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.

Milkweed Restoration in Oklahoma

Monarch Watch is engaged in a number of projects that focus on habitat restoration designed to benefit monarchs and pollinators. One of these efforts involves a collaborative project with seven tribal nations in Oklahoma. The goals of the project involve the planting of 5,000 milkweed plugs and 4,000 native forbs on the lands of each tribe. In total, 32,000 milkweed plugs have been planted to date. Production of the forbs (mostly native nectar plants) has involved training to identify beneficial native species, seed collection and processing and all the steps from seed storage to propagation and planting. This collaborative effort is known as the “Tribal Environmental Action for Monarchs” (TEAM). The images below make up a presentation prepared by Andrew Gourd, Land Use Coordinator Eastern Shawnee Tribe of Oklahoma. This presentation is now on display at the National Museum of the American Indian (part of the Smithsonian Institution).

Having established the TEAM project as a base, and by learning from both both our successes and failures, we decided to use this project as a stepping stone for a new and larger project we call TAP (Tribal Alliance for Pollinators). This outreach and training program is just getting started, but has great promise for engaging many tens of the 566 federally-recognized tribes throughout the United States.

Our partner in the TEAM and TAP projects is Jane Breckinridge, Citizen of Muscogee Creek Nation of Oklahoma and Director of the Euchee Butterfly Farm. Jane is the “boots on the ground” in Oklahoma where she has the task of coordinating and assisting the seven tribes which are widely scattered over the eastern part of the state. The distances are considerable since every tribe seems to be an hour to two hours driving time from one another. One of the rewarding, and we are told unique, aspects of the TEAM effort is that the project is bringing the tribes together. They are sharing their successes and failures and are helping each other succeed.

This presentation is also available as a PDF file.

2018 Monarch Calendar Project

NOTE: We will send an email with a link to the actual submission form after each period comes to a close (June 20th for period 1 and September 25th for period 2). Please hang onto any data sheets you have completed until those times. Thank you!

Monarch Watch is seeking the immediate assistance of hundreds of monarch enthusiasts (citizen scientists) in collecting observations of monarchs in their area during the spring and fall. This project is an attempt to assemble quantitative data on monarch numbers at critical times during the breeding season. The data from these observations will be used to assess their value in predicting trends in the population.

We are excited about the data we received for 2017 and are in the process of analyzing it. It looks like it is going to help explain some aspects of the monarch migration and “pre-migration”. We will share a summary of the results as soon as we have everything worked out.

BACKGROUND

Why do we need a “monarch calendar” and your help recording monarch numbers?

The decline in monarch numbers over the last 15 years has inspired numerous attempts to define critical factors that explain the inter-annual variation in monarch numbers. The data sets used for these analyses have had a variety of limitations which have either been ignored or underappreciated by the authors of a number of publications. The truth is that much of the data that is available is too general and does not adequately represent important aspects of the biology that underlies the development of the population each reproductive season.

There are numerous gaps in our knowledge and some of these gaps can be addressed if we can convince a large number of monarch enthusiasts (citizen scientists) to record the number of monarchs they see each day and what the monarchs are doing, along with general information about the physical conditions associated with each observation.

At this time we are not asking participants to record behavior or physical conditions (temperatures and wind speed and direction) but a few observations and notes along those lines might be useful in targeting conditions most favorable for monarch activity. The pivotal latitude is 35N (e.g., Oklahoma City) and we have provided some links below to help you determine your latitude. If the observer is located at a latitude less than 35N (i.e., “South”), we need the number of monarchs seen each day during the following two periods: 15 Mar-30 Apr and 1 Aug-25 Sep – 47 days & 56 days = 103 days total. If the observer is located at a latitude greater than 35N (i.e., “North”) the observation periods are 1 Apr-20 Jun and 15 Jul-20 Aug – 81 days & 37 days = 118 days total.

The first period in the south covers the interval during which the overwintering monarchs arrive in Texas and Oklahoma and points to the east. We need to capture a better estimate of the number of monarchs in this region that arrive from Mexico each year. This starting number has not been captured effectively. The second interval in the south captures the arrival of pre-migration monarchs from the north as well as potential local reproduction during this time. In the north, the first interval will capture some of the returning monarchs early in that period but is more likely to chronicle the arrival of first generation monarchs migrating north to the summer breeding grounds. The second period in the north should capture the relative intensity of the reproductive activities of monarchs during the period in which most of the eggs are laid that become the adults that populate the migratory generation later in August and September.

