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  • Andy Davis

That time a student tested the flight ability of captive-reared monarchs...

(picture above was taken by my brother in Nova Scotia, Canada earlier this summer!)

Hello everyone,

I have something very interesting to tell you about today, which is a bit of a memory, a bit of science, and a whole lot of anguish for anyone who still believes that they are helping by rearing monarchs in captivity. Yes, today I will wade back into this captive-rearing quagmire, and unleash the wrath of the "I'm helping because it feels good" crowd. As you can see already, it is hard to write this post without the attitude, which I've gotten after many years of trying (but mostly failing) to convey the hard facts to people who insist on doing this to "save" the monarchs. Plus, now that the IUCN has declared that all monarchs will be extinct by next tuesday, I'm afraid there will be no end to this madness.

OK, now that my stance is clear, let's get to it.

Today I'm going to tell you about the time a graduate student here at UGA conducted a study just a few years ago that examined how nectar quality affects monarch flight ability. Her name was Ashley Ballew, and she was a fantastic student. This project was for her Masters degree, which she successfully defended. She has since moved on, but unfortunately, the project has not yet been published in a scientific journal. However, her entire thesis is completely accessible online by going to the UGA library site, and I'll provide a link here.

If you download the thesis, or just look at the abstract, you can see that the project was never intended to be about captive-rearing, but more about the importance of nectar to migrating monarchs. Given the many issues monarchs are facing these days with their fall migration, she wanted to test how reductions in nectar will affect their actual flight. She did do this, but the project ended up being more about captive-rearing, and how that affects their flight. That's because in order to do this experiment, she used two collections of monarchs that had been reared in captivity in the UGA lab, as well as some that had been caught in the wild. Thus, she ended up doing some comparisons of these groups.

Let me briefly tell you about the experiment, and here, I'm only going to focus on the first of two experiments that she ran. You can check out the thesis itself to learn about the other one. For this experiment, she had three groups of monarchs. The first were monarchs that had been reared in a summer-like environment in the lab, with ample sunlight and warm temperatures. The second group had been reared in fall-like conditions, with declining daylengths, and low temperatures. For both groups, monarchs were reared singly in plastic containers filled with milkweed, and the containers were changed/cleaned daily, using sterile procedures. Since this project was done during the fall, when migrating monarchs were flying through campus, she also collected wild monarchs from local flower gardens. You can see more details of these methods in the thesis itself.

After the monarchs had either eclosed (reared), or been captured (wild), she kept them in the lab in glassene envelopes for the next 12 days. Every other day, she brought them out and fed them a solution of honey water. We have a system for feeding the monarchs in precise doses in the lab, and it may look a little strange, but it works well. A picture of the setup is below. Basically, each monarch is placed on its side on a tray, and in front of a mini trough, that we put the honey water in. We use small weights to hold them in place. Once the monarchs taste the food with their proboscis, they literally just lay there, sucking until they've had enough. It looks weird, but it is harmless, and we've been using these same trays for 20 years now!

For Ashely's experiment, she actually controlled how much food each monarch received by timing their feeding. For some monarchs, she gave them 5 minutes to feed, and for others, she gave them 10 minutes. Over the 12 day period then, you can see that some monarchs were well-fed, and some weren't - this was to simulate what happens if monarchs can't find good nectar during the migration. She also had two honey-water treatments, including a 30% honey solution (to simulate good nectar), and a 10% solution (not so good).

After the 12 days of feeding, she then began testing how well each monarch flew, using a device we have in the lab, that is basically the equivalent of a butterfly treadmill. We call it a "flight mill." I've talked about this device before in this blog, but briefly, the monarch is attached (using non-toxic glue) to a rod, which spins on a pivot. As the monarch flaps, it pulls the rod around in circles. We have an electronic monitoring system for tracking how fast the monarchs fly and how long. I'll put a schematic below. This may also look a little odd, but it works great for measuring flight ability in monarchs, and we've been using this thing for years, and for many projects. Monarchs do quite well on this thing - sometimes they fly for hours without stopping!

OK, so over the next few weeks, Ashley put each monarch on this device to see how they flew. She recorded each monarch's overall flight speed, their total distance flown, and another interesting measurement called "flight power". This is an index of how strong the flight was, that is derived from both the speed and distance. As you can guess, high numbers here mean the monarch flew very strongly, and low numbers mean the flight was lame! Remember, she had 4 different feeding treatments (high food, low food, high quality, low quality), as well as three different sets of monarchs (reared in summer conditions, reared in fall conditions, and wild migrants).

Next, I'll put a graph that shows the flight speeds of each group, which is copied directly from the thesis. Each dot here is the average of a group of monarchs (see thesis for sample sizes), and are grouped by the feeding treatments (food quantity, or food quality).

As you can see, regardless of the feeding treatment, monarchs reared in fall conditions (middle panel) flew faster than those reared in summer conditions (left panel), which was mostly expected, because we expected the fall conditions to cause monarchs to develop into the migratory "super-generation" monarchs which are good fliers. But importantly, all wild monarchs on the far right flew faster than both groups of reared monarchs, even those who we thought were the super-generation. In fact, it really didn't matter what the feeding treatment was - wild monarchs were simply better.

Next, I'll paste the graph showing the index of flight power, which is an even more powerful result (see what I did there?):

Once again, the feeding treatments were not as important as the differences between wild and reared monarchs. Don't worry too much about the numbers in the Y axis here, it is simply an index where higher is better, and lower is worse. Clearly, the wild monarchs had greater flight power than both groups of reared monarchs. This finding is consistent with the prior study that showed how reared monarchs were weaker than wild ones (link here for the blog summary of that one).

There were some other findings from this experiment that I won't get into here for the sake of brevity, but suffice it to say, this experiment very clearly showed that monarchs reared in captivity, even when given the right environmental cues, are not as good (at flying) as wild migratory monarchs are, even though this wasn't the main goal of the experiment.

OK, so why is this? Why are wild monarchs better at everything? I've touched on this before when this topic comes up, but in a nutshell, it probably has little to do with the food, or even the milkweed the caterpillars ate, or any one thing from the rearing environment. It is most likely related to the fact that captive-rearing bypasses natural selection. In the wild, only a small handful of caterpillars ever reach it to the butterfly stage, which is the way nature designed this species (plus every other insect). So the ones who do reach it to the adult stage are the ones that are the biggest and strongest, and smartest. Conversely when you rear monarchs in captivity, there are no predators, lots of food, etc., and every monarch reaches maturity, even the wimps that mother nature never intended to survive. Yes, there are also some that are large and maybe even have decent flying ability, but they are mixed in with the wimps.

Let's bring this home now and talk about what is happening now. Currently, we have a situation, both on the west coast and east coast, where the fall migration of monarchs is hurting. Fewer monarchs are reaching their winter destinations, despite having very robust breeding populations. So far, there are a variety of potential explanations for this, including climate change, lack of nectar resources, increases in the OE parasite, and car strikes during the trip. Some of these issues are being investigated now by researchers. But, there is one other thing that no one is considering - maybe the hundreds of thousands of captive-reared monarchs being released every year is watering down the population, making the monarchs themselves less able to migrate successfully.

This is a scary thought and I hope I'm wrong.

I'm going to dispense with the obvious plea that should be coming next (for people to limit or refrain altogether from bringing in eggs or larvae to rear, because the science shows it is bad for the population), because at this point, the people doing this have stopped listening to the science.

OK, I'm going to leave it here for you to ponder. If you want to know more about the project in question, please do read the thesis - it was an immense amount of work, and we at UGA were very proud of Ashley's work. Hopefully, this will make it to publication in the years to come.


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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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