MEXICO CITY Monarch butterfly colonies in Mexico more than doubled in size this winter after bad storms devastated their numbers a year ago, conservationists said on Monday although the migrating insect remains under threat.
Millions of butterflies make a 2,000-mile journey each year from Canada to winter in central Mexico's warmer weather but the size of that migration can vary wildly.
Fewer of the orange and black insects arrived in Mexico last year than ever before, researchers said, but the butterfly colonies increased by 109 percent this year to cover roughly 10 acres of forest. Researchers estimate the size of the butterfly colonies based on the area they occupy in a forest.
"Certainly this is good news and indicates a recovering trend," said Omar Vidal, director of the Mexico branch of the World Wildlife Fund (WWF).
But while the monarch colonies rebounded this winter, it is still the fourth-lowest year for the butterfly since researchers started census-taking in 1993.
Illegal loggers have picked away roughly 3 percent of a 138,000 acre reserve since it was created in 2000 but officials say they now have that illicit harvest under control.
Severe winter weather linked to climate change is more of a long-term threat, along with large-scale farming that crowds out the milkweed that the butterflies dine on during their cross-continental flight.
"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, who helps manage the authoritative study on monarch populations in Mexico.
Michoacan state is home to the country's monarch butterfly reserve as well as many violent drug gangs that have carved smuggling routes through the often-arid terrain.
While the government is confronting drug gangs on many fronts, smugglers are not inhibiting conservation work, one official said.
"We are being a bit more careful but have not had any security incident to date," said Humberto Gabriel Reyes, who oversees the butterfly reserve for the federal commission for protected areas.
While the uptick in butterfly numbers is heartening, U.S. researcher Lincoln Brower said the insects are still susceptible to harsh conditions.
"The weather conditions we saw last year were among our worst-case scenario," said Brower, 79, of Sweet Briar College in Virginia who has studied the monarch butterflies since the 1950s.
"If there were more harsh weather in Texas or more forest loss in the Mexican reserves, the butterflies could be tested even more severely," said Brower who was one of the first researchers to see the Mexican overwinter sites after they were identified by scientists in 1975.
(Reporting by Patrick Rucker; Editing by Cynthia Osterman)