Since the tracking started last year, scientists have found the first evidence of a monarch in Utah, west of the Rockies, joining eastern monarchs in central Mexico. Other tagged monarchs migrated down the Eastern Seaboard to Florida, jumped the Gulf of Mexico and are now being tracked across Mexico, a connection scientists had not seen before in such numbers. About 175 tagged butterflies have been detected in Mexico since the migration started this year. As habitat loss, pesticides and climate change pummel monarch populations, the research could help their numbers rebound.

Emma Pelton, senior conservation biologist with the Xerces Society for Invertebrate Conservation, said, “There’s just all these unique stories of their paths, connections between the population, that we didn’t know existed or we hypothesized but couldn’t prove.” She added, “We’re a year into it, and I think we’re all just thrilled,” noting that older tracking devices had proved too big or heavy.

Orange-and-black monarch swarms use environmental cues to travel some 3,000 miles (4,800 kilometers) from as far as southern Canada to spend the winter in forests of oyamel fir trees in central Mexico. The forest area is a protected biosphere reserve and a World Heritage site. For decades, scientists have struggled to map the butterflies’ routes, determine how far they fly each day and find where they settle at night. Scientists are attaching tiny tracking devices to hundreds of monarch butterflies to find critical stopover locations before they disappear, and the new tags are helping provide the missing details.

Rebeca Quiñonez-Piñón is the senior scientist at the National Wildlife Federation, a nonprofit that recently joined a tri-national science team to track monarchs. Nearly 1,750 monarchs were tagged this year with solar-powered radio tags. As a child, Quiñonez-Piñón wondered where monarchs stopped for a meal and a night’s rest on their long migrations across North America. The public can follow the progress of individual butterflies on the free app called Project Monarch Science.

Quiñonez-Piñón is leading a study that combines real-time migratory tracking with community science to understand where monarchs stop in Texas. Only some monarchs migrate. Of those that do, a big portion of the butterflies east of the Rocky Mountains flies through a narrow corridor known as the “Texas funnel” every fall and spring, heading north again to lay their eggs before dying. Depending on the year, they may favor different parts of Texas based on where they can find water, nectar and overnight shelters such as trees.

Only some monarch butterflies receive tracking devices, and not all monarchs are good candidates for the tags. The new $200 tags weigh about as much as a drop of water and were developed by Cellular Tracking Technologies. Quiñonez-Piñón said that if a properly trained person attached a tag correctly, “the monarch will be completely safe.” To avoid overburdening them, most tagged monarchs weigh more than 400 milligrams, about as much as a standard pill, said David La Puma, vice president of global market development for Cellular Tracking Technologies and coordinator of the Project Monarch Collaboration, the team the National Wildlife Federation recently joined. Other researchers and community scientists look for longer-winged monarchs to tag.

Many monarchs are caught with nets and kept in cool temperatures to calm them before tagging, a delicate process. The insect is positioned in the middle of a special board, with its legs and antennae protected. Adhesive is cotton-swabbed onto its abdomen and the tag, then the transmitter is gently pressed against its body before the butterfly is released.

Louie Yang, an insect ecologist at the University of California, Davis, said the technology is “pretty remarkable” because “we haven’t previously been able to see what path they take or how quickly they’re moving over different parts of that journey.” Yang cautioned that the system identifies the location of a receiver that detected a butterfly, not the insect’s exact position. A detection also does not mean the butterfly remains alive, and further studies are needed to determine how and whether the tags affect its behavior.

Monarchs typically live two to six weeks, but those migrating to Mexico can live up to nine months and spend their lives moving south, waiting out winter and migrating north to breed in spring. The monarch’s migration has also made it a symbol for the rights of international migrants.

Since the mid-1990s, the eastern monarch population has dropped more than 80%, while the western population has fallen about 95%. Pesticides are a pervasive threat to milkweed, the plant where monarchs lay their eggs and the exclusive food source for their caterpillars. Prolonged drought can dry up the water and nectar sources monarchs need. They also face collisions with cars and trucks, and in California, forests where western monarchs spend the winter are being razed for development.

Tierra Curry, senior scientist and endangered species codirector with the Center for Biological Diversity, said human-caused climate change, driven by burning coal, oil and gas, is a primary threat throughout the year. “One of the problems now is that it stays too hot too long in the northern areas, and so they don’t get the cues to migrate. And then if the temperature freezes, they’re probably not going to make it to Mexico,” Curry said. “The later they start, the less the chances that they’re going to get all the way to the forest.”

Late last year, the Trump administration delayed a decision on federal protections for monarchs. Several groups filed a lawsuit, and a court ordered the government to make a final decision by 2030.

Conservationists are pursuing other ways to protect the dwindling population. In Texas, nets on some highways are encouraging butterflies to fly higher so they do not get struck, especially at night when they descend to roost. Curry described other efforts involving mass plantings of milkweed and pollinator plants in gardens, along roadsides and in transportation corridors. Several studies show the plantings are boosting local monarch populations.

Quiñonez-Piñón said the uniquely famous monarch butterfly helps draw attention to the threats facing insects and their vital role in sustaining plant life across the continent. “Pollinators are crucial to protect and ensure that our ecosystems remain healthy,” she said, “and also to have the sources of food that we require as humans.”

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