It’s not just Mexico’s forests that need protecting for butterfly migration
Their route from Canada is threatened by overuse of herbicides and climate change, among other factors
Víctor Sánchez-Cordero, a researcher at the National Autonomous University’s Institute of Biology and Mexico’s lead representative on a tri-national scientific committee that studies the monarch, said that the butterflies’ route from southeastern Canada to the fir tree forests of Michoacán and México state is under threat.
He blames the excessive use of herbicides, changes in the way land is used, climate change and a reduction in the availability of nectar and pollen.
“The commitment to conserve this migratory phenomenon not only focuses on Mexico; it’s a shared responsibility between our country, Canada and the United States,” Sánchez-Cordero said.
The researcher, who along with his team developed a system to monitor the migration of the monarch, said that there is a misconception that the most important – almost exclusive – factor in ensuring the continuation of the phenomenon is the conservation of forests in the Monarch Butterfly Biosphere Reserve (RBMM), located about 100 kilometers northwest of Mexico City.
That idea “has placed great international pressure on Mexico,” Sánchez-Cordero said before adding that he and his team published an article in the journal Frontiers in Environmental Science that shows that the decline in the number of monarch butterflies migrating to Mexico is not due to deforestation in the RBMM.
Deforestation has been drastically reduced in the past 10 years but butterfly numbers have continued to decline, he said.
“The dramatic reduction in the density of monarch butterflies that arrive at overwintering sites in Mexico doesn’t correlate with the loss of forest coverage, which shows that this factor is not responsible for the population reduction. … Other hypotheses to explain the decrease must be sought,” Sánchez-Cordero said.
One possible cause for the decline, he explained, is that the excessive use of herbicides is killing milkweed, a plant that is a main food source for monarch butterflies and on which females lay their eggs. Less nectar and pollen in the United States and Canada as a result of deforestation is another possible cause, Sánchez-Cordero said.
He added that large numbers of migrating butterflies have perished in Texas and the northeast of Mexico due to drought linked to climate change.
To conserve the migratory phenomenon of the monarch – butterflies fly some 4,500 kilometers to reach Mexican forests from Canada over the course of three to four generations – a network of conservation areas along their migration routes needs to be developed, Sánchez-Cordero said. He also said that the routes followed by the butterflies should be declared protected areas.