Millions of Monarchs
The monarchs are concentrated in the Sierra Madres so migrating butterflies can be seen at exceedingly high rates. This is where the most spectacular sightings are possible. You might see a million monarchs one day—and none the next—in the very same place. Monarch biologist Dr. Bill Calvert experienced a chance encounter in October 2004.

October 17, 2004 "It was just absolutely phenomenal. Between 11 and 12 o'clock monarchs were passing overhead by the millions. They continued pouring over until about 1 o'clock. Seeing a million butterflies passing over is magical. We came back the next day and didn't see a single one." Cumbres de Monterrey, Nuevo Leon

Image by Jonathan Deuck