The Life of Birds (1998): Season 1, Episode 1 - To Fly or Not to Fly? - full transcript

Birds are the most accomplished aeronauts
the world has ever seen.

They fly high and low.
At great speed and very slowly.

And always with
extraordinary precision and control

But birds are not the only creatures in the air.

There are also small furry mammals,
bats, like these in Texas.

They are so competent in the air

that they have just made a journey from Mexico,
a thousand miles away,

simply in order to rear their young in this cave,

which is particularly suitable for them
as a nursery.

Just now they are flying out
to catch their evening meal of insects.

But they had better be careful,
because in the skies above them



there lurks a creature that can outfly them.

It is, of course, a bird. A red-tailed hawk.

Bats with their fluttering zig-zag flight
are not easy targets,

and a hawk needs all its aerobatics skills
and powers of concentration

if it is to snatch one
out of the confusing multitude.

That is one bat
that will not return to the roost tonight.

The red-tail lives beside the cave
and is well practised in bat-catching.

This prairie falcon, on the other hand,
is a visitor, but it's learning fast.

Unlike the hawk, it chooses to eat
its meals on the wing.

Bats are latecomers to the skies.

They've only been flying
for a mere 60 million years.

The air was first colonised
200 million years earlier still by the insects,

but now they can't escape the birds either.

Some insects, of course, have powerful weapons
with which to defend themselves.



But a bee-eater certainly knows
how to deal with a bee.

A rub against the perch
usually discharges the sting.

And if that doesn't, then a sharp nip
will squirt the venom harmlessly into the air.

Dragonflies first flew around 350 million years ago

and insects had the skies to themselves
for 150 million years thereafter.

And then a different kind of animal
joined them in the air.

As the dinosaurs dominated the land,
so the pterosaurs now ruled the skies.

Pterosaurs had wings of skin, stretched between
one enormously elongated finger and their flanks.

They flew over the sea as well as the land.

It seems likely that some roosted on cliffs

and launched themselves into the air
as gannets do today.

They probably snatched fish
from the surface of the sea,

and some certainly fell into it.

Their bodies were buried by mud;
the mud turned to limestone

and eventually became exposed in
great quarries like this one in Southern Germany.

Today, separating the layers of sediment

is just like searching through
the pages of a visitor's book

that hasn't been opened
for 150 million years.

0f course, nearly all
of the pages are absolutely blank.

Visitors, after all, were very few.

But every now and again you come across
a signature that is unmistakable.

A fish the size of a sardine.

A shrimp, even its antennae perfectly preserved.

One of those pioneering dragonflies,
nearly six inches across.

And a pterosaur with skinny wings
and teeth in its jaws.

With so many superb fossils,

people thought that they had
a complete list of the visitors to the lagoon.

And then, in the middle of the last century,

a signature was discovered that was
wholly unexpected and totally amazing.

This is it. It's a feather.

Its barbs are narrower on one side of the quill,

just as they are on the feathers
of a modern bird's wing.

This asymmetry is a sure sign
that such feathers were used for flight.

But what animal at the time of the dinosaurs
could have such a wing?

The answer was found
the very next year in the same quarry:

a fossil with its feathers still attached to its body.

This is archaeopteryx.

It had three toes armed with claws
and long, strong legs.

Clearly it walked and perched like a bird.

But its head was very reptilian with bony jaws.

And in those jaws, teeth.

Its spine was extended into a bony tail,
again like that of a reptile.

But on either side of the tail bones,
clearly visible,

it had those characteristic possessions of birds:
feathers.

Feathers are made of keratin, as are the scales
that many birds still have on their legs,

and reptiles all over their body.

A scaly coat must be very hot,
so reptiles, like this skink,

have to seek shade
during the hottest part of the day.

But if the scales became fibrous, they could be
fluffed up to let in cooling air during the day,

and closed down to trap insulating air
for warmth at night.

So it is not difficult to believe that scales
eventually became transformed into feathers.

But why should they have become so long
that they enabled the animal to take to the air?

Well, this Australian lizard suggests an answer.

When it is threatened by its enemies, it responds
by spreading the great frill it has around its neck.

But if that doesn't scare them off,
it runs away, on its hind legs.

If such a reptile had developed feathery scales
on its forelegs and then spread them out

then it might easily lift into the air
and so escape a land-bound predator.

