We human beings are
very latecomers to the skies,
and although we might think
that we're now pretty good at it,
the natural world, with the help of
several million years of evolution,
has produced a dazzling range
of aeronauts whose talents
are far beyond ours.
The story of how animals managed
to colonise the air is truly astonishing.
First into the skies were insects.
They initially had two pairs of wings
which in due course,
were modified in many different ways.
But after having had the skies to
themselves for about 100 million years,
a new group of animals took to the air:
Vertebrates, creatures with backbones.
They faced a different challenge,
for their bodies
were much bigger and heavier.
But eventually they evolved
several ways of solving that problem.
We will travel the globe
to trace the details
of the extraordinary skills,
of the backbone flyers.
This is Borneo.
And here there are still
great tracts of pristine rainforest,
forest that is wonderfully rich
in animals of all kinds.
I am being winched-up
into one of the tallest trees here,
in search of a creature
that can give us a hint,
of how backboned animals
first took to the air.
Hidden among these leaves, of this fern,
high up here, in the canopy,
is a very remarkable, little frog.
It's a Harlequin Tree Frog,
and it's a very, very good climber.
It spends most of its life up here,
clambering around in the branches.
Here it's away from
the numerous predators there are
that might attack it
down on the forest floor.
But if in fact, a predator
were able to get up here, to hunt it,
a snake perhaps, well the Tree Frog
has a remarkable trick for defence:
It glides.
It has membranes between
greatly elongated toes,
so that each foot becomes a parachute
which slows the frog's descent,
and so enables it to make
a relatively safe landing.
The vertebrates made their first foreys
into the air around 260 million years ago,
and it's very likely that some
of these pioneers used skinny membranes
to control their falls, in much the
same way as this little frog does.
It has to be said, that it's not
a very good aerial navigator,
it seems as though it just jumps
and hopes for the best.
But there are animals up here,
that glide around from tree to tree,
which are very good navigators indeed,
so good in fact, that they can go
from one tree to another,
and never go down to the ground
in their entire lives.
One of them is
a little lizard called Draco.
Each male has his own little territory
in the branches,
and tries to attract females
and warn off rivals,
by flashing his dewlap.
He also spread coloured flaps
of skin from his flanks,
that when fully extended,
do more or less the same thing.
But there are predators
among the branches.
Snakes also live up here,
and they hunt lizards.
But Draco's side flaps
now serve another purpose.
He uses them to glide, by hidging forward
his specially elongated ribs.
And he is so skilled in the air,
that he can steer and land
on the trunk of his choice.
So, if you live up in the branches,
it's less laborious,
and indeed safer, to travel by air,
than to come down to the ground.
But if you want to be a true flyer,
you have to be able to fly
not only downwards but upwards,
you have to have powered flight.
This is another reptile,
and one with even
greater flying abilities
than that little gliding lizard.
Today, sadly, it's extinct.
This is Dimorphodon.
We can deduce from its fossils
that it had the muscles
needed to beat its wings,
and computer imagery can show
us what it must have looked like.
Dimorphodon was one
of the first large animals
ever to travel by air,
200 million years ago.
It belonged to a group called
the Pterosaurs, the winged reptiles.
It was probably a forest dweller
and a descendant of a tree living glider.
This gliding ancestor might have
had wings like those of Draco's
that were made of skin,
and perhaps extended
from its fingers down to its ankles.
But Pterosaurs had evolved larger wings
with a hugely elongated fourth finger.
The wing membrane
was strengthened internally,
by thin rods of a stiffer tissue.
They were muscles fibres too,
that enabled it to modify
its contours as it flew.
Looking at the wings in section,
reveals a secret of their efficiency.
They have a rounded front edge
and a sharp back edge,
a shape known as an aerofoil.
It works by forcing the air
flowing above the wing, to speed up.
This faster air has a lower pressure,
and the wing is sucked upwards.
The larger the surface area of the wing,
the greater lift it can produce.
So it seem certain that Pterosaurs
were very competent flyers.
And judging from their teeth,
it seems likely, that many fed
on the great variety of insects
that had preceded them into the air.
Insects have had the skies to themselves
for around 100 million years.
Now, bigger creatures had arrived.
