The Life of Birds (1998): Season 1, Episode 3 - The Insatiable Appetite - full transcript

If you travel by air, it's very important
to keep your weight down to a minimum.

You can't afford to carry a lot of fuel around,

and what you do carry should be energy-packed
and not too bulky.

Oak trees put just such a substance
into their acorns.

It's there to fuel the growth of their seedlings,
and they protect it with a hard shell,

but jays know how to deal with that.

A beak is itself a concession to weight-saving.

It's much lighter than the jaws and teeth that
reptiles and mammals use to process their food,

yet it's also very efficient and versatile.

A jay using its beak like a pick

can cut through an acorn's armor
without any difficulty.



Beaks are closely matched to diet.

A goldfinch uses its beak like a pair of tweezers.

It's just the right length for extracting the seeds
from between a teasel's spines.

A blue tit, on the other hand, has a stubbier beak.

That gives it the strength to crack small seeds,

but it also prevents its owner from
getting them from a teasel

A greenfinch's beak is even stouter and stronger,

but it's far from clumsy.

Watch how, with the help from its tongue,

the bird delicately removes the outer shell
of these rosehip seeds.

The strongest beak in the finch family
belongs to the hawfinch.

That can even deal with the cherry-stone.

But the bird doesn't simply rely on brute force.

First, it maneuvers the cherry-stone into
the right position for easy cracking.



It gets rid of the broken shell...

..and now it starts the fiddly operation of
removing the husk that covers the kernel

Pine trees, these are in California,

protect their seeds by enclosing them in cones.

When they're still green, the seeds developing
within are beyond the reach of most birds.

But the cross-bill has special equipment.

It's the only finch that can twist its upper
and lower bill in opposite directions.

Now, right at the bottom, it can feel
the soft young seed with its tongue.

Got it!

After a meal of pine seeds,

these American cross-bills regularly fly off to
a bank of exposed clay.

They're in need of digestive tablets.

Green pine cones are resinous,
and resin may cause stomach upsets,

but clay in the stomach will absorb the resin
and so prevent any trouble.

A crossed bill, however,
is not the best implement for digging.

You have to twist your head to one side
to get the point into the ground.

But the birds seem to manage to get
a sufficiently effective dose

to allow them to take daily meals
from the pine trees.

Seeds in the temperate parts of the world,
however,

whether they are in pine cones,
cherry-stones or acorns,

all have a major disadvantage as a food for birds
- they're very seasonal

In spring and in summer there's none,
and then in the autumn there's a glut.

A single oak tree like this can produce
90,000 acorns in a season.

But there are lots of things apart from birds
that eat acorns.

Squirrels do, for a start,

so if a jay is to collect acorns in the autumn,
it will have to do so quickly,

before others grab them all.

It is carrying one in its beak,
because its crop is full,

as you can see from that bulge on its throat.

There can be as many as nine acorns in there.

But what is a jay going to do with such quantities?
It can't eat them all.

They store them - by burial

One jay, in a month,
may bury as many as 3,000 acorns.

What is more, when winter comes
and it's in need of food,

it will remember exactly where most of them are.

In North America, oaks still form huge forests

and they produce acorns on an astronomical scale.

Among those that harvest them are woodpeckers.

A woodpecker's beak is a drill,
and a very efficient one,

so it's not surprising
that it stores acorns by drilling.

There are as many as 60,000 acorns
stored in the holes drilled in this one tree.

All the members of this woodpecker family,
eight birds in all, use this one tree.

To start with, the birds deposit
newly gathered acorns in a hole

to allow them to dry off.

Then, when they have shrunk as much
as they are going to do immediately,

they're given individual storage.

This larder provides food for the family
throughout the year,

but the birds have to be very vigilant
and ready at all times to repel raiders.

There's also a lot of maintenance work to be done.

As the acorns continue to dry and shrink,
they become loose in their sockets.

That would never do. They would be easy for
someone to steal They might even drop out.

0n the other hand, if they are hammered into
a hole that is too tight,

the shell could crack and then the acorn would rot.

