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Morning in the rainforest of Panama.

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Capuchin monkeys are having
a rather wasteful breakfast.

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Inside these nuts, there's a kernel
that is very, very good eating,

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but it has such a hard shell,

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it's almost impossible to get
at the kernel inside...even...

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..if I hit it with a stone.

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Unbroken. So it's hard to believe,
but nonetheless true,

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that one animal
in these Central American forests

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can open these nuts with its bare teeth.

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But it's certainly not these monkeys.

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The best they can do is scrape off
the thin, fleshy coating.

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The nut itself, they simply throw away.

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But another animal is listening
for that telltale sound.

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(NUT DROPS)

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It's an agouti.

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(QUIETLY) The agouti is certainly
no bigger or stronger than a monkey,

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but it has the right tools
to deal with any nut...

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a pair of extremely strong
and sharp front teeth

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that can cut through even the toughest casing.

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They belong to a large, successful
group of mammals - the rodents.

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Rodents specialise
in being able to chisel their way

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through almost anything.

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What is so special about an agouti's
front teeth that enables them

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to cut a hole in the toughest of nuts?

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They have a layer of strong enamel,
but only on the front surface.

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Behind it, the body of the tooth
is made of a softer material: dentine.

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Gnawing wears down the dentine
faster than the enamel,

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leaving an edge as sharp as a chisel.

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Unlike the front teeth of other mammals,
a rodent's grow continuously,

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replacing what gets worn away.

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Armed with these formidable teeth,
rodents have become

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the most successful
and numerous of all mammals.

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The largest group are rats and mice.

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There are 1,300 species of those,

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and they're all accomplished stealers of seeds.

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Other rodents use their teeth
to cut up vegetation.

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Some even tackle wood.

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The rodent body is very versatile
and has evolved

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into an astonishing variety of shapes
and sizes to suit many different lifestyles.

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So you might find a rodent almost anywhere.

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Some are amazingly nimble
tree-climbers - the squirrels.

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They open cones and collect seeds
that few other mammals can reach.

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Abert's squirrels use their teeth
to nip off the tips of the branches

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of ponderosa pines,
where the bark is particularly nutritious.

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This is a valuable food reserve

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if the pine cones run out
during the long northern winters.

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Abert's squirrels
are such specialised feeders,

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they can only survive
where there are ponderosa pines.

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Most squirrels have more general tastes.

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High on their menus are often acorns.

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Oak trees produce a heavy crop
of acorns each autumn.

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Good news for squirrels like these greys.

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They need to eat a great deal
to fatten themselves up for winter.

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They must also bury some to eat
later on, when times get hard.

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For squirrels here in the woodlands
of the eastern US, in Virginia,

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things are not quite so simple.

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Here, there are two kind of oaks:

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red oaks and white oaks.
Their acorns are very similar.

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This is the acorn of a white oak,
and this a red oak.

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This one is slightly darker.

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But the acorns of the white oak
germinate almost immediately,

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using up their food supply.

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The red oaks, on the other hand,
don't germinate until next spring.

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The squirrels recognise the difference

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and treat them differently.

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When a squirrel finds a white acorn,
it eats it immediately,

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because otherwise it would soon germinate.

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On the other hand, red acorns
are almost always buried

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as a store for winter.

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Squirrels are colour blind,
so can't recognise the difference by sight.

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The smell tells them which should be eaten

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and which should be buried for later.

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In some years, the white oaks
produce their usual bonanza,

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while the red oaks provide hardly any at all.

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When this happens,
the squirrels change tactics.

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You might think it's tucking in
to a white acorn as usual,

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but, after only a quick nibble,
it takes it away and buries it.

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What's it up to?

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It's neatly cut away the tip,
beneath which lies the embryo of the seed.

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Once that has gone,
the acorn will never germinate,

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but its food store will remain fresh
all winter for the squirrel.

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So with dexterous paws to hold the acorn

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and sharp front teeth
to cut out the embryo,

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the squirrels get the best value

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out of these apparently well-protected nuts.

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Seed-producing plants grow everywhere,

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so, potentially, seed-eating rodents
can live everywhere, too.

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But there is one problem.

