Even before it hatches,
a bird shows the first stirrings of perception.
A sense of touch develops first, then hearing.
(High-pitched chirping)
Days before it emerges,
it will eavesdrop on the sounds outside.
Hatching is synchronised by the cygnets
calling to each other while still in the egg.
As the cygnet emerges, it is bombarded
with a barrage of new sensations.
Its eyes begin to make sense
of these changing patterns of light.
The cygnet is programmed to follow
the first moving object it sees.
It will soon learn that this is its mother.
Instinct and learning will shape
the stream of sensory information
as the chick interprets the world.
Instinct and learning continue to influence
the senses throughout life.
Each year, drought in the Serengeti
forces wildebeest to make a formidable journey
seeking fresh pasture.
They´re believed to be guided
by the smell of rain
but an overriding instinctive drive
governs their direction.
This compels them to risk their lives fording
the treacherous waters of Kenya´s Mara River.
In all this sensory turmoil,
a process of learning is also going on.
The crossing points seem to be remembered
from year to year,
the younger animals learning from
those that have made the journey before.
With animals that migrate together,
there appears to be a collective wisdom
that keeps the animals on course,
providing they can survive the ordeal.
The yearly migration of the wildebeest
covers 800 kilometres.
Prompted by an internal clock
and sometimes travelling alone,
the house martin navigates far greater distances
on its journey from Africa to Europe.
The Sahara offers few visual landmarks
to guide it,
and the Mediterranean is equally featureless.
To keep on course it relies on a sun compass
as well as magnetic cues.
General direction is dictated by instinct,
although the exact flight path
may be modified by learning.
Having flown the route before,
it will remember many landmarks.
As a young bird, it would have flown
with those that are more experienced.
As it nears the breeding area, it picks up
sights and sounds that are increasingly familiar.
Just as we recognise the features
that surround our home,
a house martin has a mental map
that covers hundreds of square kilometres.
Before they migrate, young birds make
an aerial reconnaissance of their local area,
so they can find it again the following year.
0lder birds recognise the same nest sites
and return to them unerringly.
(Cooing)
We have selectively bred pigeons
to exploit this homing ability.
Races of 1,500km are not uncommon.
But even sophisticated sensory systems
can become confused.
Like house martins, pigeons rely on the sun
to help set a compass course.
They also use a magnetic sense,
particularly at the start of the journey.
Nearer the loft smell may also be a guide,
but now both the sun and magnetism
are the most important cues.
In some races
conditions can change disastrously.
When bad weather obscures the sun,
they´re guided solely by the magnetic force lines
of the earth.
The pigeon senses the angle of these lines
to find its compass direction.
In areas where magnetic rocks
distort the earth´s field,
the bird can become hopelessly confused.
Magnetic storms erupting from the sun
may also throw the pigeon off course.
Birds have several navigational backup systems.
Accidents happen
when they´re forced to rely on just one.
Similar problems can affect the senses of
animals that navigate beneath the water surface.
Sperm whales make vast migrational journeys
of thousands of kilometres.
Here there are few visual landmarks,
so they too are believed to be guided
by the earth´s magnetic field.
Although the ocean appears featureless,
it is marked out by an invisible landscape
of hills and valleys.
As the whale migrates,
it is thought to follow these contour lines
which trace variations in magnetism
of the rocks below.
The lines connect points of
equal magnetic strength,
and in the ocean create long, invisible valleys
that the whales appear to use as roads.
This simple navigational system
is usually reliable,
but if the whale makes a wrong turning,
the contours can lead to disaster.
Sensory confusion affects more than
just navigational systems.
Like the whale, sharks use
the earth´s magnetism to find their way around,
but they detect it through sensors
which are also used to locate prey.
These electroreceptors concentrated
around the mouth of the shark,
can detect the minute electrical discharges
of muscular activity.
0ver the 180 million years
of the shark´s ancestry,
such a simple system
was an infallible guide to food.
This is no longer the case.
To the shark, unscreened communication cables
create the same irresistible signals.