So maintenance is a never-ending,
year-round labor,

and it takes a lot of care and judgment.

The result is a great acorn treasury that will last
the whole family well into the next harvest.

These neat holes are made, not for storage,
but for theft.

They're cut by another kind of woodpecker -
a sap-sucker.

They're just deep enough to tap the vessels
along which the tree transports its sap,

and sap is largely what the sap-sucker lives on.

The bird cuts its sap-wells
with an accuracy and symmetry

that would do credit to the finest cabinet-maker.

Sap normally hardens quickly and seals a wound.

This doesn't. It could be that the sap-sucker
produces an anti-coagulant in its spittle,

but if it does,
no one yet has managed to identify it.

Even so, each little well eventually runs dry
and the bird has to cut another.

These wells have been made in the trunk of a
pine tree which produces sap throughout the year.

Other trees, such as these aspens, only produce
sap in quantity in spring and summer.

When the sap-sucker moves on to these,
it cuts differently shaped wells.

With this spring increase in the sap supply,
new birds appear in the woods.

A yellow-rumped warbler.

They're quick to drink from the wells
cut by the sap-suckers.

Food is short so early in the year.

The birches are now in leaf,

and the sap-sucker moves on to them,
and makes wells of yet a different shape.

A northern oriole - another hungry migrant

only too willing to benefit from
the labors of others.

And a hummingbird.

It used to be thought that hummers
timed their arrival

to coincide with the opening of the spring flowers
from which to drink nectar.

But they arrive well ahead of that.
Their appointment is with the rising of the sap

and the work of the sap-sucker.

Sap is an excellent food - energy rich
and easily flicked up with the tongue.

But it can only be collected from many of
these northern trees during part of the year.

So when winter approaches,
warblers and hummingbirds fly south again

to where it's summer all year long.

Here in Mexico, the sap is taken,
not only by birds, but by insects.

The trunks of many of the trees
seem to be sprouting long hairs.

At the end of each, there's a tiny drop of liquid.

The hair is a tube projecting from the rear of
an insect lying beneath the bark drinking sap.

But the insect gets more sugar than it needs,
so it excretes the excess.

And that is what the hummingbirds,
with exquisite accuracy, manage to collect.

Many different warblers take it too.

The liquid, rather flatteringly called ''honey-dew'',

is so much sought after that some birds
take up residence in a particular tree

and will drive away any others
that try to feed there.

Their meals, however,
come in such small installments

that feeding has to be almost continuous.

It takes about an hour for a drop to accumulate
at the end of a tube,

so to get enough to sustain themselves,

the hummingbirds have to travel from one to
another on a regular round throughout the day.

Plants produce other edible things
as well as seeds and fruit and sap.

They sprout leaves, but in truth leaves
are not very good food.

They're very bulky and need a lot of digesting.

So animals that live on leaves,
like these cows, for example,

tend to be rather hefty creatures with massive
batteries of grinding teeth

and special capacious stomachs.

Cows, having grazed, lie down and bring up
each mouthful for a second grinding chew.

No bird does that - you can't chew with a beak.

Geese have to use a different technique.

They're big birds, as they have to be
to accommodate such bulky meals.

But instead of digesting the grass intensively,

they eat a very great deal of it and get rid of what
they can't digest almost immediately.

The appetite of geese is apparently never-ending,

and a flock of them, like these barnacles,
will work its way across a meadow

nibbling non-stop with almost feverish speed.

And pooping all the way.

It makes a terrible mess, but it does mean that
after feeding for several hours...

..the geese are not weighed down
by great quantities of undigested grass...

..and can get into the air without much difficulty.

In South Africa there's a rather
smaller leaf-eater - the mousebird.

They do make some attempt to digest their meals
a little more thoroughly.

They start feeding early in the morning.

Then, with as much nibbled leaves on board
as they can manage,

they sit for hours on end with their distended
stomachs turned towards the sun,

so that its warmth helps with their digestion.

You can't beat a siesta after a heavy meal

In all the bird kingdom, there's only one species
that is really specialized for leaf-eating.

