Monarch butterflies overwinter in oyamel fir forests in central Mexico, and the degradation of these critical sites threatens the survival of the entire eastern North American monarch population.
Overwintering monarchs cluster in dense masses on oyamel trees, dependent on the microclimate of intact old-growth forest to survive months without feeding. Forest degradation exposes butterflies to lethal temperature swings and precipitation. Intense winter storms in degraded forest kill millions of butterflies whose wet wings prevent flight and thermoregulation. The ecological welfare of the broader migration — encompassing hundreds of millions of individuals — depends on protecting these few thousand acres of critical forest. Community-based conservation with economic incentives has proven the most effective protection approach.