Reptiles.
The Pterosaur design for flight
proved hugely successful.
They used their new powers
to spread beyond the forests,
and colonize whole new environments.
A great number of them
lived and fed near water.
We know this because
fossils of many species
occur in rocks that were once mud
at the bottom of lakes and shallow seas.
This one shows the skeleton of an animal
that 150 million years ago,
fell to the bottom of a shallow lagoon.
This is its head, here's its backbone,
tail, hind legs,
and here, stretching
from these long extended
finger-bones, are its wings.
And this fossil is
particularly remarkable,
because it shows
an impression of the membrane
in extraordinary detail.
You can see every little tiny fold.
You can judge how an animal lived,
by its skull.
And this one, had these long jaws,
with forward pointing teeth,
and we think that this indicates
that it lived by skimming
across the surface of the lagoon,
and snatching up fish
which impaled on those teeth.
This, very different one,
it's just the head.
As you can see it has very long jaws,
and at the tip of the lower one is
this little tuft of very fine filaments.
And we know from other specimens
that those filaments
originally stretched
right along the length of the jaw.
This bristely fringe enabled
the creature to filter-feed,
taking in a beak full of water,
expelling it through the bristles
with the beak half closed,
and then swallowing
what the bristles retained.
And here is a skull
of a very much bigger species from Brazil.
And it had neither teeth
nor bristles in its jaws,
but microscopic examination
of the surface of the bone here,
reveals very tiny little blood vessels
and that suggests that these jaws
were once covered with a horny beak.
So that maybe this animal used
it's beak like a pair of forceps
to pick up small little reptiles,
or maybe catch dragonflies in the air.
And this particular skull
reveals something else
about the lifestyle of this specimen,
because at the back of the skull
it has this great flange.
And Pterosaur skeletons
from other species
have been found, some with such flanges
but others without.
So it's thought that maybe
this was the difference
between the sexes.
Maybe was the male
that had these big flanges
at the back which it displayed them,
and maybe it was covered with skin,
we can only guess.
Many different Pterosaur species
evolved these headcrests,
and seems very likely,
that they were coloured.
This spectacular example,
is known as Tapejara.
And it made its home beside inland lakes.
But Pterosaurs diversified
in other ways too.
Some evolved much larger bodies.
This species had a wingspan
of over 20 feet, 7 metres.
But not all Pterosaurs
lived in the forests or near water.
An open, arid landscape like this one,
was the likely home
of one of the most extraordinary.
Around 70 million years ago,
a Pterosaur appeared
that was of truly colossal proportions.
That was one of the largest creatures
that has ever flown,
it was in the size of a small aeroplane,
and it was called, Quetzalcoatlus.
Its immense wingspan allowed it
to ride on the currents of warm air
that rise up from sun-heated land.
It could then glide great distances,
searching for food.
Small creatures like lizards,
or the dead bodies
of much larger ones, dinosaurs.
But the Pterosaurs,
with their wings of toughened skin,
weren't the only group of reptiles
to make it into those ancient skies.
About 150 million years ago,
another reptilian group appeared
on the planet that also flew.
Like most reptiles, including Pterosaurs,
these creatures began their lives
inside an egg.
But they had evolved
a revolutionary new design for flight,
one that would usher in
a remarkable fresh chapter, in our story.
And unlike the Pterosaurs,
they're still with us today.
There are of course, the birds.
Some today can provide clues,
about how their ancestors
managed to get into the air.
This is the chick of a bird
found in farmyards everywhere:
A Bantam Hen.
And at this very early stage in its life,
it can show us something very interesting
about the origin of that crucial piece
of flying equipment, a feather.
Its feathers are downy, that's to say,
they're made up of simple filaments,
and their function is not for flight,
but insulation,
to keep this little creature warm.
And back in the Jurassic period,
long before the arrival of true birds,
very similar looking feathers
appeared on very different animals,
reptiles, dinosaurs to be precise.
To find evidence
for that astonishing statement,
which not so long ago was highly
controversial, we're heading for China.
Northeast of China's Great Wall,
near the borders of Mongolia,
lies the chilly province of Liaoning.
Here, there are great areas
of rocks that were laid down as mud,
in the bottom of immense
fresh water lakes.
