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May 25, 2024 54 mins

Beavers are incredible creatures and significant ecosystem manipulators, but they’ve also been subject to various written and illustrative inaccuracies. Medieval bestiaries often depict the common beaver as a weird-looking dog that bites off its own testicles when pursued by mounted hunters. In this classic episode of Stuff to Blow Your Mind, Rob and Joe explore the meaning of these inaccuracies as well as the actual biological wonder of North American and Eurasian beavers. (part 1 of 2, originally published 05/18/2023)

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Speaker 1 (00:06):
Hey, welcome to Stuff to Blow Your Mind. My name
is Robert.

Speaker 2 (00:09):
Lamb and I am Joe McCormick. And it's Saturday, so
we're going into the vault for an older episode of
Stuff to Blow Your Mind. This one originally published May eighteenth,
twenty twenty three, and it is part one of our
series on the beaver, a truly remarkable animal, far more
strange and amazing than you might imagine.

Speaker 1 (00:28):
Yeah, so have you skipped it the first time around,
thinking I don't want to hear about beavers. Beavers are boring. Well,
you were wrong. Beavers are exciting and allow us to
prove this to you in this episode and the following.

Speaker 3 (00:43):
Welcome to Stuff to Blow your Mind, a production of iHeartRadio.

Speaker 1 (00:53):
Hey, welcome to Stuff to Blow your Mind. My name
is Robert Lamb and I'm Joe McCormick. We've covered numerous
examples of this before, but obviously, in days before photography
and videography, one had to depend on illustrations and written
descriptions to convey the reality of an organism, you know,

(01:14):
be it a bird or a fish, what have you.
But this is especially true for creatures that lived in
lands beyond your direct experience. You know, what are the
what are the mammals, what are the birds? Like on
another continent. Well, you have to send people out in
the world. They can, you know, to a certain extent.
They can bring specimens back. Certainly, they can bring parts

(01:35):
of specimens back, but it's those ill in some cases,
but it's those illustrations that really bring things alive. Now,
certainly there are some fine examples of naturalist illustration out there,
especially from recent centuries. I mean there's some gorgeous, like
you say, like Audubond illustrations and paintings that sort of thing.

(01:55):
But there are also countless examples, and we've touched on
these before in the show of rough or drawings, drawings
that feel like, you know, there's been a game of
telephone at play. And this is especially the case for
examples found in various bestiaries and medieval manuscripts, among other places.
And when we think of such misconstrued animals, you know,

(02:18):
what do we tend to think about? You know, we
think about the rhino, We think about the lion, the whale,
the elephant, you know, great animals, apex, predators, and megafauna.
But in this episode, in the next episode, at the
very least, we're going to get into another creature that
has also experienced extreme inaccuracy in historic illustration, and that

(02:40):
is the common beaver. Based on just some of the
images we've been looking at, a beaver might well be
a kind of strange dog or a pig with a
with perhaps a fish tail on its body, you know,
a real hybrid feeling like it is, almost like it's
a strange like dog mermaid. It might be in almost

(03:02):
all respects a deer, like a creature with long legs
and hooves. And it may also look like a strange
and confused rodent with a great button seam running down
its chest. It may even look like a weirdly serpentine lion.

Speaker 2 (03:20):
So Rob has been sharing medieval and Renaissance illustrations of
beavers with me for a couple of days now, and
I really do love all of them. But I do
think the one I like the most is the one
that's just straight up a deer with hooves, except it
has razor blades for teeth, just like the rectangular razor blades.

Speaker 1 (03:41):
Yeah, yeah, this one. I had to go deep around
this one because I was It initially came up in
an image search and you know, I think it was
maybe on a pinterest or something. I was like, I
can't trust this. But I eventually looked it up in
the catalog of illuminated manuscripts and it is a Northern
Italian illustration from somewhere around the year fourteen forty. And yeah,

(04:04):
it just looks like a It is labeled as a beaver,
but it is in all respects a deer. So I
was just really astounded, like here, especially as an image,
that it not only gets the form wrong regarding the
target organism, it gets everything about like the energy of
the creature wrong, you know, because it's it's one thing
if you have a depiction of a rhino that okay,

(04:26):
it's like a big armor plated thing with four legs.
It's like, all right, I mean that's it's an extravagant
version of the truth. But this, it's like, how wrong
did this game of telephone go?

Speaker 2 (04:37):
Right? With the right? You like, with deerors rhinoceros, you
can see that beginning as a rhinoceros, but with embellishments, yes,
But with the beaver, it's like, oh, I'm sorry, did
you say beaver? I thought you asked for a depiction
of a of a lion with a snake neck biting
its own genitals.

Speaker 1 (04:54):
That's right, because and this is this is something we'll
probably get into mostly in the next episode, But there
is this pervasive myth that existed for a very long
time that when pursued by hunters, a male beaver would
chew off its own testicles. And so many of these images.
Be your creature more dog or catlike, or or actually
just a deer with razor sharp teeth, it is often

(05:17):
depicted nine at its testicles. That at least we have
some answers for in the next episode where that idea
comes from and why it's so pervasive.

Speaker 2 (05:26):
Right, So you've got to stick around for next time
to hear that.

Speaker 1 (05:29):
Yeah, so let's start with what we know. Let's start
with the reality. We're gonna start by talking about just
basic beaver anatomy and behavior. And I probably don't have
to tell most listeners out there what a beaver looks like.
I mean, for starters, like, we have images all over
the place of them, we have documentary footage. Many of
you can go and see a live beaver at least

(05:53):
in some sort of like a zoo environment, or you
have seen them in the past. But on the other
side of the coin, it's, like I said, still kind
of have to tell you what a beaver looks like
because the beaver is kind of in the same category
as the spouting whale, as we discussed in some of
our recent whale episodes, those particularly the ones on spouting
and spouts. Because despite all this access to actual, solid

(06:17):
documentary footage of the beaver, we still have this rich
history of cartoon depictions of beavers that inevitably cloud our
understanding of the creatures.

