Episode 7 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 most fascinating of all.

Some animals appear to protect themselves

with formidable suits of armour.

The rhino carries plates of thick hide on its flanks.

While the hedgehog is covered in prickly spines.

Both, in previous centuries,

inspired far-fetched and outlandish ideas,

but what is the true nature of their strange coats?

Some animals have mastered the art of deception.

The cuckoo tricks other birds into raising its young,

while the death's-head hawkmoth infiltrates the nests of bees

to steal their precious honey.

They're cheats and impostors.

Rhinoceroses are strange-looking creatures.

There are five kinds.

The Indian, this one, has a single horn, squat legs, tiny eyes...

Whoa!

..and thick folded skin.

For many centuries, before any had reached Europe,

they were surrounded by myth as much as the unicorn.

Few people had ever seen a live rhino, but, in 1741,

a young Indian rhinoceros called Clara came to Europe

and she transformed our image and understanding of the rhinoceros.

Thank you.

Before Clara arrived,

little was known in Europe about the rhinoceros.

A few animals arrived here in Roman times, but they didn't last long,

many being slaughtered during the brutal Roman Games.

It wasn't until the 16th century

that they first made a real mark on western society.

In 1515, a woodcut of a rhino was created by an artist called Durer.

It was a beautiful image of an elaborately armoured creature,

but it was inaccurate.

It's doubtful whether Durer ever saw a live rhinoceros.

It's little wonder that the rhinoceros was thought of

as a magical mythical creature

if Durer's woodcut of 1515 was to be believed.

He shows an armour-plated beast with a large horn

and a strange little spike on its back.

But in the 18th century, the perception of the rhinoceros was

to change when Clara came to Europe on an extraordinary 17-year tour.

Clara was captured in Assam at just a few months of age

when hunters killed her mother.

A director of the Dutch East India Company

raised her in his household as a pet.

She wandered indoors amongst the elegant furniture,

ate from a plate and was a popular attraction at his dinner parties.

But, inevitably, Clara got too big

and a little-known Dutch sea captain called Van der Meer

seized the chance to own possibly the only tame rhino in the world.

He saw the opportunity of making a lifetime's income

with an ambitious rhinoceros tour.

Clara became an orphan while she was still dependent on her mother.

Rhino calves usually stay with their mothers for up to two years,

sustained by the milk.

Only after that are they able to feed independently

on soft green grass.

Keeping a young rhino healthy was certainly a challenge,

but Van der Meer was smart and took good care of his new charge.

He travelled with her all the way from India

around the Cape of Good Hope, up the coast of Africa to the Netherlands

and his home town of Leiden.

He discovered very soon that Clara had a huge appetite

and he made sure that she always had plenty to eat.

Rhinoceros spend a great deal of time feeding.

They eat plant matter, but they don't have multiple stomachs

to digest and absorb nutrients,

so they need to eat large quantities of food to survive,

up to 100 kilos a day.

It takes a lot to fuel such an enormous body.

An adult rhino weighs over a tonne.

And the Indian rhino has a special mobile lip

to help it grasp and rip up the vegetation.

After reaching Europe, Clara lived quietly in Leiden for two years,

feeding and growing,

while Van der Meer made plans for his European tour.

At the time, a live rhino was a wondrous thing,

as Van der Meer well appreciated.

He was a clever businessman and he knew that publicity was needed

if his grand tour was to be a success.

Van der Meer made an unusual alliance with an ambitious

Dutch anatomist, BS Albinus,

who was hoping to produce a definitive medical textbook.

Both men were looking for publicity

and together they commissioned Jan Wandelaar,

an accomplished artist,

to make prints that would serve to advertise both the book and Clara.

They were strange but compelling pictures that combined

precisely drawn human skeletons and detailed images of Clara.

They were the most accurate drawings yet of the rhinoceros.

Wandelaar sketched Clara from life.

He was fascinated by the texture of her skin

and he depicted a rhino more realistically than Durer did ,

so, at last,

the myths surrounding the animal's appearance came to an end.

As the news of Clara's tour spread,

everyone was eager to see this wonderful new creature

and Clara's first trip to Vienna was for a royal appointment.

The Empress Maria-Theresa was so eager to see Clara

and so impressed by her appearance and good temperament,

that she brought her children back for another private showing.

