has more than two young that survive into adulthood, the tortoise population will grow, so she has replaced both her and her mate. And if she has more than one, the population will grow and they say, Now, consider that a female tortoise may conservatively lay five to
ten eggs annually for perhaps eighty years or more. So, just for a very conservative estimate, they say, Okay, imagine she averages one annual clutch and there's just three eggs in it. That's kind of a small estimate. But there's just three eggs per clutch. That's more than two hundred eggs in a single adult female tortoises lifetime. They say, realistically,
the number is probably a multiple of that. So they're going to have a lot of young and there before humans arrive and bring their invasive species with them, before they bring dogs and pigs and stuff. There is not significant predation at any life cycle. A part of the life cycle of a tortoise. There's some minor predation by like hawks of the babies, but most of them are going to grow and become reproducing adults.
Yeah, it's pretty amazing. Amazing. I ask one of the guides about, you know, how long are the females reproductive? Because you see some very who was pointed that My guide here was pointing out the various the old tortoises. But because you can sort of tell by looking at their shells the way that the line, like, for a while, you can sort of it's not like you can count the rings exactly, but you can sort of see the
rings and the patterns on their shell. But eventually there's kind of like a smoothing out that occurs, and those are the really old ones. And the guy was like, yeah, we're not entirely sure, but it seems like they're reproductively active for pretty much most of their lives, which is the astounding.
Yeah, it's amazing. And so the authors of this book end up concluding that before humans arrived and brought these invasive predators with them and started harvesting the tortoises themselves, which is a sad fact we'll talk about in a moment, the tortoises.
Were just.
Profuse.
They were everywhere.
They say, there's a conserva estimate of a total population of two hundred and fifty thousand tortoises just on this small group of islands. But of course, today all of these tortoise populations are at least vulnerable, and some are up to critically endangered, and that's after a significant bounce back in some cases, you know, after conservation efforts kicked in. So what happened to these tortoises. Well, one thing that happened is is something Darwin talks about in his Passage
and Voyage of the Beagle. Before he even really gets to ecological observations about the tortoises, he writes at length about people eating them. So, in describing the small human colony on what was then Charles Island what today is called Floriana Island, so Darwin writes, in the woods there are many wild pigs and goats. Now remember those are not native to the islands, but introduced by humans. Darwin goes on, But the staple article of animal food is
supplied by the tortoises. Their numbers have of course been greatly reduced in this island, but the people yet count on two days hunting, giving them food for.
The rest of the week.
It is said that formerly single vessels have taken away as many as seven hundred, and that the ship's company of a frigate some years since brought down in one day two hundred tortoises to the beach. And this brings us to a very sad fact about the human use
of tortoises. Here that tortoises were, of course very good meat sources for sailing vessels, but this was especially due to the fact that because turtles have a very slow metabolism, and they could be loaded into the ship alive and then would survive for an extremely long time without food
or water in the hold. And it's important to remember that, of course, ships at the time didn't have refrigerators or freezers or other sophisticated food preservation techniques beyond things like the nuclear option salting.
Yeah. Yeah, so this is quite sad to picture, because on one hand, it's not like these tortoises were wandering around on deck. They were stuffed below I think generally upside down and just stored away as living casks of food because they could live for up to a year without food or water, which is just crazy to think about, but also just unimaginately cruel to imagine them down there.
And on top of this, one of the other troublesome things about this for the tortoises is that the sailors would tend to grab the tortoises they could easily carry back to the ship, which meant that they tended to focus on the smaller tortoises and leave the bigger ones.
This meant that they were favoring female tortoises over male tortoises, and I guess to a certain extent also younger male tortoises, but certainly skewing more towards female tortoises, thus destabilizing the species even more than if they had managed more of a fifty to fifty split between the tortoise genders.
Yeah, so unfortunately a lot of tortoises were removed from the islands that way, but also they just remained a live meat source for hunting by the locals, and Darwin tells many interesting stories about this. For example, he writes about a time that he went up to one of the highland regions of one of the islands, and he hung out in a hovel that had been built by
two men there who spent their time hunting tortoises. And so he visits these guys and he sleeps there in the hovel one night, and what did he eat while he was there, Well, exclusively tortoise meat. That was the entire menu, about which he says, quote the breastplate roasted as the gauchos do carne conquero, which I think means meat with leather with the flesh on. It is very good, and the young tortoises make excellent soup, but otherwise the meat, to my taste, is indifferent.
