Monarch Migration

by Ann Barnes

Google Doodle, 1/9/16
Google Doodle, 1/9/16

Today’s Google doodle commemorates the 41st anniversary of the discovery of the Mountain of Butterflies. The Mountain, now protected as the Monarch Butterfly Biosphere Reserve, is located 62 miles northwest of Mexico City. Each winter, millions of Monarchs make their way to colonies in this reserve.

Monarchs overwintering in Mexico. Photo: Wikipedia
Monarchs overwintering in Mexico. Photo: Wikipedia

Canadian scientists Fred and Norah Urquhart began studying the migration of monarchs in 1937. They tagged and released butterflies and recruited citizen scientists to do the same through their organization, the Insect Migration Association. This group, now known as Monarch Watch, is still actively monitoring monarch migration. The Urquharts mapped migration routes from Canada, across the United States, and into Mexico. Ken Brugger and Catalina Aguado, citizen scientists living in Mexico located the Mountain of Butterflies in 1975 after two years of searching in remote parts of Michoacán, Mexico.In 1976, the Urquharts traveled to the area and found a tagged butterfly, confirming that the monarchs really did make the long journey south.

Migration map Credit:
Migration map

Monarchs begin migrating south in September and arrive in Mexico starting in November. The return northward begins in March. Monarchs traveling north live 4-6 weeks, laying eggs on milkweed plants along their route. Monarchs are dependent on milkweed plants as a site to lay their eggs and as the food source for their caterpillars. It takes multiple generations to make the journey north. However, in the fall, one “super generation” of monarchs is able to travel the full southern route. The super generation butterflies enter a state called diapause during migration. They do not mate while traveling and their bodies store more lipids than the generations of butterflies making the northern trip.

Populations of monarch butterflies have decreased in the years since their overwintering sites were discovered. Urbanization, the increase of large scale farms, and the use of herbicides have reduced the habitat for caterpillars and butterflies along their travel routes. Illegal logging in Mexico has also reduced their overwintering habitat. Climate change also threatens the butterflies and their habitats. Gardeners in the US can help by planting milkweed for monarch caterpillars as well as other nectar rich flowers for adult butterflies. Ideas for attracting butterflies can be found in the Extension publication “Butterflies in your Backyard“.

The story of this discovery was published in National Geographic magazine in 1976. A documentary film called “Flight of the Butterflies” was released in 2012. This film is screened at area science museums from time to time.

Want to learn more about attracting, helping, tracking, or studying monarch butterflies? has lots of information for gardeners, teachers, and anyone who would like to participate in citizen science projects to help the monarchs.

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