May 18, 2023 • 53 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 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.
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Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind, the production of iHeartRadio.
Speaker 2 (00:13):
Hey you 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,
(00:33):
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
(00:54):
of specimens back, but it's those illo 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.
(01:15):
But there are also countless examples, and we've touched on
these before in the show of rougher 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,
(01:37):
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
(01:59):
is a 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 perhaps
a fish tail on its body and a real hybrid
feeling like it is, almost like it's a strange like
dog mermaid. It might be in almost all respects a deer,
(02:23):
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 3 (02:40):
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 blades.
Speaker 2 (03:01):
Yeah, yeah, this one. I had to go deeper on
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,
(03:24):
it just looks like a It is labeled as a beaver,
but it is in all respects of 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, cause it's it's one thing
if you have a depiction of a rhino. That okay,
(03:45):
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 3 (03:56):
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 lion with a snake neck biting its own genitals.
Speaker 2 (04:14):
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 or
actually just a deer with razor sharp teeth, it is
(04:36):
often depicted g 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 3 (04:46):
Right, So you've got to stick around for next time
to hear that.
Speaker 2 (04:49):
Yeah, so let's 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
(05:12):
at least 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 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, that's particularly the ones on
spouting and spouts. Because despite all this access to actual,
(05:36):
solid 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 3 (05:44):
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 beaver's. Beavers are
much stranger and more beautiful than I realized.
Speaker 4 (06:06):
Yeah.
Speaker 2 (06:07):
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 things
(06:27):
hold up. Obviously, beavers are not going to sell you
out to the White Witch. That's absolutely true. So C. S.
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 3 (06:46):
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 chips and some
malt vinegar, I don't know they might get into that.
Speaker 2 (07:03):
All right, Well, let's start with the basics here. So
beavers are rodents and are in fact the second largest
extant 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
(07:27):
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
(07:50):
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 at 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
(08:12):
three hundred pound giant pacaranas of South America. Extant pacaranas
only get up to like 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 prehistory, all.
Speaker 3 (08:32):
Right, So no beavers today in that territory. But beavers
can still get pretty chunky.
Speaker 2 (08:36):
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 Caapi 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
(08:57):
of the things we're going to be discussing about them
lying up with their habitat. For instance, they can hold
their breath for fifteen minutes. They have transparent third eyelids
called micitating membranes to aid them in their swims much
like manates. They also famously have long, flat, black tails.
We know this from the cartoons obviously, and these aid
(09:19):
them and they're 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
(09:43):
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 3 (09:53):
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.
(10:15):
They do that all quite well in the water and
then once you see them sort of toddling along across
the dry land, it looks much more comical and awkward.
Speaker 2 (10:24):
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
(10:46):
will speak with a kind of whistle in their voice,
but we also tend to get it quite wrong.
Speaker 3 (10:52):
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 2 (11:07):
Yeah? Yeah, pretty much.
Speaker 3 (11:09):
The truth is much more shocking.
Speaker 2 (11:12):
Yeah, yeah, they have these. You know, if you look
at a skull of a beaver, it's pretty remarkable because
it's like this, the really kind of exaggerated rodent skull
with just incredible incisors, you know, with these two big
shovel like teeth coming down from the top, two big
shovel like teeth coming up from the bottom, and then
(11:35):
the rest of the back teeth or much further back,
you know, giving them some ample room to do the
kind of a woodwork that they need to do with
those chompers.
Speaker 3 (11:45):
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 2 (11:57):
That's right. The orange is key. This is something I
will 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
(12:19):
like something out of 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
(12:40):
acid as well based on their composition.
Speaker 3 (12:43):
Just some tough, rusty looking teeth.
Speaker 4 (12:45):
Yeah, yeah, the orange is really quite shyy.
Speaker 2 (12:58):
Okay. Another essential biological aspect of the beaver before getting
into their behavior is that they have a cloaca. So
most mammals do 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 mostly
(13:19):
lost these general purpose openings over the course of their evolution,
but in beaver's they seem to be present as a
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
(13:42):
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
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 the beaver. You know, leave it
(14:05):
to the professional biologists.
Speaker 3 (14:06):
Leave it to beaver scientists.
Speaker 2 (14:08):
Yes, so these 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 via the blockage of rivers
(14:32):
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 also made out of this
(14:52):
kind of stuff, branches and mud and so forth, and
they can only be accessed from underwater entrances in their
constructed ponds.
