In 2009, the butterflies faced storms that decimated their numbers as they migrated from Canada and the United States to their winter home in central Mexico, NewsScientist.com reported Tuesday.
A recent study by the World Wildlife Fund of the butterfly's Mexican habitat found that insects wintering there since November covered almost 10 acres of forest -- twice the area of the prior year.
"These figures are encouraging, because they show a trend toward recovery after a record low," says Omar Vidal, director of WWF Mexico.
The extent of the terrain occupied is considered useful as an indirect measure of butterfly numbers.
While the recovery is good news, Vidal says, the insects still face risks during their winter stay and in their yearly migrations.
While illegal logging that had threatened the monarch's Mexican habitat is now under control, climate change and farming in the United States could deplete the food the butterflies rely on during their migratory flights, he said.