There's another possibility.
Maybe that early reptile did not live on the ground

but climbed in the trees searching for food,
as today the little flying lizard of Borneo does.

It now glides from tree to tree.

It has developed wings that are flaps of skin
supported by elongated ribs.

If that early enterprising reptile with feathery
scales did have specially long ones on its arms,

then they too would have enabled it
to glide from tree to tree.

Maybe its arm muscles were even strong enough

to allow it to make a few flaps
to help it on its way.

Archaeopteryx was certainly
well-equipped for climbing,

for its wings still carried three fingers,
each ending with a hooked claw,

ideal for clinging on to twigs.

And there are birds today with very similar ones

that give a clear hint as to how
it might have used them.

These are young hoatzin, sitting on their nest
in a South American swamp,

still guarded by their parents.

A hoatzin chick has an adventurous disposition

and starts clambering about
when it's only a few days old.

The hooks on its front limbs are obviously
very useful in keeping it secure

until such a time as they become
feathered and reliable wings.

One can imagine that archaeopteryx used them
in much the same way

and for much the same reason.

Sometimes, however, there's a disaster.

There are dangerous reptiles in the swamp:
snakes and caiman.

But those claws on the wings
are once again invaluable.

Mother returns. She has been
feeding on leaves and will have a full crop.

Maybe there will be some for the chick.

The hoatzin, of course, like all modern birds,

doesn't have bony jaws with teeth
like archaeopteryx, but a lightweight beak.

When did that important change take place?

Well, this fossilised bird has a beak,
and it was found in China recently.

It's only a little younger than archaeopteryx,
so it seems that the change took place quickly.

And it must have made flight much more efficient

for it prevented a bird from being nose-heavy
and significantly reduced its overall weight.

By 50 million years ago,
the dynasty of birds was firmly established.

At that time, a great lake
lay here in Central Germany.

It's long since dried out, and the layers of mud
from its floor have turned into shales.

Excavations like the one that's going on here

have revealed
just how varied the birds had become.

This one has been set in yellow resin
to make its details quite clear.

It had a horny beak,

a fully feathered wing, a long feathered tail
with no bony support and long legs.

It probably looked like a rail

0ther fossils from these shales show that several
families of modern birds were already established.

This was a water bird,
possibly an ancestor of today's jacana.

It would have found plenty of insects
among the floating leaves on the lake.

There were birds with powerful chisel-like bills,
perhaps woodpeckers,

that even in this early period had
started excavating insects from trees nearby.

Another inhabitant of those prehistoric woods
had a stubbier, more all-purpose beak,

rather like finches do today.

There were tall birds with long powerful legs
that hunted for small reptiles on the ground

as the South American seriama does.

And there was a gigantic vulture
with a wingspan of over 20 feet,

bigger even than that of the Andean condor

and probably the biggest flying bird
that has ever existed.

There were even birds
which, judging from their skeletons,

were as agile in the air as their
probable descendants, the frigate birds.

So by 50 million years ago, several families
of modern birds were well established.

The rule of the reptiles was now really over.

Not only had pterosaurs
disappeared from the skies,

dinosaurs had gone from the ground.
So the dominance of the land was up for grabs.

There were two contenders:
the mammals and the birds.

The biggest mammal to be found
from this lake in Germany was a primitive horse.

It was no bigger than a spaniel

But the biggest bird was very different.

That was the lower part of its beak,

and this was the upper.

If its skeleton still lay here,
you would have to dig a huge pit to extract it.

This bird was immense.

It has been named, with good reason,
the terror bird.

Its wings were tiny
but it had long and powerful legs.

Flightless birds of a comparable size still exist

and can give us some idea
of what it looked like.

This, the ostrich, is
the biggest and heaviest bird alive today.

It is probably not closely related to those
monstrous feathered hunters of prehistory,

but together with the emu of Australia
and the rhea of South America,

it belongs to a very ancient family of birds
that abandoned flight a very long time ago.

It relies for its defence on speed

and, in the interests of its efficiency as a runner,
its toes have been reduced to two.

If pursued, it can sprint at over 40 miles an hour.

But although it is now flightless,

it still has many of the physical characters
evolved by its ancestors that enabled them to fly.

It still has feathers
and they are still placed on its wings

in much the same position
as those on the wings of a flying bird.