Clara became the talk of the town

and European heads of state were eager to meet her.

She travelled through Europe like a celebrity

and met both royalty and crowds of curious onlookers.

Her horn in particular attracted much attention.

In Paris she started a rhino-mania

with fashionable women styling their hair 'a-la rhinoceros!'

Some regarded rhinos as living unicorns.

The scientific name for the Indian rhino is, in fact,

Rhinoceros Unicornis,

and, at the time, it was believed that the horn was made of bone.

But this in fact is not the case.

Rhinoceros horn grows from a spongy base positioned here on the skull.

The horn has no bony core.

It's made of keratin, the same substance as fingernails

and can grow again if it's lost.

Well, in June 1750, Clara's horn fell off,

probably due to her rubbing it on the travel crate.

To Van der Meer, this seemed to be a disaster

since he had no idea that it would regrow.

But, ingenuously, he used the event as a publicity stunt and the crowds

flocked all the more to see Clara fearing that she might be dying.

Even without a horn, Clara was still a fascinating creature

and her strange armoured skin was another talking point.

Why would such a gentle creature have such thick and elaborate folds?

The rhinoceros's skin in some parts is almost five centimetres thick,

nearly three times thicker than you would expect

for an animal that size.

We now know that, in the wild,

rhinoceros are not always as gentle as Clara.

They can be very aggressive,

particularly during the mating season,

and the tough skin provides them with some protection.

But it also has other benefits.

Thick skin is a good barrier against sun, flies and other parasites,

but why the skin of an Indian rhino grows in plate-like structures

with deep grooves has only recently been explained.

We know that the thicker skin areas are good physical protection,

but something deeper is going on.

It seems that the large folds increase the surface area

of the skin and help the rhino regulate its body temperature.

The tissues around the grooves are particularly rich in blood vessels

and transmit heat to the enlarged skin plates

which act like cooling radiators.

Indian rhinoceros bathe regularly and the folds in their skin

not only trap water but hold it even after they come back onto land.

So it turns out that the Indian rhinoceros's skin

is a far more specialised structure than anyone could have imagined.

For 17 years, Clara travelled across Europe,

stopping off in all the main towns and cities.

Everywhere she went, the crowds queued up to see her.

She visited England three times,

but her third visit proved to be her last.

In 1758, at the age of little more than 20,

Clara unexpectedly died in London.

Van der Meer was deeply shocked as he thought she might live to be 100.

Life on the road was over, but Clara's 17-year tour

had changed the image of the rhinoceros forever.

Durer's classic engraving of the fierce armoured beast was now

a part of history and new accurate images were produced.

The true Indian rhinoceros, like Clara,

looked just like this wonderful animal

painted by the great 18th-century artist George Stubbs.

Van der Meer made his fortune with her on the grand tour,

but Clara, more importantly, also enabled people

to get a first realistic view of what a rhinoceros looks like

and put to rest the idea of a heavily armoured mythical creature.

There is a more familiar animal whose body armour

also perplexed us for a surprisingly long time.

The hedgehog.

This delightful little creature is one of our most familiar

garden animals and yet it's got a surprisingly unusual appearance.

Instead of fur, like most mammals, it's got a thick coat of spines.

The only part of its body not covered by them

are its face and its underside.

The hedgehog's coat may appear to be painfully prickly,

but when the hedgehog is relaxed, it can lay its spines down flat.

When it senses danger, of course, it rolls itself up into a ball

and is completely hidden and protected.

It's a formidable suit of armour, these spines.

Nothing much can get past them.

It seems obvious that spines must serve as a protection

but their function was, in fact, misunderstood for a long time.

Early books claimed the spines were used for collecting food.

The hedgehogs were said to climb apple trees,

knock down the fruit and roll on it, impaling the apples on their spines

and carrying them off to their burrows.

Today we know that hedgehogs are better at climbing

than you might think, but they still haven't been seen to climb trees.

And there were other myths.

In medieval times, farmers believed that hedgehogs would steal milk

from their cows at night.

So the Elizabethan Parliament put a three-pence bounty on the head

of every hedgehog and thousands were slaughtered as a result.

Our attitude to the hedgehog is now very different.

Today, many of us get great pleasure

from seeing this appealing little creature in our gardens.

