The Demands of the Egg The Life of Birds

These sooty terns are amongst the most aerial of birds.

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

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

makes huge demands on the energy of a bird.

In places like this island in the Seychelles,

so they are equally spaced with almost mathematical precision.

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

though whether that is safer or more dangerous is debatable.

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

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

particularly with the strong trade winds of the Seychelles.

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

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

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

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

Swifts, living on the mainland, have to take greater precautions.

To make sure 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.

Swifts, once again, exploit their mastery of flight

Great dusky swifts roost for the night

on the mist-drenched rocks beside 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.

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

is also an excellent excavating tool.

These cliffs' relatively soft sandstone is no problem for a parrot.

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

Sand martins are not so well equipped for digging.

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 being expert carpenters chisel their nestholes in trees,

but this one is digging into softer material - an ants' nest.

But they quickly get used to their lodger sitting in their mansion,

and then they attack any intruder that tries to steal her eggs.

You might think a hornbill has THE most powerful excavation tool.

So hornbills have to find natural holes or ones dug by others.

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

The male regurgitates a little food for her.

Now she has decided that this is for her,

She seals herself in, narrowing the entrance

with a plaster made of chewed wood, mashed food and her own droppings.

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

but these frigates on the Galapagos have an added problem.

Their short feet and wide wings make 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.

is the most difficult part of the whole business.

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

Once they start to develop they have to be kept warm

Ducks and geese line their nests with feathers from their breasts.

Other birds are not so self-sacrificing

and use those that they find blowing about.

Tree swallows compete with one another in collecting them.

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

is all within the rules of this particular game.

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

uses fibres and spiders' webs not just for lining but for stitching.

There is no more skilled 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.

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.

This one is in a tree covered in lichen.

And this is 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're not easily recognised for what they are.

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 were called apostle birds.

And the team works so industriously and so harmoniously

that their elegant cup is usually completed in a mere 3 days.

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

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

but as lodging houses for the whole year.

This haystack may be more than a century old.

It's so heavy that part of it has broken the branch that supported it.

It's been built and maintained as a communal effort by its inhabitants.

Weavers are closely related to sparrows.

has a considerable advantage over small isolated nests

During the day it gets ferociously hot,

And then the thatch is probably at its most valuable.

and the birds that roost inside remain snug and warm.

Not all the chambers are for nesting.

in which several of the colony snuggle together for warmth.

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.

Mated female birds have been feeding intensively

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

Pigment glands squirt little spots of colour on it.

And so, an avocet produces her egg.

These are the eggs of a golden plover.

Laid on the ground they are practically invisible,

as indeed the bird that laid them will be, once she settles down.

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

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

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.

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.

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 skilfully protected and artfully concealed they are.

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.

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

In Australia the prime egg thief is the currawong.

and the Australian birds have developed many strategies

This is the nest of a yellow-rumped thornbill.

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. It's down here.

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

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

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

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

one of the adults immediately responds.

Ahead, I can just see a bird crouching on her eggs.

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.

an injured bird or maybe a little rodent.

Having deflected me, she returns to her nest.

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

The birds have to be accurate judges of temperature.

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

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

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

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.

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

and he will have to do this for almost two months.

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 realise what has happened

The male has a redder head and neck, the redhead duck.

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

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.

And there are plenty of hazards against which a duck needs to insure

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

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

This is the nest of an Australian fantail.

It's so different that you would think the fantails would realise.

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 -

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

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?

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

But nesting material is too valuable to waste.

They begin a new nest quite close by.

destroying the old and building the new.

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 the weavers seem well aware of the danger.

as they must have been doing for many centuries.

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

Cuckoo eggs have been frequently found in the nests of these weavers.

but none seem to be getting into this colony.

The battle seems to be swinging the weavers' way.

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

The colours of their eggs are extraordinarily variable.

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

And it has no way of knowing what colour the eggs are in any one nest.

So the odds are against the eggs matching.

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

What happens if I put a pale egg in it?

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

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

and the victims finding new defences.

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

Most will produce young weaver birds, but some, equally certainly,

Whichever they are, the young chicks will have a whole set of problems

they have to solve before growing into adults.

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

On the open moorland there is plenty of room for a nest and not enough

food for lots of birds, so there is no problem of overcrowding and the

rarity of a well camouflaged nest is good protection.

If you have a chisel as efficient as a kingfisher's beak you can cut a

very safe home for yourself in a tree.

A hole like this made by the South African woodland kingfisher is not

very conspicuous and easy to defend, since the sitting bird can use its

beak not only as a chisel but as a spear.

But for the Australian crested bell bird it seems that the essentials

are not enough. A home should not only be secure, it should be

decorated. The bird goes through a lot of

trouble to garland the rim of its nest can caterpillars.

The caterpillars don't crawl away. This is because the bell bird has

given each of them a nip behind its head that has immobilised it but

they are not just decoration. They are covered with hairs that have a

particularly powerful sting, painful enough to deter a small mammal from

sticking its sensitive nose into to the nest.

For a happy and successful home, there is nothing more important than

security. Bringing up baby always causes

difficulties, and birds are no exception. This young tern is an

insatiable creature demanding to be fed over and over givenry day, but

different birds have different requirements and some face the most

extraordinary dangers, as you can discover from the problems of

parenthood, the next programme in the Life of Birds.

'We wanna do a science fiction series.'