Three-and-a-half times as many monarch butterflies as the year before returned to their home in the central Mexico mountains this winter.
Each year, the butterflies migrate 3,400 miles south to the tropical climate. Their numbers had been falling in recent years, until a resurgence in 2014. This year’s increase has been even greater.
Instead of counting all the individual butterflies, scientists and conservationists add up all the land area the monarchs cover. This winter it came to 10 acres of butterflies — up from a record low of 1.66 acres just two years earlier.
It’s a great recovery, but still has a long way to go to match the 44 acres of butterflies from 1996.
Mexico, the U.S., and Canada have all committed to helping the monarchs recover. The U.S. is reintroducing milkweed plants along 1,100 square-miles of the monarchs’ migration route to make up for herbicide use destroying huge tracts of the plant. Monarchs lay their eggs on milkweed exclusively, and find it a vital food source.
Mexico successfully cracked down on illegal logging in the monarch reserve, where the butterflies rely on the forest canopy to help shelter them during winter.
Conservationists estimate 140 million monarchs arrived this year, and if the upward trend continues they will hit their goal of seeing 220 million by 2020.
“It is time for celebration because we see the beginning of success,” U.S. Fish and Wildlife Service Director Ashe told the Associated Press. “But our task now is to continue building on that success.”