David Attenborough examines animals with an amazing ability to find their way - the dung beetle uses the sun, moon and even the Milky Way.
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The natural world is full of extraordinary animals
with amazing life histories.
Yet certain stories are more intriguing than others.
The mysteries of a butterfly's life cycle.
Or the strange biology of the Emperor Penguin.
Some of these creatures were surrounded by
fantastic myths and misunderstandings.
Others have only recently revealed their secrets.
These are the creatures that stand out from the crowd,
the curiosities that I find particularly fascinating.
Pigeons are so common that we tend to take them for granted.
But in fact, they are superb navigators
and can find their way home from hundreds of miles away.
And the dung beetle will roll a dung ball in a straight line
even though it's head down and walking backwards.
How on earth do these creatures manage to find their way?
Pigeon fanciers know that if they take homing pigeons
to somewhere where they've never been before,
even if it's tens, even hundreds of miles away, and then release them,
they will, after circling in the sky, head for home.
These come from over there.
Let's see what happens.
Well, they certainly seem to be heading in the right direction.
But how do pigeons find their way back home
over totally unfamiliar territory?
It seems the more mysterious to us because it's something we can't do
unless we have all kinds of special equipment.
But science is now beginning to find some of the answers.
The homing pigeon is a domesticated descendant of the wild rock pigeon
which lives on cliffs and ledges along our coasts.
When humans started to domesticate them, they inevitably selected
those birds that were particularly good at returning to their roosts.
Pigeons are thought to be the very first birds
to be domesticated by mankind, many thousands of years ago.
Since then, they've been bred into many different varieties,
including homing pigeons.
And the varied appearance of this flock around me
is evidence of that domesticated past.
Since then, of course, they've come to live alongside us in our cities
and giving many of us a lot of pleasure.
It was not only their homing ability that made pigeons
so popular with breeders, they are also superb flyers.
Their powerful wing muscles make up nearly half their body weight
and enable them to fly at speeds of 60mph.
They're among the greatest long-distance athletes
in the bird world.
And pigeon fanciers have delighted in breeding them
in order to race them competitively.
Mankind has also used pigeons for a very practical purpose...
It was during the two World Wars that pigeons played a crucial role
in carrying messages home from the front line.
Nearly a quarter of a million birds served in the wars
and helped save thousands of lives.
One such bird was Cher Ami,
a female donated by a British pigeon fancier
for use by the United States Army during World War I.
During one battle in France in 1918, more than 500 soldiers
from the US infantry became trapped behind enemy lines.
Worse, they were then fired upon by their own troops
who didn't know they were there.
Within 24 hours, more than half of them had been killed.
With no other options, the commander, Major Whittlesey,
desperately tried to send messages back by pigeon.
The first two birds were shot down and only Cher Ami was left.
For several moments, she flew with bullets zipping all around her,
and eventually she was brought down.
She'd been shot through the breast, blinded in one eye
and her leg was left hanging by a tendon.
Astonishingly, the injured bird managed to take flight again
and arrived back at her loft at the division headquarters
in just 25 minutes.
Cher Ami's message helped save the lives of 194 soldiers.
Her name in French, of course, means Dear Friend.
When the Second World War broke out,
Britain's pigeon fanciers once again
gave their pigeons to the war effort
to provide what was called the National Pigeon Service.
This elite squad of birds was extremely valuable and successful.
98% of their messages got through.
The Germans, realising how important the pigeons had become,
fought back with specially trained pigeon snipers.
They also retaliated in another way,
by using the pigeon's natural enemies - peregrine falcons.
Pigeons played such a vital role in the war
that many were celebrated as heroes.
In 1943, this medal, the Dickin Medal,
was founded to honour these animals.
It was awarded to individuals that appeared,
if you'll allow a little anthropomorphism,
to have displayed particular bravery.
And it's sometimes referred to as the Victoria Cross for animals.
