Original subtitles

Each year, one specific group of animals embarks on an arduous 2,484-mile long

journey over winter to the secure area of Sierra Nevada, Mexico.

2,484 miles across mountains, oceans, through winds, thunderstorms and rain,

they always keep one goal in mind.

Finding a better place to live, a place to spend the winter, and a place

secure enough for the continuation of their generation.

This is a journey that scientists find difficult to explain, a journey that

prompts many questions, and shows us once again that nature is equipped with forces

we can barely imagine.

This trip is undertaken not by a huge bird like an albatross, not by a skilled

aviator like an eagle.

No.

This trip is undertaken

by a fragile little animal with wings like paper, with a body weight of a hundredth

of an ounce.

This trip is undertaken...

by a butterfly.

The Monarch Butterfly.

During winter time, the majority of the butterfly population spend their period of

dormancy in the volcanic mountains of the Sierra Nevada of Mexico.

At an altitude of about 9,840 feet.

In the spring, the butterflies migrate from their hibernation grounds...

and proceed to the north and east.

A journey which involves the passing of several generations.

Along the way, the butterflies lay eggs in different locations...

and so allow future generations to thrive.

Animal migrations are a topic of interest around the globe, since there are many

mammals which migrate.

And we must not only think about migratory birds.

What very few people know is that there are

many species of butterflies that also migrate.

In Germany, we have a lot of butterflies during summer...

which actually migrate each year from North Africa over the Alps.

But the longest migration journey is made by the American Monarch Butterfly.

The Wandering Monarch is restricted to America.

Whilst there are close relatives who can be found on other continents,

the Monarch itself is located in several areas between Canada and Mexico

depending on the time of year.

As with all insects, and especially butterflies,

it is fascinating how the Monarch Butterfly develops itself.

First, a small caterpillar slips from an egg,

and feeds off leaves.

It must peel itself several times

because it has no internal skeleton like us

but an external skeleton,

which does not consist of cells

but is a chemical called chitin.

That is why they cannot grow inside of this.

If you may, it's a knight's armour,

and therefore must peel.

Finally, there is a cocoon,

and from this little cocoon slips a butterfly

with six legs and four large wings.

The creamy white, then dark grey, eggs

are the first home of the caterpillars.

After they hatch, they first feed from the plant,

and then pupate.

After the metamorphosis into a butterfly has taken place,

a rather weak moth emerges from the cocoon.

Only when the blood starts flowing into its wings,

the monarch butterfly is ready to fly.

The life cycle is the same for all butterflies.

Initially, the eggs are laid

from which the caterpillars hatch.

A caterpillar can be easily identified

by their distinctive black, white, and yellow horizontal stripes.

After a feeding phase, the caterpillars pupate.

After a caterpillar has left its jade green cocoon

and morphed into a butterfly,

the same cycle starts over again.

Butterflies normally do not have long lives.

You cannot make a sweeping statement

about how long a butterfly lives.

That depends on the species.

But all in all, the monarch butterfly lives a little longer.

In total, four generations of monarch butterflies emerge

in one single year.

The first three have an average life expectancy...

of about five to six weeks...

and move bit by bit from Mexico to Canada.

The fourth and last generation subsequently

is the one that starts off the trip from Canada to Mexico,

which takes about one to two months,

after which they remain there for another six months.

If we compare this with the life expectancy of a person,

it would be as if every fourth generation

would not just reach an average age of 80 years,

but rather 480 years.

What remains unclear is why the fourth generation

doesn't undertake the journey in stages

as the other generations do,

when they fly from Mexico to Canada.

Scientists attempt to explain the extended lifespan

of the fourth generation by a related hormone deficiency,

as well as a shortage in food that occurs during the autumn.

This lack of hormone and food is believed to prohibit

sex organs from fully forming,

resulting in a lack of

sexual activity within the population.

By skipping the breeding process,

the excess energy is instead solely used

to help overcome the great distance.

Monarch butterflies do it like all other butterflies.

The male and female find each other

and float around one another.

Butterfly partners find each other from smells.

So they mate,

and then the female lays the fertilized eggs

in the food plant appropriate for the caterpillar.

