Hidden forces shroud our world.
0n this journey, we glimpse their presence.
The aurora borealis sweeping the northern skies
can be a sign all is not well in the heavens.
When magnetic storms rage on the sun,
charged particles bombard the earth,
creating curtains of light as they collide with the atmosphere.
To migrants, such as starlings,
these northern lights have a darker side.
The sun“s magnetic storms can cause chaos in both our worlds.
Power surges in the atmosphere can trip the electric grid.
Away from land, the effects can be devastating,
especially if the weather worsens.
The earth“s magnetic field warps, deflecting compasses.
Radio transmissions suffer interference.
The starlings“ sense of direction is affected, too.
Lost at sea, they head for shelter.
0ther forces now materialise.
St Elmo“s fire, a ghostly glow of energised air,
warns of imminent lightning.
(Thunderclap)
In the past, the seasonal coming and going of birds
was considered supernatural.
Enter their world
and the hidden forces now known to guide their migrations
appear just as remarkable.
Each autumn, greylag geese fly nearly a thousand kilometres
from Iceland to Britain.
They use hidden forces to predict the weather
and ensure the flock sets off under favourable conditions.
0ther forces, such as the earth“s magnetic field,
help the geese keep on course.
We“ve only just begun to unravel the magnetic senses
that guide animals across an often featureless world.
Some of their feats defy belief.
These green turtle hatchlings
are starting a nomadic life roaming the oceans.
It will be 30 years before they return here to breed.
Somehow they find this remote beach again.
The secret lies in tiny magnetised particles
known as magnetite.
These internal magnets may sense
both the strength of the magnetic field
as well as its angle to the earth.
These two forces act like grid lines on a map.
Any point in the ocean has its own unique coordinates.
(Squawking)
Brown pelicans also use magnetite, but new findings have found
that birds possess an additional system.
Vision is involved.
Specialised magnetic sensors have been identified in the retina.
These see a coloured spot that shows the position
of the magnetic pole.
This head-up display allows the birds to navigate uncharted waters
by providing a constant compass bearing.
Like trawler men, they use their compass
to find the richest fishing grounds.
A free lunch is irresistible.
There are yet other ways to sense the earth“s magnetism.
Hammerhead sharks are so perceptive,
they can detect local variations of magnetism in underlying rock.
They seem to congregate where magnetised lava
from an extinct volcano creates an invisible landmark.
At night, sharks leave their staging post and follow hidden roadways
marked by abrupt changes in magnetic intensity.
The bizarre head enhances sensitivity
to these local distortions in the earth“s field.
Sharks use electrosensors to detect magnetism.
The same sensors home in on the body fields of their prey.
Their widened head spaces out the sensors, increasing sensitivity.
A sense so acute is easily confused.
(Sonar pinging)
A nuclear submarine tows a hydrophonic array
to detect other submarines.
The array gives off electric and magnetic waves.
Sharks find the combination irresistible.
These hydrophones are being redesigned
to prevent damage from shark attacks.
(Low electrical drone )
Fire ants share the sharks“ passion for electricity.
Introduced into America from Brazil in the 1930s,
the ants soon acquired a strange interest in technology.
(Low electrical drone )
Perhaps they mistake electricity for the body fields of their prey.
No one really knows.
What is known is the chaos caused by the ants.
(Car horns blare )
By severing wires and creating short circuits,
fire ants are the ultimate gremlins in the machine.
(Car horns and sirens )
In homes, they seek the electromagnetic waves
given off by domestic appliances.
A microwave oven makes an irresistible target.
Electrical attraction lures the ants into this potential hot spot.
But techno ants are not easily destroyed.
Fire ants are so small, most of the microwave energy misses them.
They also sense cooler zones.
If hot spots build up, unlike food, they can quickly move away.
Fire ants are aptly named.
Their stings burn.
- (Screams ) - (Car horns blare )
(Tyres screech, crashing)
Every year, across the southern States,
fire ants cause millions of dollars“ worth of damage.
(Siren wails)
(Woman ) There were ants in my pizza...
As each queen ant can spawn a colony of 30,000 individuals,
this alien invasion has proved impossible to repel.
Because of concerns about possible risks
from electromagnetic forces, homes are now rarely built
under high-voltage power lines.
(Low electrical drone )
Through, strangely enough, plants appear to thrive here.
They find electromagnetic fields stimulating.
Changes to electric charges in plants
affect hormones controlling growth.
Perhaps these forces help the process.
Electricity is not always so appreciated.
Bees will desert hives placed under power lines.
The explanation may lie in the bees“ own electric charge,
generated by friction with the air as it flies.
The bees make good use of this static charge.
Pollen is positively charged
and is attracted to the negatively charged bee, even while it“s flying.
For a busy bee, this remote pickup saves time.
The prize is stored in a pollen sac.
Bees probably swarm away from power lines
because of interference with the bees“ static charges.
Any electric field disturbs them.
The bees react aggressively to electricity, as though under threat.
Guard bees defend the colony at all cost.
They target any source of electricity.
We“ve learnt to harness many electrical forces.
But the untamed electricity of nature
unleashes even stronger powers.
(Thunderclap)
Besides these static discharges, the air holds far subtler charges.
Concentrations of charged molecules, known as air ions,
change with the weather.
Snakes may have the power to detect these air ions.
Friction causes static charges to build up on a snake,
just as they do on a bee.
