Meet Sam, Sophie, and Sybil, three black bear cubs.

They live with their mum, Juliet.

They're just three months old, tiny and vulnerable.

They rely entirely on Mum for survival.

I spent May in the Northwoods of Minnesota for Planet Earth Live, following the cubs as their story unfolded.

And so vulnerable.

Just ... oh, God ... just so sweet.

These woods are full of danger and challenges.

Savage cold.

Weather that can turn in an instant.