If she would lay them down somewhere else,

the caterpillar would not have a chance

of finding a food plant.

In this particular food plant,

the caterpillar develops itself.

Meaning one eats, eats, eats,

grows, grows, grows...

And if the little caterpillar hourglass runs out,

the caterpillar knows it is time for pupation.

Then the caterpillar usually searches

for a specific place on the plant.

But there are also butterflies

which pupate on the ground.

Monarch butterflies usually do it on a plant.

Which means the caterpillar becomes inactive.

It develops this cocoon.

And in this cocoon,

the caterpillar will be dissolved

and transformed into a butterfly

which then slips out of the cocoon.

Odors are how the monarchs

find one another to mate.

When a female catches the attention of a male,

the male follows the female in rapid flight.

If the female is ready to mate,

it flies upwards in a spiraling motion.

They repeat this act

until both of them finally land together

on a leaf to mate.

The female then lays its eggs

near an adequate food plant.

Once the breeding process is completed,

both butterflies perish.

First the male,

who is then followed by the female.

With each generation,

the population in the United States

of course grows.

But of course,

that depends on the food supply,

the climatic conditions,

and so on.

Therefore,

the population is never constant.

The less that migrate from Mexico

to the United States in spring,

the lower the initial population.

And the lower the population

will be in the fall.

Or vice versa,

the more that arrive,

the larger the population can be.

The butterflies have a lot of things

planned in their lives,

and there are also a lot of risks.

That starts with the little caterpillar,

which slips out of a small egg.

This is because

the American Monarch butterflies

are specialized

in the family of milkweed plants,

which are similar to rubber trees

and have a milky sap.

If a small caterpillar hatches from an egg

and just blindly bites into a leaf,

the milk juice

would make the mandibles stick completely.

That is why the caterpillar has to carefully separate

the tiny veins of the leaf, one by one.

That is a time-consuming way

of winning nutrients

out of the plant.

Some caterpillars

take in substances

from the food plants

which the plants form

to protect themselves

from being eaten.

For example,

the milk juice -carrying silk plants.

The caterpillars save these substances

so the adult butterflies

are protected against enemies.

Birds, for example.

Although there is no

absolute protection in nature,

they are still protected against

many types of predators.

From September to November.

these animals migrate

from their large habitat,

which measures more than

100 million hectares.

They gather on less than

20 hectares in the Mexican

Sierra Nevada.

On their annual journey,

they always gather

at the same resting spots,

and form enormous groups overnight.

At low temperatures and high winds,

the butterflies sit

really close together

and form even larger colonies

At temperatures below 10 degrees centigrade, the butterflies are not

capable of flight.

So, in weather conditions like these, they tend to rest, even during the day.

With the sun shining and temperatures over 13 degrees centigrade, they are able to

continue their migration.

When traveling from Canada to Mexico, the butterflies will take 8 to 10 weeks.

In the more southern areas, they need 4 to 6 weeks.

At an average, they cover about 30 miles a day during their journey.

If you were to transfer this effort and physical capacity onto a human,

it would mean that one person could cover about 621 miles a day.

So, comparing the entire journey of these butterflies and transferring their skills

to a human would be as if a single person, comparatively, would have walked across

the globe, not once, but twice.

The butterflies migrate in a southwesterly direction, starting east of Lake Huron.

However, they usually don't directly reach Mexico, but run into the Gulf of Mexico

and migrate in large flocks along the coast.

The butterflies from the east coast start off by flying south until they reach the

Atlantic coast, which they travel along before changing their direction of flight

west towards the Gulf Coast.

Around October, they pass through Texas in order to follow the Sierra Madre Oriental

in Mexico, still heading south.

They then turn west and reach the volcanic mountains of the Sierra Nevada.

We can determine the origin of the butterflies from their winter habitat.

The butterflies from the Great Plains approach the western areas, heading

towards the Great Lakes.

Those butterflies which do not reach the Gulf Coast occupy the middle areas.

Butterflies that do reach the Gulf Coast will occupy the eastern grounds.

Eventually, all the butterflies gather in one place for copulation.

Observing the butterflies on their journey has proven to be problematic.

