Monarch butterfly colonies in Mexico have seemingly bounced back from last year, when bad storms decimated their numbers by 75 percent.
The orange-and-black butterflies, which migrate from Canada and the U.S. to Mexico each year, have more than doubled since last year’s low – but their numbers remain below average, scientists say. A study sponsored by World Wildlife Federation Mexico along with the Commission on Natural Protected Areas and the cell phone carrier Telcel found that the colonies increased by 109 percent this year to coat about 10 acres of forest.
“These figures are encouraging, compared to last year, because they show a trend toward recovery,” said Omar Vidal, director of the conservation group World Wildlife Federation Mexico, according to The Associated Press.
But the numbers suggest the species remains under threat: this year’s colonies were the fourth-smallest since data collection began in 1993.
“Fluctuations in insect populations are normal in nature,” the study’s sponsors said in a statement. “With regard to the monarch butterfly, these fluctuations could be due mainly to climatic conditions.” But scientists said that natural fluctuation doesn’t account for huge drops like they’ve been seeing. Illegal deforestation in Mexico’s Michoacan state has played a role, and extreme weather conditions caused by global warming represents a long-term threat. Genetically modified crops and pesticides also hurt the butterflies’ numbers by crowding out milkweed, their food of choice during migration.
“The caterpillars feed on milkweed so changing soil use in the United States and Canada is definitely having an impact on the butterflies,” said Vidal, according to AFP.