This is how nature works.

Theme Music Music Since life appeared on earth, each kind of creature has had just a certain amount of time before its kind disappeared forever, and new creatures took its place.

Temporary environmental changes like those from hurricanes, ice storms, or fires may kill lots of organisms but they don't usually put a whole kind of living thing in much danger of disappearing.

But effects of events like ice ages, volcanic eruptions, or meteor collisions can last thousands of years.

When that happens, life is at risk.

Some scientists think dinosaurs disappeared because a meteor collision changed the environment for a long time, and dinosaurs couldn't adapt to survive it.

In the past few thousand years, people have changed the environment in big ways and for the long term.

Our homes, ranches, farms, and cities take up space.

We pollute, hunt, overfish, destroy habitats, introduce exotic species.

All this takes away from living things in the wild and from their habitats.

Living things that couldn’t adapt to a change, and no longer exist anywhere on Earth are said to be extinct.

Since people began changing the environment, organisms have gone extinct faster and faster.

Right now, 1,000 times faster than at any time in the last 65 million years.

If we keep it up, we may soon see 100 extinctions a day.

Kinds of organisms that aren't extinct, but whose populations are dangerously low are at risk of becoming extinct, or endangered.

Creatures become endangered for lots of different reasons.

The n n of Hawaii is endangered partly because of the mongoose.

The mongoose was introduced to control rats in the sugar cane fields.

As it turned out, the rats slept all day while the mongoose hunted, so instead of eating rats, the mongoose turned to the eggs of the n n goose.

Now, fewer than 100 n n geese are left in Hawaii.

Both natural and human dangers threaten the West Indian manatee.

Manatees are mammals that live in the warm waters of Florida and Georgia, and migrate north in the summer.

If they're a little late migrating back to warm water, they could die.

Many are injured by boats or are caught in nets.

About 150 of the remaining 2000 die every year.

Since they only have one calf every 2 to 5 years, their numbers are dropping fast.

Some animals are endangered because something they need in their habitat is disappearing.

Karner blue butterfly caterpillars eat only wild lupine, a plant that grows in sandy pine and oak barrens where there are occasional forest fires.

The fires burn back shrubs and plants which shade out the lupine.

Unfortunately, humans put out the fires and kill the lupine with pesticides.

After 20 years of this, just one out of every hundred Karner blues are left.

With so much development and growth concentrated on the coasts of North America, it's really important to look out for living things that are at risk.

Music Hey, Dave, isn’t that a wood turtle?

Yeah, that is a wood turtle.

Do you think you can catch it?

So why are these species a species at risk?

Well, wood turtles have a lot of different problems.

One problem is actually something that wood turtles have lived with for a long time, and that's just the fact that there's not a lot of this kind of habitat around.

So they're really limited to that area.

That creates a problem, though, when people impact those wetlands that they need.

So when the wetlands disappear, of course they lose their habitat.

Another reason is, like a lot of turtles, wood turtles will cross roads, and when they cross roads, their shells are hard but they certainly can't support the weight of a car.

And so they get killed that way.

And actually, a third way is that too many of them have been over- collected for the pet trade.

So people have purchased them and brought them home.

And unfortunately a lot of those turtles either die or they never make it back into the wild.

So that's been a problem as well.

People sometimes can help animals out too.

There's one animal that was hurt by people and then brought back from the verge of extinction.

And that's the peregrine falcon.

Music By 1964, peregrine falcons had completely disappeared from the eastern part of the United States.

The population decline was caused by DDT, a pesticide farmers and gardeners used to kill insects.

Peregrine falcons ate prey tainted with the pesticide.

Over time, DDT built up in their bodies and caused them to lay eggs with very thin shells.

The thin shells were easily crushed by adults during incubation.

Bald eagles and other bird species also experienced population declines because of DDT and other pollutants.

DDT was banned for use as a pesticide in the United States in 1972.

At that point, there were only 40 breeding pairs of peregrine falcons in the west, and no breeding pairs in the east.

People started programs to reintroduce the peregrine falcon to its habitat.

Peregrine falcons were bred in captivity and then released into the wild.

Since 1974, more than 6000 falcons have been released.

And today the peregrine falcon population is growing.

Peregrines are found in every continent except Antarctica.

They live where there's open space and nest on cliffs or bluffs over water.

Some have adapted to urban environments and nest on tall city buildings and under bridges.

They don't build nests, but they may use the nests built by other birds.

