The natural world is governed by rhythms.
The flap of a bird´s wing, the beat of a heart,
the rising and setting of the sun.
Stonehenge was built by Neolithic farmers
as they tried to decipher
the rhythm of the seasons.
The same natural cycles that were vital then
still govern our lives and those of other animals.
The sun provides the basic rhythm
that times all life, including our own.
The influence of this 24-hour cycle
is so overwhelming
most animals have developed
an internal regulator, or body clock,
that follows its rhythm.
0ur own body clock
still measures the sun´s cycle,
even though we´ve found ways
of improving accuracy.
Even in the city,
we cannot escape these natural rhythms.
We may rely on watches to time our departure,
but starlings, using a body clock,
arrive to roost just as accurately.
Although we supplement
our time sense artificially,
we still follow the same daily rhythms
as other life.
In darkness,
the body clock still keeps track of time.
It even controls the movements of plants.
It makes us feel tired at night,
changing blood pressure as well as heartbeat.
It regulates the activity of our pets
in the same way.
As the sun cycle brings a new day,
the starling´s body clock
times its departure from the city.
They use the position of the sun
as a navigational aid.
Although the sun arcs across the sky,
the bird´s time sense is so accurate it can
compensate for the sun´s changing position.
At any time of the day,
it knows where the sun should be,
and so can use it as a compass.
Without reference to the sun,
body clocks lose accuracy,
drifting away from the 24-hour cycle.
The regular variations of light and darkness
act as a synchroniser,
keeping body clocks linked
to the 24-hour rhythm of the sun.
Accurate body clocks are essential
for insects like honey bees,
that time their activity
to the opening of flowers.
At precise times each day,
internal clocks control petal movements
of plants such as bindweed.
Bees synchronise their visits
to these opening hours.
The timing varies for each flower,
and the bees are only rewarded with nectar
at these specific times.
Like birds, bees use the sun to guide them.
Their time sense not only compensates
for its movements,
but also helps them memorise
up to nine different opening times.
Flowering is so closely linked
to the bee´s activity,
many close once the pollination time has past.
A different kind of clock
controls the seasonal activity of many birds.
House martins time
their spring arrival from Africa
using a body clock
that beats to a yearly rhythm.
Away from the tropics,
nesting is linked to the seasons.
Each year, with miraculous precision,
life responds to these changes
of temperature and light.
As the ground warms after winter,
spring flowers such as wood anemones
blossom into life.
Celandines race to beat the canopy
soon to veil the light of the sun.
As well as gathering light for photosynthesis,
the leaves measure
the increasing length of daylight.
As the days lengthen,
the altering ratio of daylight to darkness
causes chemical changes
in the buds of the trees.
The leaves react to the new rhythm of light.
The fresh growth will not be left alone for long.
Just as caterpillars time their emergence
to the leaves,
there is a bird that times its life
to the caterpillars.
The lengthening days are sensed by the bluetit.
As in other birds, the light passes
directly through the skull itself
to the pineal organ in the brain.
This regulates the yearly clock
and allows the bluetit to time its brood
to the glut of caterpillars.
Some birds have such an accurate time sense
they lay their eggs on the same day each year.
These were laid on the 25th of May.
The accuracy of the sparrowhawk´s timing
relies on the information from a yearly clock
as well as day length.
It times its brood to the summer crop
of bluetits.
The sun has such power,
it also influences the yearly life of mammals.
Here the daily variations of light
are sensed by the eye
and measured in the pineal organ of the brain.
In deer it controls the amount of food eaten,
and triggers a remarkable transformation.
The rutting of stags
coincides with the shortening days.
The light changes
stimulate the release of hormones
which control the deers´ sexual activity.
The changing day length also causes
a spectacular transformation of the landscape.
The golden hues of autumn are triggered
as the days get shorter.
The brown pigments are unmasked
as green chlorophyll and other nutrients
are absorbed by the tree.
The leaves drop as a hormone
destroys a band of cells at the base.
This leaf-shedding avoids water loss
over the winter months.
As the shadows lengthen and the days shorten
further, other life prepares for winter.
These light changes
are sensed by the brown Arctic hare.
As the days get colder,
its fur becomes thicker and whiter.
Prompted by the shortening days,
the hare is now camouflaged for winter.
As winter sets in, plant life slows down
or becomes dormant.
Encased in ice, time is suspended.
With little to sustain them, many animals find
ways of opting out of winter.
In hibernation, the heart of the dormouse
has slowed from 300 beats a minute to just six.
With life and time almost suspended,
winter will be brief.
The moon also has an influence
on the timing of life.
In Africa, the full moon rising over Lake Victoria
triggers a remarkable spectacle.
These are mayfly.
After months of scavenging,
the larvae now respond to the beckoning light.
They prepare for the last brief moment
of their existence.
Thousands of these adults emerge
simultaneously to mate,
synchronised by the full moon.
The glut of mayflies
not only brings the adults together,
it ensures that predators are quickly satiated.
Within a day, they will all be dead.
The moon affects even the oceans.
Its gravitational pull
causes the sea to bulge towards it,
creating a tide.
As the moon continues its orbit,
the water begins to recede.
0nce the moon reaches
the opposite side of the earth,
centrifugal forces
create the second tide of the day.
