- Andy Davis
Seven (7!) papers about monarchs published at once - all about long-term trends
On August 5 2015 a unprecedented collection of research papers focused on monarch butterflies was published at the same time as a “Special Feature” in one issue of the scientific journal, the Annals of the Entomological Society of America.
This is probably one of the biggest events in the history of monarch research!
The collection contains 7 scientific papers, all written by researchers who are associated with a variety of citizen-science projects focused on monarchs or butterflies in general. The special feature was coordinated by Dr. Andy Davis, from the University of Georgia, and the guest editor of the feature was Dr. Lee Dyer from the University of Nevada. The goal of the collection was essentially to identify long-term trends in monarchs outside of their wintering phase (ie. in the spring, summer or fall).
All of the projects were based on citizen science data sets, like the Monarch Larva Monitoring Project, MonarchWatch, Journey North, and others. These projects have been running for nearly 20 years each, so they all contain valuable information on the long-term changes that have been happening to monarchs. So the theme of the collection was to identify any changes that have taken place in the numbers, timing or distribution of monarchs in the last two decades.
One of the biggest surprises from the collection came from a new analysis of monarch censuses from the North American Butterfly Association, and the Illinois Butterfly Monitoring Network. Leslie Ries and colleagues looked at sites in the midwestern United States to see if adult monarchs have declined in these areas. The graph below shows the results.
Essentially, the authors did not find evidence that monarch counts in the central United States have declined over the last 22 years, which is surprising, given the well-known declines ocurring at the Mexican overwintering sites.
OK, so let's talk about this paper a bit more. What were the strengths and weaknesses of it? For the strengths, one really strong point was the use of two different data sets. Both of these showed essentially the same thing, which means that the long-term trends aren't random - i.e. they reflect biological reality. Second, both of these programs are surveys of butterflies - all butterflies, not just monarchs. That means the surveyors would be completely objective on the number of monarchs they saw. The last big strength is the region of the country these counts came from - smack in the middle of the monarch core breeding range - the midwest, or the agricultural region of the country.
As for the weaknesses, there is one, and this is something that has been identified previously (by folks who don't want to believe the data): that is the people who do the counts most likely survey places around them where they know there will be butterflies. In other words, they don't survey in the middle of the farmers' fields. Since that is where a lot of monarchs are supposed to be, that means these data may not reflect any changes that may have ocurred in the past 20 years in the corn fields.
It's important to note that some people have pointed out that if you squint, you can see a recent downward shift in the trend line - in the past 7 years or so. This decline was not significant, but some may see this as a sign that there is a decline after all. So basically, this graph can be interpreted however you want it! If you're reading this at home, ask yourself how you would interpret it? Do you see a 90% decline?
Either way you look at it, this paper represents a huge deal for our understanding of monarch trends in the east. And, this is only one of the papers from the entire collection. Over the next few weeks, I'll try to post summaries of other papers from the feature. Stay tuned...