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Eastern Monarch Overwintering Population Numbers Announced

Mar 05, 2018


  • Population Trends

This announcement is translated from the WWF-Mexico News Release, originally in Spanish, which can be found here.

WWF- Mexico, 05 March 2018:

The monitoring report of the forest area occupied by Monarch butterflies in 2017-2018, carried out by WWF and Conanp, registered 9 colonies of butterflies that occupied 2.48 hectares of forests, an area that represents a decrease of 14.77 percent with respect to the previous season (2.91 ha). 

"Although there are many factors involved, this decrease of the occupied surface is attributed to the presence of two tropical storms and three hurricanes on two occasions in the Atlantic coasts in mid-September of 2017, when the migration begins. This impacted the number of Monarcas that arrived in Mexico," said Jorge Rickards, Director General of the World Wide Fund for Nature (WWF) Mexico. "The high temperatures in the Midwest and Northeast of the United States also resulted in late migration and as a result low occupancy areas in Mexico, as suggested by US researchers," he added.

Population graph for the Eastern North American Monarch Butterfly Population.

Executive summary of the monitoring report:

During the second half of December 2017 WWF Mexico and CONANP registered 9 colonies of monarch butterflies (3 in Michoacán, 6 in the State of Mexico) that occupied 2.48 hectares of forest: 5 colonies (1.50 ha) were located within the Monarch Butterfly Biosphere Reserve (RBMM) and 4 colonies (0.98 ha) out of it. This surface represents a decrease of 14.77% with respect to the area (2.91 ha) of the 2016-2017 season. The colony of Atlautla in the western part of the State of Mexico occupied - at the beginning of January - a forest area of ​​0.08 hectares. 

Download the full report (in Spanish).


Content is directly translated from the WWF-Mexico news release, found here. The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of all Monarch Joint Venture partners. Header photo by Wendy Caldwell, taken in 2012.