Parents can lay two, three, or up to six eggs at a time.

Females usually incubate the eggs and the males help care for the chicks.

Adult peregrine falcons are about the same size as crows.

They have long, pointed wings and mustache-like markings on the sides of their face.

Males and females look alike, but the females are a little larger.

They're good hunters and may be the fastest animals on Earth, diving from the sky at speeds of over 100 miles an hour.

Peregrine falcons usually strike their prey with a closed talent and knock it to the ground.

Their prey is most often small birds like doves and pigeons.

But they've also been known to catch larger birds like ducks and gulls.

Humans are still a threat to peregrine falcons.

Development can hurt the falcons’ natural habitat, rock climbers can disturb nesting places, and pollution can still affect their food supply.

Humans almost drove the peregrine falcon into extinction in the US, but worked to bring it back.

Today, populations are growing, but we have to monitor the species to make sure it stays healthy.

Monitoring the health of different species can tell us a lot about the health of the environment.

Susi von Oettigen of the US Fish and Wildlife Service is monitoring the health of dwarf.

wedge mussels, and Sarah and Octave are going to help her.

Music Wow is this where they live?

Yes, this is the Ashuelot River and it's one of the better populations of the dwarf wedge mussel, right here.

Why is this habitat good for mussels?

Okay, well, take a look.

Dwarf wedge mussels live in free-flowing running water, not in ponds or lakes.

You never find them there.

And then look over here at the canopy.

It provides shade.

And if you had them in just plain sun, you get these temperature extremes.

And also the water quality is pretty good here.

Oh.

So you want to go in?

All right.

Let me explain one thing to0, what we're going to do.

An easy way to find out what species you have is not to look for the live ones, because sometimes they’re hard, is to look for the shells, because a lot of animals eat these mussels.

What we're going to do is collect all the shells we see, and I'm going to give you a bag each.

Put them in the bag, and then we'll go through and see if we find any dwarf wedge mussel.

Music Do you know what this is?

Dward wedge mussel.

You found a live dwarf wedge mussel.

Congratulations!

That’s a - don’t put them in the bag.

Oh, oh yeah.

It's alive.

Because, that's right, it’s alive.

You remember how many species we've found now, live and dead.

Three alive.

Three species that are alive.

That's right.

And four that are dead.

We found the triangle floater.

You just found that one.

You just found that one.

Dwarf wedge.

You just found that one.

And then what's the one that's all over the place?

Common elliptio.

Common elliptio, right.

And the fourth species that we found just shells of but not live is the squawfoot.

Right.

What we're going to do is dump all the shells out gently on the ground, and then we're going to try and separate them into all the different species we have.

Okay.

Let’s put the dwarf wedge up here because they're the smallest.

All right?

We'll try and count what we have of all the different species.

Squawfoot.

Right.

You really got them, yeah.

Five.

Six.

Seven.

Eight.

Nine.

Ten.

Good, because these are not the same animal.

They're different halves of different animals.

Why is it important to save all these mussels?

Well, as you can see, there’s very few of the dwarf wedge here.

There's a lot of the elliptios less of some of the squawfoot and still a pile of the triangle floaters, which indicates to me that a, they're very rare and uncommon in this river.

The other thing with a dwarf wedge mussel, they're very sensitive animals, much more so than the elliptio, which can live anywhere.

And it indicates water quality.

If this starts to decline, if we see less and less over time but nothing else has changed physically that we can see, then we expect that the water quality’s declining.

What we do is we call these bio indicators.

So they're very important to tell us what's happening in our environment.

So that's one reason.

And the other reason is once they're gone, they're gone.

That's it.

They're history and we can't bring them back.

So it's a moral and ethical reason, that we can't afford to lose these species because we can't recreate them.

Music What have we learned today?

Animals and plant species that can’t easily adapt to environmental change can become endangered or even extinct.

Some environmental changes are caused by natural events like earthquakes and volcanoes, but other environmental changes are manmade.

There are lots of things people can do to preserve natural habitats, and protect animal and plant species from extinction.

Now you know how nature works!

Theme Music Major funding for Nature Works was provided by American Honda Foundation.

Additional funding was provided by Alice Freeman Muchnic, Alice J. Reen Charitable Trust, Cogswell Benevolent Trust, the Finisterre Fund, Greater Piscataqua Community Foundation, Morgridge Family Trust, the Natural Areas Wildlife Fund, Rawson L. Wood.

(animal sounds)