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Eastern Monarch Population Numbers Increase 144% from Last Year

Jan 30, 2019


  • Population Trends

The eastern North American monarch population estimate for the winter of 2018-2019 reports a population size of 6.05 hectares, as announced today by WWF- Mexico and the Comisión Nacional de Áreas Naturales Protegidas (CONANP). This is the largest population we have seen since 2007, an increase of 144% compared to last year.

The large population this year is an encouraging sign for monarchs, and an inspiration for us to continue our work together. Good weather conditions during the breeding season supported the increase, as well as efforts across North America to protect and restore habitats. However, we cannot rely on persistent good growing-seasons to sustain monarchs into the future. Our efforts to get more high quality habitat in the ground matter for monarchs, and they must continue

“We are invigorated by the good news about the eastern population this year,” said Wendy Caldwell, Executive Director of the Monarch Joint Venture, “but there is much work left to be done. With the recent release of an extremely small western population, we strive to embrace an all hands on deck approach to rebuilding this population and continuing to grow and sustain the eastern population.”

Of fourteen (14) colonies where butterflies were observed, the largest colony (2.46 hecatares) was observed within the El Rosario ejido. For the full report, in Spanish, click here. 

Everyone can make a difference for monarchs, through creating habitat, educating others, or monitoring for monarchs. Groups and individuals working together can find ways to get involved and learn more on the Monarch Joint Venture website.

Data from 1994-2003 were collected by personnel of the Monarch Butterfly Biosphere Reserve (MBBR) of the National Commission of Protected Natural Areas (CONANP) in Mexico. Data from 2004-2019 were collected by the WWF-Telcel Alliance, in coordination with the Directorate of the MBBR. 2000-01 population number as reported by Garcia-Serrano et. al (The Monarch Butterfly : Biology and Conservation, 2004)

The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, businesses 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 taken by Wendy Caldwell at the El Rosario butterfly reserve in March 2018.