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All seeds are full of nutriment,
but most are very small,

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like these from these desert plants.

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You need about 500 of these
to make the food equivalent

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of a typical nut like an acorn.

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Rodents wanting to store the seeds
from these face a transport problem.

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It'd be impractical to carry them one by one

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as squirrels carry acorns.

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Here in California's Mojave Desert,
a rodent has solved that problem.

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Its burrows are all around me.

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Like most desert animals,
the creature in this hole

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usually doesn't come out
until dark, when it's cooler.

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If I scatter a few seeds around its entrance,

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maybe that will tempt him
to come out a little earlier.

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Well, as it happens, it didn't.

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It wasn't until later, when the moon was up,

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that the burrow's owner showed itself.

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A kangaroo rat.

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It can carry hundreds of seeds
in expandable cheek pouches.

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The pink toes poking out
are those of its back legs,

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which support its whole body.

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That's why it's called a kangaroo rat.

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Its front legs are hidden beneath its chin,

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shovelling seeds into its mouth.

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Normally, it has to travel quite a long way

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to find enough seeds to fill its pouches.

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Tonight, because of this supply,
its shopping bags

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are soon full enough
to take back to its burrow.

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There we are. It covers them over
with sand just to keep them safe.

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Its deep burrow is a relatively safe place.

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The rat sleeps here all day
and much of the night.

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Even so, the slightest suspicious
sound from outside will wake it.

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(WHOOSHING)

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A gopher snake crawls towards the burrow.
It might find its way inside.

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It had better be seen off.

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Foot stamping is the first warning.

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That seems to have no effect.

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Perhaps kicking sand in its face
will do the trick.

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The snake doesn't like that at all.

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Victory to the kangaroo rat.

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Seeds are not the only part
of a plant that is edible.

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Some rodents, like marmots
in the European Alps,

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eat the entire thing.

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And they fight over grazing rights.

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When they come out of their burrows
in late spring after their winter sleep,

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they set about re-establishing
their territorial boundaries.

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Calling and tail-flagging
are only the preliminaries.

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(SQUEAKS)

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If that doesn't work,
there's nothing for it but to go to battle.

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Senior males do most of the fighting,

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while their female partners guard
the family burrow and watch.

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When a male wins a scrap,
he marks the boundaries

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with scent from a gland on his cheek.

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Marmots form strong pair bonds,

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and the females usually only mate
with their one permanent partner.

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By late spring, a marmot family
consists of the adult pair

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with a few of last year's offspring,
all of them females.

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Last year's males have already
been chased away.

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Although daughters can stay,

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their mothers constantly beat them up,
particularly in spring.

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They're persecuted so severely that,
if any become pregnant, they abort.

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The reason for this merciless behaviour

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doesn't become apparent until later in the year.

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By mid-summer, relative peace
has come to the mountainside.

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This season's babies emerge
from the burrow for the first time.

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There are usually between four and six babies,

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and they immediately get down
to the important business of grazing.

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Alpine summers are short,
so marmots feed as fast as they can

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while they can.

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Incisors slice with ease through
the tough stalks of flowers and grasses.

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The babies put on weight rapidly
but, by the end of the summer,

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they still do not have fat reserves
to match those of their parents.

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In autumn,
the family start on their final harvest -

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hay to line the deep burrow
where they will sleep through the winter.

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By October, the weather has turned really cold.

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In the burrow,
the marmots' body temperature

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has dropped to two degrees centigrade.

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Their hearts are beating only two or three
times a minute. They're hibernating.

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Their fat reserves will have to last them

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until the following April.

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They snuggle together to minimise heat loss.

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Youngsters are in the middle of the pile.

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With less bodyweight, they can't let
their temperatures drop as low as the adults'.

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Thermal imaging shows
that a baby, glowing orange,

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is warmer than the adults, which show green.

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The burrow, which registers blue,
is well below freezing point.

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The adults couldn't keep
more than one litter warm.

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That is why the dominant female made sure
that none of her youngsters had babies.

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But hibernating isn't the only way
to survive the winter in the mountains.

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In North America, winters can be
just as severe as in the high Alps.

