The number of Monarch butterflies wintering in Mexico plunged this year to the lowest level since studies began in 1993. Experts said Wednesday that the insects’ annual migration from the United States and Canada is in danger of disappearing.
A report released by the World Wildlife Fund, Mexico’s Environment Department and the Natural Protected Areas Commission believes that the huge loss of milkweed the monarch feeds on is a large part of the decline. The milkweed is disappearing due to genetically modified crops and urban sprawl in the United States. Also, the dramatic reduction of the butterflies’ habitat in Mexico due to illegal logging of the trees they depend on for shelter is a contributing factor.
After steep and steady declines in the previous three years, the butterflies now cover only 1.65 acres in the pine and fir forests west of Mexico City, compared to 2.93 acres last year, the previous low. They covered more than 44.5 acres at their recorded peak in 1995. Because the butterflies clump together by the thousands in trees, they are counted by the area they cover.
From my own observations, I know the summer monarch population in my area of Northern Indiana has declined rapidly in the last few years. I spend a lot time photographing nature, and where not that long ago, monarchs were a common subject for photos, in the last three or so years they have become increasingly scarce. In fact, last summer I would go entire days in the fields and woods where they once could be found in abundance and see less than a dozen monarchs. Some days, I might not see any, in fact.
The decline in the Monarch population now marks a statistical long-term trend and can no longer be seen as a combination of yearly or seasonal anomalies, experts say.
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 is now GMO 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,” Brower said.
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 that the U.S. Midwest is the main source of the butterflies coming to Mexico. “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.”
While some gardeners and activists in the United States have started a movement to plant small patches of milkweed, the effort is in its infancy. Extreme weather, such as severe cold snaps, unusually heavy rains or droughts have also apparently played a role in the decline.
It’s unclear what would happen to the Monarchs if they no longer migrated. The butterflies can apparently survive year-round in warmer climates, but populations in the northern United States and Canada would have to face bitter winters. There is also another small migration route that takes the butterflies to California, but that has also registered declines.
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.
Inhabitants of the reserve had already noted a historic change, as early as the Nov. 1-2 Day of the Dead holiday, when the butterflies usually arrive. They could always be seen flitting around the graveyards. This year was the first time in memory that there were none to be seen.