Cables are often severed by
such misdirected attacks.
Such cables are now being redesigned.
The shark´s senses evolved
long before man appeared on Earth
and have no inbuilt protection
against these inventions.
(Music playing, phone ringing)
0ur harnessing of electricity has caused
confusion to the senses of many animals.
Hatchling turtles have an urgent need
to reach the sea.
At this tender age,
they´re an easy mouthful for any predators.
Low to the ground, the sea is hidden from view,
so in this race to the water,
they orientate to the brighter horizon.
Even on the darkest nights,
this horizontal strip provides a guiding light.
To these loggerheads,
this rush to the warm Mediterranean Sea
is the start of a life of wandering.
Guided by smell and a magnetic sense,
it will be ten years before they return
to these breeding beaches.
0ver the intervening years,
great changes can happen, many caused by man.
As hotels and tavernas encroach
further along the turtle beaches,
many thousands of hatchlings
never find a safe refuge.
Artificial lights provide a stronger lure
than the faint glow from the sky.
This disorientated turtle is destined to perish
in the searing heat of the day.
Similar confusion affects animals
guided by another natural light.
Moths appear to keep a course by orientating
their body at a constant angle to the moon.
This reference angle varies
depending on the species,
and helps the moths disperse efficiently.
When there appear to be two moons,
the moth selects the brighter.
As it tries to maintain an angle to this
new reference, the moth spirals towards it.
The moth´s simple navigational system
can easily become confused.
But do the complex systems of birds
cope any better?
Starlings use many aids to find direction,
including the stars.
They too are believed to use the moon
as a guide.
Unlike moths whose reference angle is fixed,
birds are thought to compensate
for the moon´s changing position.
When the moon compass disappears from view,
the starlings fall back on a magnetic sense.
Without any other visual reference, the starlings
respond to any strong light they see.
Artificial lights become a compelling substitute
for the moon.
In bad weather,
these guides, vital for our navigation,
can destroy the sensory system of migrants.
Thousands perish on these pulsating lights.
(Twitters )
Biological beacons can be equally deadly,
for some fireflies have found ways
of exploiting sensory confusion.
This photuris female is landing among
males of a species known as photinus.
She flashes a sexual signal
to the surrounding males.
Attracted by the beguiling light,
this male is unaware he´s entering a trap.
The female mimics the flash code
of the male´s true mate.
Seduced by this femme fatale,
the male approaches to mate.
She responds...
by eating her suitor alive.
Just as lights can be used for sexual deception,
so too can smell.
The bola spider uses a unique method
to ensnare its prey.
At the end of its dangling thread
lies a bolus of sticky silk.
The spider supplements this deadly weapon
by releasing a deceptive chemical.
To a male moth this odour trail is irresistible.
It mimics exactly the sexual perfume
of the female.
The spider can even change the chemical nature
of its lure to entice other species towards it.
As the moth searches,
the spider throws its bolus.
As smell governs the lives of so many insects,
various other kinds of chemical trickery
have evolved.
These Scandinavian ants are called Amazon ants
because of their large size and ferocious nature.
0ver a thousand of them begin a deadly raid.
A scout ant has located the nest
of a different species.
These reinforcements are preparing to invade.
They enter the nest of the smaller black ant,
formica.
Alerted by their alien smell,
the formica soldiers offer predictable resistance.
The Amazon ants now unleash
their chemical weapon.
This mimics the alarm scent
of the formica soldiers and causes them to flee.
As the chemical breaks down all resistance,
the Amazon ants freely plunder the nest.
They carry out their bounty of ant pupae.
These will not be used as food,
their value is far greater.
The Amazon soldiers rely on formica ants
to maintain and feed their colony.
Their captured pupae
are destined to become slaves.
When they emerge from the pupae,
these workers, controlled by the colony odours,
tend their captors´ every need.
In this world of sensory deception,
some animals have found ways
of literally seeing through the trickery.
These cuttlefish are showing
the striking colour patterns of courtship.
The zebra stripe design
acts as an alluring display.