Speaker 3 (15:00):
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
(15:22):
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 conserve 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 2 (15:42):
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
you know, and maybe a few trees. I'm going to
(16:03):
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
(16:23):
the only 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
(16:45):
time than the removal of their predators amounts to.
Speaker 3 (16:50):
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 4 (17:00):
Right.
Speaker 2 (17:00):
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 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 aspect
(17:24):
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 3 (17:43):
Yes, sort of the same way. You could 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
(18:05):
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 2 (18:15):
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
(18:37):
the immediate environment, produces more open water, higher water tables.
And yeah, it's this entire system they have going for
them here is 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 recue huge during frozen months. They
(19:01):
don't hibernate properly, but they can hold up in there.
Speaker 3 (19:05):
One of the things I've read about is that they
often can store lots of food, so they are vegetarians
that eat actually, like you know, parts of trees, vegetation
from all around them, which they can keep stored in
the water underneath the pond created by their dams. And
that's an interesting thing. They can raise the water level
(19:27):
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 2 (19:40):
Yeah, and these these lodges and dams that they can
they even though the beavers themselves tend 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
(20:02):
was 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
(20:23):
largest beaver dam and you can see some like aerial photographs.
Speaker 3 (20:27):
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
(20:47):
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 camp. 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
(21:07):
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 2 (21:19):
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
(21:39):
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
(22:02):
you're getting flooding occurrently that 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 are stressed that it can result in a
rise in the biodiversity of water organisms. So you know,
(22:26):
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
(22:48):
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 extremes quote.
So this is not to say beaver dams will cancel
out climate change or anything like that, but in some
(23:10):
respects it kind of lessens the blow specifically as far
as water quality in mountain watersheds are concerned. Beaver 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
(23:32):
system for excess nutrients and contaminants for the water before
it passes on downstream. So today beaver's in North American
Eurasia 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,
(23:52):
but because there are a few different reasons that have
driven beaver 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 Defer, who lives sixteen forty six through seventeen twenty,
and this is just a small scene from a larger map.
(24:15):
He was a French cartographer, so this illustration is just
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. The beavers
themselves look largely accurate. There may be a little more
(24:39):
bear like, but the basic morphology is there. The main
problems here are that, first of all, there's like, you know,
one hundred beavers 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 beav that you see is standing up
(25:02):
in a bipedal posture with an armload of wood thrown
over his shoulder like a human being.
Speaker 3 (25:08):
Yeah yeah, like a Paul Bunyon carrying an axe.
Speaker 4 (25:12):
Yeah.
Speaker 2 (25:13):
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 3 (25:24):
I wonder is this one of the maps we looked
at in our Horror Vakae episodes where we were talking
about maps with excessive illustrations.
Speaker 2 (25:32):
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,
(25:53):
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
(26:13):
tool use.
Speaker 3 (26:15):
Yeah, Rob, I think you found one of these papers first,
and that's what started this whole thing. 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
(26:38):
the 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
(26:59):
of tool use, and there are different examples the 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
(27:22):
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
(27:43):
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
(28:04):
all 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 like a
function of the definition you lay out than a fundamentally
(28:25):
different type of activity itself than some other activity that
wouldn't quite fit this definition.
Speaker 2 (28:31):
Yeah, I mean, and sometimes we can almost get too
hung up, I think, on the on 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
(28:51):
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 yeah,
it seems like at times a lot of extra mental
(29:11):
gymnastics has to be utilized in order to even discuss it.
Speaker 3 (29:16):
So I'm not going to get super hung up on
definitions 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 like 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
(29:39):
older 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 the second.
