Drones Uncover Illegal Logging in Critical Monarch Butterfly Reserve

Illegal loggers have completely deforested a large portion of the most important site for monarch butterflies in Mexico, new research reveals.

The logging took place in the Monarch Butterfly Biosphere Reserve, where 10 hectares (approximately 25 acres) of vitally important trees have been cut down over the past year, according to a paper published in American Entomologist.

Lead author and noted monarch researcher Lincoln Brower of Sweet Briar College, who has studied the butterflies in the region since 1977, called the logging “a catastrophe.” The monarch population has fallen more than 90 percent over the past two decades as industrial agriculture in the Midwest has destroyed the milkweed where the butterflies lay their eggs and that feeds monarch caterpillars. In the winter, monarchs migrate by the millions to Mexico.

News of the deforestation came to Brower and his fellow researchers from local environmental activists about a year ago. The reserve, however, did not allow researchers onto the site to examine the problem, citing potential safety concerns. Instead, the scientists turned to a local filmmaker, who flew a drone over the site, revealing the scope of the logging. Satellite images further confirmed the damage.

The fir and pine forest in the Sierra Chincua in the Monarch Butterfly Biosphere Reserve, with the area illegally logged in 2015 outlined in white. (Photo: Courtesy of Entomological Society of America)

Brower questioned how this illegal activity could have gone unnoticed. “Ten hectares is a lot of wood,” he said. “You can’t have huge trucks removing all of this wood without knowledge of what’s going on. It really questions the governance of the reserve.”

Every year millions of monarch butterflies fly south to spend the winter in the reserve, where they cluster in colonies of just a few acres in size, sheltering on oyamel firs and pines at high elevations.

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But the same trees that protect the butterflies are also highly valued for timber. The area that was logged sits outside the core monarch wintering colonies, but it wiped out a critical portion of what is known as the buffer zone outside that land. That buffer zone helps to maintain the climate within the colony sites and protects the butterflies from high temperatures during the day and cold temperatures at night.

“It’s like the classic Goldilocks story—not too hot or too cold,” said Sarina Jepsen, director of endangered species programs for the Xerces Society for Invertebrate Conservation, who was not affiliated with the research. “It’s the perfect microclimate that monarchs need.”

The deforested area also plays an important role when the monarchs prepare for their annual 2,500-mile migration back to the U.S. and Canada. As the weather warms, the butterflies move down the slope. The logging site sits right in that path, just south of their most recent colony sites. “They couldn’t have picked a worse place to screw up,” Brower said. “The monarchs move right through the area that was deforested.”

The buffer zone, which has experienced logging in the past, has already lost some of its potential to protect the butterflies, he noted. A massive storm ripped through the area in March, killing millions of monarchs just as they were starting their annual migration north. “The wind blew so hard that it completely homogenized the temperature throughout the area,” Brower said. “The microclimate protection provided by the trees was completely eliminated.” Experts don’t know exactly how many monarchs died in the storm, but estimates range from 30 percent to 50 percent of the entire population.

Brower said the new loss of trees in the buffer zone could make mass mortalities like the one that happened in March more likely to occur in the future. “The wind can blow right through the trees in the areas that were cut,” he said. He has not yet investigated whether or not this wave of illegal logging contributed to the March mortality—it would depend on which direction the winds were blowing—but he said he suspects it could have had a role.

Jepsen said deforestation has been a constant problem for monarchs, although much of the effort to conserve the species over the past few years has focused on issues such as pesticides and milkweed. “More and more reports of illegal logging are coming in,” she said. “Let’s not forget about this issue.”