Mexico monarch numbers plunge

Biologists blame heat, drought and habitat loss

The number of monarch butterflies wintering in Mexico fell 59% this year, reaching its second lowest level since record keeping began, according to the latest annual count. 

The count calculates the amount of land the wintering butterflies cover rather than the actual number of butterflies. This year’s survey found monarchs (Danus plexippus) residing on 0.9 hectares in the central Mexican forest, down from 2.21 hectares last year. The lowest number of butterflies wintering in Mexico was 0.67 hectares in 2013.

Biologists said heat, drought and habitat loss are to blame for this year’s reduction. 

Researchers found almost no butterflies at some traditional wintering grounds as the monarchs seemed to seek out higher, cooler areas. About two-thirds were found outside traditional reserves.

The butterflies make up an eastern population that migrates to the U.S. and Canada. Biologists say a western population that winters in California is also struggling. 

The monarch is being considered for Endangered Species Act protections in the U.S. A decision is expected by October.

Read more from the Associated Press.

Header Image: Eastern monarch butterflies spend the winter in Mexico. Credit: Gene Nieminen/USFWS