But the observation is that a researcher named Georgio Pilleri
observes something interesting while studying two captive beavers at the
Burn Brain Anatomy Institute in nineteen eighty. So, the beavers
(30:02):
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 little holes, And
the beavers had been given a supply of sticks and
twigs to do what they wanted with, and for some reason,
(30:25):
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 for me to believe this
(30:46):
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 beaver
have like a sense for detecting gaps in dams and
plugging them, Like maybe they're good at sensing. My first
(31:07):
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 pipe or 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 and a dam if you're
(31:27):
diving near it. I thought, maybe they sensed 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 this documentary segment captured a scene
(31:51):
of beavers finding a leak in their dam and then
getting right to work retrieving wood, vegetation and clumps of
ediment 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 detect these leaks by hearing
(32:13):
the sound of trickling water, and when they do, they
begin repair work almost immediately. So 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 concrete enclosure in the eighties
make a lot more sense. So I decided to look
(32:36):
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 Arkele writing up summarizing the research
(32:57):
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 and you separated them from their
parents at birth, they would still build dams basically the
(33:19):
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 beavers didn't always build dams. In
environments with still water or only very gently moving water,
(33:43):
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 trigger for dam building, even
to the point of a discovery that I this was
the part I found most fascinating. If you put a
speaker in the beaver's enclosure and you played the sound
(34:07):
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 water sounds. They were trying to
plug the speaker to make it stop leaking.
Speaker 2 (34:24):
Oh my goodness.
Speaker 3 (34:26):
Wilson also found that if outflow pipes, so you had
a place where there was actually water leading away from
the 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
(34:47):
a damn there. 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
(35:08):
practices and the environmental effects thereof. And Kennedy says that
it can't just be about 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
(35:30):
damn construction, something that the beavers naturally detect that allows
them to know, Okay, this is about the right amount
of flow to try to dam up.
Speaker 2 (35:39):
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 3 (35:57):
Right, So the author of this article right now, it's quote,
the water in a beaver's habitat needs to be a
certain depth, for instance, to keep a food cash 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 this Goldilocks zone, an area of a
(36:20):
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 the overwhelming part of it is sound, but there
may be other cues as well, And so I don't know.
(36:43):
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
for children, all the like the most powerful drives in
(37:05):
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 or relationship to the environment.
Speaker 2 (37:22):
Wow wow, yeah, Like what would yeah, how would like
we can't help but extravolate that into like a 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 of of all naturally occurring waterfalls, or would they
(37:45):
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 3 (37:54):
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 2 (38:05):
That's the called adventure.
Speaker 3 (38:06):
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
(38:29):
Possible tool use by beaver's Castor 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 that's
(38:50):
Castor candidensis 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. Beavers
(39:15):
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
(39:37):
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
(39:59):
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 seemed impossible on further examination,
(40:22):
because 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
(40:43):
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.
Speaker 2 (40:52):
Okay, but the.
Speaker 3 (40:54):
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 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,
(41:16):
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
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?
(41:38):
The author says this would be probably to reduce foraging time.
So the longer you forage, number one, the more thermal
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. They were
(42:00):
trying to hustle as fast as they can whenever they're
out there cutting, and in this case, apparently using 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.
Speaker 2 (42:18):
All right, So they go like a little bit higher.
They just it's going to be less it's going to
be a narrower bit of wood to chew through.
Speaker 3 (42:26):
That's what I assumed. It didn't specify exactly why cutting
higher up was reduced foraging time. But that was my interpretation.
Speaker 2 (42:32):
I could be wrong, and that's why they potentially could
be using essentially a beaver ladder a beaver bit of scaffolding.
Speaker 3 (42:41):
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 2 (42:50):
Yeah. More mysteries related to and 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 of often in very rural situations,
far from human activity. They're probably doing it at night,
and they're spending as little time necessary doing it out
(43:11):
where other eyes could see them.
Speaker 3 (43:14):
Right, Okay. Second paper I came across alleging possible tool
use behaviors by beavers. 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
(43:36):
to 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
(44:00):
would include threat displays, trying to 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 a behavior that they call stick display, which
they interpreted as an agonistic display behavior. And what this
(44:25):
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 Rabi attached a picture for you to look at.
They had a photo of this. In this photo of
(44:47):
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 it's kind of like roaring posture.
But it's got a big old stick in its mouth,
and it's gripping the dick with its two four paws,
and the water is splashing all around. It's the stick,
I guess, rapidly dips in and out.
Speaker 2 (45:06):
It's impressive, and it's it's frankly a little intimidating. This
this beaver saying, behold, look at the at the feats
of strength I am capable of.
Speaker 3 (45:15):
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
and then use it in a different location or modify
the stick in any way.
Speaker 2 (45:36):
So, for instance, compare it to like human tool use
that we've discussed in the past. Rocks. This 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
(45:56):
hitting each other with the sticks. Allegedly, the hypothesis here
is that they're using them as a pure defensive display.
