They're resting up for their journey across the lake.

And as the sun warms up their bodies, they begin to move and work their muscles.

And one by one, they take off.

The butterflies also fuel up here.

They drink nectar from the flowers to get the energy they need to make it across the lake.

Get a good drink.

CHRIS: Oh, there he goes!

All right!

Before they cross, they'll check the wind.

If it's blowing south, it will help them across the lake.

There he goes.

He's ready.

Good luck!

With the forests in Mexico being cut down and more and more habitat along the way being destroyed, the monarchs could use a lot of help from us.

One thing you can do is plant a butterfly garden, your own pit-stop place for migrating monarchs.

Monarchs love to fuel up on butterfly bush, and sedum.

You can also help monarchs by helping scientists track their migration.

Tag a monarch.

That way scientists can track an individual monarch's journey.

MARTIN: This monarch's ID is NEC 650.

Then when you tag the monarch, hold it gently by the leading edge of its wings and put the little tiny tag right on this part of the lower wing.

There, the tag is light and won't bother the monarch when she's flying.

And if this monarch makes it all the way down to Mexico, a scientist may find her, and, because of the tag, know exactly where she was released and when.

CHRIS: You're ready to fly?

There he goes.

Have a good trip!

Bon voyage!

Monarch butterflies, little creatures that can do big things.

We'll see you on the creature trail.