The bodies of animals that
were swept down into these lakes,
were slowly entombed
by the fine-grained sediment
that preserved them entire
and in exquisite detail.
And from these rocks have come specimens
that solve one of the most hotly debated
of evolutionary arguments:
The origin of the birds.
The key specimens are now in Beijing,
where they've been delicately prepared,
under the microscope.
They have been studied here, by one
of the world greatest dinosaur experts,
Professor Xing Xu.
First, he showed me
one of his oldest specimens,
part of a dinosaur's arm.
But thanks to the fineness
of the mud of those ancient lakes,
there is more here than just bones.
You see here, this species
is called a Beipiaosaurus,
So because this is an animal
like two or three metres long,
so quite a big animal. And here
is an arm, hand, you see here...
dark filamentous structures...
- Yes.
along that arms and hand,
they're actually primitive feathers.
And those feathers are very simple,
very very simple,
so we believe they represent
the very primitive stage
for feather evolution.
These simple strands were made
of the same material,
as the feathers of today birds.
They were relatively thick,
and must have been quite stiff,
so they would have stuck out
beyond the dinosaur's arm.
Behind them, were shorter strands
that covered its whole body.
Like the down on the chick,
these might have kept the dinosaur warm.
But those long strands most likely
had a different function.
Clues to what that
might have been can be found
on an even more extraordinary fossil.
These claws and finger bones belong
to a creature called Caudipteryx.
The long dark shapes around them,
are the remains of feathers.
The single strands are here
rather more complex.
They had barbs, thin filaments attached
to either side of a central rod.
This looks more like a bird's feather.
Caudipteryx had around 26 of them,
along each arm.
This may look like a wing,
but the feathers were not very long.
And when you compare them
to the size of this creature's body,
and its long legs, it's clear
that they weren't big enough
to enable Caudipteryx to fly.
So, what were these feathers for?
Microscopic examination has revealed
that they were coloured, and patterned.
So, maybe they were used for display,
perhaps to wave around
during courtship, to attract a mate.
But then is seems that they also
helped the dinosaur, in a different way.
We can find a hint of how
they might have done this,
by watching the way some young birds
use their first feathers today.
These are ten day old Pheasant chicks.
Their feathers are
not yet fully developed.
At this stage they're similar
in structure, to the feathers
on that dinosaur, Caudipteryx,
and grow in a line along each arm,
in much the same way.
But these early feathers
are also too short,
to enable these creatures to fly.
Nevertheless, they're very helpful.
Pheasant chicks hatch
in nests on the ground,
but they soon need to roost high up,
where they'll be safe from predators.
Flapping these simple wings
gives the chicks a little extra lift,
to help them climb into a tree.
And when the time comes
to return to the ground,
those first feathers again, are a help.
They don't provide a large
air-catching surface,
but they're enough to slow a chick's fall,
and make that landing,
just a little softer.
Maybe the feathers that had
initially kept the dinosaurs warm,
now also helped them to get into the air.
And then, only a few years ago,
the mudstones of Liaoning produced
yet another extraordinary fossil.
It's been named Microraptor,
and it's clearly a small dinosaur.
But this specimen is particularly
exciting, because of its feathers.
Feathers on the forearms there.
Feathers on its hind limbs.
And even feathers right
at the end of its very long tail.
But there is something
that makes these feathers
different from any other feathers
we've seen on dinosaurs before.
They are narrower on one side
of the quill than on the other,
just like bird feathers.
Microscopic structures
within them, suggest that
they had flashes of iridescence.
So these feathers were
probably used for display.
But their asymmetric shape
is characteristic of flight feathers.
The air flowing over the narrow front
of the feather, can produce lift.
So could this strange looking dinosaur
with feathers all over it, actually fly?
Some people think that
those feathers on its hind legs
would have made it rather difficult
for it to walk around on the ground,
and that it would have been
more at home, climbing.
And those claws on the fingers and toes
are obviously very helpful,
in climbing up tree trunks.
But those aerodynamically shaped
feathers certainly suggest
that its arms were been used as wings.
This four-winged dinosaur must have
been a really extraordinary animal.
