The Life of Birds (1998): Season 1, Episode 8 - The Demands of the Egg - full transcript

These sooty terns are amongst
the most aerial of birds.

Every one of them has spent the first
three or four years of its life flying non-stop.

Feeding on the wing,

swooping down picking up fragments
of food from the surface of the sea,

even sleeping on the wing.

But there is one thing that compels them
to come down to earth.

This.

Flying with an egg inside the body,
let alone a clutch of three or four,

makes huge demands
on the energy of a bird.

So every female bird in existence
gets rid of that huge load

just as soon as she can.
She lays it.



In places like this island in the Seychelles,

where there are no land predators
to steal eggs,

it's safe for the sooty terns
to put those eggs directly on the ground.

The birds sit as close to one another
as they can

without getting within the range
of their neighbors' beaks,

so they are equally spaced
with almost mathematical precision.

Other kinds of terns have other ideas
about where to put their eggs.

The fairy tern, for some reason,
always puts them on a bare branch,

though whether that is safer
or more dangerous is debatable.

The females seem wildly optimistic.

A U-bend is one of their safer ideas.

The dimple left when a branch
breaks away is not bad either.

But it seems a bit reckless
to rely on a little dead twig like this,

particularly when the trade winds blow as
strongly as they do in the Seychelles.



The fact is that fairy terns' eggs
are easily dislodged if left unguarded.

Skinks know that...
..and so do the fodies, the local sparrows.

And that has solved the problem
of how to crack it.

Yolk is provided by a female bird to nourish
her chick as it develops inside the egg.

But it is equally good food
for lots of other animals,

so eggs are much sought after,

and birds may have to go to great lengths
to keep them safe.

Swifts living on the mainland
have to take greater precautions.

The nests of palm swifts are minimal,
but they put them in fairly inaccessible places,

such as an isolated palm tree.

They stick a few feathers on the underside
of one of its dangling dead leaves,

using their spittle as glue.

To make sure that the egg stays
in this flimsy hammock of feathers,

they stick that to the leaf as well.

Changing places to take over incubation
is a tricky operation

when your nest is stuck to a vertical surface.

The power of flight enables birds
to put their nests in places

that are beyond the reach
of land-bound creatures.

And there can be few more inaccessible
spots than the rocks behind a great waterfall,

like this one at Iguacu in South America,

where Argentina and Brazil meet.

Swifts, once again,
exploit their mastery of flight

to go where no other bird can go.

Great dusky swifts roost for the night

on the mist-drenched rocks
alongside the falls.

But this is not a safe enough place
for their precious eggs.

They will be deposited actually
behind the curtain of water

and to do that
the birds must find the thinnest part of it.

Behind the curtain,
they still have an awkward climb

before they reach a place
where it is possible to put an egg.

And this is it, a perpetually dripping ledge,

just wide enough
to accommodate a little muddy nest.

Many birds choose cliffs for their nest sites

even when they are not screened by water.

Seabirds around the world use them.

But these aren't normal seabirds.

They're parrots and they are nesting
on the coast of Argentina.

The powerful hooked beak that all parrots have
and use for cracking nuts and gouging fruit

is also an excellent excavating tool

These cliffs are composed
of a relatively soft sandstone.

No problem for a parrot.
Even so, digging a hole in them is hard work,

so each hole, when it is finished,
is a valuable property,

and there is a great deal of competition
and squabbling over any vacancy.

Sand-martins are not nearly
so well equipped for digging.

They use their claws
rather than their delicate beaks

and they can only tackle sandstone
if it is soft and friable.

But what they lack in equipment
they make up for with energy.

Woodpeckers, of course,
are expert carpenters

and regularly chisel their nestholds in trees.

But this one is digging into softer material,
an ants' nest.

The ants are furious,

but they quickly get used to their lodger
sitting in the middle of their mansion,

and then they act as her guardians, attacking
any intruder that tries to steal her eggs.

You might think that a hornbill would have
the most powerful excavation tool of all,

but in fact its huge beak
is a relatively delicate structure

and no use at all as a chisel

So hornbills have to find holes that are either
natural or have been dug by others.

A pair do their house-hunting together
and they are very choosy.

Perhaps this one will do.

With beaks over a foot long,

these Great Indian hornbills
have to have a pretty big hole.

But they like the entrance to be
as small as possible to deter intruders.

Maybe this is just too small.

But she can just make it.

That's good.
The search is over.

This is it.

The male regurgitates a little food for her.

Now she has decided that this is for her,

she won't leave again until her eggs are laid
and hatched and the chicks well-grown.

She will depend entirely on her mate for food.