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Yet here, there's a rodent
that manages to find food

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throughout the winter months.

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It does so with an extremely ingenious device:

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a refrigerator - a pool of deep,
cold water like this.

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And over there is its builder and owner.

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00:18:15,647 --> 00:18:19,845
A beaver, one of the family
that lives here in this lake

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at the foot of the Teton Mountains
in Wyoming.

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00:18:27,967 --> 00:18:33,325
Beavers can get around on land,
but they're most at home in water,

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where their webbed hind feet
and large paddle-like tail

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make them powerful swimmers
above and below the surface.

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Beavers feed on all kinds of vegetation
and eat wood as well as leaves.

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00:19:03,127 --> 00:19:05,846
They're accomplished engineers.

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00:19:06,007 --> 00:19:10,398
This great pond is entirely their own creation.

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00:19:13,767 --> 00:19:19,558
Only a few years ago, this shallow
stream flowed down the valley,

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00:19:19,727 --> 00:19:23,925
then a family of beavers moved in
and built a dam.

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00:19:27,687 --> 00:19:30,884
The main body of it is built of boulders.

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00:19:31,047 --> 00:19:34,517
On the downstream side,
it's been lined with logs,

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00:19:34,687 --> 00:19:36,837
some big and quite heavy.

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00:19:37,007 --> 00:19:41,205
On this side, it's been packed
with mud and vegetation.

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00:19:41,367 --> 00:19:45,963
It's been built so accurately
that it is, to within a few inches,

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00:19:46,127 --> 00:19:50,598
horizontal across its entire length
of about 150 yards

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00:19:50,767 --> 00:19:53,235
from one side to the other.

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00:19:53,407 --> 00:19:58,401
The lake it's created stretches
upstream for almost a mile.

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00:20:07,607 --> 00:20:12,601
So important is their dam to them
that, if they detect any leak,

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00:20:12,767 --> 00:20:18,364
usually by hearing trickling water,
they start repair work immediately.

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00:20:33,287 --> 00:20:36,484
Mud is needed as well as logs.

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00:20:49,487 --> 00:20:54,641
The repair team will labour away
until the leak is fully repaired.

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00:20:58,687 --> 00:21:03,886
Maintaining the water at a high level
brings beavers several advantages.

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00:21:04,047 --> 00:21:09,644
It floods the surrounding woodlands
and so enables them to swim safely

207
00:21:09,807 --> 00:21:12,605
to their main source of food.

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00:21:18,287 --> 00:21:22,485
They increase the distance
they can swim by digging channels

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00:21:22,647 --> 00:21:26,435
that lead into the very heart of the woodland.

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00:21:34,487 --> 00:21:37,206
Here they can use their sharp incisors

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00:21:37,367 --> 00:21:41,360
to strip off the bark
from a fallen tree and nibble at it,

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00:21:41,527 --> 00:21:44,917
while being close enough
to water to slip away

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00:21:45,087 --> 00:21:48,557
should a bear or a mountain lion turn up.

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00:22:18,607 --> 00:22:23,397
Their network of channels
enables them to ferry whole branches

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00:22:23,567 --> 00:22:25,558
back to their pond.

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00:22:42,487 --> 00:22:44,876
Where the water is deepest,

217
00:22:45,047 --> 00:22:49,438
they dive down and push
each branch firmly into the mud

218
00:22:49,607 --> 00:22:51,598
at the bottom.

219
00:22:52,607 --> 00:22:56,646
This is the beavers' fridge,
where vegetation will keep fresh

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00:22:56,807 --> 00:23:01,403
through the long winter
when the pond is covered with ice.

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00:23:09,207 --> 00:23:12,199
Stocking the fridge takes a lot of work.

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00:23:12,367 --> 00:23:15,564
The beavers are at their busiest in autumn.

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00:24:07,247 --> 00:24:12,480
At one side of the lake stands their lodge,
a fortress of branches and boulders

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00:24:12,647 --> 00:24:17,004
that's so strong that not even
a bear could break into it.

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00:24:17,247 --> 00:24:20,557
The only entrance
is through underwater tunnels.

