Observations of straggler migrants on the Florida panhandle
Greetings blog readers,
I know, I know, it's been a while. I've been very busy with some exciting projects lately. One in particular I hope to write about next month. Stay tuned for that.
Today I'm going to tell you about a trip the family and I made to the Gulf coast of Florida during the thanksgiving break, and where we saw monarchs - lots of them! And of course, I brought a net...
Let me first tell you where this was. We stayed at a place in a town called Carrabelle, which is right on the coast, in the panhandle part of Florida. Below is a google map of the region. We chose this location for our trip not for any particular reason other than there were some nice beaches listed there. The beaches turned out to be great, and the kids had a great time.
But what was also interesting was all of the monarchs we saw. The temperature was well into the 60s and 70s during our stay and there were hundreds of monarchs flying around in this town. It wasn't like a mass-migration, or a spectacular cloud of butterflies, but more like a low-key, leisurely trickle that lasted all day. There would be a monarch floating by once every 5 minutes or so, or we would see one nectaring on roadside wildflowers every 100 meters as we drove, etc. We would see them when we stopped for gas, or they would fly over the beach. To the untrained eye, this might have even gone unnoticed. But once we started seeing these, we sort of kept a running tally. There were easily hundreds during any given day. It reminded us very much like a small town in Mexico (Angangueo, maybe) during the winter, where you could be sitting at a cafe, sipping your coffee, and watch the monarchs fly around the square. You'd see so many, so often, you kind of stop keeping track. For the average butterfly-lover, this would be a great vacation spot.
Naturally, we wondered what they were all doing there. Were these migrants? Were they residents? After some thought, and examining some of them, we settled on the former, for reasons explained below.
Before going too far, I'll point out that years ago, Fred Urquhart had made some observations of migrating monarchs in this region too. In the Journal of the Lepidopterists' Society, Vol 30, Issue 1 (1976), he reports that he and his wife had been monitoring monarchs and other butterflies in this same spot from 1970-1975 (before they knew where the Mexican overwintering site was). They report that the monarchs travel through here, heading west, by the 'thousands', every year, peaking around the end of October. It was a very brief report, though, and I'm not sure they had carefully examined these specimens.
One thing I noticed was that the monarchs I saw never seemed to be in a hurry to get anywhere. The ones I did see flying were more or less heading west, but it was a slow, gliding, flight, with occasional dips to check out a flower. There were a lot of monarchs nectaring on wildflowers - in old fields and in roadside ditches. These were easily captured with a net, which tells me also that they were not in any hurry.
We did not see any milkweed at all during our trip - no tropical milkweed, especially. This could be because of the recent hurricane that came through this region. Hurricane Michael plowed through here about a month ago, and it caused a lot of damage. There were a lot of ripped up cottages and beach houses, and if there had been any gardens before, they were gone when we got there. So that means that none of these monarchs were produced locally - important. There were far too many of them anyway to have been reared in homeowner gardens.
So of course I had brought a net. I didn't have a lot of time to collect, but I did stop for about a half hour at one old field that was about 1 acre in size. I caught 20 monarchs in the half hour. Pretty good for not really trying. I noticed a couple of things about them. First, they all appeared to have the migrant wing coloration - brick-red, that is, but these were also pretty faded too. That tells me they were a couple of months old. So together, this means these butterflies had been traveling for a while now. There was also some wing tatter on some of them. But most importantly, they were all on the thin side. Scroll up and take a look at the picture above again, and note the abdomen of that monarch I caught. You probably didn't notice it at first, but it is thin, at least for a migrant. During the fall migration, monarchs tend to accumulate fat reserves (in their abdomens) as they travel southward to Mexico. Some of Lincoln's early work had demonstrated that by the time they reach Texas, monarchs can have as much as 50% of their weight in fat reserves. I didn't weigh these monarchs, but I would estimate less than 20% of their weight was lipids. They weren't starving, by any stretch, but they just didn't look like they had any reserves built up.
Also, the sex ratio of the ones I caught was heavily male-biased - only 25% of these were females, which is consistent with other reports from migrant collections.
And of course we brought them back to the lab at UGA to test them for OE. Of the 20 monarchs, 7 of them were heavily infected, and a few others had some scattered spores (perhaps transfer from my net?). It's probably safe to assume that the monarchs I caught at this one field are a reasonable representation of this cohort. Basically, 35% of them were infected with OE. That's a lot. For the eastern migratory cohort, up to 20% of them start the migration with OE infections, but most of these don't make it. By the time they reach Mexico, only 5% or fewer have OE infections. And recall there was no tropical milkweed in sight, at this field, or otherwise in this town.
We did measure their wing sizes too. The average wing length for all 20 was 52.4 mm. That's within the ballpark for a typical migrant, though a little on the small side.
The other thing to consider here is the timing. It was the end of November. If these monarchs were trying to reach the Mexican overwintering sites, and by following the coastline, they still have a long, long way to go. At the rate they were traveling, they likely wouldn't make it until late January, if at all. By now, the main migratory cohort either has already arrived, or is just now arriving at the site, so if these Florida monarchs really are heading to Mexico, they are way behind schedule, which is why I called them stragglers. When Fred Urquhart made his observations years ago, he didn't know where these monarchs were traveling to, so there would have been no way for him to know if they were "late."
So let's sum up these observations here.
- Based on their wing characteristics, I'm pretty sure these were migrants, and that they had been traveling for a while.
- Related to the first point, they probably were not locally-produced, because there was no milkweed
- They were heavily male-biased, consistent with migrant collections
- They are well behind schedule in terms of the migration.
- They did not have any fat reserves built up.
- A large proportion of them were infected with OE
Given all of these observations, my educated guess is that these Panhandle monarchs are unsuccessful migrants, for various reasons. Either they fell behind because of bad weather (just bad luck), or they were incapable of successfully completing the (entire) migration to begin with, such as the OE-infected ones would be. We have good evidence that OE reduces flight ability in monarchs. We've always assumed that the drop in OE prevalence along the way is because those infected monarchs die along the way, but perhaps they don't necessarily die, but just end up in places like this - coastal towns where it doesn't freeze, and where they can eke out an existence and subsist off the local wildflowers. Or they simply wander westward along the coastline of the gulf throughout the winter, somehow following some innate sense of direction.
If this is true - that OE-infections cause monarchs to build up at southern coastal locations, it may add a wrinkle to our current understanding of how tropical milkweed influences OE prevalence. Whenever we (or someone) samples monarchs at coastal towns where there is tropical milkweed, they always find a high prevalence of OE (like 50-100% infections). This is usually attributed to the fact that tropical milkweed leaves remain in leaf throughout the winter, thereby becoming covered in OE spores. However, my anecdotal observations here suggest that OE-infected monarchs are being drawn to (or simply wind up at) these coastal locations in the first place, because they dropped out of the migration. Thus, at southern locations, tropical milkweed may simply act to lure already-infected monarchs in. This in fact, was the same conclusion reached by Dr. Dara Satterfield and colleagues, in their recent paper in Ecology Letters, which I blogged about a while back.
Finally, let me end with this thought - I know that the local area has a butterfly festival every year in October (http://www.visitwakulla.com/Blog/The-2018-Monarch-Butterfly-Festival), in "celebration" of the monarch migration through this area. If the monarchs that pass through here in October are anything like the ones I examined in November, I wonder if this really is something to celebrate? It would be like holding a party for the marathon runners who did not make it to the finish line.
On the other hand, maybe these individuals are more in need of cheering than are the ones who do reach the finish line!
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