Original subtitles

There was a time when myths and science were entwined...

..when mermaids and unicorns could mysteriously appear.

Nature was weird.

When science revealed the truth behind these imaginary creatures,

it found real animals lay behind the legends.

Today science still makes astonishing discoveries,

but nature seems just as weird.

It's just that fact has broken free from fiction.

Many dances are stylised forms of courtship.

Scorpions dance for the same seductive reason,

but a Spanish scorpion must court with care.

As he takes her by the claws, he fends off her sting with his tail.

Rejection now would be fatal.

He keeps up her interest by sweeping her off her feet.

The dance may last for hours, as he tries to put her into a receptive mood.

He seals his proposal with a kiss. It stops him becoming a meal.

Next, he offers a present.

He leaves a package to fertilise her eggs on the tip of a stalk.

He guides her to pick up the gift, leaving just the stalk behind.

This weird journey explores many other strange aspects of nature's ways of breeding.

In courtship, gifts are always appreciated.

The satin bowerbird of Australia

has an eye for the presents his partner adores.

Her favourite colour is blue.

This is not his nest, but a bower,

a place of seduction.

He must keep up his maintenance to impress any females that call.

She visits all the bowers in her neighbourhood

to judge each male on his home decorating skills.

She's hard to impress.

An experienced male won't accept rejection lightly.

He just works harder at winning her over.

The more blue trinkets he accumulates,

the more he turns her eye.

His interest in home decoration is purely biological.

The harder he works, the more he proves his fitness.

CAR KEY REMOTE CONTROL BLEEPS

He has amassed the bowerbird's equivalent of wealth -

a proof of his genetic worth.

And this bird has a lot on show.

STRIDENT SQUAWKING

On this occasion, a ring seems appropriate and seems to be doing the trick.

STRIDENT SQUAWKING

We may see human parallels here,

but, biologically, OUR behaviour is stranger.

Where are my keys?

We are one of the most sexually active of all mammals,

but we're also one of the least fertile.

and few animals have such a long courtship or mate throughout the year.

But by any measure, this marsupial mouse is weird.

Antechinus squeezes its bouts of passion into a few energetic days.

In early spring, the male's only goal is to mate with as many partners as possible.

Each session lasts several hours.

As soon as it ends, he looks for a new partner.

He aims to track down every female in the neighbourhood.

Subtlety is not his forte.

All this activity leaves him little time to eat, drink or sleep

and, in time, the stress starts to wear him down.

Although exhausted, rampant hormones urge him on to yet another encounter.

But he's feeling the strain.

Over the two-week breeding season,

he ages a lifetime.

Rundown and tired, he is literally on his last legs.

All the males are soon gone, leaving the females

to bring up the babies.

His sacrifice makes genetic sense.

More offspring will survive if he isn't there to compete for food.

BIRDSONG

Male mice may cause their own demise, but in the meadows of Southern France,

it's the female that's the deadlier of the species.

The femme fatale in question is the European preying mantis.

The smaller male courts his partner carefully.

She can literally make a meal of any male.

But he has to mate to pass on his genes.

In this gruesome embrace, her love bite is the last thing he knows.

But even this trauma doesn't seem to unnerve him.

He continues to mate as though nothing has happened.

Losing his head over a female helps nourish his future offspring.

Astonishingly, decapitation improves his performance.

A tiny brain in his rear keeps him active.

This macabre coupling can last a day.

Even then, the discarded carcass doesn't give up readily.

In the oceans, courtship is even more complicated.

It's a world of sexual confusion and gender-bending.

One of the commonest reef fish are anthias.

They gather in shoals many-hundreds strong.

Oddly, most of them are female.

They can be identified by their violet eyebrow line and orange colour.

The few males are purple with a plume-like fin on their back.

Should the male be removed, something strange happens.

The leading lady takes over his role - literally!

Her sexuality is flexible.

She can perform a quick sex change to take his place.

Not only does her colour and appearance change, she becomes he by developing male sex organs.

It takes less than a week for this lady to become a fully-functioning gent.

Gender-bending is also a speciality of sea hares.

Like other sea slugs, sea hares are bisexual.

Their hindquarters are female and their head ends are male.

Sexual orientation depends on which ends meet first.

When several sea hares get together,

they often form a mating chain.

The front slug has to be female.

Those in the middle mate both ways and the last slug is always male.

If the leader joins the end of the chain, a bisexual reel forms.

Birth inevitably follows mating.

For some, bubbles hold the secret of childcare.

These Thai men

are experts on breeding Siamese fighting fish.

Traditionally, bets are placed on contests between prize specimens.

Such fights occur naturally in nearby lakes and rivers.

In either place,

the winner gains the female and a chance to show a more tender side to his nature.

An egg-like marking on her belly shows she's ready to breed -

a come-on for the male to start courtship.

He does something reminiscent of a child's game.

He blows bubbles.

He stops his bubbles popping by coating them with saliva.

Soon a cluster of glistening baubles starts to accumulate.

These will form a bubble nest for the care of his young.

Then his aggression returns.

But only to put her in the mood to accept his embrace.

His quickly siphons up the fertilised eggs.

Then spits them into the bubbles.

