Monarch Migration... & movie

I just finished reading a book called "Four Wings and a Prayer"-- about Monarch Butterflies & their migration. So I was particularly interested when I started seeing more of them around, over the past 10 days, say. I took a look over on Monarch Watch, & it turns out we've been in the peak migration window for our latitude.

Nova has made an excellent film about the migration phenomenon, and you can watch it here online.
(It focuses on migration east of the Rockies, which is different than the West Coast Monarchs.)

Butterfly at left was in our garden mid-September of 2007.