Big drop in Monarch butterflies
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 yesterday, after numbers dropped to their lowest level since record-keeping began in 1993.
Their report blamed the displacement of the milkweed the species feeds on by genetically-modified crops and urban sprawl in the United States, extreme weather trends, and the dramatic reduction of the butterflies’ habitat in Mexico due to illegal logging of the trees they depend on for shelter.
They covered more than 44.5 acres at their recorded peak in 1996.
Because the butterflies clump together by the thousands in trees, they are counted by the area they cover.
While the Monarch is not in danger of extinction, the decline in their population now marks a statistical long-term trend and no longer can 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, which saw the U.S., 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 co-operation.
“Twenty years after the signing of NAFTA, the Monarch migration—the symbol of the three countries’ co-operation—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 that “the migration is definitely proving to be an endangered biological phenomenon.”
“The main culprit,” he wrote in an e-mail, 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 noted.
Extreme weather—severe cold snaps, unusually heavy rains, or droughts in all three countries—also apparently have played a role in the decline.
But the milkweed issue now places the spotlight firmly on the U.S. and President Barack Obama, who is scheduled to visit Mexico on Feb. 19, with events scheduled for Toluca—a city 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,” he charged.
It’s unclear what would happen to the Monarchs if they no longer made the annual trek 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 apparently can survive year-round in warmer climates, but populations in the northern U.S. and Canada would have to find some place to spend the bitter winters.
There also is another smaller migration route that takes butterflies from the west to the coast of California, but that has registered even steeper declines.