Speaker 2 (06:25):
I mean, I think you get a fairly accurate mental
picture if you just cross a squirrel with a grizzly bear.
You know, you mash those two up your most of
the way there. But while that does get you sort
of the shape the outline, right, that does not tell
you everything you need to know about beavers. Beavers are
much stranger and more beautiful than I realized.

Speaker 1 (06:47):
Yeah. Yeah, there's a lot of weird and wonderful aspects
to their morphology, to their behavior, and a lot of
this is stuff that our popular conceptions of the beaver
don't get into. I mean, you know, they do get
some of the things right, you know, the basic shape
of the beaver is far better in cartoon than it
is in many of these eliminated manuscripts. You know, some

(07:07):
things hold up. Obviously, beavers are not going to sell
you out to the White Witch. That's absolutely true.

Speaker 2 (07:13):
So C. S.

Speaker 1 (07:14):
Lewis was right on that count, even if he got
the whole diet of the beaver wrong, because in Narnia,
apparently beavers like to eat fish and chips. That's not
happening in the actual natural world.

Speaker 2 (07:27):
On the other hand, I will say, there is the
kind of food and organism usually seeks out to eat
in its environment, versus what an animal will eat if
given the opportunity. I kind of wonder. I feel like
if you gave a beaver a basket of chips and
some malt vinegar, I don't know they might get into that.

Speaker 1 (07:44):
All right, Well, let's start with the basics here. So
beavers are rodents, and are in fact the second largest
extent rodent, surpassed only by the mighty capybara. Beavers can
weigh up to fifty kilograms or one hundred and ten pounds.
There are two extant species of beaver. There's the North
American beaver or castor canadensis and the Eurasian beaver caste

(08:07):
or fiber. But the Castoridae family includes some impressive extinct
species as well. In fact, there were giant beavers that
lived during the Pleistocene, reaching weights of up to one
hundred and twenty five kilograms or two hundred and seventy
six pounds, So that is more than twice as big
as extant beavers. Though I was reading they seem to

(08:31):
have had smaller brains, among other morphological differences. But yeah,
so they were bigger, and you know, maybe to some
extent they didn't have to or had not yet developed
these very impressive behaviors and abilities that we'll get into
concerning modern beavers. Now, one note on these guys. They
were still smaller than the fifteen hundred kilogram or thirty

(08:53):
three hundred pound giant pacaranas of South America. Extant pacaranas
only get up to light thirty three pounds or fifteen kilograms,
and they can still be found in the western Amazonian
River basin. But the giant ones, they were pretty massive.
A lot of rodents of unusual size in freehistory, all.

Speaker 2 (09:12):
Right, So no beavers today in that territory, but beavers
can still get pretty chunky.

Speaker 1 (09:17):
That's right. Yeah, they're pretty big, And this is like
a fact. I frequently forget that they're the second biggest rodent.
The kappy bear is easy to remember, but it's sometimes
it's easy to forget who's coming in second. Now, it's
extremely important to note that beavers are semi aquatic, having
evolved to thrive in various freshwater habitats, so a number

(09:37):
of the things we're going to be discussing about them
line up with their habitat. For instance, they can hold
their breath for fifteen minutes. They have transparent third eyelids
called nicitating membranes to aid them in their swims, much
like manatees. They also famously have long, flat black tails.
We know this from the cartoons obviously, and these aid

(09:59):
them in their swimming, but they can also use them
to sound an alarm by slapping the water slapping the
surface of the water, and they also use them to
balance when they're carrying wood or other loads across the ground.
For any of you out there who watch a lot
of animal videos on Instagram and so forth, you may
have seen videos of adorable beavers carrying carrots around and

(10:23):
if you're not looking closely enough, you might think they're
dragging their tails, But if you will look closely, you
can see that the tail is off the ground and
it's helping them balance.

Speaker 2 (10:34):
One of the things I've noticed about watching beavers try
to move objects around is how much more gracefully they
do it in the water than on the land. So
these are semi aquatic mammals, but I don't know, it
seems to me that the water is where they're really
in their element. They can swim fast and gracefully, even
carrying like an unwieldy branch that's kind of unbalanced or something.

(10:56):
They do that all quite well in the water, and
then once you see them sort of toddling along across
the dry land that it looks much more comical and awkward.

Speaker 1 (11:05):
Yeah, and this is going to be important to keep
in mind when we talk about the amazing ways that
they transform an environment to better fit their needs and desires.
Oh but before we get into that, we of course
have to talk about the teeth of the beaver. This
is something that is generally an important part of cartoon
imagery concerning the beaver. A lot of times cartoon beavers

(11:27):
will speak with a kind of whistle in their voice.
But we also tend to get it quite wrong.

Speaker 2 (11:32):
Okay, so I'm trying to picture the cartoon beaver. I
think what we always see is an overbite with two
kind of square shaped teeth grouped right together in the middle,
like a person's front two teeth, but large and overlapping
the bottom lip. Is that about it?

Speaker 1 (11:48):
Yeah? Yeah, pretty much.

Speaker 2 (11:49):
The truth is much more shocking.

Speaker 1 (11:52):
Yeah, yeah, they have these. You know, if you look
at a skull of a beaver, it's pretty markable because
it's like this, the really kind of exaggerated rodent skull
with just incredible incisors, you know, with these these two
big shovel like teeth coming down from the top, two
big shovel like teeth coming up from the bottom, and

(12:15):
then the rest of the the back teeth or much
further back, you know, giving them some ample room to
do the kind of woodwork that they need to do
with those chompers.

