The monarch butterfly has been called “the Bambi of the insect world.” These fascinating insects are famous for their bright colors and their incredible fall migratory route, which can be as long as 2,500 miles.
Starting from as far north as Canada, millions of monarchs take a two-month journey to a mountain range that straddles the border of two Mexican states, Michoacán and México, where they spend the winter. This area, known as the Monarch Butterfly Biosphere Reserve, is sacred ground for entomologists and butterfly enthusiasts. Each year thousands of tourists visit the Reserve, which was declared a World Heritage Site by the United Nations in 2008.
Unfortunately, the Oyamel firs and pines that shelter the butterflies are also valued for their timber, and illegal logging operations frequently occur in the Reserve. This is unfortunate because monarch butterflies have a tightly evolved relationship with the Oyamel firs (Abies religiosa), which thrive in high elevations. One of the most important monarch overwintering areas, the Sierra Chincua, has peaks that are 3,400 meters above sea level, and the Oyamel firs that grow on the slopes below the peaks protect the butterflies from the cold mountain air.
“The Oyamel fir forest moderates the temperature and moisture of the butterflies by acting as a blanket, keeping heat in during the night and keeping heat out during the day,” said Dr. Lincoln Brower, a research professor at Sweet Briar College who has studied monarchs for 62 years. “The firs also act as an umbrella during storms, which is important because wet butterflies are less resistant to frost.”
In April 2015, Brower and some colleagues learned that the Oyamel fir habitat was being destroyed in the Sierra Chincua after Mexican environmentalists reported illegal logging was occurring there. In an attempt to see it for themselves, the researchers tried to visit the area but were denied access.
“Neither we nor other individuals were granted permission to visit the area in order to witness the logging,” they wrote in an article appearing in American Entomologist, “but we became aware of its severity when we examined current satellite imagery.”
By comparing a satellite image from November 2013 to an image from November 2015, they were able to determine that logging had occurred on approximately 10 hectares of land – and each hectare can support about 50 million monarchs!
They were also able to determine that most of the logging occurred between April and August after examining Landsat images from April, August, and September 2015. In addition, they were able to determine the severity of the logging by examining high-resolution drone images that were taken in January 2016.
“The Sierra Chincua is a jewel in the crown of overwintering monarch butterflies in Mexico and the severe damage we report here is very disturbing,” the authors wrote. “If the migratory and overwintering phenomenon is to persist, forest protection must be enforced year-round in the entire Reserve. We hope that the [United States] and Canada will join with the people, government, and scientific community of Mexico to provide whatever support is needed to ensure that an effective level of enforcement takes place.”
Featured image credit: A 1.34 hectare monarch butterfly colony is clearly visible in the center of this aerial photograph from 2007. The brownish hue covering the trees shows the dense butterfly population. Image from “Illegal logging of 10 hectares of forest in the Sierra Chincua monarch butterfly overwintering area in Mexico” in American Entomologist and used with permission.