Curious Feeders David Attenborough's Natural Curiosities

The Natural World is full of extraordinary animals

with amazing life histories.

Yet, certain stories are more intriguing than most.

The mysteries of a butterfly's life cycle

or the strange biology of the emperor penguin.

Some of these creatures

were surrounded by myth and misunderstandings

for a very long time.

And some have only recently revealed their secrets.

These are the animals that stand out from the crowd -

the curiosities I find particularly fascinating.

In this programme, we meet two animals

whose extraordinary body shapes are determined by their diet.

The blue whale grows enormous,

by feeding on tiny shrimplike creatures,

while flamingos spend their lives eating with their heads upside down.

And yet, both ways are curiously similar.

The blue whale weighs almost 200 tonnes.

It's the largest animal on Earth and it's rarely seen.

I didn't glimpse one,

until I had been filming animals for almost 50 years -

and when I did, it was one of the greatest thrills of my life.

I can see its tail, just under my boat here.

And it's coming up, it's coming up...

There!

The blue whale is 100 feet long -

30 metres.

Nothing like that can grow on land,

because no bone is strong enough to support such bulk.

Only in the sea, can you get such a huge size

as that magnificent creature.

The blue whale was a mystery to science for a long time.

Living out in the deep oceans,

people rarely caught sight of more than the spout of this giant.

The first published description

comes from a physician, Robert Sibbald,

who found a whale stranded off the coast of Scotland in 1692.

It was first named after Sibbald,

but later given the scientific name Balaenoptera musculus.

The Latin "musculus" means both "muscle" and "little mouse" -

an ironic double meaning for the largest animal on Earth.

When the first blue whale specimens were washed up on our shores,

they must have caused quite a stir and excitement.

Here was a colossal animal, weighing over 150 tonnes.

Nothing as big had ever been seen before.

A giant of this scale must be a predator

at the top of the food chain.

But what kind of creature was it?

And what was it feeding on to make it so big?

The first blue whale specimens were found at a time

when scientists were just starting to classify animals

not only by their external appearance,

but by their internal structures,

and few animals proved as problematic as the whales.

From the outside, they looked and behaved like fish.

But their internal organs were like those of a large mammal.

The bones of the whale's front fins

are very similar to those in our own arms.

The five digits on the hand are clearly visible,

but they've been modified into paddles for swimming.

What kind of creatures were these truly extraordinary animals?

The controversy as to whether whales were fish or mammals

came to a head in a New York courtroom in 1818.

A jury was asked to pass judgment on the question,

for the purpose of the New York state law.

The issue had come up because a shrewd merchant,

who owned three barrels of whale oil,

had refused to pay tax levied on fish oil.

He pointed out that, according to the latest scientific opinion,

whales weren't in fact fish.

The inspector collecting the tax had scorned the idea.

"What, whales not fish?!" he said,

and slapped handcuffs on the merchant.

The lead witness was a respected scientist called Samuel Mitchill.

Mitchill entered the courtroom,

expecting to explain to everybody why whales were mammals not fish,

but, instead, found himself being attacked

by the most gifted lawyer in the country, William Sampson.

Sampson argued that scientists didn't have the right

to rename God's creatures and force them into absurd groupings.

The idea that humans and whales should be in the same category

seemed to him grotesque.

Mitchill and science never stood a chance.

After deliberating for 15 minutes,

the jury announced a verdict in favour of Sampson

and the fish oil inspector.

According to New York state law,

whales were deemed to be fish, not mammals.

Although the general public still considered whales to be fish,

scientists were, by now, largely agreed

that they were, indeed, mammals that had taken to living in the sea.

But what was the blue whale feeding on

to allow it to grow to such an extraordinary size?

The answer can be found by looking inside the mouth,

which contains some very bizarre-looking structures.

This is the skeleton of a right whale,

and its mouthparts are very similar to those of the blue whale.

Instead of teeth, it has these strange plate-like structures,

hanging from the upper jaw.

The plates are aligned alongside each other

and the inner edges fray

because the large tongue continually rubs up against them.

And then the frayed edges entangle

to form a thick mat that acts like a gigantic sieve.