Speaker 3 (46:03):
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
(46:25):
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
(46:49):
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
(47:10):
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 beaver 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,
(47:34):
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 2 (47:55):
Quote.
Speaker 3 (47:56):
It was clear from our observations that one female beer
and one male Froda where 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.
Speaker 2 (48:16):
Two beavers Wow, go Froda.
Speaker 3 (48:19):
But the real champion is beer Get here. She's got
more than half of them just under her belt.
Speaker 2 (48:24):
Yeah yeah, I mean really, beer Get needs to get
get most of the credit here for Froda doing pretty
well as well.
Speaker 3 (48:30):
So they say. Stick displays happened almost exclusively at the
borders of beaver family group territory, and most displays appear
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
(48:54):
not necessarily generalizable to the total world population of these beavers.
It has not really been observed in beavers generally across
the full range, suggesting it may be specific to certain populations.
Speaker 2 (49:07):
Wow like even some like some sort of like localized
beaver culture.
Speaker 3 (49:11):
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
(49:33):
the of 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
(49:56):
with breeding. 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
(50:16):
to do this.
Speaker 2 (50:17):
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. 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 these fights.
(50:38):
These fights are just would be destructive. So instead, let's
just make sure that we're very clear about how everyone
feels about these these border scenarios, and 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 3 (50:55):
The neighbors are getting nosy, and Beer get 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,
Beer gat Man. I think we've got to be out
of time for part one of Beaver's here, right, but
there will be more.
Speaker 2 (51:13):
Yeah, in the next episode, we're gonna we're going to
get back to that idea, that that false idea of
beavers 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
(51:33):
we'll 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,
(51:54):
something 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 Stuff 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 wherever you get your podcasts. On Mondays
(52:17):
we do a listener mail episode. On Wednesdays we 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 going
to put out We're going to continue to experiment, experiment
with putting out omnibus episodes that may take up like
multiple related monster facts or artifacts and put them out
(52:39):
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 3 (52:52):
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 topic for
the future, or just to say hello, you can email
us at contact at stuff to Blow your Mind dot com.
Speaker 1 (53:13):
Stuff to Blow Your Mind is production of iHeartRadio. For
more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts,
or wherever you listen to your favorite shows.
Welcome to Stuff to Blow Your Mind, the production of iHeartRadio.
Speaker 2 (00:13):
Hey you 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,
(00:33):
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
(00:54):
of specimens back, but it's those illo 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.
(01:15):
But there are also countless examples, and we've touched on
these before in the show of rougher 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,
(01:37):
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
(01:59):
is a 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 perhaps
a fish tail on its body and a real hybrid
feeling like it is, almost like it's a strange like
dog mermaid. It might be in almost all respects a deer,
(02:23):
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 3 (02:40):
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 blades.
Speaker 2 (03:01):
Yeah, yeah, this one. I had to go deeper on
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,
(03:24):
it just looks like a It is labeled as a beaver,
but it is in all respects of 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, cause it's it's one thing
if you have a depiction of a rhino. That okay,
(03:45):
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 3 (03:56):
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 lion with a snake neck biting its own genitals.
Speaker 2 (04:14):
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 or
actually just a deer with razor sharp teeth, it is
(04:36):
often depicted g 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 3 (04:46):
Right, So you've got to stick around for next time
to hear that.
Speaker 2 (04:49):
Yeah, so let's 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
(05:12):
at least 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 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, that's particularly the ones on
spouting and spouts. Because despite all this access to actual,
(05:36):
solid 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 3 (05:44):
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 beaver's. Beavers are
much stranger and more beautiful than I realized.
Speaker 4 (06:06):
Yeah.
Speaker 2 (06:07):
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 things
(06:27):
hold up. Obviously, beavers are not going to sell you
out to the White Witch. That's absolutely true. So C. S.
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 3 (06:46):
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 chips and some
malt vinegar, I don't know they might get into that.
Speaker 2 (07:03):
All right, Well, let's start with the basics here. So
beavers are rodents and are in fact the second largest
extant 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
(07:27):
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
(07:50):
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 at 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
(08:12):
three hundred pound giant pacaranas of South America. Extant pacaranas
only get up to like 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 prehistory, all.
Speaker 3 (08:32):
Right, So no beavers today in that territory. But beavers
can still get pretty chunky.
