(gentle string music) >>The monarch butterfly.

The only butterfly in the world that makes a two-way migration across North America.

But, unlike birds, this journey takes several generations to complete.

(wings flapping) Starting in spring, monarchs migrating northward from Mexico simply don't live long enough to make the whopping 6,000-mile journey as far north as Canada and all the way back again.

To make the transgenerational journey, this monarch makes a crucial stop, here in Shenandoah.

(gentle music) Like the other monarchs, she can't just stop anywhere to lay her eggs, she needs milkweed.

And luckily for her, Big Meadows is bursting with them.

(gentle music) She can thank indigenous hunter-gatherers for this sanctuary.

Starting around 9,000 years ago, they cleared this area, turning it into a hunting ground.

(grass rustling) From this land, once home to the Monacan, Manahoac, and Massawomeck, endures in a name whose origins remain a mystery, Shenandoah.

Some translate as, "beautiful daughter of the stars."

(pleasant music) (insects buzzing) Today, urban development and pesticides contribute to the sharp decline of monarchs.

(wings flapping) But beautiful havens like these help ensure its survival.

Federally protected from encroachment, the rich soil and wide open space provide the perfect growing conditions for milkweed and the monarchs.

Though the plants are poisonous to most creatures, this butterfly lays hundreds of eggs on them before she dies.

(wings flapping) Milkweed's toxicity doesn't just defend her eggs from predators, it also kickstarts a powerful defense strategy.

When the caterpillars hatch, they begin feeding on the plant.

Most animals couldn't stomach it, but monarchs have evolved this adaptation for a reason.

By absorbing the toxins, they become poisonous themselves.

Their black, yellow, and white stripes send a clear message to potential predators, stay away.

(lively tempo music) (chrysalis crunching) This chemical armor remains with them through their metamorphosis into adult butterflies.

(lively tempo music) (birds chirping) From here, the monarch's journey continues, led by the next generation.

(wings flapping) (gentle music) But how these torch bearers know to navigate these specific flight paths, and when, requires an extraordinary sixth sense, a kind of biological compass that uses the sun's position and their own circadian clock to guide them on their epic transgenerational voyage.

(gentle music) (wind howling) (gentle music)