But they are now useless for flight.

Their filaments have lost their hooks

so they can no longer
be zipped together into an unbroken blade.

Instead they are loose and fluffy.

Their only function now is as insulating blankets,

to keep out the cold at night
and the heat during the day.

0striches have become grazers,
the bird equivalent of antelope or horses.

But unlike them, they not only pick up leaves.

They swallow all kinds of other things as well,
and for a very good reason.

Just as they inherited feathers
from their flying ancestors,

so they also inherited a lightweight, horny beak
instead of a heavy jaw laden with teeth.

And without teeth, they need
another way to grind up their food.

A pebble can help them do just that.

Down it goes into a muscular compartment
of the stomach, the gizzard,

a kind of mill where bits of vegetation are churned
around and ground into a digestible pulp.

But while some birds were abandoning flight,

some mammals
were becoming formidable hunters.

0striches with their superb eyesight and tall necks

are able to keep a sharp lookout
for approaching danger.

The cheetah has to calculate very carefully
whether it's worthwhile chasing something...

..and an ostrich, usually, is not.
It is so very fast, and even if it's caught,

it has little meat on it
compared with a similar sized mammal

But birds that can't run
are a tempting target for hunters everywhere.

If they couldn't fly, they wouldn't last long.

Flight has certainly enabled birds
to colonise the entire globe.

But the compulsion
that drove them into the air in the first place,

and has certainly kept most of them there
ever since, was probably safety.

Even so, the cost of flying is high.

Flapping wings takes a lot of effort

and if there is no need to do so,
birds save their energies.

Those that live here on the Galapagos Islands,
isolated in the Pacific,

have no natural enemies from which to escape,
so some birds don't bother to fly.

Have a look at these cormorants, for example.

At first sight, they look like many another
cormorant sitting on cliffs round the world.

But these wings are stunted and tattered.

This bird could never get into the air.

Its feathers now serve only
to keep it warm in the water.

It's for that reason alone
that it keeps them well-oiled.

It is scarcely any better at walking
than it is at flying.

0nce in the water, however,
it's a very efficient mover indeed.

The position of its legs right at the back
of its body that made it so clumsy on land

is ideal for propelling
it through the water at speed

and helps it to catch all the fish it needs.

For the Galapagos cormorant,
flight has become an irrelevance.

0ther island birds have reacted in a similar way.

This is New Caledonia in the western Pacific,
and this is its special bird, the kagu.

Its ancestors must certainly have
arrived here by air,

but since New Caledonia had
no ground predators until recently,

they gave up flying
and today the kagu is virtually flightless.

It finds all its food
on the ground in the leaf litter.

It's been here so long that it's difficult to be sure
exactly who its ancestors were,

but they were probably herons.

Rails are a very widespread family of birds.

Wherever there is a big swamp,
you are likely to find one.

0n the continents, they tend to lurk shyly
in the undergrowth to keep out of trouble.

But some, somehow, have also managed
to reach a great number of islands

and there they seem to have no fear at all.

This one, it's a weka,

has also become flightless
because of its isolation on an island.

But its island is immense.

It's 1,000 miles long, if you discount
a narrow arm of sea that crosses it in the middle,

and it contains mountains over 12,000 feet high;
it's New Zealand.

The first land-living mammals
to get here were human beings

and they didn't arrive until a mere 1500 years ago.

So here you can still glimpse
what the world would have been like

if the birds had won that battle with
the early mammals and now ruled the earth,

for here they once did.

Many of New Zealand's birds
flew here from Australia,

15,000 miles away
across the sea to the west.

They started to do so millions of years ago,
and they are still doing so today.

So if you know Australian birds,
you will recognise quite a lot,

particularly those that are relatively recent arrivals.

The New Zealand pigeon is not
all that much different from Australian ones.

The saddleback, on the other hand, must have
been established here for much longer

for it has changed so much that no one is
quite sure what family it belongs to.

The tui has similarly mysterious origins.

No other bird has a costume to compare with
its lacy cape and that little white throat bobble.

The kaka is clearly a parrot.
There are lots of parrots in Australia

so it's not surprising that some of them
in the past should have found their way here.

Most of these birds have still not learned
that mammals are dangerous.

This saddleback is a fully wild bird
and certainly hasn't seen me before.

But look how trusting it is.

This is a New Zealand robin.