And when early naturalists opened up the gigantic gut of these whales,

they found not fish or other large prey,

but tiny shrimplike creatures called krill.

To everyone's astonishment, it turned out

that these whales feed on some of the smallest prey in the sea,

and these strange plates serve to filter the krill out of the water.

The rows of plates are called baleen,

and we now know that they form

a highly specialised filter feeding system.

The giant animal dives deep beneath the surface,

in search of swarms of krill.

The pleated skin on the throat and belly expand

and the mouth balloons outward to four times the size,

taking in an enormous mouthful of water.

The tongue then forces the water out through the baleen,

and thousands of tiny krill are left behind.

Today, we know a lot more about this unusual feeding structure.

This is baleen.

It's often referred to as whalebone,

but it's not bone at all.

It's keratin - the same substance as our hair and fingernails,

and it's both strong and slightly elastic.

The plates emerge from the whale's jaws instead of teeth,

and continue to grow throughout the whale's lifetime.

These bands in it are much like the rings of a tree.

Several may be laid down in the course of a year,

so the baleen can give us an indication of the age of a whale.

We also know, from other evidence,

that blue whales can live to be over 100 years old.

Recently discovered fossil whales have both teeth and simple filters,

which suggest that early filter feeding whales

may have sucked small animals from the seafloor.

There is a whale alive today that feeds in just that way -

the grey whale.

It stirs up the sediment and scoops it into its mouth

and then filters out small food particles with its baleen.

Krill is abundant in the oceans,

and blue whales can eat enormous quantities of it

with each mouthful,

soon swallowing 90 times more than they immediately need.

The surplus is then stored in the form of blubber,

and this helps them cope with periods when food is scarce.

The blue whale was a mystery to us for a long time,

but we now know that its enormous body

is fuelled with vast quantities of the tiniest of prey.

Over the course of its lifetime,

a blue whale will consume around 50,000 tonnes of krill,

and, unlike teeth, which fall out with old age,

the baleen never stops growing and is constantly replaced.

Maybe this unusual body design

not only helps the blue whale grow to this enormous size,

but also to such a formidable old age.

The blue whale has become a giant

by filtering tiny creatures out of the ocean.

Our second curiosity, the flamingo,

also has an unusual body that has been shaped by its diet.

For a long time, the flamingos were birds of myth and mystery.

Travellers in Africa saw them,

shrouded by the hazy mists rising from volcanic soda lakes,

and believed that they were firebirds.

In Egyptian mythology,

the firebird, or phoenix, was a sacred creature

with beautiful red plumage,

that was consumed by magical fire

and then rose again from its own ashes.

The flamingo's scientific name, Phoenicopterus,

reflects some of its legendary past.

It means "phoenix wing".

These beautiful and elegant creatures

are some of the most curious-looking of birds.

No other bird has a beak shaped quite like this

or, indeed, such glorious pink colours,

and yet, we're so familiar with them

that we rarely think about their strange appearance.

Why is it that the flamingo is so different from all other birds?

In that classic children's book, Alice In Wonderland,

Lewis Carroll has fun with the flamingo's oddity.

Alice plays croquet with the Red Queen,

using them as mallets, holding their heads and necks upside down,

in much the same posture as the birds take when feeding.

When you look at the skeleton of a flamingo,

the thing that strikes you most

is the extraordinary length of the legs and the neck.

The neck has 17 bones in it -

which is no more than in other birds -

but each is greatly elongated,

giving the flamingo its extra-long neck and flexibility.

But the flamingo's most curious feature is, surely, its beak,

and the reason it looks so strange,

is that it is the only beak adapted for use upside down.

In most birds, the upper part of the bill is larger than the lower one.

But in the flamingos, it's the other way round.

The lower bill is much bigger

and has a deep central groove in it that holds the flamingo's tongue.

The upper jaw is thin and moveable,

so when the bird head is upside down,

the flamingo's jaws work, as it were, normally.

When feeding, the flamingo gently sweeps its bill back and forth,

sucking water in at the front and squirting it out from the sides.

The water that goes in is murky, while that which flows out is clear,

and that gives us a clue to what it's feeding on.

The beak has tiny bristles all along its edges,

much like the whale's baleen.

And the tongue has two rows of horny spikes along its length.