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00:24:20,727 --> 00:24:25,323
The beavers take refuge here
whenever they are alarmed.

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00:24:35,207 --> 00:24:38,005
That was a warning signal

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00:24:38,167 --> 00:24:41,557
to say that danger was around,
that's to say - me.

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00:24:41,727 --> 00:24:45,322
Now I may not see the beavers for some time.

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00:24:45,487 --> 00:24:50,607
They can stay underwater for five
minutes, up to 15 if they need to.

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00:24:50,767 --> 00:24:53,759
They can get back to their lodge

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00:24:53,927 --> 00:24:57,636
without putting their head
above the surface for a second.

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00:25:01,807 --> 00:25:05,800
Most lodges have at least
two different entrances.

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00:25:13,727 --> 00:25:15,957
By October, winter is underway.

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00:25:16,127 --> 00:25:20,917
Marmots would now be hibernating,
but the beavers are still active,

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00:25:21,087 --> 00:25:25,399
and will remain that way
throughout the winter.

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00:25:27,127 --> 00:25:29,846
Even when the pond ices over,

238
00:25:30,007 --> 00:25:35,445
they can still swim under the ice
to get back and forth to their lodge.

239
00:25:36,447 --> 00:25:40,042
No one knew what went on
inside the lodge in winter,

240
00:25:40,207 --> 00:25:44,678
so when the beavers were away,
we installed infrared cameras

241
00:25:44,847 --> 00:25:47,236
in order to find out.

242
00:25:51,327 --> 00:25:56,685
A branch from the fridge is brought back
for the whole family to feed on.

243
00:26:02,247 --> 00:26:04,238
And another.

244
00:26:08,447 --> 00:26:11,837
No wonder they don't need to hibernate.

245
00:26:12,007 --> 00:26:15,204
The lodge is warm and safe even in mid-winter.

246
00:26:15,367 --> 00:26:19,565
The only sign of activity
in the snug home beneath the snow

247
00:26:19,727 --> 00:26:23,436
is hot air rising from the vent at the top.

248
00:26:31,127 --> 00:26:35,518
Inside, our cameras catch a glimpse
of what, at first sight,

249
00:26:35,687 --> 00:26:38,679
looks like a very small beaver.

250
00:26:40,407 --> 00:26:44,878
It's a muskrat.
There are a pair of them in here.

251
00:26:45,047 --> 00:26:47,766
This is a new observation.

252
00:26:48,767 --> 00:26:51,565
Do the beavers know, in the dark,

253
00:26:51,727 --> 00:26:54,685
that there are strangers among them?

254
00:27:00,487 --> 00:27:05,561
The muskrats regularly left
the lodge to forage under the ice.

255
00:27:07,247 --> 00:27:13,243
On several occasions, they returned
a few minutes later with fresh reeds.

256
00:27:14,687 --> 00:27:16,996
Perhaps they're paying rent

257
00:27:17,167 --> 00:27:20,955
by regularly providing fresh bedding
for the lodge.

258
00:27:31,207 --> 00:27:33,926
Maybe that is why the beavers accept them

259
00:27:34,087 --> 00:27:37,079
and even allow them to share their food.

260
00:27:49,327 --> 00:27:54,526
Our infrared lights, however,
are no longer welcome, it seems.

261
00:27:57,407 --> 00:28:00,797
A lodge makes a safe home for a beaver.

262
00:28:00,967 --> 00:28:05,518
Other rodents defend themselves more actively,
and one is positively dangerous.

263
00:28:08,727 --> 00:28:12,686
Darkness provides
one of the best forms of defence,

264
00:28:12,847 --> 00:28:15,315
and it's very dark right now.

265
00:28:15,487 --> 00:28:18,877
The only reason you can see me

266
00:28:19,047 --> 00:28:22,278
is that we're using a starlight camera.

267
00:28:22,447 --> 00:28:26,918
Many rodents only come out
under cover of darkness.

268
00:28:27,087 --> 00:28:32,878
That applies even to one of the most
ferocious, well-armed of all rodents.

269
00:28:33,047 --> 00:28:36,642
I think there could be one around here.

