(Hooter blaring)
You are starting a journey
into a world of senses different from your own.
( # Pop music)
(Children screaming)
How do birds perceive the world?
Even a starling responds
to many more sights and sounds than we do.
We experience life through five main senses.
But even these are better developed
in some familiar animals.
A mere goldfish can see colours invisible to us.
A dog lives in a world dominated by smell.
It?s a million times more sensitive
to some odours than we are.
Compared with many animals,
our sense of taste is surprisingly crude.
We may be aware of the touch of a mosquito,
but we?re insensitive to its sound world.
(Whirring)
Perhaps, compensating for our limitations,
we sometimes search
for a mysterious sixth sense.
(Truck engine )
For many animals, an extra sense is a reality.
(Geese honk)
We may look to the stars to divine our future,
but they were used by birds as a more practical
guide long before mankind existed.
Migrating birds
use these constellations to navigate.
Although each day
the sky patterns appear to rotate,
the north Pole Star
remains as a constant reference.
(Birds calling)
At dawn, another celestial compass is revealed.
The position of the sun
is another vital aid to navigation.
Although the sun
changes position throughout the day,
the bird?s body clock allows for this movement
and helps to keep the bird on course.
When these cues are obscured,
the birds fall back on a sixth sense,
one that detects
the magnetic force lines of the earth.
By sensing the angles these lines make
with its own body,
the bird maintains its direction.
As it faces south, so the lines arc away from it.
These force lines surround the earth
as they would a giant magnet
and so always indicate
the position of the earth?s magnetic poles.
With the help of this magnetic guide,
barnacle geese navigate the 1800 kilometres
from Greenland to Isla in Scotland.
Even greater feats of navigation
are shown by the creatures of the sea.
In the murky depths of the oceans,
there are few visible features
to help the animals navigate.
Here, dolphins and whales
are thought to use magnetic landmarks instead.
(Clicking and squeaking)
Variations
in the strength of the earth?s magnetic field
create an invisible landscape of hills and valleys.
Just as we use the contour lines
of a conventional map to indicate altitude,
so these contours show magnetic strength.
The dolphin is thought to follow these contours
to find its way around.
Just where
a dolphin?s magnetic sense organs are located
is still a mystery.
The magnetic sense of some fish
is less mysterious.
The ray can also sense
the earth?s magnetic field as it swims through it.
Tiny pores around the mouth are the organs
sensitive to any magnetic or electric field.
They can even detect the tiny electrical
discharges produced by other life forms.
By sensing such muscular discharges,
the thornback ray finds its food.
It lives on crabs and other crustaceans.
In the streams of Australia, there lives perhaps
one of the strangest of all living animals.
The platypus, although a mammal,
lays eggs like a bird
and also has a bill like a duck.
It can search for food with its eyes shut
because the bill is a remarkable organ.
Not only responsive to touch, it can sense the
electrical discharges of freshwater shrimps.
Although the shrimp?s movements generate
fields of less than a thousandth of a volt,
the platypus can detect these minute
bursts of energy from over a metre away.
For the shrimp, there is nowhere to hide.
Among mammals,
the platypus?s electric sense is unique.
Among fish, it?s relatively common.
Some African lakes
contain over 200 species of electric fish.
The elephant trunk fish uses this sense
to find hidden insect larvae.
All life generates electricity,
either through nervous impulses
or muscular discharges.
Remarkably, many fish
harness their own electricity for navigation.
Modified muscles generate a three-volt field
which is warped by any object the fish passes.
Rocks and plants
all conduct electricity differently.
As they distort the field, the fish
creates an impression of its surroundings
based on conductivity.
The long body of the electric eel
contains a battery of modified muscles.
More then half its length
is devoted to the generation of electricity.
It too
uses a low-voltage electric field to navigate.
By stepping up the voltage,
it can also use electricity to stun.
The final bolt delivers 500 volts of energy.
Electromagnetic waves from a storm
radiate for hundreds of kilometres.
They not only cause radio interference,
they appear to affect animals, too.
Beekeepers notice that bees return to the hive
and become irritable before a storm breaks.
Bees either detect
the electromagnetic waves directly
or sense the changes
in the static electricity of the air.
The same electrical charges
may affect our moods as well.
Ants are also weather-sensitive.
This winged male
is being returned to the nest by a worker.
It had tried to leave
before weather conditions were right for mating.
These winged ants
are the breeding forms of the colony,
and they emerge for only one day.
Sensitive to minute changes in humidity,
temperature or atmospheric pressure,
they spend many weeks
waiting for the perfect mating weather.
Prompted by these unseen signals,
they make their way to the surface.
Ants from nests covering many
square kilometres emerge simultaneously,
maximising their chances for mating.
They need calm and stable conditions,
for mating is carried out on the wing.
The ants swarm over huge areas.
There is safety in numbers, for predators
account for comparatively few of them.
A good weather sense
is also vital for a bird?s survival.
Migration is potentially hazardous.
