The number of Monarch butterflies wintering in Mexico plunged this year to its lowest level since studies began in 1993, leading experts to announce 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 blames the displacement of the milkweed the species feeds on by genetically modified crops and urban sprawl in the United States, as well as 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 (0.67 hectares) in the pine and fir forests west of Mexico City, compared to 2.93 acres (1.19 hectares) last year. They covered more than 44.5 acres (18 hectares) at their recorded peak in 1995.
Because the butterflies clump together by the thousands in trees, they are counted by the area they cover.
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 events, experts say.
The announcement followed on the heels of the 20th anniversary of the North American Free Trade Agreement, which saw the United States, Mexico and Canada signing 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, 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."
Butterfly guide Emilio Velazquez Moreno, 39, and other farmers in the village of Macheros, located inside the reserve, have been planting small plots of milkweed in a bid to provide food for the Monarchs if they decide to stay in Mexico year-round, which he said some do.
Sitting beside a mountainside patch of firs where the butterflies were clumping on the branches, Velazquez Moreno, a second-generation guide who has been visiting the butterflies since he was a boy, said "we have to protect this. This comes first, this is our heritage."