Of the 54 medals presented during World War II,
32 were given to pigeons.
We may have prized pigeons for centuries
for their skills in finding their way through the skies,
but for a long time we had no idea how the birds did it.
Some suggested that pigeons used the sun.
Others that they were guided by the Earth's magnetic field.
But proving either was surprisingly difficult.
A breakthrough came from an American scientist
at Cornell University in the 1960s.
William Keeton attached magnets to the backs of some pigeons,
but not to others,
and found that when the sun was out,
both groups were able to make their way home.
But when the sun was hidden behind clouds,
the birds carrying magnets got lost.
Keeton deduced that this was because the signals from their magnets
swamped the much weaker ones coming from the Earth.
So he established that pigeons can use either the sun
or the Earth's magnetism to find their way around,
according to conditions.
But how do the birds detect the Earth's magnetism?
This compass has a magnetised needle,
which is sensitive to the Earth's magnetic field.
It will always point north,
allowing you to check the direction that you're travelling in.
But what about pigeons?
What could they be using to detect magnetic fields?
Scientists were puzzled because they couldn't find
any cells or organs in birds that were sensitive to magnetism.
Then, in 2007, microscopic clusters of iron-rich cells
were found in the beaks of homing pigeons,
and it was thought that these might help them to detect magnetic forces.
But only five years later, new research shattered that idea.
It seems that the cells in fact are a defence against infection
and have nothing whatsoever to do with magnetism.
So the search for the pigeon's magnetic compass still continues.
But we are now beginning to understand the other aspects
of their navigational skills.
A compass is just one of the tools we need for navigation.
But it's not much help
unless you know in which direction your destination lies.
And to know that, you need a map of some kind.
One way of creating a map in your mind
is to memorise the prominent features of a landscape.
Scientists at Oxford University are now using GPS technology
to discover if pigeons do this.
This bird has a GPS transmitting device strapped to its back
in a specially designed backpack
which causes it very little discomfort.
And that will record the progress of the bird, second by second,
once I let it go.
It comes from a loft over there about six miles away in Oxford.
Let's see whether or not she heads in that direction.
Off you go.
Birds, like this, that are released in a new place
still ahead confidently in the direction of their home loft.
How do they do it?
Data from GPS trackers
and cameras attached to the backs of pigeons
have helped to answer that question.
At first, a bird released in an unfamiliar place
will use the sun or the Earth's magnetic field to get its bearings.
But if you plot its movements on a map,
you can see that at first it doesn't find the shortest route home.
Then something changes.
After repeated releases, the bird is able to use its experience
to take a more direct way back.
So it appears that pigeons learn to recognise features of the landscape
such as hedgerows and trees, or even roads and buildings.
They then memorise these to create a mental map of the area
and by following familiar landmarks, they find their way back home.
It seems that pigeons are creatures of habit.
They like to stick to the routes they know well.
Here are some tracks of a pigeon that lives in its home loft up here
and was taken repeatedly to this point here.
Watch what happens.
It consistently makes a beeline for the major A road
that conveniently runs past its home loft.
And even when released some distance from this road,
it will cut across to it and then follow it all the way home,
as shown by the red lines.
Some birds even fly around roundabouts
before choosing the exit that will lead them back.
So it seems that pigeons use methods of navigation
more like ours than we might have imagined.
We now know that pigeons have
a whole range of navigational techniques at their disposal
and can call on them as needed.
It's a remarkably sophisticated system
that enables them to find their way in nearly any situation.
We've learned a lot about the pigeon's homing skills,
but some mysteries still remain.
In 1997, over 60,000 British birds were released
during a pigeon race in southern France.
Most of them didn't make it and were never seen again.
In pigeon racing terms, the loss of so many birds was unheard of.
One bird might get lost, but tens of thousands?
To get back to their lofts nearly 500 miles away,
the pigeons had to cross the English Channel.
