The Mexican overwintering sites where hundreds of millions of monarch butterflies cluster are threatened by illegal logging, extreme weather events, and climate change, creating vulnerabilities for the entire eastern monarch population.
The vulnerability of the entire eastern monarch population - hundreds of millions of individuals - to conditions at a few hectares of Mexican forest creates extreme welfare risk. A single severe winter storm can kill tens of millions of monarchs in days as freezing precipitation penetrates the canopy and kills clustered butterflies. The depletion of tree cover through illegal logging removes the insulation that protects colonies from temperature extremes. Monarchs experience metabolic stress during their overwintering cluster - they must conserve energy through metabolic suppression while maintaining enough warmth to survive. Climate change is destabilizing both the wintering habitat conditions and the signals that coordinate migration timing.