top of page
  • Andy Davis

A complete list of all studies that show monarchs are not endangered (for objective eyes only)

Hello everyone,

With the beginning of a new year upon us all, I thought I would start it off with a bang with this post - yes, this will be another ultra-informative and handy summary of another very dicey topic within the world of monarchs. Today I am creating the following list of research and evidence that all show how monarchs in North America are not in trouble, despite what you've heard. I am doing this mostly for my own benefit, so as to organize my own thoughts on this topic, and also to provide a handy link for people to share. That is, if they are brave enough to share it. I am well aware that a lot of folks seem to shy away from this topic because it is emotionally charged. So don't be surprised if you don't see this list being discussed in your favorite monarch facebook group. I guess you could say this list is only for the deep-thinking folks who care enough about monarchs to want to broaden their minds, and get beyond the headlines.

I need to put this list together because there will be some major events happening in the coming year that relate to monarchs and their population status, and I suspect this list will be consulted often. First, I have it on good authority that the Canadian government WILL be uplisting the monarch to federal-endangered status sometime in 2023. That's right, across all of Canada, monarchs will become an official endangered species. This will be huge news, and it will likely impact everyone in that country. In other blogs, I've pointed out how I tried to prevent this, by describing the actual evidence to these officials, but they are hellbent on listing. More on this to come. Similarly, in 2023 I suspect there will also be some news concerning the IUCN's listing of monarchs. That group had also saw fit to list monarchs as endangered earlier in 2022. I won't get into it too much here, but suffice it to say that there have been some behind-the-scenes discussions about this listing decision, and there may be some news forthcoming relating to this. And finally, recall the USFWS had done their own assessment of North American monarchs in 2020, and they too declared the population to warrant the endangered status. I believe that assessment gets revisited on an ongoing basis. So in a nutshell, the monarch population status will continue to be a big topic of discussion in 2023.

I should point out that all of these listing decisions above are based (solely) on the declines that have occurred at the overwintering grounds, both in the east and west, and, these declines do in fact seem rather dire. So much so that if this were the only piece of evidence you considered, that of course you would come to the conclusion that the entire North American monarch population is in jeopardy. But, this is not the whole story, and frankly, it kills me that each of these organizations has not considered any other evidence, even when I show it to them. As readers know, I have done my best in this blog to share some of the other evidence here when it came out, but only in bits and pieces. So today, I'm going to summarize all of the evidence that has been accumulating for years now on this topic, and let you decide for yourself if these organizations have it right. This list will be updated as new information comes in too, so do refer back to it often.

I'm going to organize this list according to "season", starting with the spring recolonization phase, then the summer breeding period, and then the fall migration. Because of this, some of these studies may appear in this list out of order from when they were first published. At the end, I'll summarize it all with handy bullet points, for the people who don't like to read (or think for themselves!).

Spring Recolonization

As we all know, in the spring the monarchs begin their northward return from Mexico or California, and these adults lay eggs as they travel. Then, these eggs mature into adults that then continue northward, and so on, until the entire breeding range has been "recolonized." Given that the winter colonies have diminished over the last 20 years or so, people have worried that since there are fewer monarchs starting the journey, that this would mean the spring migration would suffer.

There was one study that addressed this question, and it was conducted by yours truly, in collaboration with the former director of Journey North, Elizabeth Howard. It was published in 2015 in the journal, Annals of the Entomological Society, and here is a link. That paper was an analysis of Journey North records of monarchs in the spring, and using 18 years of these records. These were all observations of the first adult monarchs people saw each spring, which combined, provide a good representation of how the monarchs recolonize their breeding territory. I'm sure most readers have seen the maps that get generated in real time from these wonderful observations. These data are some of the best that we have for monitoring the progress of the spring remigration phase. In a nutshell, in this paper we tried to estimate the cumulative size of the spring recolonization wave each year, by summing the geographic area encompassed by all of the sightings. Then, we looked to see if the size of these recolonizing waves was diminishing over time, because of the declining wintering colonies. I'm going to put a screenshot of our main finding below.

There are two patterns presented in this graph, but the most important one is the dotted line, which shows the size of the spring recolonization wave per year (# blocks). Notice it has no real downward trend over the years. In fact, this was the main conclusion of the paper - that despite the diminishing winter colonies in Mexico, the overall spring recolonization phase has not been declining. Thus, the population appears to have no trouble recolonizing its entire breeding range each subsequent spring, despite the smaller winter colony sizes. We did see a slight negative impact on the earliest phase of the northward journey (like in Texas), but this ended up not being as important - the population made up for it later in the spring.

Summer Breeding

Ok, there is a lot to cover here, because there have been many studies in the past ten years or so which have attempted to address the same question - is the breeding population declining? All of the studies have used different bits of data, from different sources, and from different geographic regions of the continent. I'm going to list the three most important ones below, and I'll keep these summaries short, so as not to get too overwhelming.

