View full lesson: http://ed.ted.com/lessons/bird-migration-a-perilous-journey-alyssa-klavans

Nearly 200 species of songbirds migrate south for winter, some traveling up to 7,000 miles. No easy task, the annual journey is dangerous to birds due to landscape change -- so much so, that only half the birds that migrate south will return home for spring. Alyssa Klavans details why bird migration is so taxing and how we can assist our chirping friends.

Lesson by Alyssa Klavans, animation by Igor Coric.