Speaker 2 (12:26):
The skull is a powerful bone hinge, and it's like
it's like a kind of alien biotechnological set of bolt cutters,
except the bolt cutters are orange teeth.

Speaker 1 (12:38):
That's right, The orange is key. This is something I
almost never see in like a cute c illustration or
a cartoon depiction of a beaver. So, yeah, these teeth
have thick layers of enamel, which has this orange colorization
because while other rodents boast magnesium enriched tooth enamel, beavers
have iron enriched enamel. They're like, I mean, it's it's

(12:59):
like something out of a comic book, right. The iron
makes their teeth stronger against this the pure mechanical stress
that they put them through. We should also note that
these teeth continue to grow throughout their lives, to the
point where they have to gnaw them down on trees
to keep them down. But yeah, they're just super resilient,
always growing, and they're also more resilient to acid as

(13:21):
well based on their composition.

Speaker 2 (13:23):
Just some tough, rusty looking teeth.

Speaker 1 (13:26):
Yeah, yeah, the orange is really quite shyy okay. Another
essential biological aspect of the beaver before getting into their behavior,
is that they have a cloaca. So most mammals do

(13:47):
not have a cloeca. There are some exceptions, you know,
you look at the monotremes, golden moles, marsupial moles, ten
rex just a few examples, but mammals have most lost
these general purpose openings over the course of their evolution,
but in beaver's they seem to be present as a

(14:07):
case of secondary evolution, perhaps as an adaptation I've read against.
It may have to do with the watery environments they
find themselves in, protecting themselves against infections that might occur
due to the state of that water. But it's also
something and this will become important, I believe in the
next episode as well. It can make it difficult to
sex a beaver, as males and females look pretty much

(14:31):
the same, unless the female happens to be pregnant or
nursing at the time that you're trying to sex them.
And when I say you, I of course mean people
who have authority and expertise to be out in the
wild trying to sex a beaver. You know, leave it
to the professional biologists.

Speaker 2 (14:47):
Leave it to beaver scientists. Yes, so these.

Speaker 1 (14:50):
Various features aid the beaver in its primary enterprise of
ecosystem engineering. We all know that beavers build dams, you know,
this is, of course is true of the cartoons. But
what does that really mean? Why? Why are beavers building dams?
What are they accomplishing, So they actively alter their ecosystem

(15:11):
via the blockage of rivers and streams with structures of
like you know, sticks, mud, chunks of trees, that sort
of thing, all cobbled together to dam up the water,
and this allows them to create new lakes, new ponds,
whole floodplains. Meanwhile, the lodges they construct for themselves are

(15:31):
also made out of this kind of stuff, branches and
mud and so forth, and they can only be accessed
from underwater entrances in their constructed ponds.

Speaker 2 (15:41):
Yeah, so this is something I don't know if I
realized before. I think a lot of people assume that
beavers live in their dams, but I think the better
way to think about it is beavers construct dams in
order to block waterways, which causes the area upstream of
the dams to deepen and have a more lake like

(16:03):
environment rather than a flowing river or stream. And then
in that flooded area that is where they build the
lodge they live in. So they sort of create a
flooded area which can it can serve multiple purposes, one
to house the lodge, but then also they can sort
of dig out from there. I think you're about to
mention something about this.

Speaker 1 (16:23):
Yeah, they're a lot like humans. Human beings do this
with their modern technology. They come to say a dry
desert environment or a swamp environment, and they're like, you know,
what would go great here? What I would like for
my purposes of living here. I'd love it to be
just like a nice little park with some nice grass,
you know, and maybe a few trees. I'm going to

(16:43):
change everything so that it fits my needs. So the
primary purpose for the beaver dam is to create a
protective body of water for that lodge, making it even
more difficult for predators to get at them. And even
if predators were to get to them, they have that
underwater escape route in the event of an attack. That's

(17:04):
the that's the only way in and out now. It's
worth noting, however, that especially in parts of Eurasia, beavers
don't always have the same predator threat they once did.
But they build anyway because no one told them not to.
And also, more seriously, like, even though they are not
predators now, I mean that's you know, any kind of
evolutionary change would occur over a much vaster period of

(17:25):
time than the removal of their predators.

Speaker 2 (17:29):
Amounts to right, So an environment full of say like
gray wolves and bears may have shaped them. And even
if there are many fewer of these predators than there
once was, that they are still the animal made by
that world.

Speaker 1 (17:41):
Right. For instance, they're still certainly nocturnal creatures. I mean
they're also active, you know, dusk and dawn a little bit,
but during the day proper, they're inside, they're resting, and
part of that is to avoid predators. Now you mentioned earlier,
Joe that you even just looking at videos, you can
tell that they're more awkward on land than they are
in the water. And that's of course another big important

(18:04):
aspect of their damming of waterways, creating this sort of
vast flood plain, like turning a stream going through a
forest or something to this effect into kind of a
flooded forest environment. This opens up speedy water routes back
to their lodge. From perspective, feeding grounds.

Speaker 2 (18:24):
Yes, sort of the same way. You can imagine it
like humans creating roads, like paved roads between say the
farms that they work during the day and the houses
they live in. But beavers would do this by instead
creating flooded areas. Especially they can sort of like dig
out channels along the bottom that the water from these
flooded areas can run into, allowing them to have a

(18:45):
sort of canals like roads made of water where they
can move quickly, where they can move submerged, which is
safer and better for them than trying to move awkwardly
over land.

