by Kristen Baum and Emily Geest (Oklahoma City Zoo)
Radio tagging brings up lots of new research questions, but also some logistical ones. We wanted to summarize data from the fall 2025 migration to address questions around the number of days between detections.
For those of you who purchased Blu+ radio tags, you also had to purchase data. The current data cost is about 7 cents per tag per day. While it isn’t a huge cost, it does make one think about how long to leave on data for tags, especially if you have tags that haven’t been detected in a while. Many researchers may have identified ahead of time how long they want to leave on data, but others may still be making that decision. Deciding when to turn off data is more of a challenge for fall deployments given the long lifespan of monarchs at the overwintering sanctuaries and the potential to obtain additional movement data in the spring. For example, MW024 from Fall 2025 had detections from September 27, 2025 through April 3, 2026. For our project this spring, we planned on 6 weeks given the shorter lifespan of reproductive monarchs, but ended up extending to 8 weeks for the monarchs tagged in Kansas because we were still getting detections.
We summarized data from the 30 tags deployed in Lawrence, Kansas during the fall 2025 migration to provide information about gaps in time between detections. We only included data through November 15, 2025, so as not to include the overwintering period. We removed monarchs that were detected for less than a week (4 individuals) and MW007, which was a tag (not a monarch) that was detected off and on in Lawrence, Kansas through the winter and spring. We calculated the maximum gap (number of days) between detections for 1) all monarchs (25 individuals) and 2) the monarchs that reached Mexico (10 individuals). The mean (average) maximum number of days between detections was 8.34 days for all monarchs and 9.75 days for monarchs that reached Mexico.
MW021 had the largest number of days between detections at 20.81 days. It is interesting to note that the max gap in detections occurred immediately after she was tagged. She had several detections on the day she was tagged (September 27) and wasn’t detected again until October 18 when she was northwest of Oklahoma City.
MW005 is another interesting example. While his max gap in detections through Nov. 15 was only 7.80 days, that doesn’t reflect the whole story. MW005 was the monarch that was detected along the Gulf Coast on October 31, 2025, and not detected again until January 6, 2026 at Cerro Pelón, which is one of the overwintering sanctuaries in central Mexico. That meant he went 67.10 days without being detected, although the time period fell outside of the dates that we used to summarize the data in Table 1.
Gaps in detections are likely due to a combination of factors, including weather and Bluetooth coverage. And, of course, determining if detections are from a tag on a monarch or just a tag is another challenge.
Filed under Monarch Tagging | Comments Off on Detection Gaps: Will the Monarch You’re Following Move Again?
Monarch Watch’s Tagging Program has existed since 1992, and during the 35 years of the program, more than 3 million monarchs have been tagged by thousands of community scientists across the eastern United States and southern Canada. Each year, tags are recovered in central Mexico at the overwintering sites and across the migration range. Monarch Watch encourages taggers to check recovery lists every year to see whether any tags of theirs get recovered, including tags from prior years, as it’s possible for a tag to be recovered a couple of years later.
What’s a lot more uncommon is a tag getting recovered 29 years later.
Director Kristen Baum tracks down the recovered monarch from Monarch Watch’s extensive archive of tagging records.
A long-time Monarch Watch collaborator holds a tag from 1997, recovered from El Rosario overwintering sanctuary in central Mexico in 2026.
That’s what happened this past tagging season, a record in Monarch Watch’s tag-recovery history! We received an email the evening of February 4, 2026, from a long-time Monarch Watch collaborator who was buying tags for us at the El Rosario overwintering sanctuary in Mexico with the subject line “How old is this MW tag?” Less than 30 minutes later, Monarch Watch Research Project Coordinator Jim Lovett replied with “Monarch Watch tag TR416 is more than 28 years old.” The tag was issued to a high school in Wamego, Kansas, and applied to a female monarch in 1997.
Left: Candi Schneider tagged the butterfly in 1997 that would be recovered in 2026. Credit: Image provided by Candi Schneider. Right: Terry Callender led monarch-tagging programs at Wamego High School from 1992 to 2003. Credit: Tina Callender.
Tagging Program Time Capsule
Candi Schneider was a second-year student at Wamego High School (WHS) in 1997 when she tagged the female monarch that would be recovered 29 years later. According to our tagging records, Candi tagged this monarch with tag code TR 416 on September 24, 1997. Her biology teacher, Terry Callender, had been leading tagging efforts for several years at WHS, one of many schools that participated in the tagging program in its early years. The news of this tag recovery came as a pleasant surprise to both Terry and Candi, and they were happy to talk with us about their experience tagging monarchs in the early years of our program.