Its front wings were broad
enough to enable it to glide,
and its muscles on the chest
were sufficiently strong
to enable it to flap every now and then,
and help it on its way.
But the wings on the hind legs
were probably not held spread out,
but kept beneath the body
to help the animal to steer.
Now clearly, these dinosaurs
were on their way
to join the Pterosaurs in the sky.
And then, discovered once again
in the rocks of China,
came creatures that are
recognizable as birds.
This is Confuciusornis.
There are two of them here.
They no longer have
heavy bony jaws studded with teeth.
Instead, they have
short beaks made of horn,
without teeth, lightweight.
And the tail is no longer supported
by a whole chain of small bones.
These bones have been reduced
to this tiny little stump here.
These are true birds.
But the long feathers attached
to the tail of one of these specimens,
can reveal something intriguing
about these early birds.
To find out what they were for,
we can look for a bird here in Borneo
that has very similar tail feathers.
This is the racket-tailed Drongo,
and it's tail feathers bare
an astonishing resemblance,
to those of its distant
ancestor, Confuciusornis.
They don't seem to help
its flight in any way.
So the Drongo must be using them
for something else:
Display.
And so, while the birds continued
to improve their flight,
they also continued to use
their feathers in courtship,
as their dinosaur ancestors
had probably done.
But birds use, not just the shape
of their feathers for display,
but also their colour, and there's
some really lovely examples of that,
here in Borneo.
These birds are colourful enough,
but one is particularly spectacular.
This is the Bornean Peacock-Pheasant.
This is the male. His feathers are emblazoned
with colourful iridescent patterns.
And that's because they're used
to attract the attention of a female.
Her feathers are comparatively drab.
First, the male lures
the female into his courtship arena,
with the promise of food.
A worm.
He begins to shake
his magnificent feathers.
He clears the ground of anything that
might interfere with his performance.
As the female dives in
after the worm, he raises
all of his feathers in a huge fan.
If she approves of his display,
she may choose him as a mate,
over other rival males.
Eventually she makes off
with the offering of food,
and it seems she was not as impressed
as she might have been.
So feathers, so lightweight,
and so easily erected,
can serve as billboards on which
to advertise for a mate,
or warn off rivals.
But to see how the early birds
used their feathers
to achieve fully powered flight,
we are returning to Britain.
Here, on a Loch in Scotland,
we can watch some of the most
majestic flyers around today:
Whooper Swans.
These particular birds were
in contact with human beings
from the very first moment
that they hatched, so they allow me
to get really close to them.
The small feathers on their bodies
are still essential
for keeping their owners warm.
But this one is a wing feather.
It extremely strong, but very light,
and the filaments on either side
of the quill, the barbs,
zip together, to form
a continuous surface which is
strong enough to hold the air.
But if the air is to support
a big bird as it flies,
it has to move over the wing very fast.
And in order for that to happen,
these Swans will move at speed
across the surface of the water,
like an aircraft taxiing before take-off.
When you're close up
to a flying bird like this,
you can see how a wonderful piece
of complex engineering their wings are,
able to change their shape and their beat,
to respond to every little change
in the currents of the air around them,
and so propel them forward
and lift them upwards.
So, how do bird wings actually work?
If we slow them down, we can watch
in detail the many subtle changes
they make, as they move up and down.
The feathers overlap to form
a smooth, contoured surface
that extends far beyond the bones within.
With a curved leading edge at the front,
and a sharp trailing edge at the back,
they have the classic aerodynamic
shape, that produces lift.
They are aerofoils.
With each downward beat,
the air pressure above is reduced,
so that the bird is sucked upwards.
Wings like these, consisting
of jointed bones covered
with closely fitting feathers,
can make very subtle, delicate movements.
The feathers slide over one another,
so that when the wing changes shape,
there is no loss of smoothness
on the contour.
When the swan slightly retracts
its wings in between beats,
the sliding feathers ensure
that the aerofoil still produces lift.
As well as lightweight beaks
and shortened tails,
some of the bones of its body
have become hollow.
The result is an extremely efficient,
light-weight flyer.
We are traveling around
30 miles an hour now,
and yet these birds
could easily accelerate,
and leave us behind if they wanted to.
