Cold weather front affects monarch butterfly migration
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Cold weather front affects monarch butterfly migration

Four weeks ago, the weather in Ocampo, Michoacán was perfect and the 22,600-something residents of Ocampo and the surrounding pueblos were celebrating good news: the monarch butterfly population had rebounded after several years of alarmingly low numbers. The butterflies migrate to Mexico, where they winter in several sanctuaries and forests, including one in Ocampo, Santuario El Rosario, and one named Sierra Chincua, just outside the nearby town of Angangueo. The sanctuaries draw tourists, both domestic and international, who come here by the busload between late fall, when the butterflies starting arriving, and early spring, when their migration cycle ends.


Agronomist Hector Gomez González estimated that this year’s migration would conclude around March 21, marking the close of a successful season during which, he said, nearly three times more butterflies arrived at Santuario El Rosario than the number recorded in 2015. Gomez and his colleagues were thrilled. A healthy butterfly population keeps local guides and other small business owners employed, boosting the local economy significantly; in turn, residents of the area feel a particular commitment to preserving the butterflies’ habitat.
Cold front
There are some factors, however, that are entirely out of anyone’s control. Last week, just as the migration season was arcing toward its close, a devastating cold snap and snowstorm blew through Ocampo. According to Gomez, who posted updates on twitter throughout the storm, more than 20,000 trees were felled by the strong winds in Michoacán and Estado de México, including many in the sanctuaries.
The butterflies appeared to have been minimally affected by the unusually cold weather, which covered the sanctuary’s trees and grounds with snow and ice. Both the government and Gomez (who is often critical of the government’s involvement in the sanctuaries) asserted that butterflies would have fallen off the trees had they been harmed by the extreme weather. He posted numerous photos and videos on twitter to show that the butterflies in Santuario El Rosario appeared to be in relatively good condition. He also shared images of the felled trees.


It’s the trees that cause the biggest concern now; the sanctuaries were already under threat from illegal foresting, and it’s the loss of habitat that has been considered most threatening to the stability of the monarch population. According to the U.S. National Fish and Wildlife Federation, that’s primary reason the monarch population has plunged from more than one billion to less than 60 million over the past two decades.
Sanctuary staff has been reforesting the reserves, but it will take years for the pines and firs trees to reach maturity. And news of the storm, which left 13 inches of snow on the ground in some places, may have shortened the tourist season even if the butterfly population remains largely intact.
Back to normal
Fortunately, temperatures have returned to seasonal norms and the temperatures for the rest of the migration cycle are forecast to be stable. Gomez, for his part, is encouraging tourists who had plans to visit the sanctuary not to abandon those plans. He posts daily updates on twitter, noting that there’s still time to see the monarchs before the 2016 migration cycle ends.
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