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Bay Area Blooms: That magical monarch migration

By Charlie Frisk

If you have been outdoors recently you have probably noticed monarch butterflies heading south.

The monarchs are traveling to the Sierra Madre Mountains of Central Mexico.

Monarchs starting out in Canada will travel up to 3,000 miles one-way, and our Wisconsin monarchs travel more than 2,000 miles.

I’m filled with awe when I watch these migrating monarchs and realize the length of their journey, as they look too small and fragile to undertake a trip of that immensity.

Monarchs don’t seem to fly fast enough for a 3,000 journey.

However, during the course of their migration, they take advantage of air currents and thermals to increase their speed.

All monarchs from east of the Rockies will merge into a single flyway in Central Texas, and huge flocks will be seen roosting.

Monarchs fly during the day, and they must find trees to roost in at night.

Biologists had long witnessed the migration of monarchs into Texas and crossing the border into Mexico, but they had no idea where they went from there.

In 1940, lepidopterist (a person who studies butterflies and moths), Fred Urquhart, organized a group of 3,000 volunteers to tag and document where the monarchs were traveling.

Urquhart was able to document the migration as far as the vicinity of Mexico City, but then he hit a wall.

Urquhart received a break in 1973 when Kenneth Brugger, an American businessman, contacted him about seeing monarchs shower down from the sky during a hail storm in mountains near his residence in Mexico City.

Urquhart encouraged Brugger to investigate, and Brugger and his wife set out on a two-year expedition in search of the monarch’s wintering site.

On Jan. 2, 1975, while hiking at 10,000 feet in the Trans-Mexican Volcanic Belt, they caught sight of gossamer wings glinting in the sunlight, and suddenly hundreds of millions of monarchs came into view.

They had uncovered the monarch’s wintering site, a patch that measured 20 by 40 miles in the mountainous forest.

The discovery was documented by Lincoln Brower, a prominent entomologist, and was made public in the August 1976 issue of National Geographic, 36 years after Urquhart began his search.

I can still remember that moment.

I was just beginning my career as a high school biology teacher, and I told my students the story as an example of how exciting, new discoveries are still being made in the world of nature.

The forests where the monarchs overwinter are at 8,000 to 12,000 feet and are continually bathed in clouds, which keep the monarchs from drying out.

The monarchs overwinter on 12 mountaintops, which provide the ideal temperature and humidity for their dormant period.

Those forests are necessary for the survival of the monarch population, so people were shocked when in the 1980s they saw images on television of logging trucks filled with butterflies still clinging to freshly cut trees.

Fortunately, in 1986 the Mexican government established the Monarch Butterfly Biosphere Reserve to protect the wintering sites.

However, illegal logging in the area still remains a threat.

Bumps in the long road

The monarchs begin their northward migration in early March.

As temperatures warm, they become active and complete their sexual development, which had halted when they began their southward migration.

Monarchs will undergo three to four generations before they return to Wisconsin, each generation dying off shortly after reproducing.

Wisconsin never gets its original monarchs back, but the descendants return to the same fields their ancestors occupied.

This makes their migration even more remarkable because it means somehow their migration route is innately programmed.

It’s thought they find their way by a combination of the magnetic pull of the earth and the position of the sun, but exactly how the information is programmed into succeeding generations is not yet understood.

Monarch populations have plummeted in recent years for a number of reasons.

At the wintering site continued, logging, both illegal and legal, reduce the size of their winter range.

Climate change is an even greater threat at the wintering site because it could disrupt the delicate balance of temperature and humidity the monarchs depend on.

Monarch caterpillars eat only milkweed leaves.

Larger farms, with fewer fencerows, and cleaner farming with more herbicide usage have reduced populations.

Replacing turf grass and non-native ornamentals in your yard with milkweeds will help monarchs recover.

Adults are nectar feeders; planting native wildflowers in your yard will fuel their growth, reproduction and migration.

Thousands of volunteers tag monarchs to provide more information about their migration and what needs to be done to help preserve their population.

If interested in tagging monarchs, go to Monarchwatch.org for information and supplies.

There is something magical about the migration of this beautiful butterfly; to lose it would be an unbearable tragedy.

By preserving their habitat, we can ensure that this wonder of nature will continue.

For another Bay Area Blooms article, CLICK HERE.

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