Speaker 2 (08:36):
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 Caapi 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
(08:57):
of the things we're going to be discussing about them
lying up with their habitat. For instance, they can hold
their breath for fifteen minutes. They have transparent third eyelids
called micitating membranes to aid them in their swims much
like manates. They also famously have long, flat, black tails.
We know this from the cartoons obviously, and these aid
(09:19):
them and they're 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
(09:43):
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 3 (09:53):
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.
(10:15):
They do that all quite well in the water and
then once you see them sort of toddling along across
the dry land, it looks much more comical and awkward.
Speaker 2 (10:24):
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
(10:46):
will speak with a kind of whistle in their voice,
but we also tend to get it quite wrong.
Speaker 3 (10:52):
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 2 (11:07):
Yeah? Yeah, pretty much.
Speaker 3 (11:09):
The truth is much more shocking.
Speaker 2 (11:12):
Yeah, yeah, they have these. You know, if you look
at a skull of a beaver, it's pretty remarkable because
it's like this, the really kind of exaggerated rodent skull
with just incredible incisors, you know, with these two big
shovel like teeth coming down from the top, two big
shovel like teeth coming up from the bottom, and then
(11:35):
the rest of the back teeth or much further back,
you know, giving them some ample room to do the
kind of a woodwork that they need to do with
those chompers.
Speaker 3 (11:45):
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 2 (11:57):
That's right. The orange is key. This is something I
will 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
(12:19):
like something out of 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
(12:40):
acid as well based on their composition.
Speaker 3 (12:43):
Just some tough, rusty looking teeth.
Speaker 4 (12:45):
Yeah, yeah, the orange is really quite shyy.
Speaker 2 (12:58):
Okay. Another essential biological aspect of the beaver before getting
into their behavior is that they have a cloaca. So
most mammals do 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 mostly
(13:19):
lost these general purpose openings over the course of their evolution,
but in beaver's they seem to be present as a
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
(13:42):
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
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 the beaver. You know, leave it
(14:05):
to the professional biologists.
Speaker 3 (14:06):
Leave it to beaver scientists.
Speaker 2 (14:08):
Yes, so these 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 via the blockage of rivers
(14:32):
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 also made out of this
(14:52):
kind of stuff, branches and mud and so forth, and
they can only be accessed from underwater entrances in their
constructed ponds.
Speaker 3 (15:00):
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
(15:22):
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 conserve 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 2 (15:42):
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
you know, and maybe a few trees. I'm going to
(16:03):
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
(16:23):
the only 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
(16:45):
time than the removal of their predators amounts to.
Speaker 3 (16:50):
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 4 (17:00):
Right.
Speaker 2 (17:00):
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 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 aspect
(17:24):
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 3 (17:43):
Yes, sort of the same way. You could 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
(18:05):
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 2 (18:15):
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
(18:37):
the immediate environment, produces more open water, higher water tables.
And yeah, it's this entire system they have going for
them here is 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 recue huge during frozen months. They
(19:01):
don't hibernate properly, but they can hold up in there.
Speaker 3 (19:05):
One of the things I've read about is that they
often can store lots of food, so they are vegetarians
that eat actually, like you know, parts of trees, vegetation
from all around them, which they can keep stored in
the water underneath the pond created by their dams. And
that's an interesting thing. They can raise the water level
(19:27):
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 2 (19:40):
Yeah, and these these lodges and dams that they can
they even though the beavers themselves tend 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
(20:02):
was 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
(20:23):
largest beaver dam and you can see some like aerial photographs.
Speaker 3 (20:27):
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
(20:47):
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 camp. 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
(21:07):
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 2 (21:19):
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
(21:39):
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
(22:02):
you're getting flooding occurrently that 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 are stressed that it can result in a
rise in the biodiversity of water organisms. So you know,
(22:26):
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
(22:48):
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 extremes quote.
So this is not to say beaver dams will cancel
out climate change or anything like that, but in some
(23:10):
respects it kind of lessens the blow specifically as far
as water quality in mountain watersheds are concerned. Beaver 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
(23:32):
system for excess nutrients and contaminants for the water before
it passes on downstream. So today beaver's in North American
Eurasia 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,
(23:52):
but because there are a few different reasons that have
driven beaver 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 Defer, who lives sixteen forty six through seventeen twenty,
and this is just a small scene from a larger map.