The first paper that comes to mind is one spearheaded by by Leslie Ries, and which was also published in 2015 in the same journal. Here is a link. It was titled, "The Disconnect Between Summer and Winter Monarch Trends for the Eastern Migratory Population: Possible Links to Differing Drivers." Basically, this paper examined trends in adult monarch abundance from two citizen science programs, the North American Butterfly Association, and the Illinois Butterfly Monitoring Project. In each of these programs, volunteers go out and look for butterflies at specific places each summer, and they've been doing the same thing for many years. The idea here was to see if there has been a long-term decline in the number of monarchs seen, in either the state of Illinois, or the NABA surveys from the Midwest and nearby regions (the core monarch breeding range). In a nutshell, there hasn't. I'll put a screenshot of the main figure from the paper below, which shows the long-term trends for both programs. The inset shows how the monarch data from the two programs are basically correlated.

Bottom line from this study - the number of adult monarchs seen in the heart of the breeding range not been declining (at least in the years included).

Next comes a study that I had blogged about when it came out, which (at the time) I called a "game-changer" for monarch conservation. It was published in 2016 in the journal, Oikos, and was spearheaded by a student in Anurag Agrawal's lab at Cornell University (Hidetoshi Inamine). Here is a link to the paper. And here is a link to my blog. This paper is similar in theme to the Ries et al study, because it too addressed the same question (are monarchs declining), only using even more data, and from more time periods. I encourage you to go back and take a look at my blog to get more details. In a nutshell, the authors also used NABA data to look for trends in abundance of adult monarchs, but across ALL of the eastern breeding range (not just the Midwest), and, they separately looked for trends in the early spring, plus in the summer, and then in the late summer. They also examined data from two different migration monitoring stations to determine if monarchs were declining in the early phase of the fall migration. Bottom line from that study - they found some evidence for declines in the early spring migration (as did the Howard and Davis study), but no declines anywhere else. The study concluded that the monarch breeding population in the east was not declining, despite the declines in Mexico.

I'll next put in a plug for yet another paper that came to a similar conclusion, and which just came out earlier in 2022 - the Crossley et al paper that was published in Global Change Biology. This is the one that I was a coauthor on, and which I have already plugged (see the blog here). I'm putting this one next in this list because it is so similar to these other two - in our paper we also looked for trends in summer monarch abundance using citizen-science NABA data (but across the entire continent), and, we also found very little evidence for declines over 25 years. You may have seen some of the news pieces about this paper (monarchs in North America are "thriving"). The thing that makes our paper stand out from the other two is that we looked at data from the entire continent - east and west, north and south, and especially in the Midwest. In the end it didn't matter because there were no declines anywhere.

So by my count, this makes three different studies, conducted by three different groups of scientists, that have all come to the same conclusion - the monarch breeding population has not declined.

So now I'll add an entry to some unpublished work I've done, which dovetails nicely with this idea. In two separate prior blogs, I had pointed out just how massive the monarch breeding range is across North America, right now. For the purposes of the blog, I had compiled data from two different sources to reach this conclusion. I counted the number of NABA survey sites where people have seen monarchs, plus, I had estimate the size of the breeding range based on sightings provided in the online platform, Then, I compared the monarch estimates to those from other butterfly species, for context. The ides here was to see how the breeding range of monarchs stacks up against some of our other, more common butterfly species. I'm going to put a screenshot below, which shows the results of both of those efforts. Notice how similar both graphs are.

Bottom line here - monarchs currently have the largest breeding range of ANY butterfly species in North America. This is important because a large breeding range is a sign of a healthy, robust population, and, it also signifies that the species can thrive in a very wide array of habitats, regions, and climates.

Fall migration

There are a number of specific sites in North America where large numbers of monarchs pass through on their southward journey to Mexico (though none in the west), and where volunteers count them when they pass through. Each of these places has their own method of counting, but the end result is the same - a final tally of monarchs per year. The great thing about these fall migration estimates is that they serve as another index of population size for that region, and one that should be closely tied to the size of the summer population there, especially if they are located in the north near the beginning of the fall journey. In other words, if the summer numbers are up for any given year, then the (initial) number of fall migrants will also be up. So, by examining these tallied numbers year after year, we can see if there are any signs of trouble for the fall migration. A number of scientific studies have done just that, and I'll list these here.

First up, is one by yours truly again, this time in collaboration with a woman who used to run a volunteer count at a place in Michigan - Peninsula Point. As the name suggests, this site is a peninsula on the north shore of Lake Michigan, and for many years, volunteers would count the number of monarchs seen there each day during September and October. Apparently, monarchs would accumulate at the site each day or night before crossing the water body. The paper was also published in 2015 in the Annals of the Entomological Society, and here is a link. For this project, I had examined these annual count data, and specifically looked for evidence of a trend over time, across the 19 years for which there was data (1996-2014). I'll put a screenshot below showing what we found (basically, nothing).