The patterning is controlled by special pigment
discs which can rapidly expand and contract.
This allows the cuttlefish to show
spectacular colour changes.
These transformations under nervous control
allow a hunting cuttlefish
to blend seamlessly into the background.
Its prey has a different camouflage technique.
The fish´s silvery appearance is part of
a vanishing trick that relies on mirrors.
Each scale reflects the light of the surrounding
water, causing the fish almost to disappear.
The cuttlefish´s eyes have a countermeasure
that can destroy this camouflage,
for they can detect light
polarised in two different planes.
They see through the fish´s
protective reflections
just as our polarised sunglasses cut out glare.
Its method of catching its prey
is just as ingenious.
The battle between predator and prey
is the main driving force
behind the evolution of super senses.
Such a sensory arms race has developed
between bats and some insects.
This noctule uses echo location
to create sound images of its prey.
(Chirps )
Many moths have evolved cunning defences that
rely on listening out for such ultrasonic calls.
(Chirps )
Alerted by these audible warnings,
they create their own ultrasonic clicks
to jam the bat´s sonar.
They twist in this smokescreen of sound.
Moths may be winning this battle,
but the long-eared bat
has evolved a new strategy.
Its enormous ears act as acoustic horns
that locate and concentrate sound.
It also hears lower frequencies
than most other bats.
It tunes in to the sound of moth wings.
The moth is most vulnerable
as its flight muscles warm up before takeoff.
To avoid being detected,
the hunting bat switches off its echo location,
relying instead on heightened hearing.
These remarkable facts
have only just been discovered.
Many other sensory mysteries still remain.
Each autumn the monarch butterfly sets off
from the northern states of North America
on a journey south of 4,000km.
This is the longest migration of any insect.
To keep on course,
it´s believed to use the sun as a reference,
a guide known to be used
by many other insects.
At the same time of year, many birds migrate
helped by the same celestial compass.
These red-breasted geese fly from Siberia
to the Caspian Sea,
a distance comparable to that
covered by the butterflies.
Just as these birds are backed up
by a magnetic sense,
there is growing evidence that it is also involved
in the monarch´s migration to Mexico.
Even in the navigation of birds,
there are many mysteries still to be solved.
How important is the information from low
frequency infrasound? From smell and vision?
Can the magnetic sense keep track of
changing latitude as well as compass direction?
Similar uncertainties shroud
the monarch´s powers of navigation.
All the monarchs from
the eastern side of America
gather together in a few small groves
high in the Mexican sierras.
Protected from the harsh extremes of climate,
100 million butterflies over winter
in this one remote glade.
In the spring, these butterflies will journey
north, breeding several times over the summer.
It will take two or three generations
before monarchs reach the far north again.
These butterflies are the offspring
from the previous summer
and have never been here before.
Their knowledge of the migration route
must be inherited.
How they find these precise locations
has yet to be discovered.
Could temperature, altitude,
or even smell be factors?
Perhaps magnetic rock discovered near the site
provides an invisible landmark.
Just as other animals
have given up their secrets,
so these mysteries will eventually be explained.
At one time bats were believed
to belong to the supernatural.
How else could they fly and catch food
in total darkness?
When science revealed
the secrets of echo location,
bats became accepted
as part of the world we know.
As our environment
becomes increasingly artificial,
it takes us further away
from many of these remarkable creatures.
But those animals that still share our lives
have senses that are no less extraordinary.
With its superior sense of smell,
a dog is more aware than we are
of the odours that influence us.
In our frenetic world, we appear to have
lost touch with our own super senses,
but the rhythms of the sun and moon
still affect us,
and it seems that we too may possess
a magnetic sense.
If we have such difficulty
identifying our own super senses,
we should perhaps keep an open mind
to the powers of even familiar animals.
If a mere goldfish can see a greater range
of colours than any other creature,
what secrets are there to discover in animals
that are less well-known?
Whatever powers the future may uncover,
we can be sure that
these will be no more supernatural
and no less remarkable than
the super senses so far revealed.
