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Are monarch butterflies’ overwintering grounds in trouble?

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Most Canadian cottagers can recognize beautiful monarch butterflies, but they may not be aware of their amazing story. Each fall, millions of monarchs travel thousands of kilometres from Canada and the U.S. to overwinter in Central Mexico. The butterflies head to about a dozen pine and fir-tree covered mountains in Mexico’s transvolcanic plateau.

But a new study on the monarch’s winter nesting grounds, co-authored by Omar Vidal, head of Mexico’s chapter of the World Wildlife Fund (WWF), shows the logging threatening these grounds may be more extensive than first thought, and this could have a huge impact on the butterfly’s migration patterns. 

According to reports, the “core zone” of the reserve has lost more than 16 hectares of pine and fir trees, and half of that depletion is due to illegal logging.

Though the study found that tree-cutting hit its peak in 2005, as the Mexican government went as far as shutting down saw mills, commercial loggers, and their equipment in recent years, small-scale logging never stopped. One reason for this is the year-to-year losses, which were too minor to detect. 

And while small-scale logging, which is often done by residents of nearby villages for firewood or building materials, may not seem significant, the study attributed nearly half of last year’s logging loss these actions. 

Cutting holes in the forest, even removing a few trees, can make the butterflies more susceptible to getting wet and more likely to freeze. It may also expose them to more sunlight, which experts say can shorten their lifespan dramatically. 

“Small-scale logging is a serious and growing concern for the conservation of the monarch sanctuaries,” the study said.

According to Vidal, residents of these local, impoverished communities need to be paid more so that they are compensated for not cutting down the trees, which would help reforest the area. 

After all, it’s the “buffer zone” that experts seem most concerned about. While the total reserve stretches across more than 55,000 hectares of mountainous terrain, less than a third of that is in the highly protected core zone. The less-protected buffer zone allows for businesses, housing, and extensive roads to be built. 

Some would like more done to protect this zone, because the swarms of butterflies often change their exact location from year to year. 

There’s additional concern surrounding the issues brought up by the study because of a report released in March that said the number of butterflies that made it to Mexico last year was the lowest on record at only 59 percent. It also marked the third year in a row that there were declines in the number of monarchs that made it south.  

It’s worth noting, however, that the logging in Mexico isn’t the only factor to blame. Changing land-use patterns and genetically modified crops further north means fewer milkweed, which is the only plant monarchs will lay their eggs on. The increasingly common use of the herbicide glyphosate has also become a severe threat to their food supply.

According to Vidal, “The conservation of monarch butterflies is a responsibility shared by Mexico, the US and Canada.”