In this excerpt from NOVA's "The Incredible Journey of the Butterflies," see just how astounding the monarch butterfly's sense of navigation is, and learn how monarchs are tracked across North America.

Watch NOVA every Wednesday night on PBS. Or join us online at pbs.org/nova.

NOVA is produced by WGBH in Boston. Funding for NOVA is provided by David H. Koch, the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and PBS viewers.

To learn more, visit http://www.pbs.org/nova/butterflies