Four Wings and a Prayer by Sue Halpern

The Monarch butterfly is the one butterfly to migrate like a bird, but still no one knows how. Four Wings and a Prayer tells of the expedition to trace the journey of the Monarch as it flies more than three thousand miles through the United States to a tiny mountainside in Mexico, than back again.
The stories of people who spend their lives to studying this butterfly are told along with their efforts to understand this bug.

I was glad I read this. There was a lot of stuff I didn't know- like how a butterfly rides on air currents, leaving and entering as needed. Cool. I did find it hard to concentrate about half-way through on, though. It just kept on going. Read it. Maybe while you're reading another too. Monarchs are amazing creatures.