Climate Change Blamed for Drop in Migrating Monarch Butterfly Population

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Courtesy / Veronica Prida

A copper mine appears to be coming soon to monarch roosting sites in Angangueo, Michoacán.

Monarch butterflies have left their roosts in Mexico and will be arriving in the "Texas Funnel," which includes San Antonio and the Hill Country in the next few weeks. Those tracking their great migration through Texas to Canada in 2018 will see nearly 15 percent fewer butterflies start the long, multi-generation journey.

The winter roosting populations declined 14.7 percent over the previous year, World Wildlife Fund officials announced. The iconic orange-and-black insects occupied only 6.12 acres at this year's winter roosts in the Mexican mountains. The population is far below the 14.82-acre goal set by the 2017 Monarch Conservation Implementation Plan.

During peak migration years in the late 1990s, the monarch butterfly population occupied about 44 acres of forest. (Scientists calculate the population numbers by measuring the amount of forest occupied by overwintering monarchs.)

In explaining the decline in monarch numbers, WWF officials blamed climate change –specifically, warming weather and a freak sleet storm that occurred in early 2017.

In 2016, a spring storm clobbered the forest, removing at least 100 acres of Oyamel firs whose evergreen foliage provides an insulation blanket for the butterflies during the cold winter months. The storm also decimated at least 50 million butterflies just as overwintering monarchs began their 2017 migration north. This contributed to the shortfall, officials said.

"These climate phenomena without a doubt have an impact on the migration," said Jorge Rickards, director of the World Wildlife Fund in Mexico, at a press conference earlier this week. The organization participates in the annual study that takes the butterfly census.

Warming temperatures raise concerns at the roosting sites and throughout the butterflies' migratory range. Hotter temperatures cause the butterflies to burn through their stored winter fats, since they are more inclined to leave the warmth of the trees in which they roost and seek nectar and water. This can result in an energy shortage when spring migration time arrives.

A changing climate can also affect the availability of the butterflies' host plant, milkweed. If the weather warms too early and too quickly, the milkweeds don't have time to sprout the leaves that will attract monarchs' egg-laying. The butterflies will keep moving north –and possibly perish before reproducing.

Courtesy / Monika Maeckle

Antelope horns milkweed, a monarch butterfly host plant, awaits monarchs in April 2016.

Warmer weather will likely continue. The National Weather Service Climate Prediction Center said in its mid-February 90-day outlook bulletin that Texas, typically the first stop for migrating monarchs, has a 60-70 percent probability of "higher than average" temperatures this spring.

San Antonio Water System, the local water utility, speculated at a recent community meeting that Texas will enter another drought this summer and suggested Stage One lawn watering restrictions will be implemented by mid-April.

Wildflowers, important nectar fuel stops for monarchs and bees, are likely to put on an "average" show this year, according to the Lady Bird Johnson Wildflower Center. Andrea Delong-Amaya, the center's director of horticulture, said bluebonnets and other wildflowers may be smaller in size due to a lack of rain, and that it's too early to determine regional milkweed availability.

In Mexico, monarch butterfly conservationists reported early departures from the spring roosting sites. "The news was early, but it was sudden and certain," read the Journey North weekly monarch migration update this week. "On March 3, two substantial sightings were reported north of the sanctuaries."

"Millions of monarchs are now en route to northern Mexico and Texas," wrote Ellen Sharp, co-owner of J&M Butterfly B&B in Macheros, situated near the entrance of Cerro Pelón in Mexico, a sanctuary to 30 percent of this year's monarch butterflies. Sharp wrote the  butterflies "seemed confused'' by warm temperatures.

Apart from climate change, pesticide use, illegal logging, and habitat loss, the Americas' favorite insect may soon face yet another threat. Reports suggest Grupo Mexico, a $500 billion mining concern traded on the Mexican Stock Exchange under the ticker symbol GMEXICOB, will reopen a long-shuttered copper mine at El Rosario, the most frequently visited of the monarch sanctuaries. Grupo Mexico, WWF, and CONABIO, Mexico's Commission on National Biodiversity, all declined repeated requests for clarification on the status of the copper mine.

Grupo Mexico has stated for years that since the mine operated until 1992 in Angangueo, Michoacán, and technically never closed, it should be allowed to reopen – despite protections put in place for the Monarch Butterfly Biosphere Reserve. The reserve was inscribed as a World Heritage site by UNESCO in 2008.

Courtesy / Monika Maeckle

On hot days, monarch butterflies puddle on mountain seeps.

Details of the mine's reopening have not been disclosed publicly, but locals and visitors report the copper mine is due to restart. "I haven’t heard anything new about the mine – just that it’s happening," Sharp said.

Eleonor Briggs, a wildlife photographer who lives in New Hampshire, returned from the area recently and said that a WWF official told her the mine is on track to reopen. "He said not to worry since this was only a 'small' reopening for two years and then they would shut for good," Briggs said. She also was told an ore reprocessing plant will be built in the town to extract the copper. Grupo Mexico, WWF and CONABIO all declined to clarify or confirm the claims.

Grupo Mexico lists Angangueo as a future mining project on its website. The company website also touts a reputation for "lowest extraction costs in the industry" and status as member of the Mexican Stock Exchange’s Sustainable IPC index, a financial indicator that acknowledges the companies with the highest commitment to social responsibility, environmental performance, and corporate governance.

In 2014, the company was responsible for the worst mining accident in Mexican history. At a mine in Buenavista in the northern state of Sonora, Mexico, the incident left dozens of miners to die underground after methane explosions. It also spilled 10 million gallons of copper sulfate acid into the Sonora and Bacanuchi rivers, 25 miles south of the U.S. border with Arizona, leaving 24,000 people without clean water.

Copper mining and processing use huge amounts of water, create problematic waste, and impact water quality, soil quality, and ecosystem loss and vegetation. The implications are huge for a forest stressed by drought and a migration taxed by climate change.

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