She seals herself in,

narrowing the entrance
with a plaster made of chewed wood,

mashed food and her own droppings.

This will be her home, you could say
her prison, for the next four months.

The majority of birds, though,
don't nest in holes.

They build their nests. And builders,
of course, need building materials.

Having no hands, but just a beak
and at best one foot, seems bad enough,

but these frigates on the Galapagos
have got an additional problem.

Their feet are so short and their wings
are so wide that they find it difficult to land,

so they much prefer
to collect their building material on the wing.

Boobies can settle and break off
the branches they need for their nests.

Frigates can't, but they can steal

So for boobies, getting building material
from its source to the building site

is the most difficult part
of the whole business.

Stolen goods, it's true,
but all the more precious for that.

Eggs must not only be kept secure.

Once they start to develop,
they also have to be kept warm

and there is no better insulation
than feathers.

Ducks and geese line their nests with
feathers they pluck from their own breasts.

Other birds are not so self-sacrificing

and prefer to use
those that they find blowing about.

Tree swallows compete with one another
in collecting them.

Miss... and a rival won't give you
a second chance.

Even when you have got it
you may not get away with it.

Tackling a bird without the feather
is all within the rules of this particular game.

The golden-headed cisticola,
a kind of Australian warbler,

collects fibers and spiders' webs,
not just for lining, but for stitching.

There is no more skilled a tailor
in the whole of the bird world.

There's little problem
about concealing this nest

for the leaves she stitches together
remain alive and green.

When she has finished, you will barely notice
that they are bent together

in a slightly unusual way.

The problem is greater when a nest sits
on the bare branches of a tree.

The sitella, an Australian
equivalent of the nuthatch,

constructs its nest from spiders' webs
and insect cocoons,

and then covers the outside
with rather coarser material

Two pairs are building here,
close to one another.

This one is in a tree covered in lichen.

And this, in one that has flaky bark.

The sitellas are not rigidly-minded birds
with inflexible habits.

They use lichen
to cover the nest in the lichen tree,

and bark on the one in the flaky bark tree.

As a result, each is as well camouflaged
as anyone could hope,

and though both nests
are plain for all to see,

they are not easily recognized
for what they are.

The apostle bird uses mud mixed with grass.

Nest building is a group activity.

A pair with their grown-up young
from previous seasons work together.

It used to be believed
that there was always a dozen in the team

which is why they are called apostle birds.

Everyone seems anxious to contribute,

and the team works so industriously
and so harmoniously

that their elegant cup
is usually completed in a mere three days.

A bird's beak, it seems,
can serve just as well as a plasterer's trowel,

as a tailor's needle.

Some birds build nests not just as cradles
for their eggs and chicks,

but as lodging houses for the whole year.

Here in Namibia in Southern Africa
lives the sociable weaver,

and very sociable it is, too.

As many as three or four hundred birds
will live in a single apartment block.

This haystack
may be more than a century old.

It is so heavy that part of it
has broken the branch that supported it

and fallen to the ground.

And it's been built and maintained
as a communal effort by all the inhabitants.

Weavers are closely related to sparrows.

Though some of their relations
do indeed weave,

the sociable weaver
builds in a rather simple way.

It just pushes straws, one by one,
into this gigantic bale.

A large communal apartment block

has a considerable advantage
over small isolated nests

when you live in a desert like this.

During the day it gets ferociously hot,

but that thick roof of thatch keeps
the apartments beneath nice and cool

As the sun sets, the weavers, having been
away feeding, come back to their homes.

At night, it can get very cold in the desert,
as much as 7 or 8 degrees below freezing.

And then the thatch is probably
at its most valuable,

because it acts as insulation
for the nest chambers,

so that they retain much of the heat
that they had during the day,

and the birds that roost inside
remain snug and warm.

Not all the chambers are for nesting.

Some are not nurseries, but bedrooms

in which several of the colony
snuggle together for warmth.

So at last some kind of receptacle,
simple or complex, is prepared for the egg,

and it is time for the female to produce one.

The male frigate welcomes his partner back.

The crucial moment has arrived.

Mated female birds
have been feeding intensively

and their ovaries are much enlarged.

Each egg,
emerging from one as a microscopic cell,

is planted on a growing globule of yolk
which will provide it with food.

It is fertilized by one of the sperm
that has been lying awaiting it in the duct.

Albumen is wrapped around it to provide it
with the water necessary for development.

It travels onwards for several hours.

Eventually, it reaches a section in the duct
where there are glands that produce lime.

Here it lingers for 24 hours
while the shell is added.

Pigment glands
squirt little spots of color on it.

And so, an avocet produces her egg.

