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Jaime Rojo (Spain) reveals the epic migration undertaken by monarch butterflies and the efforts being made to save them.

A monarch arriving at the winter roosting site manoeuvres into place on the trunk of an oyamel fir tree in the Santuario El Rosario, part of the Monarch Butterfly Biosphere Reserve in Michoacán, Mexico.

The butterflies blanket the trees and forest floor and enter a state of semi-dormancy. Their extreme closeness provides protection and warmth.

These sites were found by scientists in the 1970s, but local people had been aware of them for many years.

Though state protections were soon put in place, it has been calculated the overwintering population plummeted by 84% between 1996 and 2014.

In the decade since, declines have slowed thanks to the awareness and work between Mexico, the United States and Canada. Numbers stabilised at around 55 million.

However, ongoing monitoring and conservation are needed. Surveys done during the winter of 2023–24 showed that roosting colonies covered only a small area of forest, the second lowest on record.