This is it - the hoatzin of South America.

Like a cow it has two compartments
to its stomach,

the second of which is full of bacteria
that help ferment its meals.

In consequence it's a bulky bird
and positively clumsy in the air.

More a lumbering cargo plane than a super jet.

Birds, by stripping leaves,
eating seeds and drinking sap

are exploiting plants - stealing from them.

But many plants exploit birds
by using them as couriers.

The arrangement is such an ancient one

that both employers and employees have evolved
special ways of transacting their business.

The plants attract their couriers with flowers.

They pay them with nectar,

which is easy and cheap to produce, because it's
no more than water and sugar

and that's what I've got in here.

And these Australian rainbow lorikeets love it.

Here in Australia there are some plants that are
in flower throughout the year,

so it's possible for birds to specialize as
nectar feeders, as these lorikeets do.

Their tongues, instead of being hard and leathery,

have a feathery brushy tip
so they can lap up the nectar.

And the plants, when they have a need for
a messenger, advertise the fact

by producing flowers with
particularly bright petals.

Having collected all the nectar immediately
available on one tree,

the lorikeets move off in a flock
to feed at another,

carrying the pollen they collected with them.

But they take nectar
from many different kinds of flowers,

and if, as here, the plant they next visit
happens to be a different one

the pollen they're carrying will be wasted.

The plants way of reducing that risk
is to recruit an exclusive service

with couriers who, during their flowering season,
will visit them alone.

Here in South Africa, this species of heather
encloses its nectar in a ''floral safe''

which only a particularly shaped beak can unlock.

This orange-breasted sunbird
has a beak of that shape,

but even so, it has to probe really deeply
to reach the heather's nectar.

And every time it does,
it triggers a little explosion of pollen.

When the bird drinks at another heather plant,

some of that pollen will be brushed off
and the heather will have achieved its end.

But bird and flower can fit one another
more closely than that.

0n Mount Kenya, there's a sunbird with an even
more strongly curved bill

The golden-winged sunbird.

And this is its employer - the lion's claw flower.

The feathers on the sunbird's head look golden,
like those on its wings.

But not so - they're black.
The gold color is entirely due to pollen

which is stamped on it when the bird
thrusts deeply into the flower.

The devices used by plants to restrict
their payments to their employees

may, if taken to extremes,
defeat the object of the exercise.

This South American plant
has gone, literally, to great lengths

to shield its nectar from all but
its established partner,

and that has encouraged burglary.

This is the black flower-piercer.

It knows exactly where the nectar is stored,

and it knows a quick way of getting it, too.

Its tongue is flicking into the nectary
at the top of the flower's trumpet

so that nectar is channeled down its lower bill
into its throat.

The datura has even longer flower trumpets,
but they are robbed just as easily.

Here in South America, hummingbirds are
the main collectors of nectar,

and they will collect it any way they can.

Using a break-in by a flower-piercer is as good
a way as any other, as far as they're concerned.

The trumpet of the datura flower is so long

that you might think that nothing
could drink from it - legally, as it were.

And only one bird can -
the sword-billed hummer,

which has the longest beak in relation to its body
of any bird in the world.

A plant only flowers for a short period each year,

so a nectar drinker has to have
a succession of suppliers.

A sword-bill also drinks from passion-flowers.

The South American climate is so equable
and the number of plant species so huge

that there are always some flowers to be found.

Accordingly, hummingbirds have evolved
highly specialized equipment for nectar feeding.

They have developed a unique way of flying
that allows them to hang stationary in the air

while they drink from a dangling blossom.

Their tongues have become threads that flick
in and out a dozen times a second,

but they're virtually useless for collecting
any other kind of food.

Where most plants tend to bloom
at the same time of the year,

neither the suppliers nor the drinkers of nectar
can be so specialized.

So the coral tree, blooming in Thailand,

has no alternative but to be generous
and offer its nectar in a free and open way.

This delectable seasonal treat attracts
all kinds of birds from far and wide.

Such a large and varied clientele is pretty well
bound to do the job required of them.