Oh well, there you go. Also taking the harvesting the young tortoises, that's great as well.
But they apparently these the adult tortoises, are an amazing food source because of their immense size, and Darwin recounts a story told to him by a mister Lawson, who is an Englishman who is vice governor of the Charles Island Colony, saying that some tortoises, when caught, required six to eight men just to lift them off the ground and would provide up to two hundred pounds of meat. Darwin also later describes a strange operation performed by the hunters.
He says that you know they didn't always kill a tortoise. He says that, well, the tortoises meat is used both fresh and salted. The tortoises are also important for providing oil.
That's right, reptile lard.
And oil that I think could be used for food purposes, but also for just like lamp purposes.
I believe yeah, it's said that in the old days, the larger towns of the Galapagos would have their streets would have been lit with tortoise oil.
Bizarre though, I guess we're more familiar with that from.
Like whale oil and stuff.
But yeah, so if a tortoise will not provide enough oil, it is apparently not worth killing to the hunters. So Darwin writes, quote, when a tortoise is caught, the man makes a slit in the skin near its tail so as to see inside its body whether the fat under the dorsal plate is thick. If it's not, the animal is liberated, and it is said to recover soon from this strange operation. In order to secure the tortoise, it is not sufficient to turn them like a turtle, for they are often able to get.
On their legs again.
And I think this is something that will come up later, because there are some situations where these tortoises often do end up flipped on their backs, even under natural circumstances, and they need to be able to flip back over and get back to business.
I did not get to see that happen, thankfully. I don't want to see a tortoise in distress.
No, we're not going to ask you the quiz from the blade runner test. So what do these tortoises eat to grow so big? Well, it turns out in reality, they just they eat plants. These are entirely herbivorous creatures. There are turtles and tortoises that eat other things, but these tortoises are entirely plant eaters. And so especially in the lowlands, especially the saddlebacked tortoises, will eat succulent cactus.
This is something Darwin identifies. He says they especially favor the cactus if they live in the low and arid parts of the islands where there is little or no water. Of course the cactus becomes a principal water source, but also they eat tree leaves and berries as well as green lichen, and their diet somewhat depends on which species they are and which part of the islands which microclimate
they inhabit. Like the ones that live higher up in the highlands with more lush vegetation probably feed on more leafy stuff, and the ones that live more in the arid regions probably feed on more cactus.
Yeah, the ones I got to actually observe in the wild as it were on San Cristobo on Santa Cruz Island. They they were definitely eating the leafy green stuff. But I got to see plenty of the cacti, which of course have coexisted with the tortoises long enough that they have particular adaptations, like they have been changed by cohabitation
with the tortoise as well. And the most remarkable of these are the ones that they basically seem to grow up like trees and then branch out because they're trying to reach and reaching an optimal height at which they're hopefully above the reach of the tortoise.
There is one type of cactus there's a great picture of in this book by Creature in Laughlin I've been talking about. It's called a candelabra cactus, and I thought it was beautiful because the branches look to me like giant green tarantula legs. They kind of have these lobes that look like little hairy leg segments on a large spider.
Yeah. Yeah, And this is a nice picture too, because you got a flamingo in there. I did get to see a few flamingos on Seymour Island, I.
Believe, But the tortoises just generally seem to eat all kinds of foods that would look to us quite hostile. So of course the ones in the lowlands are going to eat a lot of cactus, but they also apparently eat plenty of poison apple or men's in illo, which is toxic. It has a sap that is poisonous to other creatures, and I think it can cause blistering if you touch it. But apparently the tortoises just chow down on this stuff, doesn't bother them.
Yeah. On San Cristobo Island, the area where we were encountering the tortoises, they had signs everywhere, do not touch the apples. Do certainly do not eat the apples. Leave this to the tortoises.
Now, coming back to Darwin's writing on the tortoises, he also observes their relationship with water. He says, they are notable, of course for their ability to survive without water for a very long time. But when they get out access to water, they go hog wild. They love it, the spring water and the mud puddles. They'll just get in there and settle in, sometimes for days at a.
