This Tiny Tracker Monitors Monarch Migration

From our collaborating partner Living on Earth, public radio’s environmental news magazine, an interview by host Steve Curwood with Dan Fagin, a journalism professor at New York University.

The amazing monarch butterfly is as beautiful as it is mysterious. Every year, monarchs take part in an epic relay, with each generation playing a different but vital role. 

Monarch butterflies that hatch in the spring and early summer live fast and die young at only two to six weeks. But those that emerge in late summer can survive six to nine months. That’s long enough to migrate thousands of miles south for the winter and start the return north the following spring to breed. 

The precise paths these brave little insects take to get from North America to their winter colonies in Mexico have long eluded scientists and butterfly enthusiasts. But thanks to new technology, our phones and other Bluetooth devices can now tell us where these tiny creatures are traveling. 

Pulitzer Prize-winner Dan Fagin is a journalism professor at New York University, where he directs the Science, Health and Environmental Reporting Program, and is writing a book about monarch butterflies. This interview has been edited for length and clarity. 

STEVE CURWOOD: Monarchs have this fascinating migration pattern. Tell me about the new way to track them.

FAGIN: Something really amazing has happened to monarch science. Monarchs are this beloved butterfly that scientists have been studying intently, really, since the 1940s. They have a lot of intriguing habits, but the most intriguing thing is this amazing migration that they do: multiple generations, thousands of miles. 

For a long time, people have been trying to understand where monarchs go and how they get there. For many, many years, the only way that they could do that was by using paper tags or sticker tags. The holy grail forever in monarch science has been to develop some kind of radio tagging, which can work for bigger animals, but to figure out a way to make a tag so small that we can actually track the entire journey of a monarch butterfly. 

Sure enough, after all these years, a startup company called Cellular Tracking Technologies based in Cape May, New Jersey, figured out a way to do it, and now we know where these monarchs are going and how they get there.

CURWOOD: What are some of the surprising places that monarch butterflies go?

FAGIN: Maybe the most amazing thing about how this technology works is that a monarch passes within a couple hundred feet of any kind of device equipped with Bluetooth, whether that person realizes it or not, if their Bluetooth is turned on, they are helping with this data collection. 

So we can now see that if a monarch is over the ocean and passes near a boat that has a cellular device turned onto Bluetooth, they will ping. And sure enough, some of these monarch tracks—which, by the way, people can see for themselves by downloading the app—pass over oceans, deserts, all kinds of unexpected places.

CURWOOD: How much does a monarch butterfly weigh and how much does this tracking device weigh? 

FAGIN: A butterfly weighs about as much as half of a raisin, so it’s very light, and the tags themselves are much lighter, a little more than 10 percent of the body weight of the monarch, which is like three uncooked grains of rice riding on half of a raisin.

CURWOOD: What are we learning about the monarchs by tracking them? 

FAGIN: A lot of things. The monarch is in trouble. Their populations are declining, especially the migratory population. They face all kinds of problems. So it’s really important to figure out what are the most popular routes that they take so we can think about how to help them in those particular places. Now we have a better idea about that, and after another few years of radio tagging, we’ll have a better idea still. 

“They have fantastic navigational abilities.”

Another thing is we can tell how affected by weather they are, because you can watch what happens to one of these monarchs when a big cold front comes by or there’s a storm. We can now see in real time that these monarchs are getting blown way off course. Now we know that weather is a very, very big deal for these guys. They’re stronger than we think, but they’re not strong enough to resist a huge storm. 

The flip side of that is they have fantastic navigational abilities.

CURWOOD: How do they navigate? How do they know where they’re going?

FAGIN: Over millions of years, they’ve evolved two different biocompasses. They need two, because one of them is sort of anchored to the sun, but that’s a problem when it’s cloudy out. So they also have another biocompass that is attuned to the Earth’s magnetic field. 

What’s especially amazing is that the sun compass actually compensates for the sun’s journey across the sky—at least as we perceive it. We’re the ones who are moving, not the sun. That could be a real problem for monarchs. If they just tracked the sun, they would constantly go off course. But this bio compass they have adjusts for this. It’s called the time-compensated sun compass, and it’s quite miraculous. A few other insects have them too.

CURWOOD: You’re telling me that monarchs can tell time, essentially.

FAGIN: They can. They adjust based on where the sun is and where south, or southwest, is—their general journey direction in the fall. And they adjust for that all day long. Even when they’re blown way off course by these storms, they can adjust and get back on track, and this new data shows us this.

