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The number of monarch butterflies wintering in the mountains of central Mexico dropped 22% from the previous year, and the number of trees lost from their favored wintering grounds tripled.
Frost and “extreme temperatures” in the United States may have played a role in the butterfly’s decline during the most recent winter season, said Humberto Peña, director of Mexico’s nature reserves.
Monarchs east of the Rocky Mountains in the United States and Canada overwinter in the fir forests of the western state of Michoacan, west of Mexico City. The total area they occupied this past winter dropped to 5.4 acres (2.21 hectares), from 7 acres (2.84 hectares) a year earlier.
The annual butterfly count doesn’t calculate the individual number of butterflies, but rather the number of acres they cover when they clump together on tree boughs.
Gloria Tavera, conservation director of Mexico’s Commission for National Protected Areas, said the area of forest cover appropriate for the butterflies that was lost rose to 145 acres (58.7 hectares), from 46.2 acres (18.8 hectares) last year.
Illegal logging has been a major threat to the pine and fir forests where the butterflies gathering in clumps to keep warm. But experts said that this year, more than half the tree loss was due to removal of dead or sick trees affected by fires, storms or pests. Tavera said a lack of rain had plunged trees into hydric stress, making them more vulnerable to diseases, pests and fires.
Jorge Rickards, Mexico director of the WWF conservation group, blamed climate change,
“The monarch butterfly is an indicator of these changes,” Rickards said.