We know that they are a gardener's friend,

feeding mostly on insects and slugs

and helping to rid our plants of pests.

Some of us even put out special food to attract them.

We now also understand more about the hedgehog's spines.

They are, in fact, modified hairs,

hollow inside but reinforced with keratin,

the same material that forms a rhinoceros's horn.

That makes them strong while keeping weight down to a minimum.

A hedgehog has over 5,000 spines

and their main purpose is indeed protection.

But hedgehogs don't start life with a coat of armour.

It would be painful for a hedgehog mother

to give birth to spiny babies.

But nature has dealt with that problem.

Tiny hoglets are born with their spines covered by a layer of skin.

Within a few hours, the thin quills break through.

A baby hedgehog's first spines are soft and white

but these soon fall out and are replaced by darker and harder ones.

Hedgehog spines are shed and regrown at various stages in their lives,

just like the hair of mammals.

Surprisingly, a spiny armour is not common in the animal kingdom.

In Europe, the hedgehog is the only one of its kind.

But in other parts of the world, there are creatures that have

evolved a similar spiky coat.

This is an African crested porcupine.

It's got a formidable coat of spines but it's no relative

of the hedgehog and the spines are in fact very different.

For one thing, they are very much longer.

Normally, they lie flat against the body but if the animal is irritated,

it directs them to give a very spectacular warning.

Even the most ferocious predator will take care

when approaching a porcupine.

The quills will break off easily and become lodged in the skin.

The lion's only chance is to attack from the front.

As they circle, the porcupine twists and turns

to keep its armoured back to them.

This time, the lion got too close.

It has no way of removing the spike and may be unable to feed.

It could prove fatal for the predator.

Although the porcupine's quills may appear thin, even flimsy,

once they get stuck in your flesh, they are remarkably difficult

and painful to remove.

Why this should be was not known until recently.

But when looked at under an electron microscope, you can see

that each quill is coated with tiny backwards facing barbs.

The barbs act like the teeth on a serrated knife,

making it easier to penetrate the skin,

but when it comes to removing the quills,

the barbs have the opposite effect and act as anchors,

preventing the spine from sliding out of the wound.

The porcupine's spiky coat seems more formidable than the hedgehog's.

But the hedgehog has a very effective way of protecting

its vulnerable underbelly.

It rolls itself into a ball, so that it is completely encased in spines.

Foxes do attack hedgehogs but a fox must wait until the animal

is on the move if it is to get at its unprotected underside.

If the hedgehog stays rolled in a defensive ball,

the fox can't harm it.

All the hedgehog has to do is to sit it out until the fox loses interest.

But if spines are such an effective defence,

why don't many other animals adopt them?

The answer seems to be connected with the difficulties

of life with spines.

Spines may be something of a hindrance when it comes to mating.

Indeed, early naturalists thought that the hedgehogs must mate

belly to belly to avoid being impaled on each other's spines.

We now know that that's not the case.

The spines seem to do nothing

to hinder the ardour of a male hedgehog.

If she is willing, he tries to oblige.

But it still looks like a tricky and uncomfortable operation.

Despite the limitations of a spiny coat,

hedgehogs have remained largely unchanged

for almost 15 million years.

New evidence suggests that the spines may play another

rather surprising role in their lives.

Hedgehogs, when encountering an unfamiliar or toxic object,

sometimes behave in a very strange way.

They will lick and bite it until they start to foam at the mouth.

The froth is then transferred to their spines.

We still don't fully understand this strange behaviour.

It may help to camouflage the hedgehog's smell,

or make the spiny coat more distasteful to predators.

Or maybe it helps hedgehogs communicate with each other.

Or make them more attractive to the opposite sex.

We might one day discover its true purpose but we haven't yet.

Our familiar British hedgehog has provoked some very strange

and far-fetched ideas, but, for many of us,

it remains one of the most engaging animals in the British countryside,

and its prickly coat makes it that much more attractive.

So, it turns out that some of the early ideas about the purpose

of the rhino's armour and the hedgehog's spines

were only partly correct.

Their true functions are far more complex than we yet realise.

CUCKOO CALLS

The call of the cuckoo has long been regarded as a sign of spring.

But, in fact, it's the call of a killer and a cheat.