(24:15):
He was a French cartographer, so this illustration is just
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. The beavers
themselves look largely accurate. There may be a little more
(24:39):
bear like, but the basic morphology is there. The main
problems here are that, first of all, there's like, you know,
one hundred beavers 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 beav that you see is standing up
(25:02):
in a bipedal posture with an armload of wood thrown
over his shoulder like a human being.
Speaker 3 (25:08):
Yeah yeah, like a Paul Bunyon carrying an axe.
Speaker 4 (25:12):
Yeah.
Speaker 2 (25:13):
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 3 (25:24):
I wonder is this one of the maps we looked
at in our Horror Vakae episodes where we were talking
about maps with excessive illustrations.
Speaker 2 (25:32):
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,
(25:53):
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
(26:13):
tool use.
Speaker 3 (26:15):
Yeah, Rob, I think you found one of these papers first,
and that's what started this whole thing. 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
(26:38):
the 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
(26:59):
of tool use, and there are different examples the 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
(27:22):
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
(27:43):
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
(28:04):
all 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 like a
function of the definition you lay out than a fundamentally
(28:25):
different type of activity itself than some other activity that
wouldn't quite fit this definition.
Speaker 2 (28:31):
Yeah, I mean, and sometimes we can almost get too
hung up, I think, on the on 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
(28:51):
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 yeah,
it seems like at times a lot of extra mental
(29:11):
gymnastics has to be utilized in order to even discuss it.
Speaker 3 (29:16):
So I'm not going to get super hung up on
definitions 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 like 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
(29:39):
older 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 the second.
But the observation is that a researcher named Georgio Pilleri
observes something interesting while studying two captive beavers at the
Burn Brain Anatomy Institute in nineteen eighty. So, the beavers
(30:02):
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 little holes, And
the beavers had been given a supply of sticks and
twigs to do what they wanted with, and for some reason,
(30:25):
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 for me to believe this
(30:46):
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 beaver
have like a sense for detecting gaps in dams and
plugging them, Like maybe they're good at sensing. My first
(31:07):
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 pipe or 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 and a dam if you're
(31:27):
diving near it. I thought, maybe they sensed 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 this documentary segment captured a scene
(31:51):
of beavers finding a leak in their dam and then
getting right to work retrieving wood, vegetation and clumps of
ediment 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 detect these leaks by hearing
(32:13):
the sound of trickling water, and when they do, they
begin repair work almost immediately. So 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 concrete enclosure in the eighties
make a lot more sense. So I decided to look
(32:36):
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 Arkele writing up summarizing the research
(32:57):
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 and you separated them from their
parents at birth, they would still build dams basically the
(33:19):
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 beavers didn't always build dams. In
environments with still water or only very gently moving water,
(33:43):
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 trigger for dam building, even
to the point of a discovery that I this was
the part I found most fascinating. If you put a
speaker in the beaver's enclosure and you played the sound
(34:07):
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 water sounds. They were trying to
plug the speaker to make it stop leaking.
Speaker 2 (34:24):
Oh my goodness.
Speaker 3 (34:26):
Wilson also found that if outflow pipes, so you had
a place where there was actually water leading away from
the 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
(34:47):
a damn there. 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
(35:08):
practices and the environmental effects thereof. And Kennedy says that
it can't just be about 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
(35:30):
damn construction, something that the beavers naturally detect that allows
them to know, Okay, this is about the right amount
of flow to try to dam up.
Speaker 2 (35:39):
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 3 (35:57):
Right, So the author of this article right now, it's quote,
the water in a beaver's habitat needs to be a
certain depth, for instance, to keep a food cash 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 this Goldilocks zone, an area of a
(36:20):
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 the overwhelming part of it is sound, but there
may be other cues as well, And so I don't know.
(36:43):
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
for children, all the like the most powerful drives in
(37:05):
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 or relationship to the environment.
Speaker 2 (37:22):
Wow wow, yeah, Like what would yeah, how would like
we can't help but extravolate that into like a 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 of of all naturally occurring waterfalls, or would they
(37:45):
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 3 (37:54):
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 2 (38:05):
That's the called adventure.
Speaker 3 (38:06):
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
(38:29):
Possible tool use by beaver's Castor 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 that's
(38:50):
Castor candidensis 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. Beavers
(39:15):
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
(39:37):
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
(39:59):
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 seemed impossible on further examination,
(40:22):
because 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
(40:43):
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.