To provide meaningful data, we need to recruit hundreds of volunteers to record what they see.

INSTRUCTIONS FOR CITIZEN SCIENTISTS

Here is what we need you, as citizen scientists, to do:

1. Register as a participant in this 2018 project (even if you registered previously) by providing your name, location (including latitude and longitude), and email address via the form at

To determine your geographic coordinates, please use any of the following sites (or others) to enter your city, state/province, and zip/postal code and retrieve your latitude and longitude in decimal form (e.g., latitude: 38.95 longitude: -95.27 for Lawrence, KS 66045).

2. Record every monarch seen in your location for specific periods depending on your latitude. To keep these records all one has to do is to list the number of monarchs seen each day in which seeing a monarch was a possibility. If you were outdoors and saw none, record a zero (0). On the other hand, if there was no opportunity to make any observation due to work or vacation, etc., leave that date record blank. There will often be days when monarchs can’t be active due to weather conditions (e.g., low temperatures, extreme overcast, heavy rainfall). These intervals, if long enough, can also impact population growth. A “W” (for weather) should be entered for each of these days.

We have provided some sample files below that you can use to log your observations but exactly how you do it is up to you. Here are some suggestions: spreadsheets (Excel, Numbers, Google Sheets, etc.), printed calendar sheets (or just a calendar), calendar applications on your computer or phone, notebooks, notes or other text files on your computer or phone. Please feel free to use whatever is easiest and most comfortable for you to log your daily observations of monarch numbers – you will then use this log to complete a simple online form at the end of the observation period.

Please note: The records for each time period should only reflect the numbers of monarchs seen on any specified day within 50 miles of your home location. If you wish to report monarchs seen at a location other than your home location (specifically, at a different latitude) please use another datasheet as this should be submitted separately.

3. Submit your data to us at the end of the observation period via an online form. We will provide a link to the submission form at a later date via the email address you give us when you register. The form will be very simple; all you will need to do is enter your name and location (including coordinates as you do when you register) then you will be presented with the appropriate time period form to enter your data for each day.

We will assemble the calendar records for each period and region then provide summaries online once we have a chance to analyze the data.

Please register for this project and start logging your observations today! Thank you in advance for your assistance – if you have any questions or comments about this project, please contact us at monarch@ku.edu

SAMPLE FILES (for logging observations)

Spreadsheets (Excel format; can be imported into other applications)
2018-spring-south.xls
2018-spring-north.xls
2018-fall-south.xls
2018-fall-north.xls
sample-data.xls (partially completed sheet for reference)

Blank Calendar Sheets (to print)
2018-spring-south.pdf (Mar-Apr 2018)
2018-spring-north.pdf (Apr-Jun 2018)
2018-fall-south.pdf (Aug-Sep 2018)
2018-fall-north.pdf (Jul-Aug 2018)
You can also create custom calendars via www.timeanddate.com

FREQUENTLY ASKED QUESTIONS

Preamble

We’ve received a number of questions about our Monarch Calendar Project. We’ve tried to summarize these questions and, through the answers, clarify how we’d like you to record the data.

We need a better way of predicting the fall migration and the size of the overwintering population. This project is an attempt to capture three aspects of the seasonal dynamics of the monarch population that will help us understand how the population develops through the breeding season. Specifically, we are trying to obtain data (with your help) that will provide information on the relative numbers of monarchs seen after first sightings in most areas of the country. In addition, we are seeking data on the number of monarchs seen during the last egg laying periods in the north and south. Lastly, records of the weather-related events, as indicated by the Ws on the data sheets, may indicate times and regions during which weather had a negative impact on the population.

Thanks for your willingness to participate in this project. We appreciate your help. As you can see, from the scope of the project, the only way to obtain these data is through the cooperation and commitment of a large number of citizen scientists such as yourself. Again, we appreciate your help and we are looking forward to receiving your data.

Questions and Answers

1. When should I start my calendar?

The idea is to keep the record keeping as simple and as accurate as possible. Here are some suggestions:
• Start with your first sighting
• Start when you find the first eggs
• Start when monarchs and/or eggs have been sighted in your area
• Start only when sightings are reasonable given your latitude.