The cuckoo lays its egg in the nests of other birds and somehow

persuades them to treat it and its chick as if it were their own.

How does it get away with it?

It's a question that has puzzled people for centuries.

In Britain, the cuckoo arrives at a time

when most birds are nesting and laying eggs.

Early egg collectors noticed that the nests of some birds

had a slightly odd-looking egg in them.

These are the eggs laid by a number of different birds.

A marsh warbler, spotted flycatcher, a linnet and a whitethroat.

Amongst each of those clutches, there is a fraudster, a cuckoo egg,

which mimics that of its host.

Although cuckoos are long known to lay their eggs in the nests

of other birds, no-one had actually described it happening.

Then, in the 18th century, an English country doctor

with an interest in natural history decided to investigate.

Edward Jenner lived here in Berkeley, Gloucestershire,

and is best known for his work on the smallpox vaccine.

In fact, he is said to be the father of vaccination and that

his work has saved more human lives than that of any other man.

What is less known is that he first achieved scientific distinction

by his observations on the behaviour of the cuckoo.

At the time, it was believed that a cuckoo removes

all of the eggs in a nest and then lays its own.

By doing so, it would ensure its own chick gets all the food

brought in by the unwitting nest owners.

But Edward Jenner's detailed observations were to reveal

a rather darker tale.

Jenner's work on cuckoos was published in 1788

here in the Philosophical Transactions of the Royal Society,

the world's first scientific society.

It was entitled simply...

"Observations on the natural history of the cuckoo"

by Mr Edward Jenner.

In it, he reported that it was not the parent cuckoo

but the newly hatched chick which pushes the eggs

and nestlings of the foster parents out of the nest.

As soon as it hatches,

the cuckoo chick's instinct is to kill anything else in the nest.

It's still blind and naked

but it has a cup-shaped depression on its back

into which an egg fits perfectly.

But sometimes the other eggs hatch earlier and Jenner's observations

of how the cuckoo chick deals with its nest mates

were quite shocking.

He writes...

"the moment of accomplishing this was very curious.

"The little animal, with the assistance of its rump and wings,

"contrived to get the bird on its back

"and, making a lodgement of the burden by elevating its elbows,

"clambered backwards with it up the side of the nest

"until it reached the top, where, resting for a moment,

"it threw off its load with a jerk

"and quite disengaged it from the nest."

The real villain had been uncovered.

Jenner's views were met with incredulity and some disbelief,

but nonetheless they earned him the Fellowship of the Royal Society.

It was the greatest honour that could be given to

a scientist at the time.

Jenner's observations had revealed

the true nature of the cuckoo's deception.

But it still wasn't clear why the cuckoos should opt for this

strange way of raising its young.

It wasn't until 100 years later that Charles Darwin finally

provided an explanation with his theory of evolution.

The cuckoo's behaviour has evolved

to increase its own breeding success.

By avoiding the task of raising chicks,

the cuckoo can lay more eggs than any other bird,

as many as 25 in a season.

While it makes evolutionary sense for the cuckoo

to lay its eggs in the nests of others, what about its victims?

Why do they put up with this trickery?

It seems that they sometimes don't.

This was revealed in an early natural history film in 1920.

The Cuckoo's Secret was made by Edgar Chance and Oliver Pike,

an egg collector and a wildlife film maker.

Chance was fascinated by cuckoos

and spent a great deal of time following them.

He was the first person known to see a cuckoo lay its egg.

The deception involves stealth and speed.

The female waits until a nest is unattended and then she strikes.

But if she is spotted, the owners fight back.

If she is successful,

the whole deception takes less than ten seconds.

She removes and eats just one egg and replaces it with her own.

The Chance and Pike film solved one mystery,

but there were still others.

How does the cuckoo choose its victim?

And why don't the nest owners reject the alien egg?

Reed warblers are one of the cuckoo's main targets

and the pair has a nest just in here.

The female warbler has laid four speckled eggs,

and, using a model egg, I can illustrate the cuckoo's trickery.

This is the sort of egg that a cuckoo would lay

in the reed warbler's nest.

It matches the reed warbler's actual egg very closely in colour.

Experiments with model eggs have shown that reed warblers

have become very good at recognising an alien egg

and either throw it out or desert their nest to start afresh.

