After years of decline, monarch butterfly populations appear to be bouncing back.
Each year, monarchs from Canada and the United States migrate thousands of kilometres, spending three-to-four months overwintering in Mexico’s Monarch Butterfly Biosphere Reserve. The number of butterflies making the trip was on a steady decline until 2013. They recovered slightly in 2014, and according to reports, this year was even better.
In December 2015, the butterflies covered about four hectares of the pine and fir-tree covered mountains northwest of Mexico City. That’s up from the 1.13 hectares they covered in 2014, and the record low of 0.67 hectares they covered in 2013.
Deforestation in Mexico, severe weather conditions, and the use of herbicides to destroy milkweed are the main factors that have contributed to their decline over the years.
The leaves of milkweed plants are the only place where monarchs lay their eggs, and the only food monarch butterfly caterpillars will eat.
In recent years, groups across Canada and the US have worked to reintroduce milkweed throughout the continent. Just last spring, Parks Canada and the municipality of Leamington joined forces to create a trail of milkweed, native grasses, and wildflowers in Point Pelee National Park. Point Pelee is the most southern tip in Canada and an important stop-off point in the butterflies’ yearly pilgrimage.
According to CBC News, the United States has also been successful in reintroducing milkweed. Through planting and designating pesticide-free areas, the country restored about 100,000 hectares of milkweed in just one year.
Efforts like these, combined with more favourable weather conditions along the monarch’s migratory route, are being credited for the past year’s higher numbers
But experts warn that we shouldn’t let our guard down: “The increase in monarch numbers is great news for sure, but the bottom line is that these butterflies must reach a much larger population size to be resilient to ever-increasing threats,” Tierra Curry, a senior scientist at the Center for Biological Diversity, said in a press release.
Just 20 years ago, the butterflies covered as much as 18 hectares of the forest.
Unfortunately, deforestation is still a big issue in Mexico. The butterflies spend their winters keeping warm under the forest canopy, and illegal logging within the butterfly reserve continues to threaten that. Cutting holes in the forest can make butterflies more susceptible to getting wet, and more likely to freeze. It could also expose them to more sunlight, which experts say can shorten their lifespan dramatically.
According to a recent research paper, co-authored by monarch expert Lincoln Brower, the reserve lost 10 hectares of forest in 2015 due to illegal logging. The researchers concluded that the protection of the Monarch Butterfly Biosphere Reserve, which was designated as a World Heritage Site in July 2008, is “inadequate,” and that “if the migratory and overwintering phenomenon of the monarch butterfly is to persist, forest protection must be enforced year-round in the entire reserve.”