Monarch Population Status 1/2

The following text was written on 10 March 2018.

Predicting the trends in the monarch population in 2018

If you have been following a number of my posts to the Blog over the years, you have surely noticed that I have a tendency to make predictions. This is all part of my process of trying to learn from my mistakes, and my few successes, as to what contributes to the increases and decreases in the population. The long-term goal is to develop a predictive model based on physical (weather) and biological factors that will provide a better understanding of the inter-annual variation as well as the dynamics of the population within each year. If successful, such a model should allow us to develop effective approaches to monarch conservation.

Most of my predictions have been made in late June or July with iterations as the seasons have progressed. I’m moving it up a notch this year by declaring that “the population will increase this year” – an increase from the recently-reported 2.48 hectares that overwintered in 2017-2018 (see Monarch Population Status). Ok, I’ve said it. If I’m wrong, we should be able to figure out why. At this juncture, I can’t tell you how large the population will be, but it should be 3 hectares or larger. I can’t explain all of my reasoning at this point, but let’s be clear, this declaration is based on a number of assumptions with respect to the numbers of returning monarchs, the conditions in the South for March and April, the conditions as the monarchs move north, the summer temperatures, and the conditions during the migration. Yes, it’s all conditional and the only justification for my approach is that the long-range forecasts are generally accurate and we now have over 20 years of data on how the population responds to a variety of weather patterns. I’ve looked at the weather records from 1895 to the present and it’s clear that monarchs have experienced much greater extremes in the past than the population has experienced since the colonies were brought to the outside world’s attention by Ken and Catalina (now Trail) Brugger in 1975. In saying this, I’m pointing out that our knowledge of how monarchs respond to weather conditions is limited to that of the relatively stable climate conditions that have occurred since the majority of the overwintering colonies were first measured (1993). That said, there is nothing in the long-range forecasts to suggest that weather events during the coming breeding season will have a negative impact on population growth. Rather, given past weather patterns associated with increases in monarch numbers, 2018 looks to be a year in which the population will increase due to favorable temperatures in the South Region in March and April, together with good recolonization numbers, May and June temperatures that will allow for recolonization of the northern breeding areas, and normal summer temperatures.

There are still a lot of gaps in our knowledge of how the monarch population functions. We don’t have a detailed understanding of when the monarchs leave the colonies, what the weather conditions are during their passage to the north, how fast they move from day to day, the paths or routes taken, the impacts of drought conditions on nectar availability, how long the journey takes and the amount of mortality experienced before monarchs reach areas in Texas with significant numbers of milkweeds. It will take some time to acquire these details, but I decided to see what I could learn about these issues from my desk and computer in Lawrence, Kansas.

Accordingly, on the 25th of February, I announced in an email to a number of colleagues that I was going to try to remotely follow the migration northward from the colonies. I’ve done just that and have accumulated numerous observation that will be summarized at a later date.