Terry, now retired, was a teacher for 45 years and taught at WHS for 25 of them. One of his biggest goals in teaching was to give students the opportunity to take what they were learning in the classroom and apply it out in the field or through hands-on experiences. When the Monarch Tagging Program began in 1992, Terry was one of 500 people who responded to Monarch Watch’s call for assistance to tag monarch butterflies, and he quickly become a leader in the program. The peak tagging years at WHS happened from 1996 to 1998. Terry’s classes still hold the record of the most monarchs tagged in any one year at 12,397 monarchs in 1996. In 1997, they tagged the most monarchs out of any one group or individual for that year at 11,405 monarchs.
Monarch Watch highlighted Wamego High School in our 1996 and 1997 season summaries. Archives of these season summaries are available on our website.
How were they able to tag so many monarchs? A lot of it came down to the right combination of location and student interest.
Wamego High School was the feature of numerous news stories over the years in local papers. These compiled clippings were provided by Terry.
“[In a local Wamego news article], they said Wamego was a hotspot, and it certainly was a hotspot, and we just happened to be at the right place at the right time and had students that wanted to tag butterflies rather than listen to me talk to them,” Terry says. “That’s one of the things I liked about Monarch Watch, is that it involved students, you know, actively in there learning, and there was a lot of learning done.”
Wamego was indeed a hotspot of monarch activity in the mid-to-late nineties. The butterflies migrated through in numbers that Terry says he hasn’t seen since. He recalls how masses of monarchs would roost in his backyard, across neighborhoods, in the city park, and in surrounding towns. In the evenings, his students would search for monarchs to tag. They’d place each retrieved monarch in an envelope for safe keeping until class the next day, when they’d tag the butterflies, record essential info on tagging data sheets, and release them to continue their migration.
Left: Some of Terry’s sons tag monarchs and record their data on tagging sheets in their front yard. Right: Terry sits with one of his sons to tag monarchs with some of Monarch Watch’s older rectangular tags used in the first couple years of the tagging program. Credit: Tina Callender.
“I do … remember tagging [the monarchs],” Candi says. “I remember putting the stickers on their wings.”
According to Monarch Watch’s tagging records from the fall of 1997, Candi tagged 23 monarch butterflies, all on September 24, 1997, including the one recovered this year.
Monarch Watch tags have evolved through the years. We started with a square tag, changed to a rectangular tag, and then pivoted to using the circular self-adhesive tags that we still use today. Credit: Graphic created by Kaziwa Abdulqader.
In 1992, Monarch Watch used square tags (called “alar” tags, originally developed by Dr. Fred Urquhart) that folded over the leading edge of a monarch’s forewing. From 1993 to 1996, we implemented rectangular tags that were attached to the discal scale of a monarch’s hindwing using glue. 1997 was the first year we used circular self-adhesive tags, as the forces of adhesion worked better on a circular tag than a rectangular one with corners. Since we started using these circular tags, the rate of tag recovery has increased from 1 in 5,000 to 1 in 100. This recovered monarch from 1997 would’ve been one of the first to have a circular tag on it.
This graphic depicts the total area occupied by the eastern monarch population at their overwintering sites in central Mexico. The last several years have been some of the lowest counts on record. Learn more about the monarch population decline via a 2024 blog post written by Monarch Watch Founding Director Chip Taylor.
A Phenomenon in Crisis
According to Terry, the monarch migration hasn’t come through Wamego in such volume since those peak years in the 1990s. This is a pattern seen not just in Wamego but also across the eastern monarch population’s range. Following the development of herbicide-tolerant crop lines, corn and soybean fields in the upper Midwest began to be applied with RoundUp in the early 2000s, which contains a non-selective systemic herbicide called glyphosate. Because milkweed can’t endure repeated uses of glyphosate, this new herbicide adoption became a major factor, among others, in the decrease of milkweed abundance throughout the Midwest. With fewer host plants available for female butterflies to lay their eggs on and for caterpillars to consume, monarch numbers declined along with the numbers tagged each fall in the Midwest.
Though the monarch population may be smaller than what it was in 1997 when Terry and Candi were tagging in Wamego, the value of community science participation has garnered even more importance. The data collected by dedicated participants, who need to work harder than ever to observe and tag monarchs in their area, both helps us understand the fall migration and how we can support the monarch population in a world where their host plant’s abundance is dwindling.
Creating, maintaining, and protecting monarch habitats, places that have nectar and milkweed plants, is a crucial way anyone can help monarchs and sustain their fall migration. Inviting students into a community science program like monarch tagging could be a first step toward a lifetime of appreciating and supporting the natural world.
Though his formal teaching days are behind him, Terry continues to live a “biology life” by studying and appreciating the natural world around him every day. Credit: Tina Callender.
