Every autumn, tens of millions of monarch butterflies make one of the most remarkable journeys in the natural world — up to 4,800 kilometres (3,000 miles) from breeding grounds in Canada and the United States to a cluster of mountain forests in the central Mexican states of Michoacán and the State of Mexico. No single butterfly makes the full round trip. The migration is passed between generations, guided by instincts that scientists still do not fully understand.
This winter, those forests were busier than they have been since 2018. New data released by Mexico's Ministry of Environment and Natural Resources, in partnership with the World Wildlife Fund (WWF), shows that monarch butterfly colonies occupied 2.93 hectares (7.24 acres) of forest during the 2025–2026 hibernation season — a 64% increase from the 1.79 hectares (4.42 acres) recorded the previous year. Nine separate colonies were counted, spread across three sites in Michoacán and six in the State of Mexico.
Researchers attribute the rebound to a combination of factors: a wetter spring and summer that boosted egg and larval counts in the breeding grounds further north, favourable conditions during the migration itself, and continued progress against illegal logging in the Monarch Butterfly Biosphere Reserve — the protected forest zone where the butterflies overwinter. WWF Mexico has reported that illegal logging in the core zone of the reserve has been largely eradicated since 2008.
The news carries a clear asterisk. Even with this year's increase, the monarch population remains more than 80% below its historical peak. In the late 1990s, colonies covered up to 18 hectares. The species still faces significant threats from pesticide use, climate change, and milkweed loss across its North American range. But the data is pointing, for now, in the right direction.