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  • Andy Davis

Summarizing the latest tech in the quest to track monarch movements

Hello readers,

It's fall! You can guess what that means for monarchs - they are on the move. Whether you are watching the progress of the fall migration online, or if you have seen waves of monarchs in person, we are all tuned in to the movements of monarchs right now. Personally, whenever the fall comes around, I always begin thinking about the latest advancements in monarch-tracking technology. Today I thought that I would write these thoughts down (see what I did there?), and also provide a bit of a summary of the various ways scientists are working to track the monarch. Some of these approaches are better than others, and I'll describe these pros and cons as well. So strap in and get ready to hear about some nerdy tech, directly from a tech nerd!

To start with, let me talk a little about the simplest form of "tracking" monarchs that we have, and that everyone already knows about, which is tagging. For those who have been living under a rock for the past 5 decades, this is where a numbered sticker is placed on a monarch's wing, and the monarch is released to go where it pleases. Later, hopefully that same monarch is spotted, captured, or found dead, and then the sticker number is reported. Then, we can draw a simple line on a map from the location of the release to the location of the recovery.

This approach was famously used to help find the location of the overwintering sites in Mexico back in the 60s and 70s, and it still has many uses today. However to be honest, this approach is woefully antiquated. Drawing a line from two points on a map does not really allow us scientists to "track" their migration. It allows us to find their destination for sure. But here's the thing - we already know their destination! And, this approach also falls short of providing information on the relative migration success rates per year, as was pointed out in a recent critical paper (link here).

In short then, we really really need to find a new way of actually tracking individual movements of monarchs. We need to know where they go throughout the entire fall migration flyway. We need to know how long they stop at each place. We need to know which migration habitats they steer towards, and which do they avoid, which can only be gleaned by following the full tracks of individual monarchs on a map. This need is so great that in 2017 the Monarch Butterfly Fund created a cash prize award of $50,000 to the first group that successfully develops such a tracking system! To my knowledge, this award has not been given yet, but we are getting close.

UPDATE (10/13/21) - I was just informed by Don Davis that the Monarch Butterfly Fund has awarded a smaller amount to one of the groups I'll mention below, because of the potential of their system! Read further...

Before getting into the monarch tracking tech, let me briefly point out how this whole scenario with monarchs compares with the science around bird migration. For those that aren't aware, I'm the Editor-in-Chief of a scientific journal devoted to animal migration (link here for the journal), and so I've been watching how the scientific approaches have been evolving to track other critters. In a nutshell, we are living in the golden age of animal tracking right now, thanks to recent advances in tracking tech! For animals such as songbirds, we now have tiny devices that can be placed on a bird, which will record exactly where that bird goes, anywhere in the world, and for over a year! The only drawback is that the data is stored on the device, so to access this information, the bird needs to be caught again. Sometimes this is hard to do for a bird that travels the world.

Here is an example from a paper in my journal, of such a device (called a geolocator) that was used to track the migrations of Cerulean warblers. It wraps around the bird's legs like a backpack. The map on the right shows the migration track obtained of one bird as it flew to its winter destination in the fall (light blue line), and then back to its summer breeding ground (purple line) in the spring. The tracks allow us to see exactly where the birds travelled to get to the destination, and how long they stopped at each place. Here is a link to the full paper if anyone is interested.

There are other devices used to track birds, and in general, the larger the animal, the larger and more sophisticated the device can be. From what I've seen in the bird migration world, researchers generally want to have a long-lasting device, but, this means it needs to have some form of power. Batteries can be used, but these are heavy. Normally, the rule of thumb is that any device used should weigh no more than 5% of the bird's weight. Solar powered devices are options for some larger animals, like storks, and so these can run indefinitely. Also, researchers need to access the data, and they would rather not have to re-catch the animal to do it. In fact, there is even a brand new tracking system that uses a special receiver on the international space station (!) that tracks animals in real-time, and beams the data directly to a researcher's laptop! Finally, the optimal device should in no way compromise the flight or movement of the animal.

OK, so let me get back to the monarchs, and here, I'll provide a list of the scientific groups and the devices/approaches being used right now. Some of these groups I've actually talked to to learn more about their system, and for some of these, I'm just going off of what I read from their papers, or other online information.