270
00:28:53,287 --> 00:28:58,680
(QUIETLY)
And there it is, and what a formidable sight -

271
00:28:58,847 --> 00:29:01,839
an African crested porcupine.

272
00:29:02,847 --> 00:29:08,240
It seems to have found something
to eat underneath that spiny bush.

273
00:29:09,367 --> 00:29:13,155
Most of the time,
those quills would be lying flat.

274
00:29:13,327 --> 00:29:19,323
The fact they're half erect is a sign
that it's not happy that I'm so close.

275
00:29:31,367 --> 00:29:34,962
Those long quills are very sharp,

276
00:29:35,127 --> 00:29:38,915
and I'm quite sure
it knows how to use them.

277
00:29:40,607 --> 00:29:46,079
It's turning its back on me, but that's
not because it's about to run away.

278
00:29:46,247 --> 00:29:51,526
If it gets really angry, it will attack
by suddenly sprinting backwards.

279
00:29:52,567 --> 00:29:54,558
And it's off.

280
00:29:56,207 --> 00:29:59,995
That's not the sort of thing
you want to stumble into

281
00:30:00,167 --> 00:30:02,886
in the middle of the African night.

282
00:30:09,647 --> 00:30:14,118
They feed mainly on roots and tubers,
but they're big animals

283
00:30:14,287 --> 00:30:19,281
and to find enough to eat, they travel
long distances across open savannah.

284
00:30:19,447 --> 00:30:24,965
And that means they have to be
prepared to take on all comers.

285
00:30:28,847 --> 00:30:33,125
This young leopard has probably
never been close to a porcupine.

286
00:30:33,287 --> 00:30:37,200
He doesn't realise it would be
dangerous to interfere with it.

287
00:30:48,487 --> 00:30:53,959
The porcupine seems to have
total confidence in its armoury.

288
00:30:57,087 --> 00:31:03,083
If it's not careful, that naive leopard
will end up with a face full of quills.

289
00:31:31,287 --> 00:31:35,121
And the porcupine goes back
to digging for food.

290
00:31:35,287 --> 00:31:37,755
There's confidence for you.

291
00:31:41,287 --> 00:31:45,166
Belding's ground squirrels
don't have that kind of nerve.

292
00:31:45,327 --> 00:31:49,400
They live in California and burrow
close to one another,

293
00:31:49,567 --> 00:31:54,960
so there's always plenty of watchers
to give warning of any danger.

294
00:31:55,127 --> 00:32:00,485
This is important during the summer
when there are babies about.

295
00:32:05,967 --> 00:32:09,323
There are always at least
one or two adults on watch nearby,

296
00:32:09,487 --> 00:32:12,877
so that the young can feed in relative safety.

297
00:32:13,047 --> 00:32:17,518
Only the females care for the young.
They're nearly all related.

298
00:32:17,687 --> 00:32:22,078
Mothers, sisters and daughters
look after nephews and nieces

299
00:32:22,247 --> 00:32:26,035
as carefully as they do their own offspring.

300
00:32:35,167 --> 00:32:39,763
When a guard spots a potential predator
such as an eagle,

301
00:32:39,927 --> 00:32:41,963
she sounds a warning.

302
00:32:42,967 --> 00:32:47,438
Those trills mean ''Danger seen,
but evasive action not needed''.

303
00:32:47,607 --> 00:32:49,199
(SQUEAKS)

304
00:32:52,087 --> 00:32:54,760
A bobcat. Another warning.

305
00:32:54,927 --> 00:32:57,680
(SQUEAKS)

306
00:33:01,527 --> 00:33:05,156
Each female is trying to keep the enemy in view

307
00:33:05,327 --> 00:33:08,637
so it doesn't catch them by surprise.

308
00:33:12,847 --> 00:33:18,080
The bobcat is getting closer.
Now the warning will change.

309
00:33:20,087 --> 00:33:23,079
That means ''Run for it!''

310
00:33:46,287 --> 00:33:50,166
Another small rodent
that would make a tasty meal

311
00:33:50,327 --> 00:33:53,125
lives here in the arid north of Kenya.

312
00:33:53,287 --> 00:33:57,075
There are dozens within a few yards of me.