The blotches and speckles
on such an egg as this, laid on the ground,

serve primarily to camouflage it.

These are the eggs of a golden plover.
They too are laid directly on the ground

and are practically invisible;
as indeed the bird that laid them will be

once she settles down.

Plovers nearly always lay four eggs.

A few birds, however,
have adopted a rather more risky policy.

They lay just two, or even one.

If they do that,
they must lay it in a nest that is really secure,

hidden, for example, deep in a burrow
as the kiwi does.

Her egg is gigantic,
the biggest laid by any bird,

and a quarter of her total body weight.

It contains so much yolk
that the chick will be fully developed

when eventually it breaks out of its shell.

Expelling such an egg
is obviously a huge effort.

The owner of this nest, a blue tit,
adopts a very different strategy.

Her egg is tiny. It weighs no more than a gram.

But she lays lots of them;

one a day, day after day,
for a fortnight or so,

but the chicks after they hatch
will face so many hazards that many will die

and the survival rate in
the end will be not unlike the kiwi's.

Few eggs are totally safe from hungry raiders,

no matter how skillfully protected
and artfully concealed they are.

Those lying in the bottom of these dangling
nests of caciques in South America

are certainly difficult to reach.

But the red-breasted toucan
has a long beak.

This toucan's bill is just
not long enough for these particular nests.

But the toco toucan has an even longer one.

The caciques are extremely agitated.

And with good reason.

If the caciques are to defend themselves
against these powerful bandits,

they will have to build
even longer nests in the future.

In Australia, the prime egg thief
is the currawong.

An unguarded nest.

An obvious target.

Another clutch gone.
Few eggs are safe from currawongs

and the Australian birds,
like birds everywhere,

have developed many different strategies
to try and foil burglars.

This is the nest of a yellow-rumped thornbill,

but in fact this neat little cup is empty.

You might think therefore,
that it has been robbed of its eggs.

But in fact this part of the nest
has never had any eggs in it.

There's another entrance to the nest.
It's down here.

You might never notice it,
until you watch the parent return.

The cup at the top is a dummy,

and it seems that many currawongs
have not yet discovered the fact.

This wren in Costa Rica
has another way of protecting its eggs.

Its nest is pretty obvious...

..and equally obvious
is another one close by, a wasps' nest.

The wren nearly always builds within
a yard or so of these formidable insects.

It is a brave thief
that risks being attacked by these.

But coatimundis are brave,
sometimes to the point of recklessness.

Out here
on the cold windswept plains of Patagonia

there are no trees
in which a bird could build a nest.

So plovers, like plovers everywhere,
lay their eggs on the ground

and trust their camouflage.

But if a stranger wanders too near it,
one of the adults immediately responds.

Ahead, I can just see a bird
crouching on her eggs. And away she goes.

And now she starts
a most bizarre pantomime.

This hardly looks like any kind of bird,
and whatever it is, it seems to be crippled.

If I was a fox or maybe a hawk,

I might quite well think that this extraordinary
performance represents an injured bird

or maybe a little rodent.

Either way it looks like an easy meal and I
might follow it and be led away from the nest.

And now she has taken me so far from her
eggs that she can abandon her play-acting.

There is nothing the matter with her.

Having deflected me,
she returns to her nest.

She has to go back
to prevent her eggs getting chilled

and the young within from dying of cold.

Keeping eggs warm, indeed, is a continuing
problem for most nesting birds.

The maleo has a very labor-saving way
of dealing with its heating problems.

It lives on an island in Indonesia.

In this one unshaded patch of the beach,
the sand is kept so hot by the sun

that the eggs will hatch by themselves,

and the whole of
the local maleo population know it.

The birds are accurate judges
of temperature. They have to be.

If they don't dig deep enough,
their eggs will bake,

and if they go too far,
they won't develop.

That's probably about right.

Now all that is needed is to fill in the hole.

And then they abandon it.

These eggs, up in Alaska,
must be tended much more assiduously.

They belong to a snowy owl

As she returns, you can see that the feathers
on her belly are rather long and floppy.

There is even a glimpse of pink naked skin.

Her body has to be particularly
well-insulated with dense plumage

to prevent it losing heat
in these near-freezing conditions,

yet somehow she has to transfer
some of that heat to these eggs.

This naked brood patch on her belly
will enable her to do just that.

Her mate is away hunting for lemmings,
not only for himself, but for her.

She cannot leave her eggs
for more than a minute or two,

so her mate looks after her, and
he will have to do this for almost two months.

The chilly lakes of North America.

Here some birds trick others into looking
after at least some of their eggs.

