Not All Monarchs Go to Mexico
Utah Students Study “Western” Monarchs

Where do monarchs in the Rocky Mountain region go for the winter?
Dots suggest areas of uncertainty.

There are two populations of migratory monarchs in North America.

  • The "eastern" population over-winters in Mexico (and along the Gulf Coast in some years).
  • The "western" population over-winters along the California Coast. (See map.)

The Rocky Mountain region has long been considered the dividing line between the two populations. But are the Rocky Mountains truly a barrier between the two populations? And if so, does the Continental Divide mark the line between the two populations? Do monarchs east of the Rocky Mountains mix with those that over-winter on the California Coast?

For years, those questions have been debated. A Utah teacher and his students helped to uncover some answers.

Mr. Ron Hellstern of Hyrum, Utah, wrote:

“My classes initiated the Intermountain Monarch Butterfly Project. We are associated with the Monarch Program of San Diego, and have helped them determine the winter migration destinations of Intermountain Monarchs.

“When we started this project back in 1994 there was little, if any, knowledge about the migration routes or roosts of the Intermountain Western population. My students helped to establish the baseline data, and recruit other schools along the western slope of the Rocky Mountains to assist in collecting this information.

"Thanks to some of our tags, our Monarchs have been spotted in Santa Cruz, California, which means these beautiful and delicate creatures cross the Great Basin Desert and the Sierra. Amazing!!! Our monarchs may not be going to Mexico, but we feel just as attached to them."

Which direction did the Utah monarch fly?

Try This!
  • Trace the course the Utah students’ monarch might have flown from Byrum, Utah, to Santa Cruz, California.
  • Can you find the Great Basin Desert? The Sierras?
  • How many kilometers did this monarch fly? How many miles? In which direction?
  • Find the Rocky Mountains on a physical map. Can you find the Continental Divide?
  • At various points in the Rocky Mountain region, predict where a monarch from this region might over-winter. Would it fly southward to Mexico or westward to the California Coast? Explain the reasoning behind your prediction.