313
00:33:57,807 --> 00:34:01,402
But this one has adopted
the safest strategy of all -

314
00:34:01,567 --> 00:34:05,606
to spend nearly all of its time
below ground.

315
00:34:11,687 --> 00:34:16,044
And this is all that most people
will ever see of it.

316
00:34:16,207 --> 00:34:18,357
A naked mole rat.

317
00:34:20,767 --> 00:34:23,235
They use their teeth for digging.

318
00:34:23,407 --> 00:34:26,399
Uniquely, their lips close behind the teeth.

319
00:34:26,567 --> 00:34:30,719
That stops earth getting into their mouth.

320
00:34:30,887 --> 00:34:34,641
With this superb equipment,
they dig a network of tunnels

321
00:34:34,807 --> 00:34:36,798
radiating from a central chamber

322
00:34:36,967 --> 00:34:40,801
where the colony gathers
and the babies are kept.

323
00:34:40,967 --> 00:34:46,360
All the babies are produced by one
big female, the colony's founder.

324
00:34:46,527 --> 00:34:49,644
The rest, and there may be as many as 100,

325
00:34:49,807 --> 00:34:52,844
are her children and none will breed here

326
00:34:53,007 --> 00:34:55,760
as long as their mother is alive.

327
00:34:55,927 --> 00:35:00,921
Their job is to tunnel away,
searching for tubers and roots.

328
00:35:01,087 --> 00:35:04,796
By doing that, they create
a vast network of tunnels

329
00:35:04,967 --> 00:35:09,358
stretching for hundreds of yards
under the African plains.

330
00:35:09,527 --> 00:35:12,837
Above ground, it's hard to find any plants

331
00:35:13,007 --> 00:35:17,000
that might provide mole rats
with an underground meal.

332
00:35:17,167 --> 00:35:21,957
Mostly there's just dry grass
and the odd acacia seedling.

333
00:35:26,007 --> 00:35:30,603
When mole rats meet, they assess
one another's status with a sniff.

334
00:35:30,767 --> 00:35:35,158
The junior one has to pass
underneath the senior one.

335
00:35:45,287 --> 00:35:50,998
Being blind, they're just as happy
travelling backwards as forwards.

336
00:35:55,967 --> 00:36:00,757
I'm about a quarter of a mile
from where I saw the mole rats digging.

337
00:36:00,927 --> 00:36:03,919
This is the plant I've been looking for.

338
00:36:04,087 --> 00:36:08,080
Now, in the dry season,
it's nothing more than a curly stem

339
00:36:08,247 --> 00:36:10,238
and a few withered leaves,

340
00:36:10,407 --> 00:36:14,400
but beneath the ground here, there's treasure.

341
00:36:31,167 --> 00:36:33,158
And here it is.

342
00:36:33,327 --> 00:36:37,525
Tubers like this are few
and far between around here.

343
00:36:37,687 --> 00:36:43,956
It's a matter of pure chance
as to whether the mole rats bump into one.

344
00:36:44,287 --> 00:36:48,280
So mole rat colonies must have
several dozen workers,

345
00:36:48,447 --> 00:36:50,642
but if they do find one like this,

346
00:36:50,807 --> 00:36:54,880
it could sustain the colony
for two or three weeks.

347
00:37:07,487 --> 00:37:11,480
Their sharp incisors cut into the tough tuber.

348
00:37:11,647 --> 00:37:15,640
Some of it, the lucky finders
will eat on the spot.

349
00:37:20,847 --> 00:37:25,967
They drag back lumps to the central chamber
to be shared by the colony.

350
00:37:30,047 --> 00:37:34,086
This arrangement, where workers
are sterile and labour away

351
00:37:34,247 --> 00:37:39,037
to support their mother, is also the basis
for the colonies of bees and ants.

352
00:37:39,207 --> 00:37:42,916
But naked mole rats are the only mammals

353
00:37:43,087 --> 00:37:45,476
that have adopted it.

354
00:37:53,647 --> 00:37:57,845
Although those long chiselled front teeth
are rodent hallmarks,

355
00:37:58,007 --> 00:38:03,240
rodents are also famous
for reproducing with extraordinary rapidity.

