National Geographic: Rhythms of Life Page #3

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Wading birds make the best of life

at the shore.

Stilts for legs let them follow the

waters' edge as it ebbs and flows.

Beyond the sandy shore,

the tide floods up

through the clutching fingers,

the roots, of mangrove trees.

Here in the muddy flats,

the fiddlers dig their wells,

preparing for the tide's return.

For these engineers,

the last act before the flood

is to batten down the hatches

with a fresh cut plug of mud.

They'll wait out the flood submerged

in underground burrows.

Like wading birds, the mangroves

will weather the waves on stilts.

The rhythm of the tides beats

both night and day.

For whenever the tide is low,

the shore's inhabitants

will come out to feed,

by sunlight, moonlight,

or in the glimmer of the stars.

Behind this constant ebb and flow

beats a second, slower tidal rhythm,

a cadence that for many,

spurs the times of mating and of birth.

This is the lunar cycle,

the month-long dance of earth,

satellite, and sun

that paints the changing faces

of the moon.

Twice each month,

the sun and moon conspire

to raise the level of the tides.

At the new moon and at the full,

the gravity of both our star

and our satellite aligns,

lifting the tide to its

greatest height.

In between,

the tides are at their weakest.

This monthly cycle of tides touches

creatures of the sea

in a place deeper then the daily

rhythms of feeding and rest.

A pair of male parrot fish swirl around

each other, jockeying for supremacy.

Their competition is a sure sign

that the full moon is on the rise.

This dance heralds the

spawning season.

When the full moon tide begins to ebb,

the females will release their eggs.

With the tug of the ebb tide,

the mating frenzy begins.

Thousands of fish, male and female,

dash through each others' wakes,

casting clouds of eggs and

sperm together into the tide.

One breed's spawn is another's feast.

Predators join the tumult,

to feed their fill on eggs.

But the spawning fish know

how to play the odds.

They have fertilized tens of

millions of eggs.

Millions will escape, pulled out to

deeper waters by the outgoing tide.

At high water, the surf storms back

over the reef,

sweeping schools of tiny fish

into the lagoon.

A silvery cloud flashing on

a watery wind.

For many, this will be

the last moment in the sun.

Trapped in quiet,

shallow waters,

they make easy prey for hunters

circling above the surface.

Moon, fish, and birds all whirling

in their own perfect harmony.

This black-naped tern lives a life

scored to the music of the tides.

On the shore, females have laid

claim to nesting sites

and some have already begun

to lay eggs as well.

While one bird minds the nest,

its mate fishes the shallows.

These seabirds time their breeding

cycle to coincide with the easy prey

washed into the lagoon

by the full moon tides.

Now is the time to eat heartily.

Soon the chicks will hatch.

And soon the moon will come

full circle,

the tides again filling the shallows

with tiny fish.

All in time to feed newly-hatched

chicks.

Although barren herself,

the moon prompts the sexual life

of many animals,

both above and below the surface.

Just after the full moon, the corals of

the Great Barrier Reef begin to spawn.

In a week, the tides will reach

their slackest point.

And over 200 different

species of coral

will launch their seed into

a galaxy of eggs and sperm.

In the still water,

there is time to drift and mix,

time for eggs and sperm

of the same species to mingle

and create a new generation.

Sea worms,

who live imbedded in the coral,

cast off their tails,

adding to the blizzard.

Writhing bags of sex cells,

the castoffs dance among a veritable

Milky Way of new life.

These celebrations are orchestrated

by the music of the spheres,

the distant dance of the solar system.

Like the moon,

the sun also sings to us

in rhythms slower than

the everyday of rise and set.

Around this star journeys the earth

at a stately, year-long pace,

initiating the cycle of the seasons,

ferrying winter and summer

from south to north, and back again.

Even at the poles,

the sun makes her mark

with the shimmering aurora,

the wake of the solar wind.

In the Antarctic,

the cycle of the seasons becomes one

with the rhythms of the day and night.

Here six months of sunlight are followed

by six months of dark and dusk,

summer followed by winter.

Even in the extremes of Antarctica,

life is tenacious.

Throughout the dark

of the polar night,

each male emperor penguin

guards a single precious egg.

Hardly moving, never hunting,

they've not eaten since autumn.

In temperatures reaching 70 below,

winds up to 50 miles an hour,

they huddle together for warmth

and protection, and wait for the sun.

In a land where evening lasts for six

months, dawn can seem to take forever.

Finally the penguin chicks will hatch,

and like their fathers,

they will be desperate for food.

Males can lose nearly half their body

weight during this incubation time.

But help is on the way.

Mother's coming.

For months, they have been feeding

on the bounty of winter seas.

Nature's biological clock is

at work here, too.

The females seem to sense the exact time

to leave for the nesting grounds,

for they have a huge trek

across the ice to get here.

Even tired and hungry, the males

may be slow to give up their chicks.

Temperatures on the ice

can be killing.

Babies left exposed too long will die.

The guard successfully changed,

males are free, at last,

to head to the sea,

and to feed.

The chicks will be fed by mother

and kept warm until the sun

climbs high into the sky.

Ever and always,

the coming of summer

depends on the swing of the earth

as it circles the sun,

and as it reels on its tilted axis.

As the earth spins through the year,

the sun's strongest rays sweep across

the globe, bringing change in its wake.

Near the equator,

the angle of the sun's rays

varies little through the year.

Still, it's enough to give the tropical

regions their own seasonal rhythm,

the cycle of drought and flood,

the wet and the dry.

September in Australia.

The air above the baking northern

plains rises with the heat.

With it comes cloud banks full of

moisture, pulled inland from the coast.

The wheeling clouds bring drama,

but no relief to a thirsty land.

They are not rainmakers,

but sky painters.

The monsoons are still months away.

Even so, deep in their nature,

plants and animals seem

to feel the rains coming.

A new cloud stirs-plant suckers rising

with the rhythms of the spring.

What looks like the bark of a tree

breathes with life,

a frill-necked lizard,

waiting out the drought.

For months it rations energy,

moving little, feeding less.

Wallabies are rainy day lovers.

While they wait for the wet season,

males joust for the chance to mate.

Now even the plants take a chance

that the drought is on the wane,

greening with fresh leaves.

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