Speaker 1 (18:56):
Yeah. Now, in doing this, of course, they alter the
ecosystem local ecosystem in a major way, opens up opportunities
for various other organisms as well, and also discuss some
of the potential downsides at least for some organisms in
a bit. But at any rate, this cements the beaver's
place as a keystone species. Beaver's just just completely change

(19:18):
the immediate environment, produces more open water, higher water tables.
And yeah, it's this entire system they have going for
them here. It's just so fascinating. You can if you
look online, you can find some some side profiles, some
cutaways of what the lodge looks like, and it's pretty ingenious.
It also serves as a place for them to store
food and even provides refuge during frozen months. They don't

(19:42):
hibernate properly, but they can hold up in there.

Speaker 2 (19:46):
One of the things I've read about is that they
often can store lots of food, so they're vegetarians that
eat actually like you know, parts of trees, vegetation from
all around them, which they can keep stored in the
world water underneath the pond created by their dams, and
that's an interesting thing. They can raise the water level

(20:08):
in order to help protect areas of food storage in
the water for the winter, because by raising the water level,
they create more area underneath that won't freeze over when
the weather gets cold.

Speaker 1 (20:20):
Yeah, and these lodges and dams that they can even
though the beavers themselves tend to only live about I
think eight years max, a single lodge and dam can
be maintained over generations, so the lodges may end up
with like several stories to them, and the dams can
get quite massive. There's an Alberta area dam that was

(20:42):
built apparently in the nineteen seventies. Initially wasn't discovered till
around two thousand and seven because it's just out in
the middle of nowhere. It's not like in downtown Alberta.
It's like out in the boonies and it's thought to
be the world's largest beaver dam known beaver Dam anyway,
covering a good half mile. There's actually an Alice Obscure
article about it. If anyone's interested. Just look up world's

(21:03):
largest beaver dam and you can see some like aerial photographs.

Speaker 2 (21:07):
You know, something interesting I was reading about was the
role of beavers in maintaining ecosystem health by allowing for
a greater diversity of different types of plant life to thrive.
I think sort of in the same way that forest
fires you might think of them as purely destructive. Of
course they are destructive, but you know, forest fires occur

(21:27):
naturally all the time, and when a forest burns, that
creates sort of new opportunities for new types of plants
and other life forms to thrive in a place that
was once covered up by you know, a lot of
tree canopy. So in the areas around beaver dams and lodges,
they will clear out lots of the trees. They literally
chew them down and they'll fall, and you know, the

(21:48):
beavers will do what they will with them. But this
creates all kinds of opportunities for other plants and other
life forms that wouldn't normally thrive in the forest to
have a shot.

Speaker 1 (22:00):
Yeah. Yeah, the paper that I came across was talking
about sort of like the pros and cons. I have
another one I'll get into about some of the potential benefits,
but just to give you a full idea of sort
of the rodent altered landscape we're talking about here, I
was looking at a twenty fifteen paper published in IOP

(22:20):
conference series, or presented in the IOP conference series Earth
and Environmental Science. This one is This was by Raskova
to Mina at All, and they talk about some of
the positive and negative consequences, at least initially stressing some
of the negatives maybe that are not at least instantly
discussed as much. But you get soil overwetting obviously, because

(22:42):
you're getting flooding occurrently it occurs. You also can have
water stagnation that results in lack of oxygen, high carbon concentration,
and the death of many aquatic organisms. And then the
flooding can also cause vegetation death. But at the same time,
the authors who are stressed that it can result in
a rise in the biodiversity of water organisms. So you know,

(23:07):
they're changing everything. They're changing the balance of the local ecosystem,
and it's creating a lot of opportunities for new things,
but it is also cutting things short for things that
we're living there already. Now, a really interesting study that
I came across this was a twenty twenty two Stanford
study by Dewey at All published in Nature Communications, And

(23:29):
in this paper they point out that beaver habitat ranges
in the US are going to continue to widen with
warming temperatures driven by climate change, but the benefits of
their dam building will actually quote overshadow climate extremesquote. So
this is not to say beaver dams will cancel out
climate change or anything like that, but in some respects

(23:51):
it kind of lessens the blow. Specifically as far as
water quality in mountain watersheds are concerned. Dams can raise
water levels upstream and divert water into soil and surrounding waterways,
and this ends up sort of, this ends up like
creating a robust filter system, a filtration system for excess

(24:14):
nutrients and contaminants for the water before it passes on downstream.
So today beaver's in North American eur Asia are both
doing great. They have bounced back from near extinction due
to hunting, and we may touch on some of that
a little bit more in the next episode, but because
there are a few different reasons that have driven beaver

(24:36):
hunting over the years. But to go back to speaking
of their construction of dams and their changing of the environment,
there's another great illustration I came across by Nicholas de
Fer who lives sixteen forty six through seventeen twenty, and
this is just a small scene from a larger map.
He was a French cartographer, so this is just you know,

(25:01):
filling in some of the blank spaces, like we've discussed
before on some of these older maps. But this illustration
shows beavers at work. They are downing trees and they
are dragging off the wood to build things. There are
the beavers themselves look largely accurate. There may be a
little more bear like, but the basic morphology is there.

(25:24):
The main problems here are that, first of all, there's like,
you know, one hundred beavers in this in this one image,
like they're working as an army. And then also like
clearly there wasn't a lot of detail on how they
carry the wood, because the central beaver that you see
is standing up in a bipedal posture with an armload

(25:45):
of wood. Thrown over his shoulder like a human being.

Speaker 2 (25:48):
Yeah, yeah, like a Paul Bunyan carrying an axe.

Speaker 1 (25:52):
Yeah. But I like the spirit of industry that they
captured here, despite some of the ridiculous details, and again
a huge improvement over some illustrations from previous centuries.

Speaker 2 (26:05):
I wonder, is this one of the maps we looked
at in our horror Vakay episodes where we were talking
about maps with excessive illustrations.