356
00:38:03,407 --> 00:38:05,398
Mole rats certainly do that,

357
00:38:05,567 --> 00:38:11,437
but the most prolific members
of the whole family are the mice.

358
00:38:14,447 --> 00:38:18,440
Tiny harvest mice produce babies
in a carefully woven nest

359
00:38:18,607 --> 00:38:22,600
among the stems of reeds or tall grasses.

360
00:38:30,847 --> 00:38:33,441
Litters of up to eight babies

361
00:38:33,647 --> 00:38:37,959
fed on their mother's rich milk
mature in only a few weeks.

362
00:38:42,687 --> 00:38:48,239
Each pair can produce three litters,
nearly 30 young, in a single season,

363
00:38:48,407 --> 00:38:53,197
provided that the adults can find
enough seeds to feed on.

364
00:39:02,727 --> 00:39:06,117
Youngsters leave the nest at only two weeks old

365
00:39:06,287 --> 00:39:08,960
and start searching for food.

366
00:39:14,687 --> 00:39:19,681
To begin with, they're not nearly
as agile as their parents.

367
00:39:32,967 --> 00:39:38,166
In fact, sometimes they seem quite unsure
about where they can safely tread.

368
00:39:49,207 --> 00:39:52,040
These little creatures
have lived in our cornfields,

369
00:39:52,207 --> 00:39:56,678
taking a small proportion
of our crops, ever since farming began.

370
00:39:56,847 --> 00:39:59,839
Usually they were only visible
when crops were gathered,

371
00:40:00,007 --> 00:40:03,317
which is why they were called harvest mice.

372
00:40:05,047 --> 00:40:09,040
Even after harvesting,
there's still the spilled grain to feed on.

373
00:40:09,207 --> 00:40:14,201
In the vast wheat belt of Australia,
a different mouse takes advantage

374
00:40:14,367 --> 00:40:17,040
of this plentiful supply of food,

375
00:40:17,207 --> 00:40:21,200
digging burrows along the edge
of the sandy fields.

376
00:40:25,127 --> 00:40:29,837
These are common house mice,
the most prolific breeders of all.

377
00:40:30,007 --> 00:40:34,717
Each new female can become
pregnant at only five weeks old.

378
00:40:34,887 --> 00:40:40,484
If there's a good supply of grain,
she will breed every month or so.

379
00:40:43,287 --> 00:40:46,996
In some years, if all the grain gets eaten,

380
00:40:47,167 --> 00:40:51,240
the mice head for the nearest
farm buildings to look for food.

381
00:40:54,807 --> 00:41:00,996
As they leave the stripped fields,
it's clear how many have been feasting.

382
00:41:11,487 --> 00:41:17,084
Once they do find their way into a grain store,
they become a plague.

383
00:41:34,567 --> 00:41:40,802
When they finish the grain, their numbers
will fall as quickly as they rose.

384
00:41:44,247 --> 00:41:49,446
On the flat, windswept plains of Patagonia
lives a much larger rodent,

385
00:41:49,607 --> 00:41:52,075
with a more leisured system of breeding.

386
00:41:52,247 --> 00:41:54,681
These are Patagonian cavies or maras.

387
00:41:54,847 --> 00:41:57,998
Although this litter appears very large,

388
00:41:58,167 --> 00:42:02,718
you can see all the young
are of slightly different ages.

389
00:42:02,887 --> 00:42:06,880
That is because they belong to different parents.

390
00:42:08,807 --> 00:42:13,597
Only one pair is on guard.
The others are away grazing.

391
00:42:13,767 --> 00:42:16,327
This is a communal creche.

392
00:42:16,487 --> 00:42:20,685
It's based around a hole often dug
initially by burrowing owls.

393
00:42:20,847 --> 00:42:24,044
The maras have simply enlarged it.

394
00:42:27,807 --> 00:42:30,799
The adults guard each other's offspring,

395
00:42:30,967 --> 00:42:35,757
but each female will only give
her milk to her own babies.

396
00:42:38,687 --> 00:42:44,557
The others must wait until their own mother
arrives to take her turn as guard.