After they are pollinated, plants produce seeds

and then many engage other birds
to distribute them.

That, by and large, is heavier work,

and the payments they offer for that are made
with a different currency - fruit.

Hornbills are on their way to do a job for a fig tree
in the Indonesian rain forest.

In northern Europe and America,
waxwings gorge themselves on autumn berries.

A plant wraps its seeds in the minimum flesh
needed to persuade the bird to swallow them.

These berries have so little that it's quickly
stripped off in the waxwing's stomach,

and then the waxwing can get rid of
the indigestible seed.

The story is the same all over the world.

In New Zealand, kokakos are great berry eaters

and distribute the seeds of many of the plants
of their native forest.

In South America, tiny wild avocados

are the special favorite of one of
the most dazzling of birds - the quetzal

The avocados may be small, but they're still
too big for the quetzal to swallow.

So the stones are ejected, not from the back end,
but from the front.

The bird has had a good meal,

and the avocado has had some of its seeds
carried to a new site.

There are other things for birds to eat in a forest
apart from the products of plants.

They may be difficult to find;
they may be even more difficult to catch,

but they're well worth having
because they're full of nutrition.

Things, for example, like this.

The morpho - a big and powerful butterfly.

A jacamar - a cousin of the kingfisher's.

A butterfly's wings aren't very digestible

and have to be stripped off before the bird
can swallow the fat, nutritious body.

Winged termites erupting from their holes in the
ground and flying away to establish new colonies.

A whole host of birds relish these.

Ants are trickier meals. They, after all, can sting.

It takes a specialist to deal with them.

This is the rufous woodpecker of Southern India.

Its beak is just as efficient at demolishing
an ant's nest as it is at drilling into wood,

and the bird seems totally indifferent
to the ants' sting.

The feathers of its tail, like those
of all woodpeckers, are particularly stiff

so that they can serve as a prop.

The most nutritious morsels
are the soft, fat, stingless grubs

that can be found in the very center of the nest.

Insects are almost everywhere on every tree;

on twigs, in buds, crawling
around in crevices of the bark,

and many birds find quite enough to sustain
themselves just by looking carefully.

But some work harder - and get greater rewards.

The nuthatch, in European woods, is indefatigable.

It will eat many things,
including seeds during the autumn and winter,

which it can crack with its workman-like beak,

but in summer, insects are a major part of its diet

and its beak serves equally well
for picking them out of the bark.

The greater spotted woodpecker
is a little more specialized.

It particularly likes
the grubs of wood-boring beetles,

and the first thing to do to find them
is to chisel away the bark.

Its tongue extends for an inch and a half beyond
its beak and has a harpoon at its tip.

When that hits a grub fair and square, it sticks.

Tree-boring insects are never safe
when woodpeckers are around.

But woodpeckers never got to the Galapagos,
far away from anywhere in the Pacific.

Insects did though, and their grubs bore into trees
here, just as they do everywhere else.

But no Galapagos birds have the physical
adaptations with which to reach them.

Galapagos finches, however,
are both intelligent and ingenious.

Their beaks are perfectly adequate
for stripping away bark.

There's a grub under there somewhere -
it can hear it.

But how, without the long tongue of a woodpecker,
can it get it out?

It needs a tool - a spine from a cactus.

A success - but only a partial one.

It has only extracted little bits of the grub.

Nearby, a bird from another clan of finches
uses a slightly different technique.

It selects a rather stouter tool that can be used,
not so much for stabbing as for levering.

That has shifted the grub a little nearer the hole.

It's not quite within reach,
but it's still got that lever handy.

Give it another go.

And that's got the rest of it.

Another remote and isolated island, on the other
side of the Pacific - New Caledonia.

It gets a lot of rain and so it has a much bigger
and richer forest than the Galapagos.

But it's so far from any of the major continents
that woodpeckers have not got here either.

This fallen tree-trunk is studded with holes;

the work of wood-boring beetles.

Their size suggests
that they're made by much bigger insects

than their equivalent on the Galapagos.