CURWOOD: In the southern journey that a single generation of monarchs might make from eastern Canada all the way to Mexico, I’m guessing most of them don’t make it. How is climate disruption and loss of habitat making things harder? What’s the survival rate?

FAGIN: Some people think that less than 5 percent of the monarchs that start the journey in September actually make it through the winter and then reproduce successfully in the early spring. Some people think it might be more like 10 percent or 15 percent. These new tags will help us figure that out, once we get a nice, big, robust data set. 

But they face so many potential risks along the journey, and really at every stage of their year-long multi-generational lifecycle. Climate change is an obvious one, because climate change creates problems for them at every stage of their yearly journey. When they’re migrating in the fall, they need access to nectar plants, or they’ll never make it. They need to fortify themselves along the way, and climate change is wreaking some havoc with where and when these plants are available in the fall and also in the spring, when they’re moving north and they need nectar plants again. 

In Mexico, climate change is creating all sorts of problems for them. They have a very narrow temperature range that they are comfortable with, and that’s why they migrate in the first place. For winter, they need to find a place that’s not too cold and not too hot, and it turns out that’s a few Mexican mountaintops, typically around 10,000 or 11,000 feet high. 

As the climate gets warmer and moisture patterns change, the monarch colonies on these mountains keep moving up, and essentially they’re going to run out of mountainside. It’s going to get too warm. Just from the trips I’ve taken down there over the last 10 years, we can see the monarchs moving up the mountain and they’re running out of mountain. That’s a problem. 

There’s also the problem that things are getting much drier all along their journey, including in Mexico, and that has caused all kinds of disease problems. Beetle infestations are a really big problem on their overwintering grounds. And climate change is only one of the big issues that they face. There are other critical problems too.

CURWOOD: I imagine we use a lot of chemicals that aren’t good for insects, and that the habitat is not exactly expanding.

FAGIN: That’s definitely true. There’s a lot of research about neonicotinoid pesticides that suggest they’re a real problem for monarchs as well as other insects. 

But the biggest problem that affects them during the summertime is that monarchs coevolved with milkweed plants. They will only lay eggs on milkweeds. Their main summer breeding grounds in the upper Midwest coincide with the Corn Belt. Anybody who is familiar with farming in the Midwest can tell you that something has changed fundamentally with the way that corn and soybeans are raised over the last 25 years, and that is the rise of genetically engineered seeds that are resistant to herbicides, which means that you can use a lot more herbicide. 

Roundup, or glyphosate, is the most famous one, and that has wiped out the most important refuges of milkweeds in the upper Midwest. There’s still milkweed in the Upper Midwest, but there’s so much less than there used to be. 

CURWOOD: You’ve visited the tropical or subtropical monarch butterfly colonies. What are they like?

FAGIN: There’s really no phenomenon quite like it on Earth. You go to these very isolated locations, in Michoacán and the state of Mexico, where there have been overwintering colonies most years, and you’re already pretty high in elevation. And then you start walking even higher in these park areas and you start to see more and more monarchs. 

After another half hour, 40 minutes, depending on where you are, you’re hiking and hiking, you’re getting tired, and then all of a sudden, you just see teeming hordes of monarch butterflies circling overhead and in the fir trees, by the millions. It’s impossible to describe how many there are.

CURWOOD: Where did your fascination with monarch butterflies begin?

FAGIN: I was very proud of my last book, but it was about an emotionally difficult topic, children with cancer, and I wanted to do something different.

I was starting to realize that this concept of a human-dominated planet is even bigger than climate change itself. Climate change is just one manifestation of this bigger question of humans essentially taking control of the future of this planet. 

We’re living in uncontrolled experiments, and we don’t know how it will end. I was really interested in that. 

I had read stories about monarchs, and a neighbor was raising monarchs, and I just started to learn more. Then we decided, hey, let’s put some milkweeds on the front lawn. We waited and waited, and then monarchs showed up. It was such an enchanting, amazing thing. On a very human level, my wife and I really loved it.

“We’re living in uncontrolled experiments, and we don’t know how it will end.”

But it also got us thinking about, what exactly are we doing here? Is this a natural environment? Not really. We’re creating an environment that’s optimized for this species. 

That is a really interesting thing to think about, because our footprint is all over this planet, and there’s no going back. As an environmental journalist, this is really the central question, and that is, what are we going to do with our power? You break it, you buy it, and we own this planet. And so the question is, can we manage it in a way that meets human needs and also maximizes biodiversity? 

This is a big question that our kids and our grandkids are going to face in all sorts of different ways. As an environmental journalist, I want to encourage that conversation.