397
00:42:47,727 --> 00:42:49,718
Here comes the next pair.

398
00:42:49,887 --> 00:42:53,675
Adults are not always related,
so the changing of the guard

399
00:42:53,847 --> 00:42:57,123
can be a somewhat tense business.

400
00:43:10,407 --> 00:43:15,800
The mara couples behave as though
they were rivals rather than friends.

401
00:43:34,567 --> 00:43:39,846
Galloping around, grazing,
the maras have evolved long legs.

402
00:43:40,007 --> 00:43:42,646
They look more like antelopes.

403
00:43:42,807 --> 00:43:46,197
That may be why they're not good at digging

404
00:43:46,367 --> 00:43:50,360
and prefer to steal holes
from the burrowing owls.

405
00:43:52,327 --> 00:43:56,320
A plover warns of approaching danger.

406
00:43:56,487 --> 00:43:59,081
(PLOVER CHIRRUPS)

407
00:44:02,367 --> 00:44:06,599
The babies, thanks to the owls,
have a hole to go to.

408
00:44:08,687 --> 00:44:13,044
It's not big enough for the adults.
All they can do is run.

409
00:44:27,487 --> 00:44:33,403
There is yet another kind of rodent
that gather in vast numbers to graze.

410
00:44:45,847 --> 00:44:49,442
They remind one of the huge herds you see

411
00:44:49,607 --> 00:44:52,405
on the savannahs of East Africa.

412
00:44:53,287 --> 00:44:55,482
But we're in South America,

413
00:44:55,647 --> 00:44:59,435
and these are not wildebeest or antelope.

414
00:44:59,607 --> 00:45:04,203
These are the biggest rodents
in the world: capybara.

415
00:45:08,487 --> 00:45:12,275
Capybara are, like mara, related to guinea pigs,

416
00:45:12,447 --> 00:45:18,636
but these are real giants that use
their rodent teeth to crop grass,

417
00:45:18,807 --> 00:45:20,843
lots of it.

418
00:45:22,607 --> 00:45:24,598
(SQUEAKING BARK)

419
00:45:26,407 --> 00:45:31,401
When they want to, they can gallop
as fast as a small horse.

420
00:45:35,807 --> 00:45:40,801
Although they're very agile on land,
they are equally at home in water.

421
00:46:15,527 --> 00:46:20,521
Within these herds, each family
sticks together in groups of 20 or so.

422
00:46:20,687 --> 00:46:25,681
There are mothers and daughters,
children and grandchildren.

423
00:46:27,687 --> 00:46:32,681
And just one large, dominant male.
That's him at the back.

424
00:46:32,847 --> 00:46:37,637
He marks his territory with scent
from a gland on the top of his nose.

425
00:46:46,447 --> 00:46:52,044
And he will chase off any rival males
that venture too close to his family,

426
00:46:52,207 --> 00:46:54,926
particularly to his females.

427
00:47:19,687 --> 00:47:23,077
Capybara will graze out on the dry savannahs,

428
00:47:23,247 --> 00:47:26,842
but they're most at home in the water.

429
00:47:27,007 --> 00:47:31,205
They have oily, water-resistant fur,
partially webbed feet,

430
00:47:31,367 --> 00:47:35,440
and their eyes and nostrils
are on the top of their heads.

431
00:47:35,607 --> 00:47:40,237
Almost completely submerged,
they can hear, see, and smell

432
00:47:40,407 --> 00:47:43,399
what is happening on dry land nearby.

433
00:47:43,567 --> 00:47:47,958
Even the male's scent gland,
which other rodents carry on their cheeks,

434
00:47:48,127 --> 00:47:52,166
has migrated up to the top of his nose.

435
00:47:53,087 --> 00:47:56,284
During the rainy seasons, the plains flood.

436
00:47:56,447 --> 00:47:59,166
The capybara are in their element.

437
00:48:00,207 --> 00:48:04,200
If maras are the South American
equivalent of antelope,

438
00:48:04,367 --> 00:48:08,804
these surely are the rodent's
version of hippopotamus.

439
00:48:08,967 --> 00:48:13,518
Rodents truly are
the most adaptable of mammals.