Real Experiences in the Classroom and Beyond
Terry continued participating in the tagging program through 2003 before he retired from WHS in 2004. Today, he’s busy spoiling his grandchildren, trying new hobbies, and continuing to study and appreciate the nature around him.
“I think I live a biology life every day of my life,” he says. “Me and my family, we’re always doing something that relates to biology.”
Candi continues to enjoy the outdoors and loves photographing and identifying wildlife.
“I identify anything I do. So, if I go snorkeling, I identify fish. I like to identify birds. I identify butterflies,” she says. “And we actually just planted a bunch of landscaping plants out [on our property]. We bought some acreage a few years ago… and I’ve worked with the designer pretty closely to say, ‘Hey, I want flowers that will support butterflies and birds.’”
Maybe all the engaging hands-on experiences she had in Terry’s class had a positive influence on her, she adds. This sentiment rings true for Terry.
“I have never had a student tell me that they really loved my lecture on cell respiration,” he says. “And I gave a good lecture on cell respiration. But I’ve had – and still do have – students come up to me and tell me about tagging monarchs, they talk about making grass collections, … going to Nebraska to see the sandhill cranes. Those are the things that they talk about and the experiences that they talk to me about that they enjoyed so much.”
Thanks to the thousands of community scientists that participate in our tagging program, we’ve been able to understand more about the monarch fall migration. Credit: Ann Dean Photo.
The Tagging Program Today
Monarch Watch continues to be a leader in studying the monarch fall migration. What started as a project in 1992 with a few hundred volunteers (plus the assistance of a few thousand students) has now become a program that involves tens of thousands of community scientists from schools, other organizations, communities, and households across every state east of the Rocky Mountains as well as in five Canadian provinces. To date, the tagging data has provided information on the timing and pace of the migration, revealed that there’s a time interval we call a “migration window” that favors migration success, and shows us that the prospect of reaching Mexico is a function of distance and the pathway taken to reach the border with Mexico. More recently, the tagging data has revealed the impact of droughts and high fall temperatures on the number of monarchs that reach the overwintering sites.
The environment for monarchs is changing, and tagging will continue to show us how these changes are affecting monarch numbers.
What’s on the menu for a monarch caterpillar? Just one plant. Monarchs depend on milkweed: It’s the only food source for caterpillars as they grow and develop, and it’s the only plant on which female monarch butterflies will lay their eggs.
Milkweed was once abundant across North America, but as development and heavy herbicide usage across the continent increased, the plant has experienced large losses. In part from this, monarch butterfly population numbers have drastically declined in recent years.
Recognizing this decline, people are stepping up to support monarchs by planting beneficial habitat in large cities, small towns, suburban neighborhoods, rural properties, and more. Monarch Watch’s Free Milkweed Programs offer an avenue for schools, educational non-profits, and those working on large-scale habitat restoration to receive flats of milkweed plugs free of charge.
One organization that received free milkweeds is the Northwest Michigan Invasive Species Network (ISN) based in Traverse City, Michigan. For the past 10 years, staff and volunteers have been dedicated to restoring critical dunes on protected property along the shores of Lake Michigan.
The Northwest Michigan Invasive Species Network has been working on restoring critical dunes along Lake Michigan for the past 10 years. In a recent project, they installed a sign alerting people to restoration efforts, which included planting milkweed. Credit: Northwest Michigan Invasive Species Network.
“The protected areas are a valued asset for the community, drawing people in to a lesser-known area just south of Sleeping Bear Dunes National Lakeshore, while providing the same sandy and stunning experience of Lake Michigan that hundreds of thousands of people flock to see each year as part of northwestern lower-Michigan’s important tourism industry,” says ISN Habitat Management Specialist Luke Kreykes.
The increased traffic can bring with it the potential for harmful invasive and non-native species to gain a foothold, so ISN has worked to remove those plants and establish native species in their place. In 2025, ISN applied and received 128 milkweed plugs through Monarch Watch’s Free Milkweeds for Restoration Program to assist their habitat-restoration efforts. Five volunteers spent several hours last September removing invasive spotted knapweed from the dunes. They then transplanted native beach grasses from other areas of the beach and established the milkweed plugs (common milkweed and butterfly weed) across 4 acres.
ISN received 128 milkweed plugs through the Free Milkweeds Program to include in their habitat-restoration project. The photos above show before (left) and after (right) the milkweed plants were transplanted at the dunes. Credit: Northwest Michigan Invasive Species Network.
“During our volunteer [workday] this past summer, we noticed a couple monarch caterpillars munching on the milkweed that we planted in 2024,” Kreykes says, “so this was especially fulfilling to be able to then apply our Free Milkweeds award plugs and bolster what we had started.”
