Another analysis of butterfly monitoring data shows good news for monarchs
- Andy Davis
- 12 minutes ago
- 6 min read
Hi blog readers,
As you can see from this title, I have some good news to share today about the monarch population; it's doing well. That's right, forget everything you've heard in the news, the click-bait headlines, the social media posts from people who think they've not seen as many monarchs as they used to, and any organization that wants you to donate money to them to "save the monarchs." Forget all of this noise, and listen to the hard, objective data. Today's post is about a little-known, quietly-performed, analysis of butterfly data that shows the exact opposite of all of this. I'm bringing it to everyone's attention here in my blog site because it deserves to be seen by the monarch masses.
I'm talking about a recently-completed masters thesis from a former grad student at the University of California (UC Davis), named Lauren Redosh. The completed thesis is posted online at the university's library, and a link to it is here. The title of the thesis is "Abundance of the Monarch Butterfly (Danaus plexippus) in the Eastern United States." From my read of this, it looks like Lauren had a good team of mentors, including Dr. Elizabeth Crone, who has done a lot of research on monarchs (among other butterfly species) in the west, using very sophisticated data analyses techniques. It looks like this thesis project is keeping in that same theme.
For the blog readers here, rest assured that I'm not going to get bogged down in any of the fancy (and boring) stats here, and frankly, a lot of it is beyond my simple brain too. But, given the team of scientists involved here, and my own knowledge of the dataset itself, I'm confident that the results are sound.
Let me give you the gist of the project here. As you can see from the thesis title, this project was aimed at analyzing the long-term trends in monarch abundance from a well-known butterfly monitoring project, the North American Butterfly Association's (NABA) 4th of July program. This is a monitoring project that I've blogged about in the past, and, one that I'm also very familiar with too, because I was part of another team that had also analyzed these same data. Recall, that in the NABA monitoring scheme, volunteers scour large sites across North America on specific days each summer, and count the number of butterflies (including monarchs) they see. They have been doing this for 30 years now, and, this dataset now represents the biggest and most comprehensive dataset we have on butterfly abundance in the summer.
Recall that my team had examined the counts of monarchs from all of these sites, using data from 1993 to 2018, to see if we could find evidence of long-term declines in the breeding population; we didn't. We saw that monarch counts were going down (slightly) in some places, but going up (slightly) in others, and in some, they were remaining steady. Across all sites (400+), there was no overall trend. In other words, the monarch breeding population in North America was stable, despite the observed declines at the wintering colonies. We published our study in 2022, and I blogged about it here.
So, it looks like Lauren conducted her own analysis of these same data, and, had a similar goal - to look for trends in abundance, while statistically accounting for other factors that may influence the monarch numbers, such as weather effects, landscape types, observer effects, and even glyphosate usage (in the county surrounding each site). Importantly, she only used data from sites east of the Rockies for some reason, and also did not include sites from Canada, but, she did have access to additional data that my team didn't have at the time - her analysis examined monarch counts from 1993 to 2022. It is also important to keep in mind that Lauren's statistical approach was different than what my team had done. From a statistical standpoint, neither approach is wrong, they are just different ways to achieve the same results.
I'm pasting a screenshot below of a map that was presented in the thesis, showing the location of all of the NABA sites that were examined as part of this analysis. You can see that the coverage was very comprehensive. And, it looks like the sites were broken down into 3 different regions, which were examined separately, to see if there were different abundance trends in each region.
I'm going to skip to the results here for the sake of brevity. For any data analysis nerds reading this, all of the nitty-gritty details are in the thesis.
From my read, especially of Table 4, the results showed 1) that monarch abundance was statistically higher in the "North Central" and "Northeastern" regions, and 2) that the number of monarchs counted was significantly affected by the counting effort. These were the only two factors with statistical significance. This second bit is something that was expected, and has to be accounted for in any analysis of these datasets. In contrast, there was NO statistical impact of glyphosate usage on the number of monarchs counted in any region above. There was also no effect of land use type on monarch counts (i.e. cropland vs grassland, etc.). And finally, but most importantly, there was NO change in monarch abundance over time, in ANY of the regions. In other words, there was no long-term decline in monarch abundance from these summertime counts - across nearly 30 years. Sadly, there was no graph to show from the thesis, so you'll just have to take my word (or Lauren's) on this.
Another way to think of this finding is, that the average number of summertime monarchs counted in this program is the same now as it was in the 1990s. That goes for all regions in the map above too.
So, this new analysis of the NABA data essentially showed the same thing as what my team had shown in the 2022 paper, but using different stats, a slightly different region of interest, but a longer timescale. The consistency here is what is important, because it means this statistical trend (or lack of one) in the monarch breeding population is real.
Remember, this is GOOD news. Since the monarchs are doing ok in the summer months, it also means there has been no widespread loss of monarch breeding habitat. If there were, then the monarch numbers would be declining during the summer.
Now, I know what you're thinking - how can this be, if there have been declines at the winter colonies that we've all heard so much about? The thing to keep in mind here, is that these can both be true, even if we don't fully understand why yet. It's not like we have to choose which dataset to believe. For example, we know that the declines at the wintering regions are (statistically) real. They just aren't reflected in the summer months. In fact, it is looking more and more like there are some serious problems during the fall migration, that are preventing monarchs from reaching their winter destination. This would explain the decline at the winter stage, and, this is the scientific explanation I favor. I have another blog describing this issue, and, the reasons for this.
Incidentally, after reading this thesis online, I had reached out to Lauren by email to get her thoughts to include here, but she told me she was not able to at this time. Perhaps if she does have something to share on this, I'll add it in later.
Finally, let me end with a thought about you, the blog reader, and what you should do with this information. If the results of this study (which is consistent with prior research) is surprising to you, if it completely changes what you "believed" for years, then you probably need to spend more time reading the actual science around monarchs, and not just the click-baity fluff pieces about monarchs. And, spend less time listening to your neighbor, or the random facebook person who tells you "they don't see as many monarchs as they used to."
As you can see, in the monarch world, the public narrative is not the same as what the data shows.
That's all for now.
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