• Andy Davis

Here is a simple way to determine how monarchs are doing, compared to other butterflies



Hello everyone,


Welcome back already! This post comes right at the heels of the study just published by myself and my colleagues where we determined that the summer monarch population in North America is not actually declining, and has even been slightly increasing over time. If you have not read the prior blog describing that study, you should do so, because it bears directly on this new post. As expected, that study drew some raised eyebrows from people, because that conclusion is directly opposite of what you have been hearing for years about monarchs - that they are in bad shape. Well, get ready to be surprised, yet again. Today I'm going to show you how you yourself can run a simple test at your computer or smartphone, where you can see how monarchs are faring compared to every other butterfly in North America.


One simple measure of an insect population's health is its breeding range. For example, the rusty-patched bumble bee is listed as endangered in the United States, largely because of declines in its breeding range - it used to be seen regularly throughout the eastern U.S. and Canada, but now it is only seen in 13 states or so. Anyway, a shrinking breeding range is always a cause for concern. So for that reason, it would be very useful to know how the monarch breeding range stacks up to other butterflies right now, and this is something that you yourself can double-check on your computer, by doing what I did. You can do this with the online platform, iNaturalist.org. If you haven't seen this yet, you should. This is a website where anyone with a cell phone can submit photos or sightings of any plant or animal, and the platform logs the sighting along with a point on a map. Then, other users can scroll through the different species and see how many sightings there were, the dates of the sightings, or look at their range maps. Importantly, iNaturalist has only been around for the last 10 years or so, so that means the range maps are current.


Anyway, for the purposes of this blog post I asked iNaturalist to give me all sightings of monarchs in the United States, and I took a screenshot of the result, below. Keep in mind this is a compilation of all sightings from the past 10 years. Yes, I know there are monarchs in Canada, but I focused only on the U.S. here just to keep things simple.



Next, I asked iNaturalist to give me the sightings for a whole bunch of other butterflies for comparison, and here, I chose the 60 most common butterfly species in the country (more on this later). I took screenshots of each map generated here too, also for the purposes of this blog. Again, each map represented all sightings from 10 years, and these are a good proxy for the overall breeding range of each species (even though it probably changes somewhat from year to year).


Then, I did some fancy computer-based image analysis of these screenshots. This is not necessarily something that you can do from home, but it was more for my own curiosity. In each of the maps, I had my computer identify the amount of area covered by the red squares, as in the picture above. Remember that each square represents the location where a monarch was seen in the past ten years. These squares are drawn by the iNaturalist program and are mostly overly-sized for the sighting, but importantly, the program used the same sized squares for each butterfly I checked, since I used the same magnification for each map. So in the end, I was able to generate an "estimated" breeding range size for each butterfly species (kilometers squared), including monarchs. Then, I graphed all of the 60 estimates together, to see how the monarch compares. I think you'll be shocked when you see it. You should be able to click this graph to make it bigger.


Crazy right? If you don't believe this graph, how about the next image, which is a compilation of breeding range screenshots of the top 20 butterfly species from the graph above. Again, you should be able to click on this and make it bigger. Look specifically at the red dots on these maps. Or, feel free to generate your own maps. Remember, each of THESE maps below are also compilations of sightings of the species in question, from the last ten years. So it is the same comparison to monarchs.



That's right, by looking at either these visual maps, or the graph above, it is clear that the monarch butterfly currently has one of, if not THE, largest breeding range of any butterfly species in North America. This isn't data from any study or paper, but simply real-time information drawn from iNaturalist sightings. You can check this for yourself too.


Speaking of data, let me also tell you about how I know what the most common butterfly species are. My colleague, Mike Crossley has access to the complete dataset from the North American Butterfly Association. As I explained in the prior post, this group of volunteers sets out each summer at selected sites across the country, and they survey all butterflies they see. Mike has been studying these data, and in one of his earlier papers he published these counts in the supplemental file. I believe you can access this for yourself, since the supplemental file is free to download. Anyway, these data show that of the 450 or so butterfly species in the list, monarchs are seen in the most sites across the country (403 sites). No other butterfly species is seen in as many sites.


So yes, we can confidently say that monarchs are indeed highly abundant right now, and they have an absolutely enormous breeding range compared to all other butterflies in the United States. And, I didn't even get into the breeding range in Canada, which according to recent research, shows signs of expanding (see my blog on that here).


In other words, right now, monarchs are probably the most abundant butterfly in North America.


Take this information as you wish.



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Direct link to this blog entry:

https://www.monarchscience.org/single-post/here-is-a-simple-way-to-determine-how-monarchs-are-doing-compared-to-other-butterflies

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The science of monarch butterflies

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