The New Caledonian crow - and crows are among
the most intelligent of birds.

Once again, the sound of a grub gnawing away
in its burrow betrays its presence.

And once again, since this grub-hunter hasn't got
the long tongue of a woodpecker,

a tool is needed.

To contact this grub,
the stick will have to be thrust in really deeply.

A spectacular catch!

Some of these crows become so attached to one
particular tool that they carry it about with them.

This log is clearly a good source of grubs

and a whole group of crows
have come here to feed.

Their technique is neither to stab nor to harpoon,

but something more subtle - to irritate.

This grub has got big jaws and, if attacked,
it can give a powerful bite.

And that's what the crows rely on.

A younger bird joins an experienced adult
to see how things are done.

Now the pupil has a chance.

It hasn't got all the details exactly right.

It will be about a year before it masters the skill.

There are insect grubs everywhere, of course.

The only problem for insect-eating birds
is getting at them.

But sometimes other creatures are of help.

You might think that this is a recent partnership,

but I'll bet when our prehistoric ancestors first
dug for tubers and planted seeds in Europe

one of these little robins appeared
within a couple of days.

Other animals must have done the same job
for them before human beings did.

Once, not so long ago,
wild pig were common all over Europe,

and they're great diggers and rootlers.

So maybe the robin's boldness and friendliness
with other kinds of animals

started in prehistory,
even before human beings arrived in Europe.

Such partnerships exist all over the world -
even in the most unlikely places.

This little bird lives on a small island in
the Indian Ocean, one of the Seychelles:

so small and so isolated that few mammals
got here before human beings.

It's not closely related to the European robin,
but it behaves just like one.

When Europeans first came to the Seychelles
and saw it,

they called it a robin because of its similar habits.

But what partner did it have
before human beings came along?

Could it be this?

Once there was a large population of these giant
tortoises on several islands in the Seychelles.

They weigh several hundredweight and those
huge legs dig into the ground with every step.

There we are!

These little birds, now even rarer than
the tortoises themselves,

are still their regular companions
as they plod around the island.

A swamp in South America.

An abundance of water and a warm tropical sun
make it a paradise for insects of all kinds.

A kind of fly-catcher - a cattle tyrant,

and another obliging partner - a capybara,
a large semi-aquatic rodent.

As the capybara moves around it inevitably
disturbs insects of some kind or another,

and what better place for an insect-eater to
spot them than sitting on the back of one.

Would the view be any better from there?

Perhaps it would be.

A few of these partnerships
between birds and other kinds of animals

have become very intimate indeed.

The hide of a hippo may not seem
a particularly rich source of insects,

but there are little ticks to be had
in the various cracks and crannies,

and ox-peckers go there to search for them.

They have extremely sharp claws, with two toes
pointing forwards and two backwards,

so that they can cling at any angle -
even on a slippery hippo.

Land animals with hair on their hide
are likely to be more productive ground.

0x-peckers pay particular attention to their ears.

That's the sort of place where you find ticks.
And if there is one, the ox-pecker will remove it.

And they also eat earwax.

Dandruff is another part of their diet.

Their beaks are flattened so that,
with their head held sideways,

they can comb through their hosts' hair.

0x-peckers spend all their life on,
or closely beside, their animal hosts.

They court and mate on their backs.

And when they fly off to make a nest, as they
must do, they pluck hair from their hosts' backs

with which to line it.
But do they do anything in return?

They remove irritating, even damaging, insects
that their hosts can't dislodge for themselves.

But the bird's main diet is blood.

Sometimes they get it by swallowing ticks
that are bloated with blood.

But they also take it directly, pecking at
an animal's wounds to keep them open.

When their hosts get irritated,
they go back to their toiletry duties,

before once again snatching a sip.

So, in spite of having such a specialized life,
living on the bodies of mammals,

ox-peckers manage to get quite a varied diet.

A maggot here, a tick there, a little sip of blood,
perhaps a little tasty earwax.

But there are some birds that literally live
on mammals - alive or dead.

They eat them; and those are the birds we'll be
looking at in the next programme in this series.