Every autumn, tens of millions of monarch butterflies perform one of nature's greatest journeys, a 4,000km migration from Canada to the forests of central Mexico. Herbicides and habitat loss pushed them to record lows by 2013. After the second-lowest count on record in the winter of 2023-24, the colonies grew to 2.93 hectares in 2025-26, but scientists warn the recovery remains fragile.
The Migration at Risk
Every autumn, tens of millions of monarch butterflies perform one of nature's most extraordinary spectacles, a 4,000km migration from Canada and the US to overwintering forests in central Mexico. For decades, their numbers were in freefall.
Herbicide use eliminated milkweed, the only plant monarchs lay eggs on, from vast swaths of agricultural land. Illegal logging degraded the Mexican forests where they spend the winter. In the winter of 2013-14, the colonies covered just 0.67 hectares, the lowest on record.
A Fragile Comeback
>> "In the winter of 2023-24, the monarchs covered just 0.9 hectares of forest, the second-lowest area on record."
Since then, habitat restoration has helped and illegal logging in the core of the Mexican reserve has been sharply reduced, but numbers swing with the weather. The winter of 2023-24 was a setback, with 59% less forest occupied than the year before. The colonies then grew to 1.79 hectares in 2024-25 and 2.93 hectares in 2025-26. But habitat loss, pesticides and climate change remain threats, and the colonies still cover only about half of the 6 hectares scientists consider necessary for a stable population. Scientists warn the recovery remains fragile and the journey more perilous than ever.
_Sources: Monarch Joint Venture, "Eastern Monarch Butterfly Population Falls to Less than One Hectare in the 2023-2024 Overwintering Season", 7 February 2024. Monarch Joint Venture, "Eastern monarch overwintering population increases from last year", 17 March 2026. Down To Earth, "64 per cent increase in Mexico's Monarch butterfly population", 23 March 2026. Riviera Maya News, "Monarch Butterfly Numbers Rise in Mexico, But Recovery Remains Fragile", 2026. U.S. Fish and Wildlife Service, "Monarch" species profile._