Monarch Butterflies mass in the Sierra Pellon mountain at the Monarch Butterfly Biosphere Reserve in Michoacan. Photo: Getty
Monarch Butterflies mass in the Sierra Pellon mountain at the Monarch Butterfly Biosphere Reserve in Michoacan. Photo: Getty

While still below levels recorded two decades ago, two recent surveys show North America’s monarch butterflies are on a rebound.

Monarchs, which gather in Mexico before flying north to Canada, today number at around 150 million, a Natural Resources Defense Council survey showed on Friday. At their height, scientists counted 1 billion butterflies in annual migration.

While an estimated 1 billion monarchs migrated in 1996, only about 35 million made the trip in 2013, according the University of Chicago.

Favorable weather and the planting of more milkweed are credited to their comeback.

“Today’s news provides a hopeful indication that we are helping them head in the right direction and curbing the loss of this magnificent butterfly. But we must be careful not to declare victory too soon,” Sylvia Fallon, a senior NRDC scientist told Reuters.

Butterflies spend the winter in Mexico’s Oyamel forest, but have suffered mightily over the years from the expansion of farmland and sprawling housing developments. Monarchs lay eggs only on milkweed plants, which grow wild throughout the United States, but milkweed can cause stomach problems for cattle, so ranchers and farmers destroy it.