Decline of the Monarch Butterfly Migration in Eastern North America
Among the countless organisms that have evolved during the history of life on earth, monarch butterflies are among the most extraordinary. Sadly, their unique multigenerational migration across our large continent, their spectacular overwintering aggregations on the volcanic mountains in central Mexico, and their educational value to children in Canada, the United States, and Mexico are all threatened. Monitoring of the butterfly population over the past two decades indicates a grim situation.
Following a long-term decline, the total area occupied by the overwintering butterflies plunged from the 20-year average of 6.7 hectares to a record low of 0.67 hectares in the current season, a 90% decrease. This winter, only seven of twelve traditional sites had any butterflies at all, and only one of those (El Rosario, 0.5 hectares) was substantial in size.
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