Speaker 2 (40:52):
Okay, but the.
Speaker 3 (40:54):
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 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,
(41:16):
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
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?
(41:38):
The author says this would be probably to reduce foraging time.
So the longer you forage, number one, the more thermal
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. They were
(42:00):
trying to hustle as fast as they can whenever they're
out there cutting, and in this case, apparently using 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.
Speaker 2 (42:18):
All right, So they go like a little bit higher.
They just it's going to be less it's going to
be a narrower bit of wood to chew through.
Speaker 3 (42:26):
That's what I assumed. It didn't specify exactly why cutting
higher up was reduced foraging time. But that was my interpretation.
Speaker 2 (42:32):
I could be wrong, and that's why they potentially could
be using essentially a beaver ladder a beaver bit of scaffolding.
Speaker 3 (42:41):
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 2 (42:50):
Yeah. More mysteries related to and 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 of often in very rural situations,
far from human activity. They're probably doing it at night,
and they're spending as little time necessary doing it out
(43:11):
where other eyes could see them.
Speaker 3 (43:14):
Right, Okay. Second paper I came across alleging possible tool
use behaviors by beavers. 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
(43:36):
to 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
(44:00):
would include threat displays, trying to 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 a behavior that they call stick display, which
they interpreted as an agonistic display behavior. And what this
(44:25):
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 Rabi attached a picture for you to look at.
They had a photo of this. In this photo of
(44:47):
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 it's kind of like roaring posture.
But it's got a big old stick in its mouth,
and it's gripping the dick with its two four paws,
and the water is splashing all around. It's the stick,
I guess, rapidly dips in and out.
Speaker 2 (45:06):
It's impressive, and it's it's frankly a little intimidating. This
this beaver saying, behold, look at the at the feats
of strength I am capable of.
Speaker 3 (45:15):
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
and then use it in a different location or modify
the stick in any way.
Speaker 2 (45:36):
So, for instance, compare it to like human tool use
that we've discussed in the past. Rocks. This 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
(45:56):
hitting each other with the sticks. Allegedly, the hypothesis here
is that they're using them as a pure defensive display.
Speaker 3 (46:03):
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
(46:25):
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
(46:49):
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
(47:10):
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 beaver 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,
(47:34):
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 2 (47:55):
Quote.
Speaker 3 (47:56):
It was clear from our observations that one female beer
and one male Froda where 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.
Speaker 2 (48:16):
Two beavers Wow, go Froda.
Speaker 3 (48:19):
But the real champion is beer Get here. She's got
more than half of them just under her belt.
Speaker 2 (48:24):
Yeah yeah, I mean really, beer Get needs to get
get most of the credit here for Froda doing pretty
well as well.
Speaker 3 (48:30):
So they say. Stick displays happened almost exclusively at the
borders of beaver family group territory, and most displays appear
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
(48:54):
not necessarily generalizable to the total world population of these beavers.
It has not really been observed in beavers generally across
the full range, suggesting it may be specific to certain populations.
Speaker 2 (49:07):
Wow like even some like some sort of like localized
beaver culture.
Speaker 3 (49:11):
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
(49:33):
the of 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
(49:56):
with breeding. 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
(50:16):
to do this.
Speaker 2 (50:17):
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. 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 these fights.
(50:38):
These fights are just would be destructive. So instead, let's
just make sure that we're very clear about how everyone
feels about these these border scenarios, and 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 3 (50:55):
The neighbors are getting nosy, and Beer get 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,
Beer gat Man. I think we've got to be out
of time for part one of Beaver's here, right, but
there will be more.
Speaker 2 (51:13):
Yeah, in the next episode, we're gonna we're going to
get back to that idea, that that false idea of
beavers 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
(51:33):
we'll 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,
(51:54):
something 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 Stuff 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 wherever you get your podcasts. On Mondays
(52:17):
we do a listener mail episode. On Wednesdays we 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 going
to put out We're going to continue to experiment, experiment
with putting out omnibus episodes that may take up like
multiple related monster facts or artifacts and put them out
(52:39):
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 3 (52:52):
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 topic for
the future, or just to say hello, you can email
us at contact at stuff to Blow your Mind dot com.
Speaker 1 (53:13):
Stuff to Blow Your Mind is production of iHeartRadio. For
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or wherever you listen to your favorite shows.
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