Time, and when.
They're drinking they will just gulp huge mouthfuls of water for a long time. And Darwin even this leads into him writing a really bizarre anecdote that I had to share. So he says, quote for some time after a visit to the springs, their urinary bladders are distended with fluid which is said to gradually which is said to gradually
decrease in volume and to become less pure. The inhabitants, when walking in the lower district and overcome with thirst, often take advantage of this circumstance and drink the contents of the bladder if full. In one tortoise I saw killed, the fluid was quite limpid and had only a very slightly bitter taste. The inhabitants, however, always first drink the water in the pericardium, which is the membrane of belief that surrounding the heart tissue, which described as being best.
So that's right, drinking the water from a tortoise's heart or from a tortoise's bladder. And Darwin tasted the tortoise bladder water.
I guess I should be happy for this, that they're using all parts of the tortoise conceivably in doing this. But of course this is still kind of sad to imagine. Yeah, but also from just a purely anatomical level, this is of course amazing.
Now, Darwin goes on to talk about how impressed he is by the long determined journeys that some of these tortoises make between He believes what the point of these journeys is is between highland water sources and usual breeding grounds in the lower districts. I don't know if that holds up as the main reason for these journeys today, though I do think some of these tortoises do make journeys between the highlands and the lowlands for the purpose
of depositing eggs the females do after mating season. But there are also journeys I think having to do with food resources in the different seasons and so forth. But anyway, Darwin says, you know, although the tortoises are pretty slow in their movements, you would be surprised how much ground they cover over time due to sheer determination. He estimates that they're going to move sixty yards in ten minutes, which is three hundred and sixty yards in an hour, or about four miles a day.
Yeah, it's pretty remarkable, and of course nowadays of course that everything has been shifted around a bit. You know, all these invasive species, not only the such harmful invasive species as pigs and goats that were introduced and then
their populations have been dealt with to varying degrees. But you also have, of course, have plants to think about, and so in some cases you have things like berries that are now grown in the Galapagos and may occur wild in some cases, and of course the tortoises love those even though they are not native, and so you
may see that interfere with their movements. So that but yeah, basically through modern conservation and through modern tracking technology, you can actually see all of these tortoise movements plotted out on maps and it's quite impressive. I think they are movements in these cases help illustrate why they're so crucial
for the island ecosystem that they thrive in. They eat so much and while they're slow, they do cover a lot of ground and defecate to spread speeds spread seeds rather, and this is very much in line with other megafona that you encounter in other ecosystems as well as the remember if you think back to our episode on or episodes on the giant moa bird, which of course is extinct, but would have we still see like the footprint of their ecological importance in the areas that they occupied, because
they were vital for consuming plants and then spreading those seeds through defecation.
Yeah, there is a great passage in the book by Creature and Laughlin where they talk about the importance of the tortoise in spreading a type a species of wild Galapagos tomato plant, which apparently it only the seeds only germinate under very specific conditions, such as being exposed to acid for a long period of time.
Now, how does that happen, Well.
It happens in the digestive system of the tortoise. So like they take this in, the seed gets exposed to the acid within the digestive juices, and then it gets it travels with the tortoise a long ways away from its original location, so that's also good for dispersal. And then once the tortoise poops it out, it of course has a bunch of nutritious fecal matter surrounding it to help it grow.
Yeah, yeah, I've got I did get to poke some tortoise dung with a stick. My son and I did, and we got to look all in there. It's, you know, quite fascinating. I think some stats would really help drive home though, why the tortoise is so great at this. And I got these from Seed Dispersal by Galapagos Tortoises by Blake at All, published in the Journal of Biogeography from twenty twelve. So, in this particular survey, the researchers looked at one hundred and twenty fresh dung piles in
both agricultural and national parkland. They found seeds from more than forty five plant species in these dung piles, eleven of which were from introduced species, you know, like various berries and whatnot. A per tortoise average of four hundred and sixty four seeds and two point eight species per
dung pile was detected. Now, this is where it gets kind of interesting, because, okay, we've already established that, yes, they eat a lot, they travel farther than you might think, But how long does it take for them to process their food? Things go a little slower with the Galapagos tortoises.
