While some butterflies are said to migrate longer distances with the onset of winter, only the monarch makes such long journeys with precise destinations and in such great numbers. The migration of the monarch is truly a butterfly phenomenon. Consider some of the impressive feats of these amazing insects.
Their flight from Canada in the autumn to their wintering grounds in California or Mexico exceeds 2,000 miles [3,200 km]. They cross large lakes, rivers, plains, and mountains. Millions of them successfully complete the migration to their destination high in the Sierra Madre mountains of central Mexico.
Only monarchs born in late summer or early autumn make the migration, and they make only one round trip. By the time next year’s winter migration begins, several summer generations will have lived and died and it will be last year’s migrators’ great grandchildren that make the trip. Yet somehow these new generations know the way, and follow the same routes their ancestors took—sometimes even returning to the same tree. How do they do it?
Canadian Geographic states: “Clearly, there is some sophisticated genetic programming in their brains, some means perhaps of reading the angle of sun rays, as bees do, or the earth’s magnetic field, which seems to guide birds. An ability to detect specific temperature and moisture conditions may help at the end. But so far the answers have eluded science.”
The monarchs are also amazing fliers. They glide at about 7 miles per hour, soar at about 11 miles per hour, and—as anyone who has tried to catch one knows—dart even faster, at about 22 miles per hour. They are most adept at utilizing the winds—even flying against prevailing westerlies to move south-west toward their destination, and they contend with variations in wind speed and direction. In much the same manner as glider pilots and hawks, they catch rides on thermals (up-drafts of warm air). According to one source, monarchs commonly travel as many as 120 miles [200 km] a day. They fly only during the daylight. At night they rest, often in the very same location each year.
University of Toronto scientist David Gibo has learned that the monarch is more than an occasional soarer or glider. He reports: “The butterflies have to play the wind in what I think are much more clever ways than migrating geese.” The routine of flapping, soaring, and feeding allows the monarchs to arrive in Mexico with enough fat to last them through the winter and the start of their flight back north in the spring. Professor Gibo also says: “Gliding is how they make the long trip and end up fit and healthy.”
It has been known for a long time that monarchs west of the Rocky Mountains migrate south and winter in California. They can be seen hanging in clusters in pine and eucalyptus trees in places along the southern coast of California. But the destination of the migration of large populations of monarchs in eastern Canada remained a mystery for some time.
In 1976 this mystery was unravelled. Their wintering grounds were finally discovered—a wooded summit in the Sierra Madre mountains of Mexico. A Canadian biologist, Dr. Fred Urquhart, had been searching for their destination for nearly 40 years. It took a network of volunteers and several hundred thousand tagged monarchs before the monarch’s winter home in Mexico was finally found. National Geographic announced Dr. Urquhart’s discovery in the August, 1976 issue of its magazine. When scientists travelled to the region they found a landscape of volcanic mountains, rising to 10,000 feet in elevation. That’s nearly two miles above sea level!
They found that the millions upon millions of butterflies were densely loaded upon the branches and trunks of the tall, grey-green fir trees called “oyamel” (“o-ee-ya-mel“).Scientists later learned the oyamel forest is very rare in Mexico. Scientists were surprised to find the monarchs in such a cold place. Overnight temperatures often drop below freezing and sometimes it even snows! They wondered why monarchs would fly across the continent to a place that’s so cold. There are a few flowers in the forest, but not enough to feed millions and millions of monarch butterflies all winter. How could the monarchs survive for five months in a place with so little food? Ever since the monarch’s winter sanctuaries in Mexico were discovered in 1975, scientists have been trying to understand the monarch’s basic biological needs. They are still learning about the unique conditions, or micro-climate, of the oyamel forest and why it’s critical for monarch survival.
One of the best places in Canada to see the monarchs en masse is at Point Pelee National Park, Ontario, where they cluster in preparation for their migration south. In late summer they congregate in this southerly point in Canada, waiting on the north shore of Lake Erie until the winds and temperature are favourable before taking off on their southern journey to their wintering sites in Mexico.
Starting at Point Pelee, they island-hop across Lake Erie to begin the long journey across the continental United States. En route, other groups of monarchs join them in the migration. High in the mountains north-west of Mexico City, an estimated one hundred million congregate to spend the winter.
Other migrations take place through Florida and across the Caribbean, and these may end up in destinations yet to be discovered in the Yucatán Peninsula or in Guatemala. Whether in Mexico or in their other winter havens, the monarchs crowd together in a few relatively small patches of mountain forest.
One might think that their long flight to their winter home would take them to a land of warm, sunny meadows. But not so. The Trans-volcanic Range of Mexico, where they go, is cold. The climate provided by the mountain peaks, however, is just right for their wintering. The fact that the monarchs can survive for five winter months in Mexico is as amazing as their spectacular migration.
It is cold enough to cause them to spend their time in a state of almost total inactivity—thus stretching their life span to eight or ten months, which allows for flying to Mexico, wintering there, and starting back.
Spring arrives, and the monarchs become active again. As the days lengthen, the butterflies flutter in the sunlight, begin to mate, and start their flight back north. Some, it is believed, may make the complete journey back, but it is generally only the progeny that arrive in the summer ranges in Canada and the northern United States. Three or four generations of eggs, caterpillars, pupae, and butterflies gradually move back up the continent. The female—loaded with a hundred or more fertilized eggs—flutters through the patches of wild flowers and lays her eggs one at a time on the undersides of young, tender milkweed leaves. And so the cycle goes on, and the journey to the monarch’s summer home continues.
Many scientists are concerned about the eastern population of monarchs, which summer east of the Rocky Mountains. This group is occurring in ever smaller numbers, and its survival may be threatened by a series of natural disasters in the Mexican wintering grounds, as well as by reduced acreage of milkweed plants in their summer home.
Truly, the monarch is a fascinating creature. What a privilege humans have to observe and study its activities. Not surprisingly, though, the monarch’s long-secret wintering grounds in Mexico, as well as destinations in California, are being threatened by human enterprise. Commendably, efforts are being made to protect them from such an eventuality.
Like the creatures mentioned in the Bible book of Proverbs, “they are instinctively wise.”—Proverbs 30:24.