So in autumn,
birds like house martins and swallows
wait many days for perfect conditions.
They need rising pressure, falling temperature
and winds blowing to the south.
0nly when these conditions are imminent
will they begin their long migration.
But their weather sense is believed
to respond to changes in barometric pressure.
This sensitivity may also give them information
about the pressure changes of altitude.
While on migration,
birds continually adjust their flying height
to make the most of favourable winds.
They also change course to avoid bad weather.
With stops en route for refuelling,
house martins take some weeks
to complete their journey to Africa.
The efficiency of flight
relies on sensing air currents.
Birds have many flight techniques.
Large birds like flamingos
save energy when they can by gliding.
But they need to flap their wings
to maintain height.
Small birds such as quelia finches
use a form of bounding flight,
folding their wings periodically to save energy.
To maintain efficient flight,
birds need information from air currents.
Beneath its breast feathers,
tiny feathers called filoplumes
monitor the changing eddies of air.
This continual feedback
gives the bird fine flight control.
Like birds, the senses of insects are delicately
tuned to changing currents of air.
The locust?s airspeed indicators are its antennae.
As it accelerates,
air resistance causes the antennae to bend.
The locust compensates
by slowing down its wing beats.
It also uses vision to monitor groundspeed.
These flight checks help save energy.
The locust?s flight is so efficient,
it can make vast migrational journeys
of several thousand kilometres.
No animal is more sensitive to air currents
than the scorpion.
Fine hairs on its pincers can detect
the air movements from passing insects.
They monitor the air as the scorpion moves
and help to keep it on course.
For centuries, animals such as scorpions
have been endowed with mystical powers.
Some have even been credited with
foretelling earthquakes or volcanic eruptions.
The snake has this mythological reputation.
With its body
in continual contact with the ground,
it can sense the slightest vibration,
perhaps even the tiny tremors
that sometimes precede a quake.
(Horse whinnying)
0ther animals
also seem to anticipate earthquakes.
Cattle stampede, cats retrieve kittens,
birds sing at the wrong time of day.
(Dog whines )
Heightened senses
may account for much of this strange behaviour.
Traces of volcanic gases
may warn of impending danger.
Electrostatic charges in the air
may provide another sign.
(Rumbling)
(Kitten miaows )
Water animals
can sense vibrations of a different nature.
The gyrations of whirligig beetles
create a flowing pattern of ripples.
By detecting their watery echoes,
the whirligigs can sense their surroundings.
These pond-skaters are using ripples
for a more deadly purpose.
The raft spider has similar skills.
Hairs on its legs
are sensitive to the slightest disturbance.
(Geese honking)
A ripple sense has evolved to perfection
beneath the water surface.
The synchrony of the mackerel shoal
is maintained by a ripple sense.
Each fish creates its own bowel wave.
By reacting to the ripples created by others,
a fish monitors its position in the shoal,
even in darkness.
The ripples are detected through the lateral
line organ that runs the length of its body.
As well as helping this synchronised swimming,
the lateral line
is used to sense the fish?s surroundings.
It?s even sensitive
to the movements of nearby predators.
The grey seal is a master fisherman.
Its success in even the murkiest of water
means it does not simply rely on vision.
Even blind seals are relatively common.
The secret of their success lies in their whiskers.
Not only sensitive to touch,
they also respond
to the slightest water movement,
even the ripples of a fish.
Although the fish?s lateral line helps it
to detect the seal, it cannot always escape.
In the caves of Mexico, there are fish
that construct a view of the world
solely through ripples.
The eyes of the Mexican cave fish
have degenerated totally.
Using only its lateral line,
it can detect the smallest obstacle
and negotiate its way around the cave.
The powers of the vampire bat are legendary.
But superstition ignores the facts
of the vampire?s real super senses.
Like other bats, it can navigate in total darkness
using echoes as a guide.
0nce it has found its victim, the vampire
uses a different technique to locate its food.
The nose leaf is a sophisticated heat sensor.
Insulated from the heat of the bat?s own body,
it is tuned to the blood heat of its host.
It guides the vampire
to those tissues richest in blood.
(Horse snorts )
The heat sense of some snakes
surpasses even that of the vampire.
The North American cottonmouth
finds food by tasting the air or using sight.
But just below the eye,
a special pit provides a second image,
an image formed from the heat
emanating from its intended prey.
Tracked by this pit organ,
darkness provides no sanctuary for the rat.
At the final strike, other heat sensors
in the mouth ensure deadly accuracy.
The shark, perhaps the most feared
of all animals, has an array of supersenses.
It can smell blood from over a kilometre away.
Its eyes are ten times more sensitive to light
than our own.
It can detect subtle changes
in the earth?s magnetic field.
Like rays and certain other fish,
it can also sense the electricity of life itself.
Tuned also to the sound of swimming
and the movement of water,
the shark is the perfect killer.
Electricity will guide the final attack.
0n its next journey,
Super Sense will explore the world of vision.
