Koalas: When Stupidity is a Survival Strategy

published on July 2, 2020



home to some of the world's most

dangerous venomous species

both on land and under water

and high up in the trees lives an animal

that consumes so many

toxins that it has few natural predators

the koala

hi i'm danielle dufoe and you're

watching animal logic

today we're in great outway national

park and we're on the lookout

for koalas

found along the eastern coast and parts

of southern australia

the koala is the species of marsupial

best known for its chill attitude

cuddly appearance and teeny tiny brain


today we're going for a hike along

kennett river

and it's well known for its population

of koalas

just off the great ocean road the atway

coast is

prime koala territory


only a few dozen meters in land from the

stunning cliffs and beaches of the coast

the giant eucalyptus trees tower over

this mountainous terrain

growing upwards of 130 meters tall

these eucalyptus trees serve as the

perfect home

for australia's biggest chillers

we're really hoping that we might catch

a few today just not too sure yet about

how high we have to look up

some of these trees are enormous


a sure sign that we're in the right

place i just found a bunch

of koala scat i mean i might be in the

danger zone of uh

having some fall down on me too


guys this is insane we've been hiking

for just a couple minutes

and already oh i don't know if you can

see it way up there

in this tree right where i'm pointing

there's a koala

high up in the tree canopy we've caught

a koala red-handed

munching away on his favorite meal

we having a snack up there

koalas are not good fighters they're not

good runners and

they're not good showboaters if they had

to compete with other animals

they would lose in every category

lucky for them they are unique in the

animal world

and face zero competition why

well it's because their food is toxic

they're one of the only species that can


on eucalypt leaves alone and eucalyptus

leaves are super toxic

consuming more than just 35 milliliters

of eucalyptus oil

can be fatal to humans

koalas have guts of steel

they're able to digest toxic eucalyptus

thanks to a specialized gut bacteria

that they get from their mothers

when they're close to leaving the pouch

the mothers will feed their joey's pep

a specialized form of feces that

contains the bacteria

necessary to break down the toxins in


not only is eucalyptus toxic but it's

also not very nutritious

and so koalas need to eat a lot of it

they can eat up to 500 grams every

single day but it doesn't give them much

energy so they're not

very excited creatures


they actually sleep for up to 22 hours a


and a lot of that time is spent

digesting all that food

they have an elongated digestive tract

in order to process such

large amounts of low energy food the


where most of the necessary gut bacteria

is located

can be up to two meters long the largest

relative to body size of

any animal the eucalyptus can stain the

cecum for over 100 hours

fermenting and breaking down toxins with

their specialized digestive enzymes

koalas actually obtain most of the

moisture they need from the eucalyptus


females who are a little bit smaller

usually tend to depend entirely on their


to obtain the water they need to survive

males are a little bit larger and

especially in breeding season

they'll seek out other sources of water

for the most part it's all

all in the package of one leaf

if almost exclusively eating a toxic

leaf wasn't enough

koalas are quite particular about which

of those leaves they'll eat


australia has hundreds of species of

eucalyptus tree

when it comes to choosing food and

refuge koalas are actually very very


about what trees and what species

they're going to use

a lot of that different flavor depends

on what kind of soil it's growing on a

richer soil will taste better to them

they tend to dislike eucalyptus trees

that are growing in poor soil

koalas are so adapted to the specific

strain of eucalyptus they like

that often once they've eaten all the

leaves that they like in their range

they'll simply give up and starve to

death unable to digest a new type of


the other consequence of their diet is

their teeny tiny brains

koalas have one of the smallest brain to

body size ratios in the mammalian world

but don't hold it against them this

might be an adaptation for life with a


calorie deficient diet big brains are

very energetically expensive

and being a dumb dumb means you have to

eat less

but the biggest advantage they get from

having a toxic diet

is not only do they have zero

cross-species competition for their food


but they have almost no natural


they're pretty much the only animal that

does feed on eucalyptus which is

considered to be

poisonous for just about every other

animal except for these guys

they end up taking a lot of those toxins

into their own tissues

and end up tasting pretty terrible

but their gut and brain aren't their

only evolutionary tools for a life in

eucalyptus trees

koalas like the one behind me have super

well adapted dentition

that's designed to help them clip and

pinch off

all those leaves and then grind them in

their back molars

koalas are perfectly adapted for life in

the trees

and they have one specialized adaptation

that not only helps them sleep without


but makes them amazing climbers as well

their hands

he's got some very impressive claws

there which

help him hang on to branches and climb


look at that he's got he's got quite a

good grasp on there

i'm impressed


not only do they have really great claws

for gripping onto branches

but they have almost like two functional


so they can grip around a branch and

climb really really efficiently

they're quite amazing spending their

lives sitting in the trees

they have one clever adaptation that

makes their lives a little bit more


along the base of their spine they have

a cartilaginous pad

that kind of creates a buffer and a

little bit of protection for wedging

itself between

between tree branches and

being able to sit like this comfortably

all day long

but all those adaptations are useless if

they stand out

okay there's a koala up here somewhere

but i need to try and

find it koalas are really hard to see

because they blend in so well with these

stripped bare trees they're about the

same color as the bark

oh there he is he's way at the top up


i see him

he's scratching himself

if you do happen to see a koala in the


just don't get too close you might get


oh and don't stand under the koala

you might get an accidental shower

koalas differ in size depending on

location and sex

in the south of australia they're almost

twice as large as koalas from the north

you can tell the males apart from the

females mostly by size the males get

quite a bit bigger and burlier

the males are always larger than the

females and have a broader face

and a chest gland that they use to mark


one thing that really sets apart male

koalas from female koalas

other than the obvious is that they have

scent glands

in their chest you might be able to see

right between

his pectoral muscles there's a little

patch of exposed skin

where he secretes his scent and

that's used for marking territory and

these boys are very territorial

males will hold territory of around

three hectares

and they defend their territories quite


they'll put up quite a fight against

other male koalas

they are in fact quite muscular animals

despite looking kind of chunky

it's all fur and muscle

in 2019 australia had the hottest summer

on record

and the resulting bushfires were

devastating to the koala population

across the country fortunately

the numbers lost during the bushfires

turned out to be much lower than


and reports of them being functionally

extinct in the wild

were exaggerated

unfortunately koala populations have

been in decline for years

and in just the last three generations

of koalas

their numbers have declined by 28

they are a protected species but much of

their territory

isn't habitat degradation fragmentation

and climate change exacerbating natural

forest fires are their biggest threats

as their continent continues to warm the

days for australia's cuddliest marsupial

may be numbered


we loved spending time in the eucalyptus

forest and it would have been so

fun to look at koalas from up close our

friends at nature on pbs

are getting even closer to the action in

their new miniseries

spy in the wild 2 in this sequel to the

popular spy in the wild series

the team introduces more than 50

incredibly realistic spy cameras

shaped as hummingbirds gorillas and even

turtle eggs to allow them to record

nature as you've never seen it before

each episode explores a different region

of the world

my favorite episode so far transports

viewers to australia

where a spy koala cam is accepted by

other koalas

and films breeding behaviors up close

and personal

nature spy in the wild 2 is streaming

right now

at pbsorg spy in the wild with new

episodes airing wednesday nights at 8

eastern time

7 central on pbs through may 20th

be sure to stream all the episodes on

the pbs video app

so that you don't miss a single species

what should i talk about next please let

me know in the comments and be sure to

subscribe for new episodes of animal

logic every week

thanks for watching

oh this one's this one's peeing

as one does

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