Viatouch Teacher Articles
Science

Migrating Monarchs
by Anjali Amit

See them go—thousands upon thousands of monarchs. Colorful swirls blanket the skies and turn their roosting trees orange. They are monarch butterflies, on their annual migration from the cold north to the warmer southern climes.

Super strong fliers
Can you imagine anything more delicate than a butterfly's wing? Why, hold a butterfly by its wings and the color rubs off on your fingers. Yet these wings carry the butterfly on a journey of more than two thousand miles. The butterflies fly as fast as twenty miles per hour, covering around eighty miles per day. If they meet an obstacle on their way, they fly over it, even if it would be easier to fly under or through it. They weigh less than a gram, yet these "flying flowers" rise as high as two miles to overcome an obstacle.

Flight Plans
The Rockies stand on the North American continent like a poky spine, creating the great divide which the migrants had to cross when they were urged to "Go West." It is also the divide for the migrating monarchs. Those west of the Rockies fly to California for the winter. They roost along the Pacific coast, near San Diego and Santa Cruz. Here the climatic conditions are similar to that in Mexico.

The butterflies from central and eastern United States and Canada migrate to Mexico. Theirs is a more complicated flight route. Many clusters form and make their way across the United States. In Central Texas, the various clusters come together, making a cone-shaped pattern as they sweep southwards to the Oyamel forests that are their winter home. No air traffic control here, yet the swarms fly on towards an unknown destination.

Winter Home
The Transvolcanic Belt of Central Mexico is home to the Oyamel forests. It is the ideal Monarch habitat. The mountain fir trees provide a roosting place for the butterflies. The undergrowth of young trees offers protection from predators if the butterflies fall off their perch and are too cold to fly back to the trees.

The Oyamel forests flourished millennia ago, in a cooler, wetter age. As temperatures increased, the forests left the lowlands to grow higher up the mountains where it was still cool and moist. These same conditions are best suited to the monarch butterfly. The weather is cold enough for the butterflies to work slowly through their food reserves, but not so cold that they would die. It is warm enough so they stay clustered together, but not so warm that they burn through their fat reserves speedily. It is wet enough to provide moisture and to prevent forest fires, but not so wet that the monarchs drown. Fog and clouds on the high mountaintops keep the air moist.

Journey North
Many bird species are migratory. Whales migrate too. For all these creatures migration is an annual two-way journey. Can the butterflies that fly south make the long return journey to Canada and the eastern shores of North America? They can, and do, with one caveat. The butterflies that start their journey back are not those who will reach their northern homes. It is the great and great-great grandchildren of the migrating monarchs who make it to the northernmost end of the journey.

How it works
As the days get warmer, the overwintering butterflies begin their return to the cooler lands. Their eggs, laid along the way in northern Mexico and the southern United States become the first generation adults. Their children—-the grandchildren of the original butterflies—fly on towards the Appalachians and the East Coast. Each generation moves a little further north and east, heading towards the Great Lakes and Canada. The third and fourth generation butterflies are born in the north. The third generation continues to lead brief, egg-laying lives. The great grandchildren—the fourth generation—-stop laying eggs and go into a diapause, eating and conserving their energy for the long southern journey they know instinctively they will have to undertake.

One-Way Ticket
What an amazing feat that is. The butterflies flying south have not seen their forest destination. Their great-grandparents traveled on one-way tickets, leaving their descendants to figure out the return path. Without maps and GPS, they set out on their great journey. Yet unerringly they return to the forests of their ancestors, sometimes to roost on the very same trees and color them orange again.

Bibliography:
Herberman, Ethan. The Great Butterfly Hunt The Mystery of the Migrating Monarch. NY: Simon and Schuster Books, 1990.
Hook, Patrick. The World of Butterflies. NY: Grammercy Books, 1999.
Latimer, Jonathan P. and Karen Stray Nolting. Butterflies. Boston: Houghton Mifflin Company, 2000.

Interesting Web Sites:
http://www.fs.fed.us/monarchbutterfly/migration/index.shtml
http://www.learner.org/jnorth/tm/monarch/jr/BookletList.html
http://www.monarchlab.umn.edu/background/index.aspx

Anjali is a children's book author whose first book, Folk Tales From Rajasthan, was published when she was in college. Upon graduation she "sold her soul to Mammon"-went to work for a bank. She writes fiction, non-fiction, and edits technical documents. Her articles have appeared in various magazines. "Bedtime Stories from Around the World", her second book, was published a few years ago.