Monarch butterflies equipped with tiny GPS transmitters monitor their routes and fine-tune conservation efforts

On November 11, the monarch butterfly arrived in its winter home in the forest between Michoacán and Mexico. It had been more than a month since it left Ontario, Canada, entered the United States, crossed southwest through Ohio, Kentucky, Tennessee and Mississippi, then turned east into Louisiana and then crossed into Texas. They crossed the border at Ciudad Acuña in Coahuila and headed south, passing through Zacatecas, San Luis Potosi, Aguascalientes and Jalisco, before flying west through Michoacán toward the oyamel tree, where it will sleep until spring. A journey of approximately 3,000 kilometers to reach the Monarch Butterfly Biosphere Reserve. In 2025, for the first time ever, you will be able to know this much. Any tips? This butterfly, like 499 others this year, has a small transmitter attached to its body.

The transmitter, called BluMorpho, was developed by Cellular Tracking Technologies and the Cape May Point Arts & Science Center and weighs just 0.06 grams, reads text from the Xerces Society for Invertebrate Conservation, which helped test the chip. The novelty is that these models can communicate with any mobile phone, whereas previous models could only be detected with special receivers. If you download the Project Monarch app and spot a flock of monarch butterflies flying nearby, simply enable the “scan” option.

“Recently, David La Puma from Cellular Tracking Technologies has succeeded in developing a chip that can be implanted in monarch butterflies. The chip is very fragile and light so as not to cause problems in flight, and we used a special adhesive to ensure that it remains throughout the entire migratory journey,” explains Jerónimo Chávez of the Profauna organization, which helps track these butterflies. With this data, he says, they can track migratory routes and see how they change depending on weather patterns. “Using this technique, we observed monarch butterflies this year as they made their way along the east coast of the United States, passed through Caribbean islands, and entered Mexico through Veracruz,” Chavez explains. His team believes it will hibernate in Hidalgo.

Profauna is the organizer of one of the conservation programs, Correo Real, and has been active since 1992. Although Profauna has an educational focus and works with organizations and governments in Mexico, the United States, and Canada, it also operates a citizen monitoring network in which hundreds of individuals record and document the spring and fall migrations of monarch butterflies. Correo Real’s research was key to understanding butterfly migration routes within Mexico.

The monarch cycle begins in the spring on milkweed plants in the north-central United States and southern Canada. The only plants that lay eggs and the only food source for the larvae, these plants nurture several generations of monarchs until the daylight hours and temperatures decrease towards the end of summer, giving rise to the so-called Methuselah generation. Unlike previous species that die in six weeks, they live for eight to nine months, long enough to migrate to hibernate in the fir forests of Mexico. They then head to the United States, primarily Texas, to lay the first generation of eggs, which later return to milkweed plants in the north-central United States and southern Canada. Through this migration, they carry pollen from flowering plants and support the continent’s genetic diversity.

Right next to the milkweed is where Dr. Karen Oberhaus developed the Monarch Butterfly Larval Monitoring Project, a citizen project that has been operating since 1996. “We have volunteers all over the United States, Canada, and Mexico. What they do is monitor milkweed areas once a week and count how many monarch butterfly eggs and caterpillars are there,” Oberhaus said. By monitoring 400 sites each season, we can determine monarch butterfly density and survival rates.

How to become a collaborator —community scientistthat’s what it’s called in English. Volunteers can be trained at the project’s annual in-person workshops or using the resources on its website, where they can also see all the data from every point since 1997.

“The reality is that there are far fewer monarch butterflies now,” Oberhaus laments. “What’s interesting is that when we analyze breeding habitat, it’s not really decreasing that much. We’re seeing the biggest changes in Mexico, where there are fewer and fewer monarch butterflies that can overwinter. This shows that there are fewer and fewer hibernating habitats, and fewer and fewer places for monarchs to breed,” he points out.

In Mexico, one way to measure and compare the number of individuals arriving each winter is by the hectares of the Monarch Butterfly Biosphere Reserve’s influence range. With an area of ​​500 square kilometers, it was founded in the 80s of the last century and has fir, pine, oak and cedar forests in several municipalities of the states of Mexico and Michoacán.

Each December and January, a group of engineers visits hibernation areas to measure the surface area occupied by monarch butterflies. In 1996, a record year, the butterfly’s habitat was 18 hectares, but in 2013 it reached a low of 0.67 hectares. That year, Canada, the United States, and Mexico began working together to increase the amount. The efforts were successful, and the population recovered, reaching 6 hectares in 2018, but has since been in decline, falling to less than 2 hectares in 2024. Researchers believe this is due to years of drought, which prevented the butterflies from finding sufficient resources to migrate, and a decline in international cooperation following the COVID-19 pandemic.

In recent research, Expanding avocado monoculture threatens monarch butterfly wintering habitat in central Mexicopredicts that climate change and rising avocado prices will combine to put pressure on the Monarch Butterfly Biosphere Reserve. This article analyzes the expansion of avocados from 2006 to 2024 within the reserve’s buffer zone (an area established as a kind of shield around the center of the reserve) and hypothesizes several scenarios based on different climate models.

“We found that under the current climate, 5,000 hectares are suitable for growing avocados,” elaborates one of the authors, Jesús Eduardo Sáenz Ceja, PhD in Biology and member of the Ecosystem Sustainability Institute of the Autonomous University of Mexico. “If we include the variable of climate change, the surface area increases to 10,000 hectares because the currently cold or temperate highlands provide the conditions necessary for avocado cultivation,” he warns. These new potential crop fields are forests.

He cautions that growing avocados is not illegal as long as they are produced sustainably. “The problem is that 94% of producers are non-compliant and use pesticides.” Furthermore, of the 1,345 hectares of cultivated land currently within the reserve, 25% was due to illegal land conversion of old forest.

There are people in Mexico who are trying to get ahead of the disappearance of the ecosystem. Another article titled Establishing wintering grounds for monarch butterflies in future climates: Expanding the upper elevation limit of the Abyss religion through migration assistancedescribes the efforts of a group of scientists from the University of Michoacán to plant fir trees in areas that will have a climate similar to that of the Michoacán Mountains, such as the Nevado de Toluca Mountains, over the next 40 years.

The plan is to create colonies of mature fir trees at higher elevations to compensate for the 2.3 degrees Celsius rise in temperatures expected in 2060. By then, even if Michoacán’s forests are no longer able to protect Methuselah monarchs due to climate change, they will have trees they can reach after migrating, transferring pollen from flower to flower and continuing to support the continent’s genetic diversity.