Speaker 1 (26:12):
I don't believe it is. I looked at a bigger
version of the map and I almost included it in
our notes, and I don't think I had seen it before.
It was a map that it's known as the beaver
map and has to do with the locations of beavers
because it has to do with the hunting of beavers,
which again was quite a big industry for a while there,

(26:33):
so big that it just about wiped them out. So
the large semi aquatic rodents have come to flood the
world and to remake it according to their designs. But
the weirdness and the complexity doesn't stop there. Joe tell
us a little bit about beaver society and about beaver

(26:54):
tool use.

Speaker 2 (26:55):
Yeah, Rob, I think you found one of these papers first,
and that's what started this whole. But I got lost
on a going down a rabbit hole or maybe a
beaver canal, trying to search out examples of possible tool
use documented in beavers, and in fact, there are a
few very interesting different observations corresponding to each of the

(27:18):
extant species. Beavers clearly are an interesting type of animal
to look at for signs of tool using intelligence, since
they are masters of manipulating their environment through the dams
and the lodges they build. Though I think it's interesting
that nest building is often not typically thought of or
not sort of front of mind as an example of

(27:40):
tool use. And there are different examples that different zoologists
or animal behavior experts will use to try to define
tool use. So in the papers I was looking at,
a few different standards were cited. One is a definition
of tool use by a researcher named Alcock, who says
it is quote the manipulation of an inanimate object that

(28:02):
improves the organism's efficiency in altering the position or form
of some other object. So, you know, using an inanimate
object from the environment to better alter the former position
of something else. Another definition I've found cited. This is
from Beck in nineteen eighty quote the external employment of

(28:24):
an unattached environmental object to alter more efficiently the form, position,
or condition of another object, another organism, or the user itself,
when the user holds or carries the tool during or
just prior to use, and is responsible for the proper
and effective orientation of the tool. Now, I appreciate all

(28:45):
of the conditions on that, because I think it is
important for people to be specific about what they're talking
about when they look for examples of tool use. But
I also wonder, once you're specifying that many conditions, is
the category of tool use becoming more or like a
function of the definition you lay out than than a
fundamentally different type of activity itself than some other activity

(29:09):
that that wouldn't quite fit this definition.

Speaker 1 (29:11):
Yeah, I mean, and sometimes we can almost get too
hung up, I think, on the on the the idea
of tool use and the definition of tool use, because
we'll look at the most complicated burden, nest or bower
that you can imagine and will be like, well, it's intricate,
it's amazing, it's beautiful. But have you seen this monkey
stabbing a smaller monkey with a stick. You know, it's

(29:32):
you know, you know, it can almost you can almost
set it up as this this thing that is the
thing that we do. You know, that is a very
there's something very human about tool use, and you know,
obviously a huge, huge aspect of human life and human development.
But but yeah, it's it seems like at times a
lot of extra mental gymnastics is it has to be,

(29:54):
it has to be utilized in order to even discuss it.

Speaker 2 (29:57):
So I'm not going to get super hung up on
definition of tool use or what really counts as tool
use today. We've talked about some of those debates in
plenty of episodes in the past. Instead, I'm just going
to talk about some studies describing specific behaviors, and you
can make up your own mind about whether it seems
like tool use to you. So the first thing I
want to talk about is an older observation. It's older

(30:20):
than either of the two papers that I'm going to
discuss here, but it's cited in the first of them,
and I'll get to that paper itself in a second.
But the observation is that a researcher named Georgio Pilleri
observed something interesting while studying two captive beavers at the
Burn Brain Anatomy Institute in nineteen eighty three. So the

(30:42):
beavers were living in a concrete pool that was supplied
with a constant flow of fresh water, and overflow of
this pool was routed away through a series of three
drain holes, each zero point eight centimeters in diameters, so
little holes in. The beavers had been given a supply
of sticks and twigs to do what they wanted with,

(31:04):
and for some reason, what they did is they selected
and cut three sticks from their supply to the exact
dimensions needed to plug the tiny drain holes that where
water drained away from their pool. And this completely stopped
the flow of water away from the pool. Now what's
going on here? At first, it was kind of hard

(31:26):
for me to believe this would be fully intentional behavior,
as in, like the beavers understood that they were plugging
the drains to stop the flow of water from their enclosure.
But then I thought, you know, I guess I wouldn't
be surprised if beavers have like a sense for detecting
gaps in dams and plugging them, Like maybe they're good

(31:46):
at sensing. My first instinct was maybe they sense like
the delta pee. You know, the difference in pressure, like
when water from a large pool is flowing out of
a small piper hole and you could feel that pressure
that would like get your hands stuck to the hole
if you held it there, or which in larger scenarios
can be of a great danger to divers. You know,
you don't want to go near like the intake hole

(32:07):
at a dam, if you're diving near it. I thought
maybe they sense the delta pee, and so they sense
that and they naturally want to plug it up, But
I didn't know. However, I then sort of came across
an answer. So I was watching a segment on North
American beavers from BBC Earth narrated by David Attenborough, and

(32:29):
this documentary segment captured a scene of beavers finding a
leak in their dam and then getting right to work
retrieving wood, vegetation and clumps of sediment down from the
bottom of the pond to plug up the leak in
the dam where water was running over the top. And Attenborough,
in this documentary segment narrates that beavers are thought to

(32:51):
detect these leaks by hearing the sound of trickling water
and when they do, they begin repair work almost immediately.
It seems to be fastidious, almost compulsive. This compulsive desire
to fix the holes when they hear the water trickling,
and this would make the drain plugging behavior in the

(33:11):
concrete enclosure in the eighties make a lot more sense.
So I decided to look into this further to see
if this was indeed true to some degree. It seems
it is, and so I didn't have time. This was
soon before we started recording. I didn't have time to
find the primary reference on this, but I did find
a good twenty fifteen Gizmoto blog post by Esther inglis