The mean digesta retention time for a tortoise is twelve days, but twenty eight day retention times have been reported, so that's the time time it takes for the food that they've consumed to process through their body and become dung, so.
They can really cover some ground in that time.
Yeah. During that time, according to this paper, the tortoise may travel between three hundred and ninety four and four three hundred and fifty five meters on the high end, that's two point seven miles or four point three kilometers.
So you can see how these tortoises would play an incredibly important role in helping the reproduction and dispersal of local flora.
Yeah. Absolutely. I mean, as with any species, they don't they're not existing in isolation in their ecosystem. They have a roll, they have a place in it. And if you disrupt them, if you disrupt their numbers, or in the very worst case scenarios, if their extinction is brought about, then there is there's something missing. There's a you end up pulling the carpet out from everything, and unlike with the parlor trick, all the plates and the dishes are not necessarily going to stay standing up.
Now we've been talking about a lot of the predation and hunting of these tortoises. But barring that, how do tortoises die?
What happens?
Well, Darwin writes, quote the young tortoises as soon as they are hatched, fall preying great numbers to the carryon feeding buzzard. I think that would actually be referring probably to the Galapago's hawk, unless he's talking about some other species that came in after humans arrived. But and Darwin goes on, the old ones seemed to die generally from accidents,
as from falling down precipices. At least several of the inhabitants told me that they never found one dead without some evident cause, which, oh, that kind of gave me a shiver.
Yeah, yeah, I mean, it's just impressive how long they live. That and I did the first point about P's worth pointing out that the tortoise sanctuaries that are up and running now they care for the little ones to protect them from you know, not only the hawk, but also all these introduced species that may be about once they
get big enough. Though, Yeah, there's only really three ways they're going to die old age eventually, accident, vehicular especially of course being the main threat, though on the Galapico sidelands today a lot of you know, laws and messaging have been put in place to prevent this from occurring. And then of course in the past human hunting was the big thing.
Now you mentioned they can die of old age, of course they do, but that can take.
A good long while.
I was reading about this in a Creature in Laughlin and they say that it's possible, though we have no way to know for sure, that there may be tortoises still alive on the islands that were present when Darwin visited in eighteen thirty five, and a Galopago's tortoise named Harriet lived to an estimated age of one hundred and seventy five before she died in an Australian zoo in two thousand and six, so they can live a long long time.
Yeah, I was doing some crunching on this as well. I think one of the sources I was looking at had listed like one hundred and seventy one years as being one of the oldest stage is known for the tortoises. And even if you're just going to go with that, if you consider the idea that you have a tortoise born in eighteen thirty five when Darwin is visiting, if it lived one hundred and seventy one years, it would
live to the year two thousand and six. Wow, which is just crazy to think about the idea that just one tortoise lifetime would bridge our time to the time of Darwin, and that a single tortoise lifetime could encompass basically the two worst centuries of the impact of humanity
on Galapago's tortoise numbers as well. Now, again not to come back too much to the horrors of human tortoise interaction, but yeah, there are these accounts read too of like times when roads to various villages were just lined with like the bones or the shells of these creatures. It was it was a rough time to be a Galapagos tortoise.
Yes, no, I now I think it's worth talking about Galapagos tortoise mating and reproduction, which there's some interesting stuff. For one thing I was reading about Maybe we can get to the actual mating in a minute, But first I was reading a section in Creature in Laughlin about the nests and egg laying of the Glopagos tortoise. So mating season typically occurs during the rainy season, and after having mated, a female tortoise will generally travel toward the
arid lowlands to build a nest. Darwin has a section about this where he correctly observes that they will seek out arid sandy soil to dig a nest in, but then he says others. He says, sometimes they will just drop their eggs where like in a precipice, like in a crevice in the rocks. I didn't find any other evidence of that, so maybe that was true when he was there, but I'm not aware of other evidence for that other than what Darwin says. But generally what they
do is they're going to dig down in the arid regions. Now, for the saddleback tortoises, which tend to live more in the lowlands, this is not much of a trip. But for the domed tortoises it can be a really great journey down from the highlands into the place where they're going.
To lay the eggs.
