every year, in In early November, one of the most impressive natural spectacles in the world takes place in Michoacán, Mexico. Hundreds of millions of migratory monarch butterflies settle in the forested massifs of the country’s Monarch Butterfly Biosphere Reserve, approximately 100 kilometers west of Mexico City. Having flown south for eight months and beginning their journey in the northern United States or southern Canada, they hibernate here during the winter before mating in the spring.
After flying for more than 4,000 kilometers, the butterflies land in the fir trees of the Ejido el Rosario region, where for weeks they congregate, protecting themselves from the wind and the cold nights. Without these trees, the butterflies would not be able to survive their grueling journey.
The fir tree grows in a very small climatic space, humid but cold. “Its distribution is very limited to the highest mountains in central Mexico,” says Cuauhtémoc Sáenz Romero, professor at the Universidad Michoacana de San Nicolás de Hidalgo. Sáenz Romero is the main author of a recent study which predicts that this forest will gradually deteriorate to the point of disappearing as a result of climate change, putting butterflies in danger.
For resting monarchs, the fir canopy acts as a buffer for local temperature and humidity, explains Sáenz Romero. “During the day, under the shade of the fir tree, the environment remains 5 degrees Celsius cooler than outside. It is a protection against high temperatures. At night it happens the other way around, resulting in an environment that is 5 degrees Celsius warmer.” The density of the canopy also protects against winter rains. “If the temperature drops below zero degrees and the butterflies get their wings wet, they can freeze. That is why these trees represent such a particular habitat,” says Sáenz Romero.
After waking up from hibernation and mating in central Mexico, the insects fly north to Texas, United States, where they lay their eggs. “For all this, they need energy reserves to return, which they do not have to spend fighting the cold in wintering places,” he explains.
This delicate balance for their survival is provided only by the oyamels. However, some models indicate that a favorable climate for them will have disappeared in this area by 2090. “Due to the increase in temperatures, we are observing a process of forest decline,” says Sáenz Romero, who leads an initiative to establish new wintering sites. for the monarchs, who are in the red list of threatened species.