Because the snake“s skin is a good insulator,
it“s perfectly adapted to hold static electricity.
The synthetic clothing used by cyclists
holds static charges in the same way.
(Hissing rattle )
The snake uses the rattle as a warning.
0ur static is easily discharged.
But the snake“s dry skin holds its charge.
The rattle also generates static by friction
and this could top up the snake“s static electricity.
0nce the snake is charged up, its forked tongue could be deflected
by other charges in the air.
By sensing this deflection, the snake would detect air ions.
Air ions are exhaled in the breath of prey.
They also drift from holes in the ground.
The snake may use this extrasensory system
to its own advantage.
(Squeaking)
The snake“s tongue is better known in its role as an organ of smell.
The orange ladybird has extraordinary powers
of sensing hidden forces.
It forecasts the unpredictable British winter.
Human meteorologists consider such long-range prediction impossible.
But the ladybird can choose its overwintering site
depending on the weather to come.
If the winter outlook is mild,
it selects exposed spots like this weather screen.
If harsh, it spends the winter underground.
A hundred ladybirds may choose the same location,
one offering just enough protection.
In these exposed sites, they may still experience the odd cold snap.
They can even be quick-frozen.
Providing the temperature stays above a critical minus ten degrees,
the ladybirds survive the ordeal.
Choosing an exposed site gives them a head start in the spring.
Each year the ladybirds achieve the human impossible.
Their forecasting methods remain a mystery.
In ten years of study, the ladybird“s long-range forecasts
have never failed.
Migrating birds, such as the greylags,
specialise in short-term forecasts.
In autumn they set off when air pressure is falling.
A north wind helps their journey.
They possess a natural barometer in their inner ear
sensitive to atmospheric changes.
It also helps them sense altitude changes as small as three metres.
By monitoring weather and altitude,
birds can modify their flight plans
to make the best of changing conditions.
With favourable winds, the greylags can fly
from Iceland to Scotland in as little as 12 hours.
0ur ancient ancestors tried to understand the hidden forces
that controlled nature.
They built the stones of Callanish on the Isle of Lewis
as a lunar calendar.
Twice a day, the tides rise and fall
in a rhythm driven by the moon“s gravitational pull.
All life within coastal waters is affected.
Even when removed from their tidal home,
a body clock still keeps track of their home“s tidal cycle
as long as they stay alive.
Winkles in the seafood restaurant lie almost still,
waiting for the time their home tide comes in.
When water would have immersed the winkles, they become active,
responding to a rhythm that has ceased to have any meaning.
The timing of the tide varies with location,
as does the activity of the inhabitants.
Razor shells become active on an outgoing tide,
squirting water to propel themselves
under nonexistent sand.
The moon“s pull may drive the tides,
but its influence extends far beyond the intertidal zone.
Scallops live in deeper water, but nevertheless have a body clock
that predicts the tidal currents.
They become active when the currents flow.
( # Jaunty piano )
Dancing helps them drift in the current,
an easy way to find a new place to live.
The moon affects more than just the tides.
Many of its influences are still mysterious.
The colour vision of freshwater guppies varies
with the monthly lunar cycle.
At the full moon, they“re more sensitive to yellow than violet.
Two weeks later, at the new moon, they see violet better than yellow.
Why this bizarre change of sensitivity occurs is puzzling.
Early farmers built stone circles
to try and make sense of the moon“s mysterious influence.
Farmers always believed the moon affected crop ripening and yield.
Until recently, science dismissed this as folklore.
But recent research confirms plants do grow best
around the full moon.
Plant growth also shows a twice-daily cycle
that coincides with the lunar one.
Plant stems expand and contract with an internal tide
on this 12-and-a-half-hour cycle.
Potatoes are affected too, breathing in more oxygen
at times of the moon“s greatest influence.
How could lunar gravity affect a breathing potato?
The moon“s orbit warps the earth“s magnetic field.
Plants may somehow detect these twice-daily magnetic tides.
Folklore, it seems, was right all along.
The moon“s twice-monthly cycle
also creates earth tides in the ground.
This can precipitate earthquakes.
Folklore suggests animals can predict these cataclysmic events.
(Squeaking)
Rats and other creatures have been observed
carrying their brood to safety.
In the Far East, zoo animals are monitored for unusual behaviour
that might foretell a quake.
Hippos are sensitive to sounds pitched below our hearing.
Perhaps they hear rocks grinding
under immense pressure deep below.
(Squeaking)
This infrasound is also heard by elephants.
Their feet, sensitive to the distant stomps of other elephants,
can detect pre-quake tremors too slight for us to notice.
- (Snorting) - (Rumbling)
Spiders, too, are sensitive to these micro-tremors,
but ones vibrating at a higher frequency
than those picked up by elephants.
(Rumbling)
The tarantula“s drum-like vibration detectors are buried in its legs.
(Squeaking)
Rocks under stress create high voltages.
Static electricity reaching the surface
can be felt by any furred animal.
(Squeaking)
(Rumbling)
The earth“s magnetic field can warp, causing magnets to fail.
In China, in the “80s,
a million people were saved from an earthquake
through the simple observation of strange animal behaviour.
Just before a quake, a shift in the water table can drive animals above ground.
(Trumpeting)
Forces once hidden make their presence felt.
0n our next journey, Supernatural explores the time warps of nature.