More monarch butterflies in Mexico

More monarch butterflies in Mexico, but numbers still low

MEXICO CITY—For the first time in 4 years, scientists have seen an uptick in the number of monarch butterflies migrating from the United States to Mexico. As of mid-December, the butterflies covered 1.13 hectares of forest in Michoacán and Mexico states, up from an all-time low of 0.67 hectares last year. But despite a nearly 70% increase in forest coverage—the established proxy for butterfly numbers—the 2014 to 2015 number is still the second lowest since recording began in the winter of 1993 to 1994.

The increase is “good news, but the numbers still remain very low,” said Omar Vidal, director general of the World Wildlife Fund (WWF) Mexico, in a press conference here today. WWF Mexico administers the winter colony count, surveying the sites where monarchs are known to gather to wait out the winter before returning to the United States to breed.

This year’s population increase was probably largely due to “good monarch breeding weather” last summer in the upper Midwest, says Karen Oberhauser, a conservation biologist at the University of Minnesota, Twin Cities. The region saw relatively mild temperatures and regular rain to nourish milkweed, on which monarchs lay their eggs. That allowed more caterpillars to survive to adulthood and boosted the number of butterflies attempting the journey to Mexico, Vidal explained.

More monarch butterflies in Mexico, but numbers still low