So the cuckoo has to make sure that it produces an egg

that is a very good match.

The cuckoo and its victims are evolving competitively.

With each generation, cuckoos improve their mimicry,

while the nest owners become better at spotting a foreign egg.

While many birds are very good

at detecting a strange egg in their nest,

they seem incapable of recognising

the monstrous cuckoo chick as an impostor.

But the deception is not complete.

The young cuckoo is much larger than the reed warbler chick

so it also needs a lot more food.

How does it get enough?

The cuckoo has a solution.

It now uses vocal deception to trick its foster parents

into providing more food.

This is a sonogram of the sound waves produced by a single

reed warbler chick begging for food.

Below it is the call of a cuckoo chick,

and, as you can see, it looks very different.

In fact, it more closely resembles

the calls of a whole nestful of reed warbler chicks.

So, the cuckoo chick's call is a super stimulus

that sounds like a whole nestful of chicks.

And it appears to work.

The adult birds rush back and forth,

providing the impostor with the same amount of food

as they would for an entire brood of their own.

At three weeks old, the cuckoo chick

has spilled out of the nest.

It's now almost eight times the size of its foster parent.

It was over 200 years ago

that Edward Jenner first shocked us

with his revelation of the cuckoo's extraordinary lifestyle.

Now we know that its unusual behaviour

is due to an extraordinary arms race

that has resulted in one of the most fascinating

specialisations in nature.

The cuckoo's success relies on deceiving just two parent birds.

But our second subject is a moth

that is able to deceive hundreds of bees.

How does it infiltrate

one of the most heavily guarded nests in nature?

This wonderful creature was once

one of the most feared insects in Europe.

It's a death's-head hawkmoth,

and it's easy enough to see how it got its name.

It has this mark on its back

that looks just like a human skull.

This gave it a bad reputation that lasted for centuries,

but now there are new ideas about this moth's strange appearance

that may help explain its extraordinary ability

to rob hives without being stung.

Death's-head hawkmoths are a rare sight Britain,

for they spend most of their lives in Africa and Asia.

But every summer a small number of migrants

arrive in northern Europe,

and, if the weather is warm enough, they breed.

Their caterpillars, unlike the drab adult moths,

are beautifully coloured.

After feeding for several weeks

they can grow to a length of 13 centimetres.

Once ready to become adults, they pupate in the soil

and emerge as the sinister, strangely patterned moths.

In the early 19th century,

a region of northern France was hit by a terrible pestilence,

and, at the same time, a large number of hawkmoths

were seen in the area.

The local people linked the deaths to these night-flying insects.

But there was another even more disturbing side to this moth.

It could make an unusual noise.

SQUEAKING

There.

A strange squeak.

And that only added to its chilling reputation.

Moths don't usually squeak.

Tiger moths sometimes produce ultrasonic warning clicks

that tell bats that they're poisonous and not good to eat,

but this is not a noise we can generally hear.

Perhaps the death's-head hawkmoth squeaks

to scare predators like birds.

However, other large migratory moths

don't make such a sound.

This makes the death's-head hawkmoth's squeak

all the more surprising,

and it has intrigued people for centuries.

These moths are more than 200 years old.

We know that because the handwritten label there tells us

they were collected in 1801 by a Robert Darling Willis,

the personal physician to King George III.

George III is well-known as the king

who suffered from bouts of madness,

and, on a visit to see the king during one of them,

Dr Willis discovered these large moths in the monarch's bedchamber.

Unable to identify them, the doctor sent them to his grandson,

who was at that time superintendent

at the Museum of Zoology in Cambridge.

He confirmed that they were death's-head hawkmoths,

and, unusually for an insect,

this moth produces a loud call

that has been likened to the mournful cry

of a grief-stricken child.

Did the disturbed king hear the plaintive calls of a hawkmoth?

That we don't know.

But certainly many of the ordinary people of the 19th century

were struck with a sense of terror whenever this moth appeared.

The moths' unusual appearance and strange behaviour baffled people.

But, in nature, such traits usually have a purpose.

And it may be for the death's-head hawkmoth

that they enable it to break into beehives and steal their honey.

These are the giant honey bees of south-east Asia,

and they form some of the largest bee colonies in the world.

I once got up close to one in order to demonstrate

their response to a predator.