And the eggs are laid sometime between June and December. A clutch can contain anywhere from like two to twenty eggs. The eggs are sort of billiard ball sized or maybe a little bit larger. And the nest building process is what interested me because apparently it involves a good bit
of pa. So the tortoise will find a spot in the soil and she will dig a hole about thirty centimeters deep, scooping the earth out with her hind legs, and this is an involved process that can take up to about twelve hours, and the tortoise will often urinate on the soil in order to soften it for digging. But the mother tortoise, after she lays her eggs in the hole and covers it up, then also peas on the soil again to form a kind of cement layer in it.
This is interesting. We've discussed a number of different nest building egg laying scenarios over the years, but I don't remember one that was so urine intensive.
Yeah, there may be other species that do pie cement, but this is the first time I remember reading about this. So anyway, the eggs incubate in the cemented earth for like four to eight months, where the sex of the hatchling is ultimately determined by the temperature which the egg incubates.
That's kind of interesting. It's not chromosomally determined as it is for some other animals, and so afterwards they dig their way out of the nest to begin their lives, and of course this is the most vulnerable time for a Galapagos tortoise when they're a hatchling, but the ones that survived make it out. They find food, they avoid predators, and they eventually grow up, though apparently the growing up also takes a good bit of time. The tortoises do
everything pretty slow, including reaching maturity. I've read that they don't reach sexual maturity until several decades later.
The mating itself is also kind of interesting because they basically consists of the males chasing the females around until they can corner them. But then there's also, given these are large shelled creatures, the male's shell has like an indention on the bottom that allows for it to mount the female, because otherwise, unless there was some arrangement of the shells in this capacity, that they would not be compatible.
Right, And there was also a fact I came across that I thought was funny. In this book, they talk about how the larger size of the Glopagos tortoise can make the physical active mating sometimes kind of cumbersome and laborious, and the authors note that quote, males often slide off, even inadvertently, landing upside down, at which point they must right themselves and try again, which I don't know if it's juvenile that I found that funny, but I did.
The authors also note that the male tortoises sometimes get confused. For example, they try to mate with large rocks.
Well, that's just, in and of itself funny. We can't help but laugh at that.
But there's also surprising. For these very slow moving animals, there is some surprisingly fierce competition between males for access to mates, and Darwin notes this. He says, during breeding season, you can hear the males emit what he calls a horse roar. And I think this roar is probably indicative of male on male competition, which sometimes leads to these mock fights where they will raise their necks up at each other. Rob, I think you actually maybe saw one of these going on.
Yes, I got to see this happen, and I actually got to film it. I was able to my wife was like, quick, get your camera out, make sure you're getting this. So I did. Yeah, it's amazing to watch because you'll have these two lumbering giants that are kind of on a collision course with each other, and you're like,
what's going to happen, what's going to happen? And then as they get closer, they'll both rear their heads up and they'll have this showdown that doesn't it does not come to blows or bites or anything like that, but it is a competition to see who to determine who is the tallest and the tallest tortoise, who had the one that can raise its head up the highest, he's the winner, and the other one accepts defeat and carries on. And that's as violent as it seems to get. But
it's spectacular to watch. And this was the finest nature footage I have ever captured or will ever capture.
Now, one last thing I wanted to read from Darwin here where he's talking about the tortoise's reaction to humans. This is another infamous section from the Voyage of the Beagle chapter. Darwin says, I was always amused when overtaking one of these great monsters as it was quietly pacing along, to see how suddenly the instant I passed it would draw in its head and legs and uttering a deep hiss, fall to the ground with a heavy sound, as if
struck dead. I frequently got on their backs and then giving a few wraps on the hinder part of the shells, they would rise up and walk away, but I found it very difficult to keep my balance.
Oh, Charles, no doing, Why are you riding a tortoise? I mean it is kind of I mean it based on this account, the tortoise is doing exactly what you know I observed, and all these sources say they do if someone gets too close or something gets too close. But it is kind of interesting this added detail that apparently eventually the tortoise is like, Okay, I guess this
weird British man is not going away. I have things to do in places to be I'm just going to start walking around with him on there and maybe I can sort of shake him off.
