Monarch Butterfly Population Shows Signs of Stabilization, But Challenges Remain

After decades of decline, the eastern monarch butterfly population is showing tentative signs of stabilization, according to latest data from WWF-Mexico. Whereas still far below historical averages, the number of monarchs overwintering in the forests of central Mexico increased significantly in the past year, offering a glimmer of hope for the iconic species.

A Slight Rebound in Numbers

Researchers with WWF-Mexico reported that monarchs covered approximately 7.2 acres of forest in Mexico this winter, a substantial increase from 4.4 acres the previous year and 2.2 acres two years prior. Vox reports this positive trend, though numbers remain well below the 21-acre average observed during the first 10 years of monitoring and the 15 acres considered sustainable.

“We are in a period of relative stability where the population has stopped declining,” said Karen Oberhauser, a professor emeritus at the University of Wisconsin Madison and a leading monarch expert, in an interview with Vox.

Factors Contributing to the Increase

The recent increase is partially attributed to favorable weather conditions, specifically ample rainfall along the butterflies’ migratory path, providing abundant nectar sources. Yet, experts also believe that ongoing milkweed restoration efforts across North America are playing a crucial role in supporting the monarch population. Even small-scale plantings in urban areas, like New York City gardens and parks, are contributing to the butterflies’ survival.

The Threat of Habitat Loss and Glyphosate

The dramatic decline in monarch populations over the past quarter-century is largely linked to the widespread use of glyphosate, a herbicide used with genetically modified corn and soybean crops. Glyphosate kills milkweed, the sole food source for monarch caterpillars. As milkweed disappeared from agricultural landscapes in the 1990s, monarch populations plummeted.

Endangered Species Act Listing and Legal Challenges

In late 2024, the Biden administration proposed listing monarchs as threatened under the Endangered Species Act. However, the decision was paused when the Trump administration took office in September 2025, with the US Fish and Wildlife Service indicating it would not finalize a rule before late September 2026. Vox reports that two environmental groups have since sued the US Fish and Wildlife Service to compel a binding deadline for a final decision on the listing.

The US Fish and Wildlife Service stated it “continues to evaluate the monarch butterfly using the best available science and in accordance with all requirements of the Endangered Species Act,” and emphasizes “voluntary, locally driven conservation as a proven tool for supporting species and reducing the demand for additional federal regulation.”

The Importance of Overwintering Sites in Mexico

Monarchs east of the Rocky Mountains undertake an extraordinary 3,000-mile migration to overwinter in a small region of forested mountains in central Mexico. World Wildlife Fund highlights the significance of this annual journey, with millions of butterflies congregating in these oyamel fir forests from November to March. These overwintering sites are considered critical to the survival of the eastern monarch population, and are vulnerable to severe storms and illegal logging. The Butterfly Network details how WWF-Mexico conducts annual field surveys to monitor the size of these colonies by measuring the area of forest they occupy.

Looking Ahead

While the recent population increase is encouraging, experts caution that monarch butterflies remain vulnerable. Climate change poses a growing threat, potentially exacerbating weather extremes that can negatively impact monarch populations. Long-term recovery will require significant habitat restoration and continued conservation efforts across their entire range. “We need to regain a lot of habitat to be able to get numbers back up,” said Lori Nordstrom, a retired Fish and Wildlife Service official, according to Vox. “We are still a long way from where we need to be.”