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  • Andy Davis

While we were all in lockdown last year, two new winter colonies were discovered

Hello readers,

I have some very exciting news to share, as you can see from this blog title. And really, it is not even "new" news. Last year, a scientific paper was published on monarchs which did not make any headlines, or create any buzz in the monarch circles, and, I had not even seen it myself. It came across my desk only earlier this year, and I was astounded at what I read. And, I was equally astounded that I had not heard about this earlier from other monarch scientists, given the ramifications of this discovery. I suspect that the reason this paper was not noticed was because the entire world was in the grips of covid, and/or lockdowns last year, and I guess we all had bigger fish to fry. Anyway, today I'm going to tell you about this new study, and, I'll fill you in on my conversation with the authors of the study too. Be warned, your thinking on the monarch winter colony measurements will forever be changed after hearing about this - mine has.

Let's get the basics out of the way - the paper was published in the scientific journal, Insects, and it is free to download - here is the link: The authors of the paper are researchers from two official organizations in Mexico (but not the WWF): the "National Center of Interdisciplinary Research on Conservation and Enhancement of Forest Ecosystems" and the "National Institute for Forestry, Agriculture and Livestock Research." Their names are Ramiro Pérez-Miranda, Víctor Javier Arriola-Padilla and Martín Enrique Romero-Sanchez. From a simple google search, the last author, Martin, is a scientist who studies forests using remote sensing (such as satellite images). This is important to know going forward.

I actually had a zoom conversation with two of the authors recently. I had gotten in touch with them to hear more about this discovery first-hand. Here is a screenshot of us! Wonderful people.

So my synopsis of this paper, and my conversation with the authors, goes like this. There are over a dozen or so "known" monarch winter colonies in central Mexico, most of which are located within the protected area of the Monarch Butterfly Biosphere Reserve. In the last 10 years or so, there have been scattered anecdotal reports from local peoples about "other" colonies located outside this region. I've occasionally heard rumors about these other colonies over the years, but it was always just that, and it was always difficult to find hard evidence. Maybe Martin felt the same way, because a number of years ago, he and his colleagues set about trying to map out where other colonies "could" be in Mexico, using remote sensing tools and satellite images.

Basically, these researchers took what is known about the known winter colonies, like the elevation, temperature, tree species, moisture, etc., and then extrapolated this to map out (on a computer) where there might be other locations outside of the MBBR with these same conditions. I'm really paraphrasing here, based on what Martin told me, and I probably oversimplified this. Anyway, this remote analysis showed them where there "might" be other locations. Using this information, they then set out to visit some of these locations in the winters of 2013, 2016 and 2017. And bingo! There were indeed monarch colonies at two of the sites they visited. This new paper is thus a report of what they found at these two sites. The two new sites were called "LaJoya" and "Tlachanon."

In the paper, they state that "The locations of the La Joya and Tlachanon monarch butterfly colonies were in the municipalities of Ecatzingo and Atlautla in Mexico State, respectively, approximately 5 km from the foothills of the Popocatepetl volcano and around 165 km from the MBBR." There is a detailed map given in the paper, though don't expect to visit these, as I'll explain below. I'll add a picture here taken from the paper, which shows the forest and colony at LaJoya.

Note the condition of the trees - these are tall, healthy Oyamel fir trees! In the paper, they describe how they measured the size and density of trees in each colony. These measurements showed that the forests around each colony were very healthy. There was no logging anywhere nearby either. Martin and Ramiro told me that these site were VERY remote; there were no roads leading to them, and they had to hike for two hours to get there. Also, these two sites were much higher in elevation than are those in the MBBR. So I doubt these sites would even see much foot traffic by tourists. Maybe that's a good thing? See prior blogs on that here and here.

OK, so now the other important part - how big were these colonies? Well, not that big actually, compared to those in the MBBR. The estimated area occupied by butterflies in La Joya was about 0.076 ha; in Tlachanon, it was about 0.088 ha. For comparison, sizes of the larger, known, colonies are typically 1-2 hectares or more. Based on prior work showing that there are about 21 million monarchs/ha, this means that there are only about 1.60 and 1.86 million monarchs in each of these new colonies. This sounds weird when I write it - only 3.5 million monarchs!

However, I did ask Martin if he thought that these new sites were large enough to hold additional monarchs, and he said, "oh yes, very much so." What I was wondering was if it is possible that these sites could hold more in the future. In other words, since the researchers only visited each site in one year, we don't really know if these colonies have always been small, or if they are currently growing. If the second scenario is the case, then it is good to know that these sites exist, where there is really good forest quality around them. In fact, since these sites are higher in elevation than the MBBR colonies, it is entirely possible that they would become more important in the future - Martin's other research on forest quality in Mexico has shown that climate change will push wintering monarchs into higher and higher elevations in the future.

To me, the actual size of these new colonies is not as important as is what this discovery means for our understanding of the winter population. As everyone in the entire world knows by now, the size of the monarch winter colonies in Mexico has been declining over the last two decades, based on data provided by WWF Mexico, who does the annual monitoring. Their people go out each winter and measure the area of each of the known colonies, and then add up all of the colony areas to create a single number to denote the overall size of the "winter population." The long-term decline in these "population" numbers is really the main factor behind the push to list the monarchs on the endangered species list. Buuut...this long-term trend has always had one giant freaking assumption along with it - we have always assumed that we have been counting ALL of the monarch colonies in Mexico! What if we haven't been all along? I've wondered about this for a while myself, especially since discovering that the summer population numbers are showing no downward trend (see prior blog). And, now I'm REALLY wondering!

Think about it here for a sec and you'll see what I mean - I have always wondered what if there are other winter colonies in Mexico that have never been counted? What if there are places where there are no roads leading to them, or people living nearby, to tell us if there are butterflies there. And, what if, over time, the monarchs at the MBBR colonies have been gradually shifting their locations to go to these unseen sites? This would give the illusion of a decline at the known sites, while really, the total number of monarchs wintering in Mexico has not really changed.

This new discovery makes it sound like this is possible, and, it is really making me question the official winter colony "population" count. This is what I was referring to at the top of the blog when I said your thinking will change too.

That's not all. In my conversation with Martin and Ramiro, I asked them about their other satellite mapping efforts. I asked, how many other potential sites did they think there could be in Mexico that had these same conditions? Their answer - maybe a hundred. Mic drop.

I'm going to leave it here, and let you draw your own conclusions, and hopefully, read the original paper yourself. As you can tell, I'm flabbergasted by this "new" discovery, and I suspect that other people will be too. So, for my blog readers, share this post with others in the monarch community, and make sure that the word gets out.


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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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