It's no relation to the European robin
and, if anything, it's even braver.

The New Zealand bush is full of food,
of one kind or another.

And as the birds once had it all to themselves,

some were able to adopt diets and ways of life
that elsewhere were claimed by mammals.

The kokako eats much the same thing
as squirrels: fruit and leaves and insects.

European squirrels run along the branches.

Asian squirrels, using a skinny parachute stretched
between their legs, are able to glide as well.

And that is very much how the kokako
gets around in the trees.

Having glided down to the lower branches,
it runs back up them

and jumps from one to the other.

So if the kokako, up in the trees, feeds in the
same way as a squirrel might do,

what lives and feeds
like a mammal on the ground?

The leaf litter in these forests
is full of food of one kind or another.

There are earthworms and insects
and beetle larvae.

In any other land
there would be some small native mammal

that was burrowing around seeking that food.

But not here in New Zealand.
Here there's something quite different.

You will only see it after dark.

It is, of course, a bird,
but what an extraordinary one. The kiwi.

It's territorial and calls stridently
to proclaim its ownership.

It finds its prey by smell,
uniquely its nostrils are on the tip of its beak.

It's found a worm.

But once it drops it,
its eyesight is so poor that it can't see it

and it has to smell for it, with its beak.

Its tiny vestigial wings are invisible, buried in
its plumage and it has lost all sign of a tail

If the kiwis live in
a patch of forest close by the sea,

then in the evening they may come down
on to the beach to look for these:

Sandhoppers. They love them.
And that will give us a chance, a rare chance,

to see them out in the open.

To do so properly, we have to use
our special starlight camera.

The kiwi is hunting along the strand line

where there are lots of hoppers
feeding on the decaying seaweed.

Its sense of smell is so acute
it can pick out the largest juiciest hoppers

deep in the sand without even seeing them.

0ur starlight camera
can see much better than I can.

I need a torch to see this extraordinary creature
properly, but it doesn't seem to mind.

Its feathers are just filaments,

so that it almost looks as though it is
covered with coarse fur.

Probing sand with your nostrils is all very well,
but it does clog them up,

and so you need to blow them clear
every now and then.

It's nocturnal and furry:
It finds its way around by smell.

It lives in holes and digs for worms and grubs.
It's a bird equivalent of a badger.

But there's plenty of other food to be found
in the New Zealand bush.

Here on the forest floor, there are lots of leaves.

They may be a bit twiggy and coarse
but they are food nonetheless.

What could have browsed on these?

Well, not far from here,
bones like this have been dug up.

It's obviously a leg-bone,

and at first sight you might think it
was a leg-bone of a mammal, say perhaps, a cow.

But when you look at it closely you can see
that it's got a honeycomb structure.

It's a bird bone,

but the bone of a very big bird indeed,
as we know from the rest of its skeleton.

It had just three toes.

Its pelvis and its spine
lead up to an extraordinarily long neck.

This bird stood over six feet, two metres tall.

The first human settlers on these islands
saw these giants alive and called them moas.

Among them were the tallest birds that ever
existed, that weighed over 200 kilos, 400lbs.

There were about a dozen different species
of varying size and weight.

Up on the high moorlands, there were smaller
species with thicker feathers to keep them warm.

The absence of mammals
didn't mean that the moas had no enemies.

They were hunted by, of course, another bird.

An immense eagle
that could manoeuvre through the patchy forest.

The only prey that was abundant enough
to sustain such a giant were other birds

and it's probable that
it was able to tackle even the biggest moa.

Its talons were certainly long enough
to stab right through a moa's flesh

and into its pelvis, as some of the bones show.

Nevertheless, the moas survived
for a million years or more

and spread all over New Zealand.

But eventually mammals
did reach these remote islands.

Apart from bats which flew here, the first to arrive
were those most dangerous of all,

human beings.

They hunted the moas for meat
and soon they had hunted them to extinction.

But a different kind of flightless bird
does still survive, up in these high mountains.

Like so many of New Zealand's native birds
that had abandoned flight,

it had no defence against the alien mammals
that Europeans brought with them

and that soon escaped and ran wild.

Rats ate their eggs and killed the chicks,
and cats and stoats massacred the adults.

There was a giant flightless coot
that was originally very common.

But it got scarcer and scarcer
and by the middle of the nineteenth century,

it was thought to be totally extinct.