This bubble-wrapping protects them from predators or infection.

Two days later, the fry hatch and start to feed from their egg sacks.

The fighting fish keeps up his vigil.

Stray fry are caught and returned to the care of the bubble nest.

Caring for young by bubble-wrapping them is popular in nature.

The preying mantis lathers up a foam of microscopic bubbles to cocoon HER offspring.

The foam hardens into a protective case that cossets her young.

CHILDREN SHOUT

Foam-nesting frogs also get into a lather tending their young.

The mother secretes a fluid that the pair whip up into a foam similar to egg white.

She lays her fertilised eggs inside.

The outer wall of bubbles hardens like meringue

and protects the eggs from predators, bacteria and the weather.

Three days later,

the first of several hundred tadpoles emerge.

While some bubble-wrap their young, others literally splash out

on childcare.

In the Amazon, splash tetras stage a leaping contest.

These strange fish out of water lay their eggs on leaves.

The males leap to inspect suitable sites.

They prefer protected leaves with a surface that's easy to stick to.

The leap requires perfect posture.

The fish must align itself

so it grips the leaf by surface tension as it lands.

The male guards his chosen leaf until a female arrives.

They line up under the leaf and perform the ultimate act of synchronised swimming.

As a cue, the female nudges the male with her head,

then a flick of their tails propels them in perfect unison.

They are so synchronised,

to the human eye they appear as one.

The eggs are laid. The male's work has just begun - he must keep them wet until they hatch.

The splash tetra must have the most labour-intensive childcare of any fish.

But his eggs are safer from predators on leaves, rather than in the river.

After two days of hard splashing, the fry emerge.

The Surinam toad's version of parenting is even more eccentric.

Her young literally get under her skin.

They develop from eggs to tadpoles in a wad of skin on her back

and emerge as fully-formed toadlets.

Most toads lay hundreds of eggs and only a few survive.

Using skincare ensures that all the Surinam's offspring become baby toads.

Once free, they fend for themselves.

For some, parental care is the father's responsibility.

The African bullfrog is one such doting parent.

Tadpoles develop in shallow pools where he acts as their lifeguard.

But water is siphoned up by many thirsty creatures.

Faced with towering competition, the bullfrog retreats,

but as the water levels drop, he still remembers his offspring.

The sun also causes the precious water to vanish.

Soon the mud will be concrete-hard.

His poor tadpoles are left high and dry.

They call to their father for help.

He reacts by digging an escape route.

It's a race against time.

He paddles away to soften the rock-hard earth as he digs a canal.

Their pleas for help urge him on.

Breakthrough happens in the nick of time.

He leads his offspring to safety.

The bullfrog is one of the world's most devoted fathers,

but he has competition.

The Siberian dwarf hamster

must win the prize for being nature's new man.

The male acts as midwife during his partner's labour.

Male midwifery is unique among mammals and - even in humans - it's a recent development.

Biologically, human birthing behaviour is strange.

Only humans have such painful extended labour. Few animals have such helpless young.

Human males traditionally stay away at the birth.

However, the hamster's mate is her constant birth companion.

Russian hospitals follow tradition, excluding fathers from the birth.

But the hamster's partner shows a feminine care and concern.

He cleans each newborn baby in turn.

His human counterpart can only wait in the sidelines.

At birth, the hamster even cuts the umbilical cord with his teeth.

BABY CRIES

Traditionally, women continue to help once the birth is over.

Again, the male hamster takes on this caring role.

He retrieves any youngsters that wriggle from the nest.

In many countries, human fathers are now encouraged to attend the birth,

but in Russia, old traditions die hard.

The hamster may be the only mammal that naturally acts like a new man.

But there's a catch - he soon reveals a less sensitive side.

His partner can only mate over the next three hours.

Helping at the birth stops him missing the moment.

But the dwarf hamster has a rival for his new-age credentials.

Sea horses are the only animals in which the male

actually becomes pregnant.

He carries his partner's eggs in a brood pouch on his stomach.

The pouch lining acts like a placenta

and nourishes the developing young.

When the times comes to give birth, he even suffers contractions.

They become more violent as the birth approaches.

He gives birth to around 100 young.

Each is a miniature replica of their father.

Sea horses are the only animals

whose males experience the birth process.

His young grip the nearest thing they can find - even each other.

He may be the spitting image of his father, but from now on, he's on his own.

For sea horses,

parental care stops at birth.

Extended childcare is most common in mammals.

The Asian musk shrew has perhaps the oddest way of keeping her young in line.

Moving a large family between nests is a big responsibility.

To avoid getting lost, each youngster bites the fur by its neighbour's tail and hangs on.

To the young, it's a game of follow-my-leader.

Wherever their mother goes, they keep in step.

But if the mother becomes separated from her brood,

the youngster grab any moving thing that passes.

Their persistence and strength of grasp is phenomenal.

As long as the train keeps moving,

they'll hold on tight...

..even in the air.

Stop the train and they let go.

When the mother returns, order is restored to her chaotic brood.

She guides her daisy chain to safety.

Such care may seem odd, but in a world

of bizarre breeding, we are stranger.

No other animal tends its young for as long as us.