Yeah, and this is actually not an isolated report. Again, we are not recommending riding the tortoises, and other other people talk about how well you can get on their backs and ride them and they'll just go about their business. And this is apparently a common occurrence. There was a common occurrence.
Back in the day.
Sometimes they say, you can get two people on one of these tortoise shells and just ride them and they'll do their thing, like you know, they don't seem they don't seem bothered. Now, I'm sure that puts extra strain on their muscles and their energy requirements and all that. So it's not like okay to do. But just showing the strength of the tortoise and how powerful and huge this animal is that it could just continue on its way trying to graze with like multiple humans riding on its back.
Oh, poor creatures. Yeah, again, do not attempt to don't do not get close to the tortoises, and do not ride them. Now, we have a fair amount of variety with the Glapygos tortoises that they're all of the genus Chellinitis, and you get into some discussion about the different varieties like the exact variety count. And then we have two that are definitely extinct. There's the Floriana Island subspecies that's thought to have been hunted to extinction by I think
eighteen fifty when Darwin visited. This is I believe the one where he only describes seeing their bones. The Pina Island species is extinct as of twenty twelve, with the death of Lonesome George, who was of course famous for being the last of his variety. He died and that was seemingly it for this variety of tortoise.
Yeah.
I've read that there are either twelve or thirteen extant species.
Yeah. So, coming back to the challenges that tortoises faced during the age of humans, we've thoroughly discussed. I think the human hunting and human harvesting of tortoises, at least
for our purpose, is here. But of course there are all these invasive species that humans introduced, and while we are dealing with cases in some cases where you'll have animals directly going after young tortoises, there are also other ways that these creatures were harmful and are and can still be harmful to the native Galapagos tortoises.
Right, And in fact, one example of this came up in some episodes we did back in October on goats, right, the issue of goats competing for resources with tortoises.
That's right again. Goats, as we discussed, are amazing at what they do at roaming around finding odd bits of vegetation to consume, and yeah, they're they're ultimately better at it than tortoises. They're more thorough than the tortoises, and ultimately so thorough that they can be even more disruptive to like the to the ground itself, like you know, getting in there and actually making it unstable. So that's that's one thing to consider. Also when you're dealing with
any creature that lays its eggs in the ground. Not only do you have to worry with certain species, like especially pigs and rats going after those eggs and then going after the young. Potentially, you also have to deal with cattle because there are still cattle on the islands, and cattle were brought to the islands, and cattle aren't interested in really eating those tortoise eggs, but they will definitely step on those tortoise eggs if they happen to be ranging in the same area.
Now, in the previous episode, we talked about some hypotheses about how marine iguanas first arrived on the Galapagos Islands, probably via some kind of rafting from the mainland. Is that also the idea of what likely happened with the ancestral tortoises.
That's my understanding based on the sources I was looking at, and based on conversations with some of the naturalist and guides in the Galapagos Islands. The idea is that it would have been much the same tortoises in South America, swept up in river floods, washed out with vegetation which they were able to raft on, and reaching these far flung islands.
So it's amazing to imagine these extremely unlikely, kind of one off events that allowed the population of each island, because it's not something you see happening every day. But you know, all it takes is a is a small seed population to get there and then wow, what's this. You know, there's all these food resources and no predators and you can really boom once you arrive.
Yeah. And I'm not sure if the numbers on this are you know, certified as it were, but it seems like the first Glapacos tortoises probably reached the islands two to three million years ago via rafting. They would have probably arrived on the eastern islands of Espanola and San Cristobile first and then spread west from there. So it's yeah,
it's interesting to think about. Now. The other question that I guess came up for me, and this was like, how big were these tortoises when they first arrived, because at least some sources out there make the case that they were already big, that they were already quote unquote gigantic, while plenty of other sources also discuss Glapago's tortoises as a case of island gigantism.
Yeah, so island gigantism is something that often occurs. There's known as island dwarfism and island gigantism. These kind of runaway pressures on the size of animals that can really bulk them up or shrink them down when they're in
a contained ecosystem like an island. And I don't think we know exactly what all the pressures would be, but you could imagine something like, well, maybe there is always sexual selection on, say the size of adult male tortoises, to make them bigger and bigger, because the bigger you are, the more likely a female is to be receptive to mating. So there's a sexual selection driving them to be bigger. But then there's naturally some kind of other pressure that
wants to keep their size smaller. You know, like you there's that advantage in being bigger. But once you're bigger, maybe you're more at risk of predation, or it's harder to thermoregulate or something like that. And you can imagine cases where you get on an island and suddenly those other pressures are relieved and so you can just keep getting bigger and bigger than you would have been allowed to on the mainland.
