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For Love of Nature: Monarchs make unbelievable journey in fall
For Love of Nature

For Love of Nature: Monarchs make unbelievable journey in fall

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As a child, I watched in wonder as a monarch caterpillar spun its chrysalis, and within two weeks, emerged as a beautiful black-and-orange striped butterfly.

At that time, we had no idea that eastern monarchs migrated to the mountains of Mexico in the winter. It was 1975 before their remote wintering grounds were discovered.

Monarchs in western North America overwinter in California, where they are verging on extinction.

Monarch butterflies typically live from two to six weeks, except for the last generation of the year, when they can live eight to nine months.

Happily, I have seen several monarchs stopping by our yard in recent weeks to sup from a butterfly bush and zinnias as they head south.

How these fragile creatures can fly between 50 and 100 miles per day is beyond comprehension. It seems hard enough for a bird to migrate thousands of miles.

The monarch is the only butterfly known to make a two-way migration. Unlike other butterflies that can overwinter as larvae, pupae or even as adults in some species, monarchs cannot survive cold winters.

Monarchs use a combination of air currents and thermals to travel as far as 3,000 miles to reach the Sierra Madre Mountains of Mexico.

Millions of monarchs roost in oyamel fir forests at an elevation of nearly 2 miles above sea level from October to late March. The humidity in the forest assures the monarchs won’t dry out as they hibernate in massive clusters.

The returning monarchs stop in the south as soon as they find milkweed, the only plant on which they lay eggs. Each successive generation travels farther north, with three to four subsequent generations reaching the northern United States and Canada.

But as we know, this grand migration is under threat. Climate change in both their winter hibernation and summer breeding grounds can disrupt their temperature-dependent life cycles.

Deforestation in Mexican forests along with the conversion of grassland to farmland, the use of herbicides and pesticides and a reduction of milkweed have combined to drastically reduce their population.

Every year for the last 17 years, World Wildlife Fund (WWF)-Mexico assesses the population of monarchs in the Monarch Butterfly Biosphere Reserve in central Mexico.

The teams measure the amount of forest area occupied by the monarchs, providing an indicator of their population status.

While monarch populations vary, the Eastern population has declined an estimated 80% in the last two decades.

Nearly 45 acres of forest in the region were covered with monarchs in the winter of 1995-96. Their populations fluctuated annually until 2003-04 when scientists recorded only 27.5 acres of forest coverage.

Since then, surveys have documented a continued downward average trend. According to the latest survey, in the winter season of 2020, monarchs occupied slightly more than 5 acres — a 26% decrease from the previous year.

WWF is working with Mexico to preserve forests and with the U.S. to increase monarch habitat.

Everyone can help these amazing migrants by planting wildflowers and milkweed and not using herbicides and pesticides.

Shannon Brennan can be reached at


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