Many other projects like ISN’s restoration work are happening around the country as people restore native habitat and provide monarchs more areas to support their life cycle. To date, Monarch Watch has distributed more than 1 million milkweed plants through the Free Milkweed Programs, and many more are needed to help bring back monarch populations. The generosity of Monarch Watchers makes this effort possible.
“ISN is incredibly thankful for those who donate to the Free Milkweeds [for Restoration] Program. It helps us keep costs down for partners and municipalities that may not have funds available for such projects but are very much interested in protecting such a special area for the community along with supporting monarch populations,” Kreykes says. “In addition to helping restore critical dune areas from invasive species, we also utilized this opportunity to empower volunteers with the knowledge and skills to bring this project home and hopefully make their own changes to their landscape to better support pollinators.”
Donations given during One Day One KU will help support the Free Milkweed Programs so people and organizations like ISN can continue on-the-ground efforts to provide monarchs with the milkweed they need to survive and thrive – and inspire others to do the same.
The WWF-Telmex Telcel Foundation Alliance, in collaboration with the National Commission of Natural Protected Areas (CONANP), the National Autonomous University of Mexico (UNAM), and the Monarch Butterfly Biosphere Reserve (MBBR), announced the total forest area occupied by overwintering monarch colonies today. Nine (9) colonies were located this winter season with a total area of 2.93 hectares, a 64% increase from the previous season (1.79 ha).
Figure 1. Total Area Occupied by Monarch Colonies at Overwintering Sites in Mexico.
Additional details will be posted as they become available.
Note: The WWF-TELMEX Telcel Foundation Alliance collaborates with CONANP to systematically monitor the hibernation of the Monarch since 2004, and they join the Institute of Biology of the National Autonomous University of Mexico (UNAM) to analyze changes in forest cover in the area core of the Monarch Butterfly Biosphere Reserve in order to have scientific bases that support the implementation of conservation strategies for the benefit of the species, ecosystems and human beings.
It has been an interesting week if you have been following the BlūMorpho tagged monarchs at the overwintering sanctuaries in Mexico! If you aren’t familiar with BlūMorpho tags, the tiny solar radio tags allow the paths of individual monarchs to be detected; you can find more information in previous blog posts (Feb. 16).
I’ve been eagerly watching for northward movement by the monarchs tagged during the fall migration. I was excited to see movements by XSTI and JMU011. XSTI was tagged on Oct. 6 in Stillwater, Oklahoma. XSTI went undetected from Nov. 11 to Jan. 3 and then was detected multiple times in January. XSTI then traveled about 40 miles north on Feb. 20 before stopping at the northeast corner of the Monarch Butterfly Biosphere Reserve. XSTI was then recorded 35 miles west by the end of the day on Feb. 22:
JMU011 was tagged on Sept. 26 in Harrisonburg, Virginia then recorded just north of the Monarch Butterfly Biosphere Reserve on Feb. 20 and traveled about 68 miles to the northwest by the end of the day on Feb. 22:
And then, I noticed PP0017 and CHI007. PP0017 was tagged on Oct. 3 at Point Pelee in Ontario, Canada, while CHI007 was tagged on Feb. 11 at Sierra Chincua. They both ended up about 120 miles west from where they were last detected on Feb. 21 to where they were detected at the end of the day on Feb. 22:
That is a lot of westward movement! I previously posted about the challenging winds during the fall migration and there appear to be similar challenges in the spring. Stay tuned as we watch for path corrections and wait for the first arrivals in Texas. We will be learning lots from the BlūMorpho tagged monarchs over the next few months! Join us in following the spring migration in real time using the free Project Monarch Science mobile app (download via your device’s app store).
These detailed insights into monarch biology are possible thanks to the Project Monarch Collaboration, which is led by Cellular Tracking Technologies (CTT) and the Cape May Point Arts & Science Center (CMPASC). More than 25 organizations make up the Project Monarch Collaboration:
Logos of 2025 Project Monarch Partners.
Filed under Monarch Tagging | Comments Off on Monarchs on the Move!
If you haven’t been following the BlūMorpho tagged monarchs since they reached the overwintering sanctuaries in central Mexico in November, it is time to start watching again by using the free Project Monarch Science mobile app (download via your device’s app store). Monarchs typically start their northward migration from the overwintering sanctuaries in late February, with the first individuals reported in Texas in early to mid-March.
Update on BlūMorpho Tagged Monarchs
If you go back and read my previous blog posts (Nov. 7 and Nov. 17) about the 30 monarchs that we tagged with Blū+ tags in Lawrence, Kansas at the end of September, you will notice that I mentioned we had 9 monarchs that had been detected in Mexico. We were excited to increase that number to 10 when MW005 was detected at Cerro Pelón in early January. Prior to that, MW005 was last detected on October 31 near Matagorda Island, which is northeast of Corpus Christi, Texas.
