John: Monarch butterflies make one of the most extraordinary migrations in the natural world, often traveling thousands of miles across North America.

Scientists are using new tracking technology to get a greater understanding of those journeys.

We spoke with a pulitzer prize-winning journalist who teaches science journalism at New York university and is writing a book about monarch butterflies.

Reporter: Thank you so much for joining us.

I have to be honest, I was not aware of the complicated and long journey that these monarch butterflies take when they migrate.

Tell us about their migration patterns.

>> It is kind of amazing what they do.

They live one way during the warm weather months when those of us in the U.S.

Are more familiar with them.

When the weather gets cooler, they change.

Instead of just living a few weeks, they live the entire winter if they are fortunate enough to survive.

They undertake this amazing migration.

In the eastern U.S.

They go to Mexico.

In the west they go to the California coast.

They go there because they are very sensitive.

They cannot survive if it is too cold or too hot.

They have found these havens where they can safely stay over winter.

That is what they do every year.

Reporter: You have written about these new tiny sensors that scientists have created to be able to track individual butterflies?

>>.

How does>> This work it is really an amazing development.

People have been using paper tags and sticker tags on monarch butterflies for a very long time.

80 years.

You can see where the monarch started and where it ended but you had no idea where they have been in between.

Which is sort of like trying to read a book but only reading the first and last page.

Now thanks to this new technology developed by a startup company, they create radio tags and they have now figured out how to miniaturize these radio tags so they are small enough that even a butterfly can handle.

Now for the very first time after all of these years of trying to understand the migration of monarch butterflies, we really know exactly where they are going.

It is quite fascinating.

Reporter: To build on your book analogy, now that we know that is happening in the middle of the story, what have we learned?

>> We knew that monarchs are affected by whether.

But we did not really realize until we have these new tracks just how far off course they get blown when the wind is blowing the wrong way.

Or if there is a rainstorm.

They can be blown hundreds of miles off course.

The amazing thing is there navigational adaptations.

One that works on the sun and when it is not.

Those are so accurate.

Hey can recover.

And head back down in the correct direction.

All the way to Mexico.

Another thing that really was not understood was we kind of assumed that almost all of these butterflies went to the same small area and also some specific areas in California.

We also know they are going lots of other places as well.

That suggests that maybe the monarch will be resilient.

Reporter: Populations have been declining.

What are some of the leading factors in that and why should we be concerned about what is happening?

>> Monarchs need to find just the right narrow temperature range to survive in the winter.

And in the summer.

Limate change is changing temperatures, habitat, making it harder for them to find that nectar that they need.

You asked me why we should care.

Hat monarch butterflies really are is they are beautiful.

They do fascinating things.

It would be just incredibly sad to lose the migration.

Which is such an amazing natural phenomenon.

Not duplicated anywhere else in the natural world.

Reporter: The fact that they are gorgeous is quite enough.