(33:34):
Arkell writing up summarizing the research of a Swedish zoologist
named Lars Wilson who studied beavers back in the nineteen sixties,
and according to the summary, Lars Wilson found that dam
building was instinctual rather than learned, and the way Wilson
identified with this was that if you took young beavers

(33:54):
and you separated them from their parents at birth, they
would still build dams basically the same way, using the
same techniques as their parents, even though they were clearly
not having the opportunity to be taught to do that.
So it seems based on that at least this is
probably a routine behavior. It's based on beaver DNA. They
don't have to be taught. But Wilson also found that

(34:15):
beavers didn't always build dams. In environments with still water
or only very gently moving water, dam building was not
a priority. The beavers would just maybe they like dig
a hole in the mud and just chill there, you know,
they just wouldn't build. And so by manipulating different variables,
Wilson identified the sound of trickling water as the primary

(34:37):
trigger for dam building, even to the point of a
discovery that this was the part I found most fascinating.
If you put a speaker in the beaver's enclosure and
you played the sound of trickling water through it, the
beavers would go to the speaker and start building on
top of it. They would start piling up sticks and
mud and branches over the speaker playing the sounds. They

(35:01):
were trying to plug the speaker to make it stop leaking.

Speaker 1 (35:05):
Oh my goodness.

Speaker 2 (35:06):
Wilson also found that if outflow pipes, so you had
a place where there was actually water leading away from
the pool, but you carefully designed the pipe so that
they made no noise, the beavers would not be able
to find and cover them. So this might lead you
to think, okay, so like the louder the rushing of
the water, the more beavers want to make a damn there.

(35:28):
But it also seems like it's not quite that simple,
because I was reading a news article from the Harvard
Graduate School of the Arts and Sciences called Damned If
They Do by Paul Massari. This article profiles the research
of an environmental engineer named Jordan Kennedy who has done
research on beavers and their dam building practices and the

(35:50):
environmental effects thereof. And Kennedy says that it can't just
be about the like the magnitude of sound of moving water,
or beavers would be trying to build dams across Niagara Falls,
you know, just like loud, violent, rushing waters where building
would be totally impractical. So instead, there's got to be
a kind of Goldilocks zone for dam construction, something that

(36:12):
the beavers naturally detect that allows them to know, Okay,
this is about the right amount of flow to try
to dam up.

Speaker 1 (36:20):
Yeah, yeah, damming up Niagara Falls, like obviously, that would
be great like, that's kind of like the beaver fan fiction.
That's the pipe drain, But is it practical. No, you
need to have that just the right environment that can
then be manipulated to make the ideal environment for the beaver.

Speaker 2 (36:37):
Right, So, the author of this article writes, quote, the
water in a beaver's habitat needs to be a certain depth,
for instance, to keep a food cache from freezing to
the bottom in winter and to enable them to evade predators.
The plants that beavers prefer to eat flourish best when
water flows at a certain velocity. So you're looking for

(36:58):
this goldilocks zone, an area of a certain amount of
water flow, maybe a certain narrowness of the channel or
certain depth of the channel, and that's the place where
you want to dam it up. And beavers apparently they
locate that. A big part of the sense data informing
them of that area appears to be sound. Maybe maybe

(37:18):
the overwhelming part of it is sound, but there may
be other cues as well, and so I don't know.
I thought this was so interesting, and I'm just trying
to imagine what it's like to be a beaver, to
have this powerful instinctual drive to plug leaks. So imagine
the same kind of base level instinctual drive that humans
might have for sex, or for food, or to care

(37:42):
for children, all the like the most powerful drives in
our brains. But there's a drive like that to hunt
down the source of anything that sounds like trickling water
and to just plug it with junk. You know, I
don't know. That's like, that's another that's another type of
mind experience, a relationship to the environment.

Speaker 1 (38:03):
Wow wow, yeah, Like what would yeah, how would like
we can't help but extrapolate that into like a human
like intellect and human like culture, Like what would advance
beaver civilization be? Like would they actually go after like
complete inundation, like a complete flooding situation, the destruction of

(38:23):
all naturally occurring waterfalls, or would they just kind of
dream about it? Or what would their TV shows be?
Would it just be like countless channels of leak plugging
and so forth.

Speaker 2 (38:35):
The speaver thought she had it all, but then she
heard the trickle and couldn't find it searching, Like all
dramas begin with the conflict of hearing a trickle.

Speaker 1 (38:45):
That's the call to adventure.

Speaker 2 (38:47):
Yeah, but anyway, all that stuff I just read about
got kicked off because I was reading that anecdote about
the findings of Giorgio Pillari in nineteen eighty three, which
was cited in a paper by D. M. Barnes called

(39:10):
possible tool use by beavers cast Or canadensis in a
Northern Ontario watershed published in the Canadian Field Naturalist in
two thousand and five. So this is one of the
main two papers I was looking at about possible cases
of tool use in beaver's Barnes says that this report
is based on evidence relating to the North American beaver

(39:30):
that's Castor canadensis at a remote damn site in the
Chapleaux Crown Game Preserve in northern Ontario. The author says,
at this location they found a clump of willow stems,
so like little small tree trunks that had been cut
by beavers. But the fascinating thing was they were cut
at the extraordinary height of approximately one meter off the ground.