2. How do I make counts? Suppose I see a monarch six times in my garden during a day do I count that as six butterflies or one?

The rule here has to be to use common sense and be conservative. Egg laying females in the morning and patrolling males in the afternoon will often return to the same patch over and over on a given day. If during the sightings, the observed butterfly appears to be the same color, size and condition, count it as a single butterfly. Females are darker than males and male/female behavior is different. Careful observations should help you distinguish one butterfly from another. However, if you are uncertain, be conservative and record the lower number.

3. What if I am in an area in the northern part of the range where monarchs are seldom seen before 20 June?

Actually, we want to confirm that monarchs aren’t seen above certain latitudes until after the 20th of June. Please indicate that to be the case, if true, and only record data for the critical egg laying period from 15 July to 20 August. This directive is likely only to apply to a few of you who report sightings from 46N or further north.

4. What if I work during the week and can’t make observations? Or, do I have to observe for a certain length of time on a given day to record a number seen or a zero?

We expect the opportunity to observe will vary greatly for each observer over the calendar period and that some observers will, by virtue of opportunity, activity or lifestyle, see more monarchs than others. That’s fine. We want to capture relative numbers over large areas and long time periods for multiple years. Don’t worry if you don’t see monarchs or don’t spend a lot of time looking for them. Just record what you see and, if you think there was a good opportunity to have seen a monarch and didn’t, just record that day as a zero. If you had no opportunity to observe, that’s a blank. We expect more blanks and 0s with some Ws (for “weather” – see #7 below) than actual numbers sighted on nearly all the data sheets.

5. If I raise and release monarchs, do I count those?

The short answer is no. We are trying to record the dynamics of the wild population.

6. What about species that are easily confused with monarchs?

Yes, there are species that are sometimes confused with monarchs, most commonly the viceroy and the queen. In flight, the viceroy flies closer to the ground than monarchs and frequently lands on the ground. It is also less likely to visit flowers. However, when on flowers, viceroys and queens can be easily mistaken for monarchs. Monarchs are larger than both of these species. All we can tell you here is to learn your butterflies, observe closely and do your best.

7. When should I record a W for weather? What weather conditions limit monarchs?

Low temperatures (mid 60s and lower), extremely high temperatures (95 and higher), extreme overcast, rain, and high winds can completely stop monarch activity. When that happens, please record a W for weather. The Ws are important. There is no reproduction during a W – no mating, no egg laying and, if the temperatures are low, larval development slows down as well. Monarchs can get off to a good start and then be slammed by weather that shuts down reproduction. We need to capture that. Five consecutive days of low temperatures and rain can have a strong negative impact on a population that can easily be missed if projections are based on mean monthly temperatures. We aren’t really concerned about the weather before monarchs arrive. If necessary, we can capture weather data from “Weather Underground” for the periods prior to the arrival of monarch in any region.

8. Does this project apply to Hawaii, Southern California or Florida or other continuously breeding populations?

No, it doesn’t. Continuously breeding populations are found in Florida, some regions along the Gulf Coast, Southern California, Hawaii and numerous Pacific Islands. It’s probable that some or all of these populations cycle with the seasons and this should be captured. However, that will require a different protocol.

9. Why aren’t you asking us to record eggs, larvae and migrating monarchs?

The reason is simple; there are other programs that provide data on these aspects of the life history. Please see the following links if you wish to participate in any of these programs.

First eggs – these sightings can be reported via Journey North (learner.org/jnorth/tm/monarch/SpringWatch.html)

The Monarch Larval Monitoring Project (MLMP) at the University of Minnesota tracks both larvae and eggs (mlmp.org)

Migratory monarchs are tracked by Journey North through sightings of overnight roosts (https://www.learner.org/jnorth/tm/monarch/FallWatch.html)

Monarch Watch’s tagging program captures data related to the size and dynamics of the migratory population (monarchwatch.org/tagging)

Monarch Population Status

World Wildlife Fund Mexico in collaboration with CONANP and the Monarch Butterfly Biosphere Reserve (MBBR) announced the total forest area occupied by overwintering monarch colonies this week. Nine (9) colonies were located this winter season with a total area of 2.48 hectares, a 14.77% decrease from the previous season:

Figure 1. Total Area Occupied by Monarch Colonies at Overwintering Sites in Mexico

We will provide additional details as we receive and process them.