And then, just 50 years ago,

someone in these remote valleys
found something like this.

This is the dropping of a takahe

and here, the severed stems
of tussock grass on which it's been feeding.

It's still here.

And here is her nest.

She's sitting tight, hiding her brilliant red bill
so that she is not conspicuous.

Indeed, when only
her lovely moss-green back is visible,

she is well camouflaged from her only
native enemy, a bird of prey, circling overhead.

0nly about forty pairs of takahe
survive today in the wild.

So the eggs she is sitting on are very precious.

This high country was probably not
the takahe's original home.

Most of the population in the last century
lived at lower altitudes

and there they had lush vegetation to feed on
in the warm swamps.

But most of those were drained
and turned into farmland.

So now these high empty valleys,
only recently scraped down to the rock by glaciers,

are the takahe's last refuge and there is
little to eat up here, except tussock grass.

Extracting something nutritious
from tussock is not easy.

The takahe's technique is to pull up a whole stem
and then nibble just the bottom inch or so.

That's where most minerals and sugars are

and it's the only bit
tender enough to be easily cut.

At first the chick doesn't know
how to do this and has to be fed.

It will stay with its parent for a whole year.

0nly then will it be strong enough
and skilled enough to feed entirely by itself.

Now it's summer, but when winter comes,
life will be even tougher.

Then the pools freeze over
and the tussock has no fresh shoots,

even if they could be reached beneath the snow.

Then the takahe is reduced to digging for tubers
in the freezing earth.

So the birds' continued survival up in these
barren moorlands is by no means assured.

One other flightless bird found refuge
from mammals in these high mountains;

and in many ways,
it was the most extraordinary of all.

It was a giant parrot, the kakapo.

It lived in very much the same way as rabbits do.

It created tracks through its territory
generation after generation, trudging along here

and feeding by plucking these grasses
and eating the succulent base.

This particular path runs under this bush

and continues upwards
along the highest edge of this narrow ridge.

The track leads to this shallow bowl,

and there are others like it
spaced out along the track.

They were excavated by the male kakapo
whose territory this was.

He would dig them out;
and then in the night, he would come here

and, crouching low, make a deep booming call
which echoed out across these valleys,

summoning the females to come to him.

But there were no females
seen after the 1970s up here.

One lone male continued
trudging up here and calling.

But in vain.
And in 1985, his call was heard no more.

And then when hope was almost gone,

a new population of kakapos was discovered
on the southernmost island, Stewart Island.

They too were being harried by cats and stoats,

so the survivors were caught
and taken to three small cat-free islets.

There were only 61 of them.
The kakapo's survival was on a knife-edge.

A male, after slumbering all day in his burrow,
emerges for his evening meal

His hearing is acute, he listens for danger.

He's following his regular track that will lead him
to the highest slopes of his mountain.

A female has clambered up into the top
of the bushes, looking for fresh shoots and fruit.

Her dappled green plumage
camouflages her against attacks from falcons,

but even so, she won't dare to venture
into the topmost branches until it's dark.

Nightfall, and now we need our starlight camera
to see what's happening.

By midnight the male has plodded his way
right to the summit of his mountain.

He has reached one of his bowls from which
his calls could echo out over the valley below.

He begins to tidy it up.

The female has found
what she wants up in the branches.

She will need all the most nourishing food
she can find if she is to produce an egg.

Even at the best of times,

she will not be able to accumulate
enough bodily reserves to lay every year.

The male begins to inflate air-sacs on his chest

that will act as resonators and so amplify his calls,
sending them booming out across the valley.

There are probably
only 12 fertile female kakapos left alive.

In the first 10 years after they were moved
to the safety of their new homes,

only three chicks were reared.
But then in the last two seasons,

seven young kakapo were successfully hatched.

Maybe the species will come back
from the brink of extinction after all.

0f course, only a minority of New Zealand's birds
have become flightless.

Most, like these handsome spotted shags,

have retained that characteristic talent of birds,
the ability to travel by air,

and worldwide, birds have exploited that ability
to an extraordinary degree.

Some can make journeys of over a thousand miles
without coming down to earth.

Some can fly to altitudes of over 25,000 feet.

Some can even fly backwards.

How they manage to get into the air
and sustain themselves there

is what we will
be looking at in the next programme.