Bottom line from this project - while there were up years and down years, we found no evidence that monarch abundance during the fall migration in Michigan was declining.

Next I'll add an entry for the migration monitoring being done on the other side of the border, along the north shore of Lake Erie. There are two places where migrating monarchs are censused each fall - one at Long Point Ontario, and one at Point Pelee, Ontario. Both are geographic peninsulas which act to funnel or lure migrating monarchs each fall. Each day during the fall, people count the number of migrating monarchs at these sites. At the end of the season, these numbers can be tallied to derive an abundance estimate per year. For the Long Point site, there have been two studies that have examined these data, spearheaded by Tara Crewe. But one recent study actually examined all data from all monitoring sites, so I'll just highlight this one.

It was written by Danielle Ethier, and published in 2020, also in the Annals. Here is a link to the paper. I recall reading this when it came out, but I don't think it was widely publicized, so I wouldn't be surprised if you haven't heard of this one. From my read, it was a very objective assessment of the monarch population status in Canada, using all of the available migration monitoring data. I'll cut to the results next, and I'll paste a statement from the abstract - "Results suggest that during the past 10 yr, the number of migrating monarchs along the north shore of Lake Erie has been stable..." The author also stated that there was a slight decline detected at one of the monitoring stations, but this was not observed in others.

I'm going to also add a graph below that I myself made from the data presented in this paper. This graph shows the number of monarchs counted at Point Pelee over time. These are all counts of migrating monarchs roosting on the peninsula. You should be able to click this graph to make it bigger - you may need to since there are a lot of years of data!

Note there are a few years with no surveys, but the overall trend here is basically nothing. There are up years and down years, but no long-term decline.

Next I'll put an entry here for the work being done at Cape May, NJ. This is the site of the longest-running migration monitoring program in existence - this team of (mostly volunteers) has been tracking monarchs since 1992! Each day during the fall, people drive their car on a specific back road around this area, which traverses a variety of habitats, and they count the number of monarchs they see. There have been a number of studies done that have discussed and examined these data, and I've even done some of these. But the most recent paper from 2021 was spearheaded by Kat Culbertson. Here is a link to the paper, and I blogged about that paper when it came out, and I even recorded a video chat with the author.

In a nutshell, the paper was an analysis of the entire 29-year dataset, with two goals in mind. First, the authors searched for evidence that the timing of the fall migration was/is shifting later because of global warming (which they found), and second, the authors looked for evidence of a decline in the overall numbers of monarchs observed each fall. They found none. Once again, there were clearly some up years and some down years, but overall, there was no evidence that the abundance of migrating monarchs in this region (the Atlantic coast) was declining over time.


OK, let's do a recap of everything that was covered here, in bullet form.

- We know that the size of the wintering colonies in North America has declined over the last 20-25 years.

- That decline has not affected the population's ability to recolonize their breeding range in the spring. Each spring the population completely fills its entire breeding range in North America. This is true even when the winter colonies are small.

- The current breeding range of this butterfly is in fact the largest of any other butterfly species in North America

- There has been no long-term decline in the size of the breeding population. This has been studied many times, by many different groups using different datasets. The results are nearly always the same.

- The number of monarchs counted at fall migration monitoring sites has not declined (though with one exception where there was a slight decline). Since all of these sites are in more northern regions, they reflect the overall size of the migration cohort near the beginning of the journey.


Finally, let me end by presenting you with an EXTREMELY unsettling thought, and one which will probably haunt you, and make you question everything you thought you knew about monarchs. I know I have been thinking this ever since I began sifting through all of these studies over the years. Are you ready for it?


Wow, right? Think about it. I know, I know, you're probably thinking that it "matters to you," or matters to the people in Mexico, or something like that, which I know it does. But that is not the question I'm asking. I'm asking if the decline in Mexico (or California) matters at all to the monarch population. I know that this is a different way to think about the winter colonies than what you have been told by the media and press - you've been told over and over that the declining winter colonies mean the entire population is declining. And, this idea is what has driven the Canadian government, the U.S. government, and the IUCN to list monarchs as "endangered." But it is abundantly clear now that this idea is wrong. These assessments are wrong. By every objective analysis of data we have, the population is not declining, and monarchs in North America are doing great.

Bottom line - the smaller winter colony declines now just don't seem to matter. I defy anyone to prove me wrong (using data, not emotions).

I'm going to leave it here for you to ponder.


Direct link to this blog entry:




The science of monarch butterflies

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

bottom of page