Yeah.
Yeah, I guess on the like supporting the idea that they were already big there is. There is, of course, fossil evidence of gigantic tortoises existing on I think every continent except Australia and Antarctica at some point in the past, so it's not like these forms only emerged on various islands island environments. But I don't know. On the other hand, it seems like plenty of sources are discussing this as gigantism.
One paper I was looking at this is from Jaffe at All, from a twenty eleven paper in the Royal Society Biology Letters, The Evolution of Island gigantism and body size variation in Tortoises and turtles. They point out that they do point out that quote, the other evolutionary determinants of size diversity in Chilonians are poorly understood. But they also point out that Chelonians span some four orders of magnitude in their sizes, and that there is quote a
pronounced relationship between habitat and optimal body size. Also worth noting that the apparently the closest living relative to the Galapagos tortoise is not a direct ancestor of those tortoises, but it is itself a relatively small bodied variety of tortoise that's found in South America, the Chaco tortoise, I believe it is called now. I also mentioned that there are other giant tortoises still in the world outside of
the Galapagos. These would be giant tortoises that survived in the Western Indian Ocean in the form of Aldabra giant tortoises leave.
When Darwin arrived, he thought that these were the same species, like that the ones on the Galapagos were the same as those, or at least the same as some other island gigantic tortoise he was aware of. I think it would have been those, because those are the only other ones I know of, and he was mistaken in that in fact that they're just they're different parallel forms of
gigantic tortoises. But one last thing I wanted to talk about with these tortoises before we wrap up today is the differences in the shell shapes, because we mentioned earlier that some species have more dome shaped shells and some have these saddle shaped shells, and there are also intermediate species that have sort of somewhere in between. A creature and Laughlin have a great section on this in their chapter on the tortoises, and I wanted to talk about
it a bit. So one of the questions is why you can observe some things that might lead to these differences. The tortoises with the domed shells tend to live more in the highlands and around caldera rims, where vegetation is much thicker and lush all the time, whereas the ones with the saddle backed shells tend to live more or even exclusively in the low lands, where conditions are more often dry. Of course, the differences in these shells is that while as the domed ones are more just kind
of like an upturned cup over the reptiles back. The saddleback tortoises, their shell tends to have like a relief area above the head and neck. It's almost like a collar that's pulled back. And there are some other differences too. The domed tortoises tend to have a larger body size, but shorter legs and necks, whereas the saddleback tortoises tend to be smaller overall but have longer legs and longer necks.
Now, remember in the.
Last episode when we talked about the marine iguanas and we were trying to come up with the biological explanation for why the iguana kept returning out of the water after Darwin threw it in, even though you know it's got to go in the water all the time to eat, So why doesn't it just stay in the water to
stay away from him? And the answer we came up with that the Darwin did not land on himself is that it's probably for thermoregulation reasons because the water is cold and it was removing heat from the iguana's body and the iguana needs to get back up on land
to heat back up. I think a good explanation for One of the explanations for the different body plans of these different tortoises probably also has to do with reptile thermoregulation with the regulation of body temperature, because of course, animals with a larger body volume also tend to retain more heat because they have less surface area proportional to their volume. So if you're living in a cold place and you're trying to retain body heat, it's easier to
do that if you're bigger. You've got there's just more body in there and less relatively less surface area, and vice versa. It's easier to cool off if you're smaller, because a bigger percent of your body is surface area
that you can lose heat through. This would seem to correlate with the observation that the domed tortoises, which live up in the highlands where it tends to be a little bit cooler, tend to have a larger body size but also shorter legs and necks, so less extremities poking out that can lose heat, whereas the saddleback tortoises tend to be smaller overall, with longer legs and longer necks and they live down in the lowlands where things tend to be hotter.
Yeah.
