Dip in winter monarch count spurs population debate


Monarchs overwinter in central Mexico’s oyamel fir forests. (Photo by Pablo Cervantes, Alianza WWF-Telcel)

An unexpectedly dramatic drop in the number of monarch butterflies (Danaus plexippus) roosting in the forests of Central Mexico over the winter has alarmed experts and further fueled an ongoing debate about how threatened the migratory insect really is. The area of oyamel fir (Abies religiosa) forest occupied by monarchs in the states of Michoacán and Mexico fell from 2.2 hectares (5.4 acres) during the 2022-23 winter to 0.9 hectares (2.2 acres) in the winter of 2023-24, the environmental group World Wildlife Fund (WWF) says. That’s the second-smallest population on record. The smallest, recorded a decade ago, covered 0.6 hectares (1.5 acres). Scientists assume that approximately 21 million monarchs occupy each hectare of forest, though their density varies year to year. The current population, which should soon begin migrating north, is now threatened by snow, says Tierra Curry, a scientist with the Center for Biological Diversity, a Tucson, Arizona... [Log in to read more]

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