Migrating Monarchs, El Rosario Preserve, Mexico, 2004

A colony of monarch butterflies clings to a tree in the El Rosario Monarch Butterfly Preserve in the mountains of central Mexico. The Mexican government is working to encourage tourism and discourage illegal logging in the preserve, where millions of these delicate orange-and-black butterflies come to nest each winter.

(Photo shot on assignment for, but not published in, "Signs From Earth: Heating Up…Melting Down…" September 2004, National Geographic magazine)