It was not an unusually long or difficult journey
for a racing pigeon, so why did the birds not make it?
Well, there was a strange coincidence.
At the very same time the racing pigeons were crossing the Channel,
a Concorde supersonic airliner was flying along the Channel
on its morning flight from Paris to New York.
The Concorde generates a shock wave almost 100 miles wide.
The pigeons flying below could not have escaped it.
Could it be that this enormous wave of sound blotted out
all other acoustic information?
We know that pigeons can hear low-frequency infra-sounds
such as those generated by ocean waves.
And these might provide them with an acoustic map of their surroundings.
The jury is still out as to whether pigeons really do use
infra-sound to navigate
and whether that explains the case of the disappearing pigeons.
But it's an intriguing possibility.
The familiar pigeon continues to surprise us.
And even today, we're a long way off from understanding
all its route-finding techniques.
The small dung beetle has a brain no larger than a grain of rice.
But, like the pigeon, it is capable of astonishing navigational feats.
Moving large loads by walking head down and backwards
must surely be one of the most bizarre ways
of collecting your food.
Dung beetles are well known
for rolling their balls of dung in this way.
But why do they do so?
And how can they see where they are going?
Ball rolling by dung beetles is probably
one of the oldest recorded accounts of animal behaviour,
dating back nearly 2,000 years.
These insects were held sacred by the ancient Egyptians,
and in the fifth century, an Egyptian scholar called Horapollo
described the dung beetle as rolling its ball from east to west.
It seems that he was suggesting that the beetles always
moved their dung in a particular direction.
But how true is that?
In the following 2,000 years, little was done to examine the question.
Dung beetles feed on what is, to the animals that produce it,
a waste product - dung.
But in fact, there's more than enough nourishment in one dropping
to sustain a great number of beetles.
They locate a newly dropped pile using their sense of smell.
Their strong and powerful legs enable them
to break up the dropping
and their mouthparts are specially shaped
to extract the nutrients and moisture that they need.
They are, in fact, one of our planet's great recyclers.
Dung beetles are found all over the world.
There are over 6,000 species and they come in all shapes and colours.
But they have one thing in common -
they all feed on dung.
Some of them, like this scarab beetle...
..have rows of projections on the head,
which were likened by the ancient Egyptians
to the rays of the rising sun.
The broad front legs also carry spines.
These are adaptations for digging and shaping dung balls,
while the back legs are flattened
and have tiny hairs for controlling the ball.
But most dung beetles don't roll balls.
They live either in the dung itself
or tunnel directly into the soil beneath the dropping.
Only 10% transport dung above ground.
And they do so because competition near a pile of dung
can be very fierce.
The first ones at the scene are usually the rollers.
They take a little lump, mould it into a ball and then start rolling.
But that's easier said than done.
Rivals are on the lookout for an easy meal
and will only too quickly steal a ball if they can.
With competition so intense, some species roll their ball away
as quickly as possible and then bury it.
They can then eat it later
without the risk of another stealing their meal.
Dung beetles appear to roll their balls of dung with great purpose.
But it's only recently been discovered just how determined
they can be to do so in one particular direction.
Watch what happens if I put this dung beetle
on this board here.
And then put an obstacle in its way.
And what does it do?
It's going to go around.
And it resumes its previous direction.
It's clear that the beetle knows exactly
in which direction it wants to travel
and will continue to do so even when it's deflected by obstacles.
Now, let's make things even more difficult
using this turntable.
Let's see which direction
he wants to go.
He's going to come towards my hand.
Now I'll turn the world through 90 degrees beneath his feet
and yet he maintains
the same direction.
Why should it want to do that?
It's quite extraordinary.
He corrects his course instantaneously.
How does he know how to do this,
and why is he so determined to travel in a set direction?
The answer is, in fact, quite simple.
The fastest way to make a getaway
is to roll your ball in a straight line.
And that is exactly what the beetles try to do.