(39:55):
Beavers are not that tall normally, these beavers cut at
an average height of about thirty centimeters, so the beavers
were chomping off these willow trees at three times the
normal height they could reach with their teeth. Barnes writes, quote,
I made a careful examination of the area and found
that there was no apparent way the beavers could have

(40:17):
cut the stems at such a height. When I studied
the willow clump more closely, I noted that there was
a freshly cut willow stem approximately twelve centimeters in diameter,
leaning against the main stem of the willow clump. Its
approximate angle was forty five degrees. In addition, I observed
cutting at both ends of the leaning willow segment, and

(40:39):
then there was a There was a photo accompanying this
in the article. Now, at first the author thought that, okay,
so this is a log propped up forty five degrees
against the tree that is cut off very tall. The
author thought maybe this log there had simply fallen that way.
I don't know, it's something that the beaver cut and
then it fell. But that's impossible on further examination, because

(41:02):
the log was clearly from a different tree than the
stem it was leaning against, like there was different bark
texture and color and so forth, and its position just
did not seem plausible if it had fallen from above.
Another possibility the author considered was that these willow trunks
had been foraged while there was heavy snow on the

(41:23):
ground in the winter. So maybe the beavers were able
to reach a meter up the trunks of these trees
by crawling around on top of the snow. Okay, but
the author things that's really unlikely. Given the position of
the willow clump relative to the beaver dam and lodge
and its entrance and exit. It seems it would have

(41:44):
required a major overland journey by the beavers on the
top of the snow in the winter at a time
where this just would not fit with their normal behavior. Instead,
the author suggests that maybe what happened here is the
beaver used a prop. The beaver used a piece of
a log that it had cut off at both ends

(42:06):
and propped it up against the base of the trees,
and then climbed up that and was able to chew
off the willow stems at an upper level rather than
a lower level. Now, why would this even be beneficial?
The author says this would be probably to reduce foraging time.
So the longer you forage number one, the more thermal

(42:26):
stress you're exposed to not being the right temperature. But
more importantly, the longer you are exposed to predation. Apparently
beavers do not like to spend a lot of time
out on the ground out of the water, so they
are trying to hustle as fast as they can whenever
they're out there cutting, and in this case, apparently using

(42:47):
a cut stem to climb up the willow trunks to
access a higher up part of the tree to chew
through would have meant that they had to spend less
time chewing and less time cutting all right.

Speaker 1 (43:00):
Like a little bit higher they just it's gonna be less,
it's gonna be a narrow or bit of wood to
shoot through.

Speaker 2 (43:06):
That's what I assumed. It didn't specify exactly why cutting
higher up was reduced foraging time, but that was my interpretation.

Speaker 1 (43:13):
I could be wrong, and that's why they potentially could
be using essentially a beaver ladder, a beaver bit of scaffolding.

Speaker 2 (43:21):
Right, But we don't know. This is just one observation.
And also they didn't see them doing it. They just
found this strange piece of scaffolding there later.

Speaker 1 (43:30):
Yeah, more mysteries related to I mean, I guess this
is kind of cutting into some of the mysteries involved
in these wildly inaccurate depictions of beavers is that these
are creatures that live often in very rural situations, far
from human activity. They're probably doing it at night, and
they're spending as a little time necessary doing it out

(43:52):
where other eyes could see them.

Speaker 2 (43:54):
Right, okay. Second paper I came across alleging possible tool
use behaviors by This is called tool use in a
display behavior by Eurasian beavers or castor fiber in the
journal Animal Cognition by Thompson at All in two thousand
and seven. So here the authors write that documentation of
tool use is relatively rare in rodents, and prior to

(44:17):
this paper there were no documented cases they knew of
of tools being used by rodents in what are called
agonistic displays. Now, agonistic is a word used in the
study of animal behavior to describe conflict or fighting. So
an agonistic behavior is not necessarily fighting itself, but also
could include social behaviors related to fighting. So these would

(44:41):
include threat displays trying to, you know, look big or
otherwise intimidate another animal, displays of aggression, as well as
things like submission or retreat behavior. The authors of this
paper say that in their field observations of the Eurasian beaver.
They witnessed the behavior that they call stick display, which
they interpreted as an agonistic display behavior. And what this

(45:05):
consisted of is beaver would go pick up an object,
usually a stick, whenever a stick was available, and then
it would rise up on its hind legs and then
move the upper body rapidly up and down while holding
the stick or other object in its mouth and front paws.
And Rabbi attached a picture for you to look at.
They had a photo of this. In this photo of

(45:27):
the beaver is in the shallow part of a waterway.
It's standing up on its back legs. It's kind of
I don't know how to just it's kind of like
roaring posture. But it's got a big old stick in
its mouth, and it's gripping the stick with its two
four paws, and the water is splashing all around as
the stick I guess, rapidly dips in and out.

Speaker 1 (45:47):
It's impressive and it's frankly a little intimidating, this beaver saying, behold,
look at the feats of strength. I am capable of.

Speaker 2 (45:56):
So several observations about this behavior. First of all, they say,
beaver's only picked up these display sticks or other objects
at the same location where they were used, and they
were never seen modifying the objects, so it wouldn't It
wasn't like they would carry a stick around and then
use it in a different location or modify the stick
in any way.

Speaker 1 (46:16):
So, for instance, compare it to like human tool use
that we've discussed in the past rocks. This would not
be on the level of picking out favored rocks for
throwing at other humans, polishing them, changing them, etc. This
would be more on the level of when threatened, you
might look down, grab a rock and use it. Though
of course, in this case, the beavers are not hitting

(46:37):
each other with the sticks allegedly, the hypothesis here is
that they're using them as a pure defensive display.