I had a model of a large hornet,

which produced a kind of Mexican wave,

and that makes it very difficult for an aggressor to land.

BUZZING

This covering of bees looks impossible to penetrate.

But at night

a thief can break through their ranks.

A death's-head hawkmoth lands on the carpet of bees

and pushes its way through without being attacked.

In just a few seconds, it takes some sips of honey

and emerges unharmed.

Getting past the guard bees is quite a feat,

but surviving inside is even more astounding.

Death's-head hawkmoths raid domestic beehives too,

and can be quite a pest.

Somehow, the moth slips past the guards and, as if invisible,

walks through the hive, heading straight for the honeycomb.

It then feeds unnoticed.

How does it do this?

One theory proposes that its spooky appearance

may help it avoid being attacked.

BUZZING

Miriam Rothschild, a great entomologist

and expert on fleas and butterflies,

suggested that the moth's skull pattern looks like

the head of a worker bee,

and that this could play a role in the moth's deception.

Well, this is a photograph

of a worker bee face taken through a microscope.

Let's see how it looks next to a close-up photo

of the skull pattern of the moth.

There.

Well, I suppose there's a slight resemblance,

but given the fact that most moths raid beehives and nests

during the night, it's unlikely the bees

could see that much detail.

The most likely answer lies in the scent the moth gives off.

In America in the 1950s,

a German entomologist called Thomas Eisner

studied chemical ecology - in particular,

the chemical defences of insects.

Most famously, he illustrated how bombardier beetles

fire hot acid onto a predator.

He also studied moths,

and showed that the feathery projections on their abdomens

and their large antennae were used to produce and pick up scent.

It seemed that many insects were using scent in surprising ways.

Tests on the chemical scents produced by hawkmoths

reveal a remarkable similarity to those produced by the worker bees

in the hives that they raid.

Their scent is not identical,

but it contains several key chemicals

that exactly match those produced by bees.

So the death's-head hawkmoth's scent

acts as an invisibility cloak

that makes it undetectable to the worker bees in the nest.

With thick scales on its body,

clawed feet that grip the honeycomb,

and a short, pointed proboscis to pierce the honey cells,

the moth has evolved into an effective hive robber.

But there is another, even more impressive impostor

that can also penetrate the protective defences

of an insect colony.

Its victims are not bees but ants.

The impostor that invades this ant nest

doesn't get in there by flying.

Nothing as blatant as that.

Instead, the caterpillars of some species of blue butterfly,

like this one, wait for red ants to collect them.

Remarkably, passing ants don't kill them.

They pick them up and take them back into their nest.

The cuckoo caterpillar will stay inside the nest

for up to ten months.

Just like the death's-head hawkmoths,

it produces a chemical scent that deceives the ants.

This pink caterpillar, which belongs to the alcon blue butterfly,

has been collected because, to them,

it smells just like the young of their own nest.

They become controlled by the impostor's intoxicating scent,

and feed the butterfly larva even more regularly

than they do their own.

There's another way this impostor pulls off its deceptive trick.

When it's inside the nest,

the butterfly larva makes a strange chattering noise.

To our ears, it's very faint,

but it's clear enough to other insects. This is it.

CHATTERING NOISE

And this is the sound that's made by a queen ant.

SIMILAR CHATTERING NOISE

To worker ants, these calls are very similar,

and they react by treating the butterfly larva

as if it's one of their own.

Caterpillars of the blue butterfly are impressive impostors.

Not only do they mimic the scent of the ants,

but their queen's calls too.

This seems to trump the death's-head hawkmoth's ability

as a nest invader.

But the hawkmoth may also be using sound to trick its victims.

Remember the eerie squeak that was thought to be so frightening?

SQUEAKING

There.

The hawkmoth makes this sound inside the beehive

when it enters to steal honey.

It's been suggested that this might calm the bees,

because the squeak is thought to sound like the piping call

that the queen honey bee makes to pacify her workers.

We can't be sure if the call and the strange skull marking

evolved to deceive bees, but we can be certain

that the death's-head hawkmoth's life as an impostor

is more curious than the superstitions

that have surrounded it for hundreds of years.

The cuckoo and the hawkmoth are both audacious impostors,

but the cuckoo's ability to make its victim raise its young

is perhaps the most accomplished deception of all.