FLAMINGOS SQUAWK

When feeding, the bristles and spikes form a sieve,

trapping any particles inside.

And the large tongue acts as a pump, pushing water in and out.

It's a unique design for a beak.

No other bird has one like it.

FLAMINGOS SQUAWK

Although at first sight, they may look the same,

flamingo beaks, in fact, come in two different shapes

and this is because they eat slightly different food.

This is the beak of a greater flamingo,

which feeds on crustaceans,

which are usually found near the bottom of a lake.

It's long and shallow,

so the birds can feed in water only a few millimetres deep.

This beak, on the other hand, is from a lesser flamingo.

Its bill is shorter, but more bulbous and deep-keeled.

The lesser flamingo feeds on microscopic algae,

which usually float just below the surface of the water

and the deep keel acts as a buoy,

bobbing along just at the right depth,

as the bird moves through the water.

These different bills allow two species of flamingo

to live side by side.

In Africa's Rift Valley,

greater and lesser flamingos are found on the soda lakes,

having specialised on food that others can't reach.

The waters are so hot and toxic,

that they would strip the flesh off any other animal.

But flamingos thrive here.

Their long spindly legs have tough scales

and their webbed feet prevent them from sinking into the soft mud.

The birds can even drink the water,

which is two or three times saltier than the ocean.

But it's not just the mud and water which are poisonous.

The blue-green algae, which many of them feed on,

actually contain nasty, toxic chemicals.

If that were to accumulate in the internal organs of the bird,

they could be lethal.

But the flamingo deals with that,

by directing these chemicals into the feathers and the skin,

where they do no damage.

The feathers of flamingos contain very high concentrations of toxins,

but they also contain another chemical - carotene.

Carotene is the reddish pigment

that gives flamingos their distinctive pink colour,

and it also comes from their diet.

But carotene is not harmful.

On the contrary, it's a source of vitamin A

and boosts the immune system, protecting against illness.

So, a pink bird is also a healthy bird.

This glorious pink colour

was probably an incidental by-product of their diet.

Nonetheless, over time,

it has evolved to play an important role in the flamingo's social life.

The flashes of colour are an integral part of their courtship display,

and recent research has shown that the pinkest flamingos

are the most popular, when it comes to finding a mate.

When flamingos breed, much of the carotene in their diet

gets channelled into the developing young.

Even the eggs receive pigments,

so much, in fact, that the yolk can be virtually blood-red in colour.

These eggs are from captive flamingos and are infertile.

Let's have a look.

There!

Well, it's nothing like the colour

of any other bird yolk that I've ever seen.

Flamingos are so efficient at collecting their specialised food,

that the yolk is actually packed full of protein and fat.

This allows the chick to grow particularly quickly

and gives it a good start in life.

FLAMINGOS SQUAWK

Despite the colour of the yolk,

the chicks hatch with fluffy grey feathers.

They are fed on special milk from their parents' crop.

This is not regurgitated food,

but a secretion produced by the lining of the digestive tract,

and it's deep red in colour.

The flamingo chick relies on this for the first few weeks of its life,

and it will eventually enable it to grow its glorious pink plumes.

FLAMINGOS CRY AND SQUAWK

We now know that much of the flamingo's bizarre appearance

has been shaped by its diet.

But one question continues to baffle scientists -

to which group of birds do the flamingos actually belong?

Some thought that they must be related to ducks and geese,

because of their webbed feet and short, duck-like beaks.

But others were convinced that, with their long legs,

they are more like waders, such as storks.

Recent DNA studies contradict both these suggestions.

They reveal that the flamingo's closest relative

may, in fact, be a small diving bird that looks nothing like a flamingo...

..the grebe.

Further studies found other similarities

in the structure of the eye

and the number of feathers on the wing.

So, it seems that flamingos and grebes

are, indeed, each other's closest relatives.

But over time, diet and lifestyle has shaped the flamingo

into a very different looking bird,

far removed from its grebe-like ancestor.

It's fair to say, there's nothing else quite like a flamingo.

The flamingo and the blue whale are two very different creatures -

one living on land and one in the deep oceans.

Yet, their bodies have been shaped in a similar way by their diet,

making each of them a curiosity within its own group.