This female canvasback duck
is sitting contentedly,

incubating and minding her own business.

Out on the water, another female
canvasback is mating with a drake.

The mated female
has not yet built a nest of her own,

so she makes her way to the one who has.

The sitting female
clearly doesn't like this intrusion,

but equally,
she's not going to abandon her eggs.

The intruder pushes her to one side
and quickly lays.

Sometimes the sitting bird
doesn't seem to realize what has happened

and accepts the egg.

But not this time.

There's a different kind of duck here, too.

It is a little smaller and the male has
a redder head and neck, the redhead duck.

His female has also cast her eye
on the canvasback's nest.

Perhaps she can try the same trick.

A canvasback egg is pale green,
a redhead's white,

so the redhead female
tries to make hers less obvious

by placing it
in the middle of the canvasback's clutch.

The male redhead awaits.

And the deed is done.

The female canvasback
leaves her nest for a meal

and reveals that this last intrusion
was not the first.

There are three white redhead eggs
in her nest.

Meanwhile, the redheads sail away
to make a nest of their own.

Distributing eggs between several nests,
as both canvasbacks and redheads do,

is like taking out an insurance policy.

And there are plenty of hazards on the lakes
against which a duck needs to insure,

if she possibly can.

Night is a time for burglary.

A raccoon.

This clutch is finished,

but there is still a chance that one or two of
this female's eggs laid elsewhere will survive.

There really is sense
in not putting all your eggs in one basket.

Some birds, however,
don't care for any of their eggs.

As parents, they are totally irresponsible and
the most famous, of course, are the cuckoos.

This is a nest of an Australian fantail

The two little eggs belong to the fantails,
but the very big one is a cuckoo's.

It is so different that you would think
that the fantail would immediately recognize

that something is wrong.
But watch.

The fantail female is around,
but it's the male who comes back first.

He seems quite unaware
that anything is wrong.

The female cuckoo
is also keeping an eye on things.

The fantail has accepted the egg,
and that will be disastrous,

because when the bigger cuckoo chick
hatches, it will push out the baby fantails.

Maybe cuckoos
have only just started to do this

and fantails haven't yet developed a defense.

In North America,
the cowbird is also playing this game.

It has put an egg
in the nest of a gnatcatcher.

It's slightly bigger, but very similarly marked.

Will the gnatcatchers notice the difference?

They have.
They are destroying their own nest.

There is no future
for their own chicks in this one.

But nesting material is too valuable to waste,

so they are going to start again.

They begin a new nest quite close by.

Day after day they labor,
destroying the old and building the new.

And there goes the alien egg.

The cowbird has lost this particular duel

Africa.
The duels are being fought out here, too.

This is a colony of lesser masked weavers

and sitting in the trees nearby are,
once again, cuckoos.

These are diederick cuckoos.

The cuckoos, if they can, will dump
their eggs in the weaver birds' nest

and leave them there
for the weaver birds to rear.

And the weavers
seem well aware of the danger.

They are taking precautions, adding long
entrance tunnels to their globular nests

as they must have been doing
for many centuries.

The cuckoo watches for a recently finished
nest in which a female has just started to lay.

There's one.

But the cuckoo
is having a lot of trouble getting in.

In the past, cuckoo eggs
have been frequently found

in the nests of these weavers.

But none seem to be getting
into this colony.

Maybe the weavers are beginning to make
those entrance tubes just a little bit narrower.

The battle seems to be swinging
the weavers' way.

Nearby, there's a colony
of a slightly different kind of weaver,

the marginally bigger masked weaver.

They don't put entrance tubes to their nests,

perhaps because they themselves
are nearer the size of a cuckoo,

so any entrance they can get into,
a cuckoo could also.

They have a different defense.

The colors of their eggs
are extraordinarily variable,

ranging from pure white
to blue and speckled.

But any one cuckoo
can only lay one kind of egg.

And it has no way of knowing what color
the eggs are in any particular nest.

So the odds are against the eggs matching.

Now I happen to know
that this nest contains speckled eggs.

Let's see what happens
if I put a pale egg in it.

Back comes the owner.

No doubt about
who's winning here either, this time.

The battle between cuckoos
and other birds is a continuing one.

The cuckoos developing new stratagems
and perhaps finding new victims,

and the victims finding new defenses.

Soon, in those nests behind me,
eggs will start hatching.

Most will produce young weaver birds,
but some equally certainly, will be cuckoos.

Whichever they are, the young chicks
will be faced with a whole set of problems

that they have to solve
if they are to grow into adults.

And the ingenious and sometimes
touching way in which that is done

is what we will be looking at
in the next programme in The Life of Birds.