Speaker 2 (46:44):
Right. Second thing, This often happened in shallow water, so
the shaking of the stick would cause splashing in the
surrounding water, but occasionally it also took place on dry land,
such as in weeds, where there was no significant sound produced.
So the authors think because it took place in both
scenarios and when it was on dry land it didn't
really make a noise, they think it is primarily a

(47:06):
visual signal. An important bit of context is that Eurasian
beavers are territorial. They live in family groups with usually
a dominant breeding pair and then assorted offspring of that
breeding pair. And they defend the borders of their territory
from encroachment by other beavers. So they mark their territory
by scent. This is done with secretions from the anal

(47:29):
glands or castorium. Which castorium, I believe, we'll talk about
more later in the series in part two allegedly smells
like vanilla, but we'll come back. When rival beavers come
into a family group's territory, the home turf beavers will
react first of all with tail slapping. Rob you mentioned this.
This is a loud signal that beavers make by repeatedly

(47:50):
smacking the water surface with their tails. This is also
used to alert members of the family group when a
predator is cited. They also respond to unwelcome presence by
visual displays or sometimes with actual fighting, though physical fights
are relatively rare. The observations carried out in this study
were conducted on wild Eurasian beavers in southeast Telemark, Norway. Overall,

(48:14):
the researchers observed one hundred and thirty one cases of
stick display behavior that met the criteria for inclusion in
their study by four adult males, two adult females, and
five unidentified animals. However, it seems that some individual beavers
engaged in stick displays far more than the others.

Speaker 1 (48:35):
Quote.

Speaker 2 (48:36):
It was clear from our observations that one female beer
Git and one male Froda were the main performers, with
a contribution of fifty one point nine percent and thirty
five point nine percent, respectively, of the total number of
stick displays observed. So what does that add up to.
It's like eighty seven percent of stick displays were from

(48:56):
two beavers.

Speaker 1 (48:58):
Wow, go Froda.

Speaker 2 (49:00):
The real champion is beer Get here. She's got more
than half of them just under her belt.

Speaker 1 (49:04):
Yeah yeah, I mean really, beer Get needs to get
get most of the credit here from Froda doing pretty
well as well.

Speaker 2 (49:11):
So they say, stick displays happened almost exclusively at the
borders of beaver family group territory, and most displays appeared
to be directed at rivals. The displays were often preceded
by scent marking, so this kind of suggests it probably
is being used as an agonistic display. However, this behavior,
while common in the groups observed in this study, is

(49:34):
not necessarily generalizable to the total world population of these beavers.
It has not really been observed in beaver's generally across
the full range, suggesting it may be specific to certain populations.

Speaker 1 (49:47):
Wow, like even like some sort of like localized beaver culture.

Speaker 2 (49:51):
Yeah, maybe apparently something. At the time of the study,
the author said there were some isolated reports of similar
behavior in a few North American beavers, but not most,
and it was not found in all Eurasian beavers either.
So the authors argue that stick displays might be especially
favored in high pressure situations. From reading their description of

(50:14):
the area, it seems like the groups observed in this
study might be in especially crowded beaver territory, where like,
you know, the areas around different family dams and lodge
sites are sort of all butting up against one another.
They also observed higher rates of stick displays in springtime,
meaning it's possible it could have some association with breeding.

(50:38):
But if the stick shaking is a genuine agonistic display behavior,
the evolutionary purpose would probably be to convey honest information
about the beaver's size and strength, so it's like, I'm
big and strong. Look at how I can shake this stick.
You don't want to bother actually getting into a fight
with me, right, we don't have to do this.

Speaker 1 (50:58):
I like these sort of levels of communication that seem
to exist between beaver groups here. You know, it's like,
at the end of the day, all beavers really want
to do is build things and plug holes. Uh. You
know they have they have a lot of hole plugging
to do. They have they have a lot of work
to accomplish. They don't really have time to get into

(51:18):
these fights. These fights are just would be destructive. Uh
So instead, let's just make sure that we're very clear
about how everyone feels about these these border scenarios, and uh,
if need be, let me just show you, give you
a taste of what could happen. Just look at this
stick lifting ability here.

Speaker 2 (51:36):
The neighbors are getting nosy and beerget shakes a branch
and it's like, no, don't make me do it. Don't
make me do it. And it seems most of the
time they're like, Okay, I won't make you do it. Bergeit, man.
I think we've got to be out of time for
for part one of Beaver's here right, But there will
be more.

Speaker 1 (51:53):
Yeah, in the next episode, we're gonna we're gonna get
back to that idea, that that false idea of beaver
whilst being hunted deciding to chew their own testicles off
again that you see various examples of, particularly from like
illuminated manuscripts and so forth and bestiaries. We'll come back
and to discuss that, plus who knows what else we'll

(52:14):
uncover about beavers in our research. In the meantime, we'd
love to hear from everyone out there if you have
any especially since a lot of times we do these
Tuesdays to Thursday. This one's going to be a Thursday
to Tuesday, so who knows, you might be able to
get some really core beaver facts and beaver experiences into
us before we record the next episode. You know something

(52:35):
you've picked up somewhere or just you know, accounts of
observing beavers in the wild. I'd love to hear about that. So,
whatever your feedback, whatever your thoughts, share them with us.
We would love to hear from you. Just a reminder
that Stuffed to Blow Your Mind is a science podcast
with core episodes on Tuesdays and Thursdays, So look for
those in the Stuff to Blow Your Mind podcast feed

(52:55):
wherever you get your podcasts. On Mondays we do a
listener mail episode. On Wednesday's do a short form artifact
or monster fact episode. I know sometimes people say I
wish they were longer. Well, they're short. That's part of
how it works. But occasionally we're gonna put out We're
going to continue to experiment, experiment with putting out omnibus
episodes that may take up like multiple related monster facts

(53:18):
or artifacts, and put them out so periodically you'll get
a longer one in there as well. So yeah, let
us know if you're liking that, and we can keep
doing it. Oh and then on Fridays we set aside
most serious concerns to just talk about a weird movie
on Weird House Cinema.

Speaker 2 (53:32):
Huge thanks to our audio producer JJ Posway. If you
would like to get in touch with us with feedback
on this episode or any other, to suggest a topic
for the future, or just to say hello, you can
email us at contact at stuff to Blow your Mind
dot com.

Speaker 3 (53:53):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from my Heart Radio, visit the iHeartRadio app
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