The population of monarch butterflies that spend the winter in Mexico has jumped more than 144 percent over last year, Mexican officials announced this week.
The butterflies occupied about 15 acres of the high-altitude Mexican forests this year, up from about six acres in early 2018. Such a large population has not been observed since 2006. In 2014, the worst year for monarchs, the population occupied only about 1.5 acres.
Representatives of the National Commission of Natural Protected Areas (CONANP) and the World Wildlife Fund (WWF) hailed the population increase at a Mexico City press conference on Wednesday. They attributed the boom to decreased logging in Mexico and trilateral habitat and conservation efforts.
The news was welcome in San Antonio, the nation’s first Monarch Butterfly Champion City. San Antonio sits in the heart of the Texas Funnel, the migratory pathway through which all migrating monarchs east of the Rocky Mountains must pass on their multi-generation migration from Mexico to Canada and back each year.
“This is such a great endorsement of our conservation efforts,” said Cathy Downs, Texas and South Central region conservation specialist with Monarch Watch, a citizen science butterfly tagging program based at the University of Kansas at Lawrence. “We just have to keep it up so we don’t lose momentum.”
Monarchs lay their eggs only on milkweed plants, which include anything in the Asclepias family. Over the course of a month, the eggs hatch into caterpillars, morph through their stages and become a butterfly. The butterfly moves north in the spring and subsequent generations repeat the cycle on emerging milkweeds. In the fall, monarchs cease reproductive activities, conserving their energies for the long trip south to Mexico, where they spend the winter.
“This good news gives us hope that our combined conservation efforts and education events are making an impact,” said Laurie Brown, volunteer coordinator for the Alamo Area Monarch Collaborative, a local coalition of monarch butterfly conservationists and education manager at the San Antonio Zoo.
The announcement from Mexico stood in sharp contrast to a report out of California earlier this year. The western monarch butterfly population, which moves up and down the California coast, plummeted 86 percent, according to the most recent census.
Mexican officials noted that 14 monarch colonies had been identified this year: eight colonies of about 12 acres within the protected Monarch Butterfly Biosphere Reserve and six of about 2.6 acres outside the preserve. For the first time, a colony was registered in the Ojo de Agua community, located in Nevado de Toluca, about 65 miles southeast of the preserves.
Counting monarch butterflies is an inexact science at best, and scientists and others have called for improving the way the migrating population is calculated. Currently, technicians and scientists walk the forest and map the trees occupied by monarchs at each roost. They measure the perimeter of each colony, then calculate the number of hectares occupied. They then multiply the number of hectares by a factor of 20 million.
Using that formula, which has vacillated between 10 million and 50 million over the years, the 2018-2019 population represents an estimated 121 million butterflies. The 2017 -2018 season was estimated at about 50 million using the same formula.
Jorge Rickards, managing director of WWF Mexico, attributed the increase to pollinator-friendly initiatives throughout the three-nation migratory path, favorable conditions in Texas, and generally favorable climate throughout the breeding zone.
Andrew Rhodes, director of Mexico’s National Commission of Natural Protected Areas, pointed out that butterfly populations fluctuate wildly and cautioned that “it’s important to not lower our guard in addressing threats such as climate change, land use, and changes and forest degradation.”
Monarch Watch Founder and Director Chip Taylor
told National Public Radio this week that the migration effectively “dodged a bullet” this year, with excellent weather and habitat conditions that increased the availability of milkweed. Plenty of nectar also was available. Monarchs require the nectar of late-blooming flowers to fuel their flight throughout the season, especially in the fall when they head to Mexico.
Threats still loom, however. Warmer temperatures can cause problems for monarch butterfly reproduction. When it’s warmer, the butterflies wander further north too early and the milkweeds are not out of the ground yet. As a result, the population suffers.
Meanwhile, a catastrophic climate change event like the freak freeze of February 2017 that occurred at the roosting sites in Mexico, could wipe out all progress. An unusual sleet storm moved through the monarch sanctuaries that spring, just as the monarchs were beginning to make their way north. At least 1.5 million butterflies perished.