Left: Track of MW005 showing the time and distance between detections in Texas and at the overwintering sanctuaries in central Mexico. Right: Tracks of the 10 “MW” monarchs that have been detected in Mexico.
In the Project Monarch Science app, you can find the monarchs tagged by Monarch Watch in the data tab by selecting the monarch icon at the top of the screen then searching for “MW”. We have 5 monarchs (MW001, MW005, MW020, MW024, MW026) that have been detected at the overwintering sanctuaries in February. Recall that Blū+ tags are solar-powered transmitters that use Bluetooth crowd-sourced location networks to increase the number of detections. This means that the tags have to be in the sun to be detected and a Bluetooth device or other receiver (e.g., Motus tower, Terra station) need to be nearby for a detection to occur. We will be checking frequently for any northward movement by the “MW” butterflies and others as we get closer to the end of February.
Locations of MW001, MW005, MW020, MW024, MW026 from 9-15 February.
We also recommend searching the Project Monarch Science app for monarchs labeled with the prefixes CHI, ROS, and MES, as these individuals were recently tagged by World Wildlife Fund – Mexico (WWF-MX), the National Commission of Natural Protected Areas (CONANP), Cape May Point Arts & Science Center (CMPASC), and Cellular Tracking Technologies (CTT) as part of the Project Monarch Collaboration. More than 25 organizations make up the Project Monarch Collaboration:
Logos of 2025 Project Monarch Partners.
Monarch Watch Tag Recoveries
We have also started receiving information about Monarch Watch tag recoveries, referring to our circular tags with unique letter and number codes that are applied to the hind wings of monarchs by community scientists to study the monarch’s fall migration. In contrast to the BlūMorpho tags, Monarch Watch tags rely on people to observe and report or recover tags. Both tagging approaches provide unique and complementary information about the monarch’s fall migration, as well as different ways for people to engage with monarchs. We look forward to sharing information about tag recoveries this spring, so please check our Monarch Watch Tagging Program page for updates.
Filed under Monarch Tagging | Comments Off on Get Ready to Follow the Spring Migration in Real Time
We’re in the middle of winter here in Kansas, and while there’s no monarch activity around Monarch Watch, there’s still plenty happening as we receive updates about the eastern population’s journey in Mexico and await their return in the spring.
Over the last several weeks, we’ve received reports from Estela Romero of Monarchs Across Georgia, who’s a longtime monarch supporter and provides overwintering updates from Mexico on the monarch population. Below is what she’s recently shared with us this January, with updates in both Spanish and English, and more updates will be coming soon.
The monarch butterfly overwintering colonies at the El Rosario & Sierra Chincua sanctuaries appeared to be growing and re-arranging in early January. Credit: Estela Romero
Estela Romero’s Monarch Updates
January 7, 2026
How to describe the air gently blowing through the forest?
The delicate dew drops shining on the leaves of plants and trees at sunrise?
The capricious clusters our spectacular monarchs form on oyamel fir branches at their hibernating spots?
The new year begins with much milder climate conditions than those we had at Christmas. Sunny and warm days now welcome the unstoppable peak of local and international visitors, increasing from now to March.
Sierra Chincua Sanctuary remains at its same location, getting beautifully higher in population, acquiring an indescribable beauty in the way it concentrates and forms incredible cluster shapes.
El Rosario Sanctuary has now moved a few hundred meters south to another of its first traditional arrival spots called Los Horcones, 19.5952 -100.2617, gaining population but re-arranging in concentration too, which will considerably change the impression of the site each time.
Dramatic beauty shall be occurring day by day at both sanctuaries from now on.
Enjoy the sound of monarchs flying around at the El Rosario sanctuary. Credit: Estela Romero
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¿Cómo describer el viento corriendo suavemente en el bosque?
¿Las delicadas gotas de rocío brillante en las hojas de plantas y árboles al amanecer?
¿Las formas caprichosas de los racimos de Monarcas en sus ramas de árboles de Oyamel en sus sitios de hibernación?
El Año Nuevo abre con condiciones de clima mucho más generosas que las que tuvimos en Navidad. Días soleados y calientitos dan la bienvenida a la imparable oleada de visitantes tanto locales como internacionales que seguirá aumentando de aquí a Marzo.
El Santuario Sierra Chincua se mantiene en su mismo sitio aumentando en población y adquiriendo ahora una belleza indescriptible por la forma en la que se concentra y forma racimos de formas increíbles.
El Santuario El Rosario ahora se ha movido unos cuantos cientos de metros al sur a otro de sus puntos tradicionales de llegada llamado “Los Horcones”, 19.5952 -100.2617, entre ganando población pero reacomodándose también, lo que cambia la impresión del sitio cada vez.