Using only its front legs,
a beetle can move a dung ball that is up to 60 times its own weight.
But walking head down and backwards has its own problems.
You can't see where you're going...
..or watch out for danger.
With competition around the pile of dung so intense,
it's obviously a good thing to get away from it as quickly as possible.
But how do the beetles decide in which direction to go?
Well, it seems it's all to do with a little dance that they perform
on top of their dung balls.
Let me see if I can persuade this one to do it.
I'll try to get it to walk up this ramp
until it falls off the end
and is separated from its ball.
Watch what it does then.
This little dance was once
regarded as being a sign of happiness,
that the beetle was delighted to have found a dung ball.
But actually, it's much more than that.
It's a way of deciding which direction it should go.
And what does it use as a cue to make that decision?
Well, recent research is beginning to produce the answer.
What appears to be a dance is actually
a way of looking around to get its bearings.
But what exactly is it looking for?
We can test what the beetles are using for a cue
by fitting them with caps.
This cap allows the beetle to see the ground beneath,
but not the sky above.
Compare that with this one without a cap.
Making up its mind.
And away it goes.
This one is still baffled.
The beetle with the cap clearly can't decide
in which direction to go.
Such experiments show
that dung beetles have to see the sky in order to orientate.
Their eyes are split in two halves by shovel-like extensions
on the sides of the head.
So, as they roll their balls of dung,
the upward-facing half can watch the sky above
and use the sun as a celestial compass.
But, contrary to what that ancient Egyptian scholar claimed,
they don't always travel from east to west.
Each beetle seems to choose a particular direction
away from the dung heap and then keeps to that course.
But why should anyone suppose
that the dung beetle always rolls its dung from east to west?
Well, the ancient Egyptians believed that their sun god, Khepri,
was responsible for rolling the sun across the sky every day
in just that direction.
The scarab, the Egyptian dung beetle,
similarly rolls its dung ball from dawn to dusk
and came to symbolise the sun god.
And so the god Khepri was often depicted with a scarab for a head.
The Egyptians also saw the scarab
as a symbol of life and resurrection.
The adult beetle would disappear underground with the ball of dung,
and when the eggs hatched, shiny, new scarab beetles
would seem to appear magically out of nowhere.
So the scarab came to symbolise creation, life
and even rebirth.
It's easy to see how the sun helps dung beetles
to navigate during the day.
But some beetles are nocturnal.
How do they keep on a straight course?
On a clear night,
the moon and millions of stars illuminate the sky,
just as they appear to do in this planetarium.
This is a nocturnal scarab beetle.
And scientists have recently discovered that it can use
the light from the sky to navigate.
But there is a puzzle.
The scarab beetle has very, very small eyes.
And whereas it can certainly see the moon,
it can't distinguish individual stars.
So how then does it navigate
on a moonless night?
The brightest light in the night sky
comes from the great band of stars known as the Milky Way.
And in the southern hemisphere, where these beetles live,
the Milky Way is particularly vivid.
Researchers have discovered that, as long as the Milky Way is in view,
the beetle and its ball can roll along and stay on course.
Without this bright band of light,
the beetle has no reference point and is lost.
The revelation that the beetles used starlight to navigate
astonished the scientific world.
How extraordinary that a tiny insect could use
the edge of our galaxy to find its way around.
Had the ancient Egyptians known that, surely they would have
felt vindicated in giving the scarab the status of a god.
So, the dung beetle and the pigeon are both ordinary creatures
that have found extraordinary solutions
to the problem that faces us all -
how to find the way.
Some animals have an extraordinary ability to find their way. The dung beetle, an insect revered by ancient Egyptians, uses the sun, the moon and even the Milky Way to move its prized ball of dung in the right direction. Pigeons are often considered feeble birdbrains, but they have incredible memories that can recall several complex travel routes with amazing accuracy and they even use man-made roads and hedgerows to find the quickest way home.