Of all migrations by small creatures, few are as astonishing as the one performed by the Monarch butterfly. The embodiment of fragility, these insects travel between 1,200 and 2,800 miles or more between their starting and ending points -- a feat without parallel. What is even more remarkable is that the ones that return to the places where Monarchs hibernate have never been there before. These are the great-great-great-grandchildren of those that performed the intrepid journey from southeast Canada and the United States to central Mexico.
Like several species of birds, bats and whales, the Monarch butterfly of Canada and the United States migrates to places where the climate is less extreme. Winters are too cold in the places where the butterflies reproduce; Monarchs would not be able to withstand either heavy snowfall or the lack of plants on which larval caterpillars feed. As such, the Monarch heads south each fall, where it will stand a greater chance of survival-as well as the chance to "return" to reproductive sites in North America and give rise to future generations of reproductive adults that will complete the annual cycle.
The Monarch butterflies that migrate southward in the autumn are guided by the sun's orbit as they travel through North America. Even on cloudy days they stay on track thanks to an internal biological compass that functions according to the movement of the sun.
The migration moves at a pace of about almost 50 miles a day, though there are some butterflies that have flown up to 80 miles in a day. Throughout the migration, they continue to store and replenish energy each day by extracting nectar from flowers they encounter along the way. But the butterflies also suffer from illnesses and infections that can be fatal, and must face other dangers including bad weather, predation by birds during hibernation, and big losses in the population due to winter storms.
At the end of October and the beginning of November, after traveling two months, the butterflies settle into hibernation colonies in the mountains of central Mexico, where the States of Mexico and Michoacan meet. There they will spend the winter hibernating.
From mid-November until mid-February, the Monarchs' hibernation colonies remain relatively stable. During the second half of February, when temperatures rise and humidity decreases in the forests, the butterflies come down from the slopes to mate. And the butterflies that survive the hibernation in Mexico return in the spring to the southern United States. --
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