Belleza dramática ha de ocurrir día con día en adelante, en ambos Santuarios.
Monarch butterflies fly and roost at the El Rosario sanctuary in mid-January. Credit: Estela Romero
January 19, 2026
Being mid-January, a drastic drop in temperature was expected in Central México due to a polar wave entering Northern México and heading south-east.
The polar wave did not hit Central México as forecasted. Apart from a wonderful rainy evening last Friday, our chilly weekend has been splendidly sunny too!
Sierra Chincua Sanctuary is now dispersing in concentration at its site; the various heavy, wonderful clusters from last week have now dissolved, with only two remaining. The rest of the colony appears to have slightly diminished.
Local Ejidatario guides do not speak of a second separate colony anywhere around in this Sierra Chincua oyamel forest, and with no unusual mortality event having occurred, we can conclude that the colony simply keeps re-adjusting and fluctuating in population.
Winter blooming seems healthy and abundant enough to provide nectar for the hibernating colonies.
El Rosario Sanctuary has now moved a couple of hundred meters downhill, to the north-west.
While at first sight the colony seems slightly dispersed, once we come closer the very center of the colony, we notice that its population just remains in moderate movement and rearrangement.
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Siendo mediados de Enero, era esperado que se anunciara alguna caída de temperatura debido a una Onda Polar entrando al Norte de México y dirigiéndose al Sureste.
¡La Onda Polar no nos golpeó en el Centro de México como se había anunciado. Aparte de la maravillosa tarde lluviosa del Viernes, nuestro fin de semana ha sido, aunque frío, esplendorosamente soleado también!
El Santuario Sierra Chincua se ha dispersado en concentración en su mismo sitio; los varios racimos grandes que vimos la semana pasada se han disuelto quedando solamente dos de ellos. El resto de la colonia da la impresión de haberse disminuido ligeramente.
Los Guías de Ejidatarios no mencionan la existencia de una segunda colonia en el área de bosque ni tampoco ningún evento de mortalidad que hubiese ocurrido, por lo que podemos concluir que la colonia se mantiene simplemente re-acomodándose y fluctuando en población.
La floración de invierno parece suficientemente sana y abundante para proveer de néctar a las colonias hibernando.
El Santuario El Rosario se ha movido un par de cientos de metros hacia abajo y al noroeste.
Cuando a primera vista la colonia parece haberse dispersado ligeramente, una vez que uno se ubica en su centro, nos damos cuenta de que la concentración se mantiene en movimiento y re-acomodo moderado.
What may look like leaves at first is actually butterflies! When overwintering, monarchs will cluster together and cover whole trees and branches. Credit: Estela Romero
January 26, 2026
January draws to its end, and while temperatures for Canada and the United States in North America are said to be the lowest recorded within recent years, the terrible winter storm has been far from impacting central México.
A winter with only chilly temps in the early mornings and nights contrasts with sunny and slightly warm days, giving the impression that our short winter might be over soon, without bringing, up to now, signs of any real winter event – whether frost, sleet, or snow – to the mountains of the oyamel fir forests at over 10,000 feet elevation.
Population density at El Rosario Sanctuary (19.5950 -100.2619) this weekend will serve as a base reference for the coming days, when a traditional increase in numbers should occur, with February being the highlight of the season, attracting thousands of visitors and providing us with official population density numbers for this winter’s great migration.
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El mes de Enero termina y mientras las temperaturas en Canadá y los Estados Unidos en Norte America presentan las temperaturas más bajas registradas en los últimos años, la terrible tormenta invernal ha estado lejos de afectar el centro de México.
Un invierno con solamente temperaturas frías por las mañanas y las noches contrasta con los días soleados y ligeramente tibios dando la sensación de que nuestro corto invierno podría terminar pronto, sin traernos hasta ahora, señales de ningún evento verdadero de invierno ya fuera puntos de congelación, agua-nieve o nieve en puerta para nuestros bosques de Oyamel a un promedio de 3,400 msnm.
La densidad de población en el Rosario (19.5950 -100.2619) este fin de semana habrá de mantenerse como referencia para los próximos días, cuando el tradicional aumento en números habrá de ocurrir siendo Febrero el esplendor de la temporada que atraerá a miles de visitantes y que nos informará de los números oficiales en densidad de población para esta Gran Migración de Invierno.
Estela Romero is an environmental educator with Monarchs Across Georgia. Reporting from Angangueo, Michoacán, Estela Romero’s work is made possible by funding from Monarchs Across Georgia and the Monarch Butterfly Fund.