Life in the tidal zone
needs to predict these changes.
Rock pool activity is based
on this twelve-and-a-half-hourly rhythm.
Many of these animals have a body clock
that measures the tidal cycles.
They need to predict the time
of the outgoing tide
to avoid the danger of drying out.
The gravitational pull of the sun
also influences the tides.
As the relative positions
of the sun, earth and moon change,
they create the lunar phases.
When the gravitational pull of the moon
combines with the sun,
it creates the greatest tides.
These spring tides happen twice every month,
at both the full and new moons.
Twice a month on the half moons, the pull of
the moon and the sun cancel each other,
and result in the small neap tides.
The lives of many marine animals
are governed by this cycle.
This prehistoric creature comes ashore
at the full moon in summer
along the coast of North America.
In a ritual unchanged since the age of dinosaurs,
the horseshoe crabs emerge to lay their eggs.
They synchronise their lives
to the highest spring tides
so they can leave their eggs
on the high-water mark.
Protected by sand and away from water,
the eggs will be safe from predatory fish.
During the next month,
the eggs undergo a dramatic change
also linked to the lunar cycle.
By the time of the next spring tide,
a miniature horseshoe crab is fully developed.
Hatching is synchronised so that the young
are washed out by these large tides.
Along the shores of California,
the full moon causes perhaps
the strangest behaviour of any fish.
The mass stranding of the grunion
is in fact vital for the survival
of the next generation.
This female is laying her eggs
at the high-water mark.
The fish are ashore for the briefest moment.
Each wave brings in another shoal.
As the female lays her eggs,
the males crowd around to fertilise them.
Protected by sand,
the eggs will hatch on the next spring tide.
Before our lives were disrupted
by modern living,
the moon´s cycle may once have been linked
to our own reproduction.
The female´s menstrual cycle
still averages exactly one lunar month,
and pregnancy lasts nine lunar cycles.
As we sleep, time appears to pass quickly by.
If our time perception can change,
how does time appear to other creatures?
To a fly, our world must appear to move slowly.
Its eyes can perceive
far smaller time intervals than we can.
It lives its short life at high speed.
To a fly, even our fastest actions
must appear ponderously slow.
Its reaction time is ten times faster
than our own.
Birds also live a high-speed existence.
The precision manoeuvres of flight
require fine timing.
Locked in our own time world,
we imagine all life
perceives time in the same way.
But in one brief moment of our existence,
the fly is unhurriedly caught
by the house martin.
The life cycle of a fly is only three weeks.
That of a shrew is a year.
Each animal exists for a different time period
before its body returns to the earth.
These different life spans
affect the rates of living.
Most mammals,
whether elephant or elephant shrew,
average the same number of heartbeats
in their lives.
The elephant shrew
lives only two and a half years,
but it carries out life at high speed.
Its heart beats 600 times a minute,
and like most creatures, it will average
800 million beats by the end of its life.
The elephant has only 25 heartbeats
each minute,
and lives for 60 years.
It would need to speed up 24 times
to enter the time world of a shrew.
The different rates of living
are governed by body size.
The largest animals live the longest,
and carry out their life cycles slowly.
We can never be sure
just how other animals perceive time,
but to a sleeping cheetah it must pass quickly,
just as it does when we´re asleep.
Time perception appears to be affected
both by speed of living
as well as the rate the senses
receive stimulation.
In the excitement of the hunt,
time must take on a different meaning.
Adrenalin pours into the bloodstream,
the heart rate doubles,
the senses bombard the brain with information.
Just as time appears to stretch for us
in an accident,
to a cheetah and gazelle
the same may happen in a chase.
The difference between life and death
is literally a split second.
It´s rare for an animal to reach old age,
for older animals move more slowly
and are easier to catch.
How this change of living rate
affects time perception
can be seen in our own ageing.
0lder people spend many hours in inactivity
and their hearts beat slowly.
Children are more active
and their hearts beat faster.
As we age, our rate of living slows,
and with it, it seems, our perception of time.
For an adult, the years speed by,
for a child, a week is a long time.
In the ground beneath Cincinnati
live creatures with a time sense all of their own.
For 17 years, these animals
have lived a subterranean existence.
They´re now emerging into the world
for the first and only time.
The invasion of the periodic cicadas
numbers literally millions,
for the same event is happening simultaneously
over much of North America.
They left the trees 17 years ago,
immediately after hatching.
Since then, an internal timer
has been measuring the passing years.
They´re now prime to transform into an adult.
Each emergence takes 20 minutes.
The wings are pumped up with blood.
The body begins to darken and harden.
The winged forms are now ready
to disperse across the city.
They´re the longest lived of any insect,
but their lives are nearly over.
As we begin a new day,
the cicadas gain strength by sucking sap.
In a passing moment of our lives,
the cicadas have to complete their life cycle.
They will pair up for only a few minutes.
The eggs are laid down a sharp tube
that cuts a furrow in the bark.
These will provide the next generation.
Their useful lives over, they fall to the ground,
creating a mass of spent bodies.
The cicadas will not appear again for 17 years.
0ur own swarms persist far longer.
We live at the same moment
but in a different time.
0n our next journey, Super Sense
will explore the world of sensory deception.
