Millions of monarch butterflies are beginning their epic 3,000-mile autumn migration from Canada and the US to the fir forests of central Mexico.

There is rare good news: the World Wildlife Fund’s annual survey found colonies covered 7.24 acres of forest in winter 2025-26, up 64 percent from 4.42 acres the previous year. But numbers remain far below the 45-acre peak of the late 1990s.

Scientists warn the migration itself is threatened by climate change. Models project suitable habitat could shrink up to 40 percent by 2070, fracturing routes. In Mexico, researchers are experimenting with “assisted migration” — planting oyamel firs at higher elevations on the Nevado de Toluca volcano.

People can help by planting native milkweed, the only plant monarchs lay eggs on, and nectar-rich flowers along the route.

The Xerces Society and other groups urge gardeners to plant milkweed free of pesticides. Each fall, volunteers across North America count migrating monarchs, and their data feeds the annual population estimates.