With today’s New York Times article (We Can Now Track Individual Monarch Butterflies. It’s a Revelation. 17 November 2025) and press release from Cellular Tracking Technologies (CTT) and the Cape May Point Arts & Science Center (CMPASC), we want to share more information about our participation in the Project Monarch Collaboration.
BlūMorpho Radio Tags
BlūMorpho solar-powered radio transmitters (also referred to as “tags”) provide an amazing opportunity to track the paths of individual monarch butterflies. In particular, the ultralight tags can use Bluetooth crowd-sourced location networks to increase the number of detections. Visit the CTT/CMPASC Project Monarch website to learn more about how the project started and how BlūMorpho tags work. In contrast to these radio tags, our Monarch Watch Tagging Program uses sticker tags and relies on people to observe and report or recover tags with unique letter and number codes. Both tagging approaches provide unique and complementary information about the monarch’s fall migration, as well as different ways for people to engage with monarchs. We are excited about the research questions that can be asked with the new technology and look forward to continuing to study the monarch’s fall migration with both the BlūMorpho tags and Monarch Watch sticker tags. We hope you will share our excitement!
Monarch Watch deployed a total of 30 BlūMorpho tags towards the end of September. Of the 30 monarchs that we tagged, 30% (9) have been detected in Mexico, 63% (19) in Texas, and 70% (21) in Oklahoma. Previous estimates (see Monarch Population Dynamics: Issues of scale) have suggested that 20% (or 1 out of 5) or fewer of monarchs that start the migration across the breeding range make it to the overwintering sanctuaries in central Mexico. While we do not know the origins of the wild-caught monarchs that we tagged with BlūMorpho tags in Kansas, we do know that they had many fewer miles left to fly (1370 miles) by the time we tagged them than those tagged by many of our colleagues and collaborators on this project. For example, those tagged in Long Point, Ontario, had to fly at least 1960 miles to reach the overwintering sanctuaries, while those tagged in Harrisonburg, Virginia, flew at least 1830 miles. Based on the preliminary results from this year and expected mortality during the migration, the success of the BlūMorpho tagged monarchs is very good.
Monarch Tracking Data Visualization
Using the free Project Monarch Science app (download via your device’s app store), you can view lots of information about many of the tagged individuals. You can find the monarchs tagged by Monarch Watch in the Data tab by selecting the monarch icon at the top of the screen then searching for “MW”. When you look at the map view, make sure to zoom in as far as you can so that you are not missing any monarchs.
We had some excitement on Nov. 9 when JMU004 was the first monarch to be detected at a known overwintering site (El Rosario), but MW026 was detected in the same location a couple of hours later, obscuring the view of JMU004, as you can see in the images captured from the app, below.
Monarch MW026 obscuring the view of monarch JMU004.
I mentioned in a previous blog post (Radio-tagged monarch MW001 arrives at the MBBR) that monarch movement was slow due to winds from the south. The BlūMorpho tags capture this in a way that was not possible before. Using MW026 as an example, some graphics below illustrate that point. Keep in mind that winds are reported based on the direction they are coming from. That means that North winds (those blowing north to south) help the monarchs move south when they are starting in Kansas, but South winds (those blowing south to north) make the migration more difficult.
Full tracking of monarch MW026 through 16 November 2025.
If you are looking for some monarchs to check out in the app, a good starting point might be MW026, XOKC006, NOK015, LPM093, and JMU004, which are grouped together (at least at the time I am writing this!) in the Monarch Butterfly Biosphere Reserve. There are also lots of other monarchs doing interesting and even unexpected things, so look around!
You could also check out the nine monarchs that we tagged that made it to Mexico: MW001, MW002, MW003, MW008, MW020, MW021, MW023, MW024, M026. Their tracks appear below.
Tracks of nine monarchs in Mexico, tagged and released by Monarch Watch.
Below are the tracks of all 30 monarchs that we tagged.
Tracks of 30 monarchs tagged and released by Monarch Watch.
Project Monarch Collaboration 2025
More than 25 research organizations make up the Project Monarch Collaboration this year (see logos below). Not only is this project an amazing contribution to science, but it has also been a lot of fun, in particular sharing the experience (including lots of ideas, information, questions, answers, etc.) with so many other dedicated scientists.
Logos of 2025 Project Monarch Partners.
Filed under Monarch Tagging | Comments Off on Tracking Individual Monarchs with Radio Tags as Part of the Project Monarch Collaboration
Monarch Watch is participating in the Project Monarch Collaboration to deploy BlūMorpho radio tags on monarchs during the fall migration this year. The Project Monarch Collaboration was founded through a partnership between Cellular Tracking Technologies and the Cape May Point Arts and Science Center and involves lots of conservation organizations and scientists and an amazing group effort. BlūMorpho tags are extremely lightweight, solar-powered radio tracking tags that can be attached to the thorax of monarchs.