First up, I am aware of at least one group that has been using old-fashioned "radio-tracking" devices to follow breeding monarchs in Iowa. This work is from the lab of Jim Aldeman at the University of Memphis. A phd student from this lab recently published a paper describing this approach and their initial findings (link here). I'll put a picture of the device below, taken from the paper.

From reading the paper, it sounds like this device is glued to the monarch, and it has a long antenna. The device itself weighs 200mg, which is absolutely horrific. I'll come back to this. But, the monarchs can fly short distances with this thing attached, and, the researchers could successfully follow the monarchs as they moved around the fields in Iowa - remember these were breeding monarchs, and they weren't really traveling that far. Apparently, the researchers simply wanted to know where they go during the summer, i.e. which fields, habitats, etc. do they visit. This tech is a little on the old-fashioned side. Scientists have been using this approach to track wildlife (birds, bats, mammals) for decades. The device emits a unique radio signal, and a scientist has a receiver antennae and you walk around listening for the tagged animal on your receiver box. You can pinpoint which bush or tree the animal is in by walking around and triangulating the signal. I've done this in years past, and it can be frustrating to lose track of your animal, because then you have to randomly walk around until you hear it again. But, with many hours of walking, listening and recording, one can eventually map out where the animals are going. The benefit of this approach is that you don't have to recapture the animal to download any data.

Next up is a system that is being employed by the lab of Ryan Norris at the University of Guelph in Canada. They have been using something called the MOTUS network to track monarchs, as well as birds. This is a network of receiving towers that are established around the eastern seaboard that continuously "listen" for the radio signal of any animal that comes near and that is carrying one of the special motus devices. In the past 5 years, this lab has published two papers that describe projects tracking monarchs with this system. One of them went viral because they had used this approach to try to prove that captive -reared monarchs could orient properly during migration. Below is a picture from one of their press releases.

Once again, this device is glued to the underside of a monarch, and it has a long antenna. This device also weighs 200mg, which again is terrible. The reason I keep saying this is because the average migrating monarch weights 500mg. That means these butterflies are effectively carrying a device that weighs nearly half their body weight. For the Iowa breeding study above, I think this is acceptable, since summer monarchs typically don't fly very far and can rest often. But, here, the Guelph lab is trying to track migrating monarchs. As you can tell, I have some reservations about this system being used for this purpose. It does work great for tracking birds and bats, but I think the jury is still out on its use for insects, at least with the size of the current devices. On the positive side, this approach allows researchers to track the movements of monarchs (or birds, etc) without having to recapture the animal, since the towers simply record when each animal flies by.

Last up is a system that I think has the most promise, and, it sounds like the MBF is in agreement - this lab was awarded a small grant to help develop this system. The lab of Dr. André Green at the University of Michigan has been developing a super-tiny computer chip device, called the Michigan Micro Mote (M3). This device weighs 50 mg (about 10% of the mass of a typical monarch), and it gets glued to the upperside of a monarch, as shown below.

There have not yet been any formal papers written on this device, but I did talk with André about it last year. Also, there is a university press release to read about it here. Apparently, this chip can record daylight and temperature on a daily basis, and I think other info too. Apparently, from just knowing these things, the approximate location of the butterfly can be estimated. But I believe this also requires knowing the daylength and temperature from around the country, which is why their lab has been asking people to work with them to set up environmental monitoring boxes in their backyards.

Now here's the fun part about this tracking system - each chip stores the data internally, so to access it, the researchers are working on a remote "receiver" apparatus that they will place within the winter colonies in Mexico. Apparently, the receiver will remotely link with any nearby chip, and download the data! I think the plan is to systematically move the receiver around the colonies so it can connect with as many chips as possible. Very cool. And obviously, the weight of the device seems much more appropriate here.

OK, so by my knowledge of the science so far, these are the only electronic tracking systems being employed right now for monarchs (and I'm purposely not including the science around chemical tissue analysis). Each has some advantages and disadvantages, but so far, I don't think any of these rival what we have right now for tracking bird migration. Ideally, the perfect device would employ all of the advantageous properties of those listed above, such as long-term life of the device, being able to remotely pull the data (i.e. not have to capture the butterfly again), and not impede the flight of the butterfly, of course.

Maybe if a tech company is reading this, they should be taking notes! In fact, if this post inspires the winning design, does that mean I get some of that prize money?

Till next time.


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The science of monarch butterflies

A blog about monarchs, written by a monarch scientist, for people who love monarchs

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