WWF release (in spanish): Superficie forestal ocupada por las colonias de hibernación de la mariposa monarca en México durante Diciembre de 2017.

Forgotten Victims of Harvey – the Pollinators

We recently received the following account of the hurricane and the alarmingly low number of pollinators post-Harvey. ~Monarch Watch

I am writing from Sugar Land, Fort Bend County, Texas where my home is located approximately 2 miles from the Brazos River, which is scheduled to crest at 59 feet above sea level, the highest level ever recorded. Over the course of three days, we’ve received a record-breaking 51.5” of rain from the category 4 hurricane Harvey and are under a voluntary evacuation order. Hospitals, grocery stores, pharmacies and restaurants are all closed. Some people in my subdivision are using kayaks and canoes to navigate their street. Coast Guard helicopters fly overhead on a regular basis. Our latest social media communication from the city stated “If you can’t flush toilets, no cause for alarm – just give it time, the system will catch up as water recedes.” And after watching 3 days of hurricane coverage showing others more badly affected, I was grateful for that communication. You really can’t imagine the number of things we take for granted until faced with disaster. Now imagine that disaster is a 1000 year flood resulting from a hurricane going on outside while you have 389 Monarch caterpillars to feed inside…

Pre-Harvey

As I rushed to complete pre-hurricane Harvey preparations, one more task was added to my list that was different from previous storm preparations, picking up monarch caterpillars. My first call came from the leader of a partnering organization. I met to accept my first box of caterpillars in the parking lot of Gallery Furniture, which one day later would become a temporary shelter for local evacuees and an overnight hostel for the activated National Guard. I accepted my final container of monarch caterpillars at the HEB parking lot where I expected to make a quick grocery run and instead found a 50 minute wait in the pouring rain outside locked grocery store doors manned by the store manager to prevent uncontrolled crowds fighting for necessities like water, eggs and milk. People deliver caterpillars in all manner of open boxes, and so my normal 10 minute drive home became a much longer drive through traffic, high waters, windshield wipers unable to keep up with falling rain, and moving caterpillars trying to escape their box.

Over the course of two days I collected caterpillars, farming some out to local enthusiasts until I ran out of available enthusiasts. I already had 80 caterpillars of my own I was raising for our 2017 annual Monarch Madness Festival. Some of the people asking me to adopt their cats were evacuating. Others couldn’t slosh through wet yards to collect milkweed. Still others expressed fear the caterpillars would die in the rain and some were simply running out of milkweed, having misjudged the number of plants it would take to feed the quantity of caterpillars on their plants. Surprisingly, nobody feared losing their caterpillars to flood which turned out to be the greatest threat.

I thought long and hard before accepting the caterpillars. Unlike some of the donors, I knew exactly how many plants it would take to feed 389 caterpillars. I also knew that many of the caterpillars I was accepting were likely born of butterflies infected with OE, a dormant protozoan carried by the monarch that is then deposited onto the egg sack and consumed by the caterpillar. Still others were likely preyed upon by tachinid flies, as it is the height of their season.

The value of saving these caterpillars was about much more than the cats themselves. These caterpillars represented Houston and Sugar Land monarch enthusiasts I had a part in growing. The reality of monarch conservation is that children and adults grow to love the butterflies produced from THEIR school, park and backyard gardens that I asked them to create and that love will help this species recover. Now those monarch enthusiasts trusted me to keep the product of their work and love alive. I said yes.

Last May, at the Texans By Nature Milkweed Symposium, Dr. Chip Taylor of University of Kansas’s Monarch Watch proposed that monarch butterflies are a metaphor for ourselves and our ability to save them speaks to our ability to sustain our own species. If that is true, I reasoned, then my ability to save these 389 caterpillars could be said to represent Houstonians’ and my own ability to survive hurricane Harvey. So I committed to become the surrogate guardian of more caterpillars than I ever raised in the middle of the worst hurricane in US history. I set up an indoor operation which included mesh butterfly cages and little cup nurseries. I sloshed through ankle deep water, hail, sleet and stinging rain blowing sideways twice a day to collect my own and my neighbors’ fresh milkweed.

