- Andy Davis
A summary of the monarch observations made by volunteers of the North American Butterfly Association
Hello blog readers,
It is summer, and that means it is time for gardening, butterfly-watching, and participating in your favorite butterfly citizen science programs! Today I'm going to spend some time talking about some of the monarch-related data gathered by volunteers from the North American Butterfly Association (NABA). This is a program where everyday people get together and spend 1-2 days each summer looking for butterflies at specific places around the U.S. and Canada. I've talked about this project before in this blog, because its data are so important; this program has been operating since the 1990s, and each year it grows. That means these fine folks have generated an enormous amount of observational data, which scientists like me can use to study butterfly populations over time. And, my colleagues and I have done just that recently. Earlier this summer, my team and I published a study that examined monarch observations from these NABA data, in order to determine how the breeding population is doing in North America. See the prior blog post about that. Hint, they are not endangered!
In many of the ensuing conversations that have been had since that study, I got the sense that there are a lot of folks out there who still don't really know much about this citizen science project, or what their volunteers have been seeing. So, since I have a copy of the raw data leftover from the aforementioned study, I sat down at my computer just now and made a few graphs and tables to share, which should give a snapshot of what these data show, at least for monarchs (which are the only butterfly we care about, right?). Hopefully then, this post will be useful to people want to know how monarchs are doing.
Anyway, let me get everyone on the same page here first, by quickly describing how the surveys work. In a nutshell, each survey group is assigned a large area to cover - a circle drawn on a map with a diameter of 15 miles, as shown below. This is a picture of one circle in the middle of Kansas. The circles are designed to encompass a wide range of habitats and landscapes, so as to be able to see as many different butterfly species as possible.
There can be as many observers as possible, but usually there is one "compiler" who enters all of the observations. The volunteers then traverse as much of the circle as possible in 2 days, counting every butterfly they see. They can do this by car or by foot, just as long as they try to visit as much of the circle as possible. In the end, they report the number of butterflies they saw, plus the number of people looking, and the number of hours spent looking.
Actually, just as I was writing this, I saw a Facebook post about a very recent NABA survey effort, organized by my friends at the Coastal Virginia Wildlife Observatory, a place where I worked decades ago! I'll add the picture from that post below, plus the text of the Facebook post.
August 4, 2022 - "Twenty-five butterfly enthusiasts gathered at the Eastern Shore of VA National Wildlife Refuge on July 31 to count butterflies and skippers in a circle of 15 miles diameter. This count is sanctioned by the North American Butterfly Association (NABA). Five teams spread out from the tip of the shore to north of Oyster and tallied 42 species — 27 butterflies and 15 skippers. This was the 24th annual butterfly count for this area. The most numerous species were Spicebush Swallowtails (100 individuals) and Silver-spotted Skipper (129 individuals). “Nice-to-find” species included Giant Swallowtail (3 at the Refuge), Palamedes (7), Juniper Hairstreak (3 at Kiptopeke), Viceroys (10), Common Sootywing (4 in the Oyster Sector), Swarthy Skipper (3), and Southern Broken-Dash (1). Many thanks to the volunteers who traveled from as far away as Chesapeake, Virginia Beach, Gloucester and Williamsburg to join in with the local Northampton County residents to tally a total of 676 individuals."
Andy here again - Anyway, I thought this post nicely summed up the makeup of the volunteers and what they do each year, and the timing was serendipitous. Also, I'll put in a plug here for the CVWO organization - they do some great work. Their website is www.vawildliferesearch.org.
OK, so I have a copy of the entire NABA dataset up to 2018, which is what we used for the earlier study. Let me first describe it. There are nearly 246,000 observations going back to 1993. It's a really big file. There are about 450 different butterfly species represented in the whole thing, which is (I think) most of the butterfly species common to North America. And it looks like there are about 500 different survey sites across the continent. From what I can tell, there is at least one survey site in each state, including one in Alaska! Collectively, it is a massive dataset!
I'm going to put a picture of a table I just made that shows the top 15 butterfly species seen (out of the 450 total), and for each of the three decades of the program. This can give you a sense for where the monarchs fit in. This table was made using the entire dataset, and all sites, from east to west.
As you can see, monarchs have consistently been one of the top 15 butterfly species seen, across the 25+ years of the program. And, it looks like there hasn't really been much change in their rank order. It looks like Pieris rapae (the non-native cabbage white) is consistently one of the most abundant species!
Now, lets talk about how wide-ranging the monarch is. We can get to this by looking at the number of sites where monarchs have been seen. I had recently written a blog related to this, where I showed how we can visualize the breeding range of any butterfly species by using a related citizen science program, iNaturalist. Anyway, recall that there are about 500 or so survey sites across the continent. Some butterfly species have breeding ranges only in the northeast, for example, and so they would only been observed in those northeastern survey sites. I went through the entire dataset and counted the number of sites that each butterfly species has been seen in, and then I graphed these numbers, below.
You may have to click this graph to expand it, if you are using a desktop.
In this chart, each butterfly species is represented by a single blue bar, and I've ordered them by decreasing abundance so that the top species is on the left. There are 450 or so bars in this graph! As you can see, monarch is the top species - monarchs are seen in 403 different survey sites, the most of any species. For regular readers, you may notice that this graph looks very much like the one I made using iNaturalist data. The fact that two completely different projects showed similar patterns means this is real. In other words, monarchs have the largest breeding range of any butterfly species in North America.
Finally, let me get to the issue that is on everyone's minds these days - have the monarchs declined over time? In other words, how has their breeding abundance changed over the 25+ years of this program? In the aforementioned published study, my team addressed this question using some insanely complex stats, which is needed given the complexity of the issue. But, nowhere in that study did we have a simple graph showing the changes over time. I have made one below, which is grossly oversimplified, but I think it suffices.
These two graphs show how the abundance of monarchs has changed over time in the western survey sites (States including WA, OR, CA, ID, NV, NM, WY, and MT), as well as the eastern sites. To try to account for the varying levels of survey effort each year, I calculated the relative number of monarchs (compared to the total of all butterflies per year). There are probably other ways to do this, but I chose this approach for the sake of simplicity. So, don't kill yourself looking at the actual numbers on the y-axis, it is the squiggly lines that are important.
From these graphs you can see how the abundance of monarchs has changed over time in the east and west. Remember, these trends show you how many adult monarchs were seen each year in standardized surveys made during the middle of the summer. In other words, these lines show how the breeding population has (or has not) changed over time. Basically, there appears to be wide variation from year to year, which is not surprising - most insects have high years and low years. But in fact, there is no real long-term decline in monarch abundance. If anything, the abundance in the east is increasing.
So, let me sum up what I've showed in this blog post, in some handy bullet points.
1) The NABA butterfly counts are a monstrous pile of scientifically-important data, and an incredible testament to the efforts of thousands of volunteers over the years.
2) Of the 450 different species monitored, monarchs are consistently in the top 15 in terms of abundance.
3) Monarchs are seen in the MOST survey sites across the continent, indicating their breeding range is huge.
4) The relative abundance of monarchs seen each year (compared to the total number of butterflies seen) goes up and down, but has not been declining over time, in either the east or west.
5) By these objective measures, monarchs are crushing it.
By the way, if any of this is surprising to you, I encourage you to go back and read the prior post describing the growing problem of "dogma" in the world of monarchs, and how it is leading people to believe something other than the reality.
OK, I think this about wraps up this post. I'd like to end by giving my thanks to the thousands of dedicated volunteers out there, like those in the photo, who take time out of their summers each year to count butterflies. We should all try to remember this when these data are being discussed.
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