every year, but In early November, one of the world's most impressive natural spectacles takes place in Michoacán, Mexico. Millions of migratory monarch butterflies inhabit the forests of the country's Monarch Butterfly Biosphere Reserve, about 100 kilometers west of Mexico City. After flying south for eight months, beginning their journey in the northern United States or southern Canada, they hibernate here for the winter before mating in the spring.
After flying more than 4,000 kilometers, the butterflies land on the oyamel pine trees of the Ejido El Rosario area, where they congregate for weeks, protecting themselves from the wind and cold nights. Without these trees, butterflies would not be able to survive their tiring journey.
Oyamel fir grows in a very small climate zone, which is humid but cool. “Its distribution is very limited to the highest mountains of central Mexico,” says Cuauhtémoc Saenz Romero, a professor at the Universidad Michoacana de San Nicolás de Hidalgo. Sainz Romero is the lead author of recent study It is predicted that this forest will gradually degrade to the point of extinction as a result of climate change, putting the butterflies at risk.
Sáenz Romero explains that for settled monarchs, the oyamel canopy acts as a buffer to local temperature and humidity. “During the day, in the shade of the oyamel, the atmosphere is 5 degrees Celsius cooler than outside. It provides protection from high temperatures. At night the situation is opposite, resulting in the atmosphere becoming 5 degrees Celsius warmer.” The density of the canopy also protects from winter rain. “If the temperature drops below zero and the butterflies' wings get wet, they can freeze. That's why these trees represent such a special habitat,” says Saenz Romero.
After awakening from hibernation and mating in central Mexico, the insects fly north to Texas in the United States, where they lay their eggs. “For all this, they need energy reserves to return, which they don't have to spend fighting the cold at winter sites,” he explains.
This fine balance for their existence is provided only by the oyamel fir. However, some models indicate that the climate favorable for them will disappear in the region by 2090. “Because of rising temperatures, we are seeing a process of forest degradation,” says Saenz Romero, who is leading the initiative to establish new wintering sites. For the kings, who are on red List Of endangered species.