The monarch butterfly only weighs a fraction of an ounce, which makes it

difficult to equip one with a transmitter or something similar in order for us to

determine its whereabouts and subsequently observe it.

It's still unclear how the monarch butterfly manages to reach its goal and

travel a 2,484 mile journey every year.

Unlike migratory birds, new generations cannot learn the route formed by their

parents as none of these insects survive long enough to fly to Canada and again

back to Mexico.

It is assumed that the path is passed down from generation to generation like a road

map of some kind.

This is an unusual phenomenon in the animal kingdom.

The monarch butterflies is the longest living butterfly in the world.

They live for eight months.

This is just this generation which is born by mid-September and lives up to mid-May.

So from mid-September they arrive to Mexico at the beginning of November and at

the end of March they fly back for the month of April.

Then the female lays 400 eggs.

So the survival ratio is 200 to 1.

The people of Mexico, of course, have known that for generations millions

of those monarch butterflies have been coming every year around the same time as

All Saints to stay during the winter.

In North America they've wondered for decades where those butterflies have been

during the winter as there were no traces of eggs, caterpillars, nor cocoons.

It was presumed they had some sort of wintering ground, as the whole population

of the most common butterfly in North America

would vanish from the face of the Earth.

They had to be somewhere.

Not until the mid-90s was this wintering ground in Mexico discovered.

A Canadian named Fred Urquhart spent decades of his life every fall labelling

wings of butterflies with tiny notes which had his address on.

He did this so he could get responses from people who found those butterflies and

find out their whereabouts.

"They could find a butterfly with a little backpack

somewhere and notify him to find this place."

There is no one single explanation accepted by all the scientists that why do

they come here and for so many years.

That is, they come to Mexico for hibernating.

Just to escape the very cold winters of Canada and USA.

Even down here they are at 3000 meters elevation and the night temperature during

December and January is 0 degrees centigrade.

But that's good enough for them because back home it's minus 30 degrees.

So that's the reason that they come here to hibernate.

And there is a...

they always arrive exactly by November 1st.

So their starting point - it is always the inclination of the sun rays of the autumn

equinox of September 21st.

So that is every year for thousands of years has been the same.

So that's the signal to start flying down to Mexico.

They spend their winters in southern Mexico on a plateau of volcanic origin.

The 30 colonies over winter are spread across nine separate volcanic massives

which are located 70 to 170 miles from Mexico City.

The Madre and Pine Oak woodlands dominate the mountain area and are where oaks,

pines and firs are mainly found.

Less common are cypress forests, juniper heaths, and grasslands' finger herbs.

In some places there are agricultural and bush land.

When the butterflies arrive in the mountains they fly around, watch the wind

direction and seek shelter in trees, preferably on Abies religiosa.

When the first butterflies have settled, the others join with no regard to wind

direction and form dense clusters of butterflies which can cover whole trees.

When the tide turns, the butterflies that were previously leeward are now exposed to

the cold winds.

Since they cannot fly during the low temperatures in winter, they fall to the

ground when the trees bend due to rainstorms

or snow storms which often occur in

late December 'til early January.

Large amounts of butterflies are shaken from the

tree tops and consequently die on the ground.

From mid January to February, the major butterfly groups dissolve on the peaks and

these butterflies travel downhill to form smaller and looser clusters.

Time and again the butterflies then leave the trees to drink from the edge of small

puddles or mud.

Towards the end of February when the climate gets warmer they leave the

mountains and migrate to the north.

Only a very small portion of the population is left behind in Mexico.

Just imagine the whole population of the eastern United States.

So, anything that is east of the Rocky Mountains up to southern Canada.

All these many millions,

these tens of millions of butterflies of this one kind,

come together year after year to the same location at this tiny place:

15 by 15 acres in Mexico,

where they meet over winter in these huge aggregations.

Since there are so many butterflies sitting on branches, some branches break

because of the weight.

Just a reminder, a butterfly weighs a hundredth of an ounce.

Up until the end of April last year, the butterflies reached the space between the

northern border of North Carolina and Oklahoma after their hibernation in Mexico

during their migration to the north.

It seems that the butterflies would like to return to the place where they lived as

caterpillars.

The females only lay a few eggs in Mexico;

most of them lay their eggs at the end of their migration to the south of the

United States.

