Renewed Hope for Eastern Monarch Butterfly?

The yearly count of monarch butterflies overwintering in Mexico, released Wednesday, shows an increase of 144 percent from last year's count and is the highest count since 2006. That's good news for a species whose numbers had fallen in recent years, but conservationists say the monarch continues to need Endangered Species Act protection.

The count of 6.05 hectares of occupied forest is up from 2.48 hectares last winter. The increase is attributable to favorable weather during the spring and summer breeding seasons and during the fall migration. Monarchs have lost an estimated 165 million acres of breeding habitat in the U.S. to herbicide spraying and development.

"This reprieve from bad news on monarchs is a thank-you from the butterflies to all the people who planted native milkweeds and switched to organic corn and soy products," said Tierra Curry, a senior scientist at the Center for Biological Diversity. "But one good weather year won't save the monarch in the long run, and more protections are needed for this migratory wonder and its summer and winter habitats."

In 2014 conservationists led by the Center for Biological Diversity and the Center for Food Safety petitioned the U.S. Fish and Wildlife Service to protect the butterfly under the Endangered Species Act. The Fish and Wildlife Service's initial decision was that endangered species protection may be warranted, and a final decision will be issued by June.

"The question is whether the Trump administration wants to do Monsanto's bidding or protect monarchs for future generations," said George Kimbrell, legal director at the Center for Food Safety. "This year's count is a temporary reprieve that doesn't change what the law and science demands, which is that we protect monarchs under the Endangered Species Act before it's too late."

As recently as the mid-1990s, monarchs covered nearly 21 hectares of forest in their wintering ground, falling to less than 1 hectare in 2014. Scientists estimate that 6 hectares is the threshold to be out of the immediate danger zone of migratory collapse.

About 99 percent of all North American monarchs migrate each winter to oyamel fir forests on 12 mountaintops in central Mexico. Scientists from World Wildlife Fund Mexico estimate the population size by measuring the area of trees turned orange by the clustering butterflies.

Monarch butterflies west of the Rocky Mountains overwinter on the coast of California. Their numbers dropped to fewer than 30,000 this year, down from 1.2 million two decades ago.

A recent study found that if current trends continue, the western population has a 63 percent chance of extinction in 20 years and more than an 80 percent chance of extinction within 50 years. The western population is now at the threshold of extinction.

The caterpillars only eat milkweed, but the plant has been devastated by increased herbicide spraying in conjunction with corn and soybean crops that have been genetically engineered to tolerate direct spraying with herbicides. In addition to glyphosate, monarchs are threatened by other herbicides and by neonicotinoid insecticides that are toxic to young caterpillars.

Climate change also threatens to disrupt the monarch's migration and render its overwintering habitats unsuitable by the end of the century.

Graph by Tierra Curry, Center for Biological Diversity