For our part of the project, we received 30 BlūMorpho tags. On September 26th and 27th, we attached each tag to a monarch butterfly and released them. The tagged monarchs can be tracked through the Project Monarch Science app, which you can download to follow along. The monarchs that we tagged are named MW001 through MW030, and you can search for them in the app by searching for “MW” to bring up all of our tagged monarchs.
Our monarchs were slow to move due to winds out of the South. They finally reached Oklahoma on October 7 and Texas on October 21. That is really slow movement! Our first BlūMorpho tagged monarchs reached Mexico on October 29. MW001 reached the Monarch Butterfly Biosphere Reserve (MBBR) yesterday afternoon! MW001 is a male that weighed 0.6 grams when we first caught him in Lawrence, Kansas on September 25, and he had a wing length of 53mm. Several of the other ones that we tagged are close to the MBBR, including two more males and two females.
The path (1360 miles!) of monarch MW001 from Lawrence, KS to the MBBR.
A close-up view of the current location of monarch MW001.
A view of the many BlūMorpho tagged monarchs that are approaching the MBBR. Those labeled MW were released by Monarch Watch in Lawrence, Kansas, PP were released at Point Pelee in Ontario, Canada (1800 miles away!), BCA were released in coastal Alabama, JMU were released in Virgina, LPM were released at Long Point in Ontario, Canada, and XSTI, NOK, and XOKC were all released in Oklahoma.
Filed under Monarch Tagging | Comments Off on Radio-tagged monarch MW001 arrives at the MBBR
Thank you to everyone who’s been participating in our tagging program this year! This program relies on the participation of many people to tag monarchs and send their data to us, helping us study the monarch fall migration. One of our goals for this tagging season was to increase the number of “domestic” tag recoveries. “Domestic” recoveries are tagged monarchs that are observed during the fall migration in the United States, Canada, and northern Mexico. Following each migration season, we post tag recoveries on our website, and ahead of recoveries being posted next year, we want to share a story about one of these “domestic” tag recoveries. The monarch that was observed made quite the journey.
One Monarch’s Migration
On October 15, 2025, someone reported a tagged monarch south of Perryton, Texas, a female with the tag code ALNT377. After looking through our records and contacting the tagger, we discovered that this monarch had been tagged in Biddeford, Maine, on August 28. Plotting these two locations on a map (below), we can estimate that this monarch traveled close to 1,700 miles in about six weeks. We won’t ever know exactly what this butterfly’s route was, but to see the distance between Biddeford and Perryton on a map really puts into perspective how far these insects can travel during the migration.
We plotted the great circle distance between Biddeford, Maine, and Perryton, Texas, which is just shy of 1,700 miles.
When spotted in Texas, this butterfly was roosting with several others in a tree (see images below). Who knows where she is now, but hopefully she’ll make it to Mexico’s overwintering grounds. This story is a reminder of the monarchs’ incredibly long journey.
We have an important role to play if monarchs are going to continue their spectacular migration. This butterfly wouldn’t have made it to Texas without nectar plants to fuel her flight, and she wouldn’t have become a butterfly without milkweed, the host plant on which female monarchs lay their eggs and monarch caterpillars exclusively feed. For the migration to continue, we need to keep planting milkweed and nectar plants so monarchs have resources to support their life cycle and migration.
This tagged female monarch had made it all the way to Texas from her original tagging location in Maine, traveling almost 1,700 miles. This person who observed this monarch in Texas included these photos as part of their recovery report. Photo credit: M.D.
How the Tagging Program Works
Monarch Watch’s tagging program is a mark-and-recapture program. Monarch butterflies are tagged with a weatherproof sticker that has a unique letter and number code, and the location, date, and sex of the butterfly is recorded. Tagged monarchs are reported all along their migration route and recovered every year from the overwintering grounds in central Mexico, providing us important data about the monarch migration. This data has revealed new information about the timing and pace of the migration, where migrating monarchs come from, how weather can affect the migration, and more.
Once all the data has been verified and processed, we’ll post domestic tag recoveries from Canada, the United States, and northern Mexico around March 2026 and recoveries from the overwintering sites in central Mexico around April/May of 2026.
If you haven’t submitted your tagging data yet, go to our Tagging Program page and follow the instructions under the “Submitting Your Tagging Data” section to share your tagging data with us. Additionally, if you have any “domestic” recoveries of tagged monarchs this season and haven’t reported them yet, use our online form to report your recovery – and if you have any photos to go along with your observation, we’d love to see them in the report as well!
Filed under Monarch Tagging | Comments Off on A Remarkable Recovery
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