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Originally published January 29, 2014 at 5:59 PM | Page modified January 30, 2014 at 6:56 AM

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Number of monarch butterflies drops, migration may disappear

The black-and-orange Monarch butterflies cover only 1.65 acres in the pine and fir forests west of Mexico City this year, compared with 2.93 acres last year.

The Associated Press

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MEXICO CITY — The stunning and little-understood annual migration of millions of monarch butterflies to spend the winter in Mexico is in danger of disappearing, experts said Wednesday, after numbers dropped to their lowest since record-keeping began in 1993.

The experts blamed the displacement of the milkweed on which the species feeds, extreme weather trends and the substantial reduction of the butterflies’ habitat in Mexico due to illegal logging of the trees they depend on for shelter.

After steep and steady declines in the previous three years, the black-and-orange butterflies cover only 1.65 acres in the pine and fir forests west of Mexico City, compared with 2.93 acres last year, according to a report by the World Wildlife Fund, Mexico’s Environment Department and the Natural Protected Areas Commission. The butterflies covered more than 44.5 acres at their recorded peak in 1996.

Because the butterflies clump by the thousands in trees, they are counted by the area they cover.

While the monarch butterfly is not in danger of extinction, the species’ decline in population marks a statistical long-term trend and can no longer be seen as a combination of yearly or seasonal events, experts said.

The announcement followed on the heels of the 20th anniversary of the North American Free Trade Agreement (NAFTA), which saw the United States, Mexico and Canada sign environmental accords to protect migratory species such as the monarch. At the time, the butterfly was adopted as the symbol of trilateral cooperation.

“Twenty years after the signing of NAFTA, the monarch migration, the symbol of the three countries’ cooperation, is at serious risk of disappearing,” said Omar Vidal, the World Wildlife Fund director in Mexico.

Lincoln Brower, a leading entomologist at Sweet Briar College in Virginia, wrote: “The migration is definitely proving to be an endangered biological phenomenon.”

“The main culprit,” he wrote in an email, is now genetically modified “herbicide-resistant corn and soybean crops and herbicides in the USA,” which “leads to the wholesale killing of the monarch’s principal food plant, common milkweed.”

While Mexico has made headway in reducing logging in the officially protected winter reserve, that alone cannot save the migration, wrote Karen Oberhauser, a professor at the University of Minnesota. She noted that studies indicate the U.S. Midwest is where most of the butterflies migrate from.

“A large part of their reproductive habitat in that region has been lost due to changes in agricultural practices, mainly the explosive growth in the use of herbicide-tolerant crops,” Oberhauser said.

Extreme weather — severe cold snaps, unusually heavy rains or droughts in all three countries — have also apparently played a role in the decline.

But the milkweed issue places the spotlight on the United States and President Obama, who is scheduled to visit Mexico on Feb. 19, with events scheduled for Toluca, a few dozen miles from the butterfly reserve.

“I think President Obama should take some step to support the survival of the monarch butterflies,” said writer and environmentalist Homero Aridjis. “The governments of the United States and Canada have washed their hands of the problem, and left it all to Mexico.”

It’s unclear what would happen to the monarchs if they no longer made the annual trip to Mexico, the world’s biggest migration of monarch butterflies and the second-largest insect migration, after a species of dragonfly in Africa.

There are monarchs in many parts of the world, so they would not go extinct. The butterflies can apparently survive year-round in warmer climates, but populations in the northern United States and Canada would have to find someplace to spend the bitter winters.

There is another smaller migration route that takes butterflies from the west to the coast of California, but that has registered even steeper declines.

Oberhauser noted that some Monarchs appear to be wintering along the U.S. Gulf Coast, and there has been a movement in the United States among gardeners and homeowners to plant milkweed to replace some of the lost habitat.

But activists say large stands of milkweed are needed along the migratory route, comparable to what once grew there. They also want local authorities in the U.S. and Canada to alter mowing schedules in parks and public spaces, to avoid cutting down milkweed during breeding seasons.

The migration is an inherited trait. No butterfly lives to make the full round-trip, and it is unclear how they remember the route back to the same patch of forest each year, a journey of thousands of miles, to a forest reserve that covers 193,000 acres in central Mexico.

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