The emerging first generation hatches around late April up until the

beginning of June.

The migrating butterflies reach North Dakota, Minnesota, and the area around the

Great Lakes at the end of May.

And also lay their eggs around those areas.

The butterflies of this generation are to be found at areas from southern

Texas and the Gulf Coast to the north of the Great Lakes.

Only a few butterflies move from south Florida to north and go on to lay

eggs in central and north Florida.

So consequently only a few from the first and last year's generation fly east of the

Appalachian Mountains in the northern territories.

The development is often slow due to the low temperatures and it takes 40 to 50

days for the caterpillar to become a fully formed butterfly.

The second generation hatches in June and July and migrates only slightly

further north.

Reaching approximately the 50th latitude, the northern boundary in

southern Canada.

They migrate more towards the northeast and colonize the space between the St.

Lawrence River and the Atlantic and fly as far east as Newfoundland.

The food plants in the southern U.S.

dry up in the summertime.

Consequently the local butterflies migrate to the north and so there are no more

butterflies to be found south of the 33rd longitude.

Music Since the development in every region advances at a different pace,

the third and fourth generation of butterflies fly together in late August to

early September and form a strong late summer population that migrates to the

south soon after.

While previous generations are fertile only a few days after hatching,

many of these animals remain infertile until after the diapause.

Some females that are fertile lay eggs on their way to the south and sporadically

make it possible for a fifth generation to emerge.

This delay in development, or the dormancy period as it is called, is triggered by

the short days, the lower temperatures and the dying crops.

One might wonder how old this phenomenon of migration in the American monarch

butterfly actually is.

There are reflections from some colleagues who say that the United States was of

course, before the white man came, fully forested.

And caterpillar food plants don't grow in forests.

They need open spaces.

Perhaps the phenomenon of migration is a relatively new phenomenon, which has only

existed for a few hundred years.

After North America was cut down, the larval food plants could multiply and

therefore could occur in larger areas.

This was the foundation for the monarch butterfly.

But they cannot survive the entire year there because of the frost.

So about five, six years ago in America, because they want always to know why this

happens, they made an experiment having in a large room 500 butterflies.

With all the walls, ceiling and floor black except the small opening when

they introduced the light.

And they were changing the inclination of the light coming into the

room and at the inclination of September 21st, all the 500 butterflies started

flying southwest in the room.

So that was a big finding, you know, what was the real reason that

they will always arrive here on time.

And so next day to be sure that it was it, next day they repeated the

experiment changing the magnetic polarity of the room 180 degrees.

And they repeated the experience with the light and again at the

inclination of September 21st of the sun rays, they started flying southwest of the

magnetic polarity of the room.

But actually geographically they were flying northeast backwards.

So this was a big finding and this happened about five, six years ago.

The orientation mechanism of the butterfly is obviously a very, very big question.

So there are various questions around magnetic orientation.

Recent attempts in the field of molecular biology show that magnetic

fields really do play a role.

And also responsible is the wind.

The butterflies do not fly all the way by beating their wings up and down,

but also get carried by the wind.

So their use of wind is similar to a glider.

It is a very complex behavior which is still not fully understood.

Yes, we hope that this phenomenon is still noticeable by our children, and

grandchildren, and even our great -grandchildren.

But there are also risks at the wintering ground in Mexico.

There could be a snowstorm which kills tens of hundreds - maybe even millions -

of butterflies.

It may also be that in the future, the problem of illegal logging still exists.

The butterflies need specific plants around them to hold certain amounts in

particular tree species.

There is a lot of illegal logging.

I'm still trying to reduce it.

Even if there is no more logging - legal or illegal - the tree count may be

reduced, as there are microclimatic changes.

So there are still a lot of things that can happen, and the risks are still not

fully understood.

Especially, as there is nothing we can do to prevent some of them at the moment.

Almost like a king, the monarch butterfly flies with its sublime blaze of colors

through its Mexican winter residence.

The butterfly shows us, unlike any other being, that even the smallest among us,

are capable of extraordinary achievements.

On their journey, they will always have Mexican prayers on their side, for an

old Mexican belief says that the monarch butterflies are the souls of the dead.