Yeah, Now, most of the tortoises I got to observe were definitely in highland environments, but their relationship with temperature is notable as well. In one case, we've got to go out and see these tortoises out there in this this this this highland area, and it was early enough in the day that some of them were essentially sleeping in. They were still bedded down in the mud where they could they could, you know, keep their temperature relatively stable
throughout the night. And some were already getting up to begin their their day of eating. Others just weren't quite ready yet.
Oh yeah, And I've read that these tortoises just love the mud, like they'll love to get in the mud puddles and they'll just hang out there for days sometimes.
Yeah, so you'll see them trooping around and yeah, on one level, they kind of look like bulldozers because they're just covered with mud, and of course they've been eating too. There are lots of pictures you included one here of one with just this spectacularly messy's face from all the vegetation and or fruits it's been consumed. It's just smeared all over.
It's like one of those gross baby pictures where the baby just looks they've been face down in a play of spaghetti.
Yeah, and their face, the face of the Glabgos tortoise does kind of look like like old baby, so it really matches up with that well.
But there are other differences in the environments that might explain the different body plans of these tortoise species, So a lot of it probably has to do with vegetation.
Right.
Domed tortoises tend to live in more lush highlands with dense undergrowth and a creature in Laughlin right quote. The domed shells, smoothly rounded as they are, may prove adaptive. Is the tortoises move tank like through dense plant cover, which is of course also the animal's food source. On the other hand, saddle type shells with a large forward notch can actually become snagged in low vegetation, impeding the
movement of the tortoise. Saddle shells are not very adaptive in low dense vegetation, so it's just going to be easier to move around with a more rounded shell. In all that thick brush in the Upper Highland forest regions, whereas if you had the saddle shell with the turned sort of collar in the front, Yeah, they'd just be getting hooked on stuff all the time.
And I mean they are little bulldozers. They can tear stuff up. Like for instance, you know there are gonna be limits. They could continue, you know, be slowed down or I guess stuck in vegetation. But to give one example that I was told about, do you have again individuals who are still ranching in these in these parts of the Highland, they have cows. They need to contain
those cows. But if they're gonna be tortoises moving through, they're gonna they're just gonna take down your barbed wire fence or your your whatever kind of fencing you have. So in many cases they'll have the fencing, they'll have this big gap at the bottom that will allow a tortoise to move through, because that way you still get to have your fence and the tortoise won't won't tear it down when it makes a bee line for whatever wherever it's going.
Yeah, fortunately the cows can't crawl under Yeah.
I guess not. It did raise some questions like, well, yeah, can the cow what about really short cows? I don't know, but apparently it works.
But the final thing with the difference between the domed tortoises and the saddlebacks is probably food sources as well, because again, the domed ones are going to be munching on a lot of you know, lush, low lying vegetation, so you know, that's just that's okay to have a
normal kind of dome dome shaped shell for that. But the saddleback tortoises, which live in the more arid lowlands, are going to be eating cacti, often tall cacti that they need to reach up to get to, and so the upturned front of the shell allows more room to raise the neck, and of course, of course, as I said as well, they've got longer necks and longer legs to help reach Robin, I think you said you observe stuff about those cactuses sort of reacting to that by
growing taller and taller to try to escape the munching tortoises.
Yeah. Yeah, And it's it's remarkable to see because yeah, here's this, here's this cac that has evolved to thrive alongside the tortoises, and it ends up, Yeah, it ends up feeling more like a tree than a cactus, if that makes sense. Yeah, it's a remarkable ecosystem.
All right.
So there you have it. Hopefully we gave just at least a nice snapshot, a nice overview of the Galapagos tortoise. Obviously, there's a lot of research out there about these creatures, so perhaps there's some details that we managed to leave out. If you think that we left out something that is particularly exciting, then right in. We'd love to hear about it. We'd love to see it for ourselves and to share
it in a future listener mail. Likewise, as I mentioned the first one, if you've traveled with the Glabgos Islands, if you live on the Galapagos Islands or are an Ecuadorian, we would also love to hear from you. We love your thoughts on these fabulous creatures that we've discussed here, or any of the other creatures of the Glabgos Islence, I'm always excited to hear more. Just a reminder to everybody's Stuff to blow your mind. Publishes us it's core
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