Fifteen Wisconsin monarchs reached Mexico. What can their signals tell us?

Enough to connect an insect held in someone’s hand in early September with a living migrant more than a thousand miles away. Not enough to know everything that happened between those encounters—or what will happen through the winter. By November 4, 2026, 15 monarchs fitted with tiny radio transmitters in Wisconsin had been detected in Mexico, out of 68 tagged statewide, according to Paul A. Smith’s November 5 Milwaukee Journal Sentinel report, republished by Wausau Pilot & Review. That is a documented migration milestone, not a survival rate.⁠3

For Maggie Steinhauer, research manager at Milwaukee’s Urban Ecology Center, the connection is unusually personal. Three of the center’s 14 tagged monarchs had reached Mexico. She has banded birds before, but this is the first time she knows with certainty that an animal she tagged traveled more than 1,000 miles. Checking the Project Monarch app has become part of her daily routine and something to share with coworkers and the community.⁠3

The Wisconsin effort brought together the Urban Ecology Center, Beaver Creek Reserve in Fall Creek, BioCorps at the University of Wisconsin–Madison and the Southern Wisconsin Bird Alliance at Goose Pond Sanctuary in Arlington. Mark Martin, a retired state conservation biologist who cares for Goose Pond with his wife, Susan Martin, supplied the statewide total. Most tagging took place in early September.⁠3

Wisconsin Public Radio’s account of the deployment described 30 monarchs receiving solar-powered radio tags at Goose Pond. Those butterflies belong within the statewide tagging effort; they are not 30 additional arrivals in Mexico. Keeping deployment counts separate from detection counts matters when the story is about animals that cannot be continuously observed.⁠8

The transmitter is called BluMorpho, developed and manufactured by Cellular Tracking Technologies in Rio Grande, New Jersey. It weighs 0.06 grams, or 60 milligrams, compared with a monarch’s approximate body weight of 0.5 grams. The solar-powered device attaches to the butterfly’s back, on the thorax. Small enough to travel on an insect, it still represents a physical load—not simply an invisible dot on an app.⁠3⁠8

These are radio transmitters, not verified onboard GPS recorders. A participating phone or wildlife-tracking receiver, including receivers in the Motus network, can pick up a tag’s signal. Project Monarch’s app logs the detection’s time and location and plots it on a map. The resulting record is a succession of encounters with the detection network, not an uninterrupted account of every turn and stop.⁠3⁠17

That distinction does not diminish the advance. For decades, researchers attached numbered, adhesive-backed paper tags to monarch wings. Recovering one in Mexico could connect a tagging location with a winter destination, but it revealed much less about the journey between them. Repeated radio detections offer opportunities to investigate migration paths, timing and places where butterflies pause to rest or feed.⁠3

The Wisconsin arrival totals do not yet provide that detailed account for each butterfly. The available reporting supplies no individual route reconstructions, exact travel times or named stopovers for the 15 arrivals. It cannot establish a particular migration bottleneck or tell land managers which specific site this group most urgently needed. The promise is a better way to investigate those questions, not a finished answer to them.

There is evidence that the technology can keep revealing movements beyond the fall journey. Smith reports that tests in 2025 showed monarchs could carry the tags from the United States and Canada to Mexico. Several hundred tags were deployed that season, including in northern Illinois, and some butterflies survived winter and were detected returning to the United States earlier in 2026. Those were earlier tagged butterflies, not proof of what will happen to this year’s Wisconsin migrants.⁠3

The most tempting calculation is also the wrong conclusion: divide 15 by 68 and call the result the share that survived. That would turn the limits of observation into a claim about the butterflies’ fate.

An undetected monarch may still be alive elsewhere or may have passed through without being recorded. The available information does not quantify receiver coverage, detection probability or tag failures for this group. Without those measures and subsequent observations, the missing detections cannot be sorted into deaths, continuing journeys and animals the network simply missed. Nor does a detection somewhere in Mexico establish arrival at a final winter colony, much less survival through winter.⁠3⁠18

The arrival totals also rest on one published report, rather than an independently available, tag-by-tag accounting of the Wisconsin butterflies. That is a reason to identify where the figures came from and keep their meaning narrow—not to dismiss the journeys they document. The evidence supports detected movement into Mexico. It does not support a complete accounting of the group’s survival.⁠3

Beyond Wisconsin, hundreds of other monarchs carry transmitters deployed in other states and Canada. Scientists involved through the Xerces Society, Monarch Joint Venture and Monarch Watch will lead collection and analysis of the data. The conservation value will come from understanding how movement relates to weather, food and available habitat—not from how compelling the map looks.⁠3

Martin describes the long-term objective as providing adequate food and habitat throughout the monarch’s life cycle, with benefits for other grassland and prairie species too. Meanwhile, Steinhauer’s exchanges with tagging partners already include observations about weather patterns and habitat availability. Public fascination and scientific inquiry are feeding each other, although neither is evidence that the monarch population has recovered.⁠3

More migrants are expected to gather at wintering reserves northwest of Mexico City in the coming weeks. Later detections could show which tagged butterflies survive winter and move north, and help researchers investigate where reproduction passes the journey to the next generation. Marsicek says plans already extend into 2027. For now, the achievement is both substantial and specific: butterflies that people handled in Wisconsin have been detected in Mexico. The next consequential signals will tell us what happened after they got there.⁠3