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 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.
After steep and steady declines in the previous three years, the black-and-orange butterflies now cover only 1.65 acres in the pine and fir forests west of Mexico City, compared to 2.93 acres last year, said the report released by the World Wildlife Fund, Mexico's Environment Department and the Natural Protected Areas Commission. They covered more than 44.5 acres 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 can no longer be seen as a combination of yearly or seasonal events, experts 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 now places the spotlight firmly on the United States 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.”
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 can apparently survive year-round in warmer climates, but populations in the northern United States and Canada would have to find some place to spend the bitter winters. There is also another smaller migration route that takes butterflies from the west to the coast of California, but that has registered even steeper declines.
Losing the butterflies would be a blow for people such as Adolfo Rivera, a 55-year-old farmer from the town of Los Saucos who works as a guide for tourists in the Piedra Herrada wintering ground. He said the butterflies had come later and in smaller numbers this year, a fact he attributed to a rainy winter.
“This is a source of pride for us, and income,” Rivera said.