So feathers, since they're first appearance
on the bodies of dinosaurs,
have acquired several
different functions.
Initially, they served
to keep their owners warm.
Then, some grew large
and acquired colour, and
were probably used in courtship displays.
And only then, after millions of years,
were they used to help
their owners get into the air.
So around 150 million years ago,
birds joined the Pterosaurs
and insects in the skies.
Then, around 66 million years ago,
came the global catastrophe
that triggered the disappearance
of a vast proportion
of the animal life of this planet.
An asteroid hitting the Earth,
was the most likely cause
of this mass extinction.
In the devastation that followed,
the dominant creatures of that age,
the dinosaurs, disappeared.
The Pterosaurs were completely wiped-out.
And only a few of the birds survived.
The skies for a short period,
must have been relatively empty.
But then, a new kind
of flying animal appeared.
Now is a chance for a group
of furry warm-blooded little creatures,
that had been scampering around
the feet of the dinosaurs
for several million years.
They were the mammals.
The first of them to take
to the air were doubtless gliders.
And one mysterious creature
still alive today,
can give us an idea
of what they were like.
It lives in the rainforests of Borneo,
and its called the Cobego.
It has an enormous blanket
of furry skin, that stretches
from the side of its head,
right down to the very tip of its tail.
But to see how it travels through the air,
we must wait until nightfall.
As soon as it lands, it regains
the height it's inevitably lost,
by clambering up the trunk.
It's by far the most skilful
of the forest gliders,
and can travel over
a hundred metres in one leap.
It's undoubtedly a very ancient animal,
and some believe that it may well
have survived virtually unchanged
from that time long ago,
when mammals first took
to the skies as gliders.
But soon, the mammals
did better than that.
This is a fossil that dates
from about 52 million years ago.
Here's its head, with very
well-developed teeth, backbone and ribs,
and long tail, hind legs,
and most important of all,
from our point of view,
hands with enormously elongated fingers.
And there was skin between those fingers.
These were wings, and they could flap.
This is the earliest fossil
yet discovered, of a bat.
We have new evidence to show
exactly how a bat's fingers
first began to lengthen,
to support their wings.
But we can understand
how those early bats flew,
by looking at their modern descendants.
These are some of the largest.
They're so big,
that they're often called Flying Foxes.
And they have a wingspan of over a metre.
When you slow a bat's flight
down like this, you can see
that its four fingers
are spread wide on the down-stroke,
keeping the membrane wide and taut,
and then clump together on the up-stroke,
with just a thumb at the top free.
This folding of the wings
reduces the bat's air resistance,
between each beat.
To maximise the size of its wing,
the back edge of the wing membrane
is attached to the ankles.
Bats roost by hanging upside down.
And this is how they tend
to spend their days.
It's thought that the first mammals
were nocturnal,
that doubtless was the best thing to be,
out of the way of the dinosaurs
that were rampaging
around during the day.
So the bats continued
the nocturnal habit of their ancestors,
and they had also inherited
the acute sensors, needed
to move around at night.
Eyes specially adapted
to operating well in low light,
and an acute sense of smell that
enables them to find food in the dark.
In any case, birds already
dominated the daytime skies.
With their wings of skin
and nocturnal senses, the bats
became a huge global success.
Today, there are
over 1,100 species of them,
that's over a fifth of all mammals.
So, by 50 million years ago,
three groups of large backboned animals,
had joined the insects in the air.
The pioneers were reptiles, Pterosaurs,
with membranes of skin,
stretched from elongated fingers.
Then, came a group of dinosaurs,
that acquired feathers and became birds.
But when the Pterosaurs
and Dinosaurs were swept away
in a global extinction event,
the stage was set for the birds,
and the newly emerge bats
between them,
to take command of the skies.
Each of these two groups
had evolved its own techniques
for getting into the air,
and each was destined
to bring their skills
to astonishing extremes.
Next time, we see how birds
adapted and diversified
to become the remarkable creatures
we see in our skies today.
Lethal hunters.
Formation flyers.
And aerial acrobats.
We explore how the bats
developed a new super sense,
that enabled them to hunt
in the pitch-blackness of the night.
And we visit one spectacular place,
where the battle for the skies,
between insects, bats and birds,
still continues.