On day one a tree fell on our fence and in the dark of night two, I stepped into the kitchen to feel water on my feet. Sleet, an unusual occurrence in Houston was clinging to shingles, brick and overflow pipes damaging our roof. Water was dripping from the roof into our kitchen cabinets, filling all the dishes before dripping into the controls of our electric stove below and across our kitchen. One of our hoop house type greenhouse roofs left the premise on high winds never to be found again. But all-in-all we are good and our damage was minor. I feel survivor guilt even voicing our damage when others are being evacuated from roof tops and had lost everything.

In some ways we are nearing the end of this storm and in others we haven’t yet seen the worst conditions. When the Brazos River crests, it has the ability to impact Monarch Gateway’s signature event, the annual fall Monarch Madness Festival, a family friendly, monarch butterfly and pollinator conservation festival. During this event Monarch Gateway awards the annual Catalina Aguado Trail Young Naturalist Award and scholarship to a young person contributing to monarch conservation. If Brazos Bend State Park is flooded when the river crests, as happened last year during the Memorial Day floods, the park will close for cleanup, impacting our September 24th festival.

Post Harvey, Pre-Brazos River Cresting

Texas Parks and Wildlife Department announced the closure of Brazos Bend State Park which is already flooded and expects to sustain additional flooding when the river crests.

Figure 1A. 200′ to left is the BBSP Monarch Waystation which is not flooded but the only way to access the park is by canoe. David Heineke, photographer.

Staff at Brazos Bend State Park and George Observatory, a satellite site of the Houston Museum of Natural Science inside the park informed us we would need to find an alternate location for Monarch Madness as both are closed through October and expect a months-long cleanup period.

Figure 2. I live one mile down the road in center of this picture.

I left our home for the first time post-Harvey for an appointment in South Houston and as I drove, I looked for butterflies, which were absent in my yard since Harvey. I returned home aware I saw none, no bees, no butterflies, or even dragonflies, all of which usually return to my yard shortly after any storm. The life of the monarch butterfly is short, sometimes just 2-4 weeks long and it makes sense that many probably perished in hurricane Harvey as did the caterpillars on plants under flood waters.

I was grateful this storm did not occur just a couple of weeks later as monarch butterflies begin their annual migration through Texas to Mexico because Harvey’s heavy rain bands extended into many areas in the I35/migration corridor and its impact could have been great. All but the smallest caterpillars have now become chrysalis and the City of Meadows Place has agreed to host our annual Monarch Madness event if we can plan for the rescheduling of an entire festival in 3 weeks amidst all else.

Epilogue

We now know Harvey was a 40,000 year flood event by some calculations and a 1000 year event by others that delivered 9 trillion gallons of water to Texas with catastrophic results. In the week since hurricane Harvey, I have only seen one tiger swallowtail butterfly. Because my backyard is designed for wildlife and I’m in the business of noticing pollinators as I travel throughout my day, I estimate I normally see between 25 and 100 per day. My awareness of the various pollinators flitting around is a bit like white noise, I’m most aware when it stops. Harvey has presented me a real-life opportunity to view my city with no monarch butterflies or pollinators and it has piqued my determination.

As we all get back to normal life we can’t help but walk among people in various stages of grief and acceptance but in the end, we are all determined to survive, to rebuild our habitat, find the foods that sustain us and have a safe, dry place to rest at night, just like the monarch butterfly. There are many ways to help people after a natural disaster and each organization and person will gravitate toward that topic that speaks to their heart. My heart says go rebuild pollinator habitat so that the forgotten victims of Harvey, the pollinators, in all their life stages from caterpillar to winged adult can once again thrive in our communities. My heart says make as much of that habitat native prairie with its 15 foot deep roots that also help absorb future hurricane and storm runoff. If I can save hundreds of monarch caterpillars in the worst hurricane in U.S. history, increasing the monarch population is doable. I challenge you to stand with me, with Houstonians, with the Texan will to survive and help the monarch butterfly and other pollinator species survive too.

HOUSTON, UNITED STATES
08.29.2017

Gallery Furniture. Photo by Sgt. Steve Johnson, 100th Mobile Public Affairs Detachment

Monarch Population Status

I’ve done many things in my career that I’ve enjoyed greatly and among those was teaching a course in honey bee biology. The course incorporated some hands-on lessons in how to manage bees for pleasure and the sweet rewards bees could provide. To manage bees for honey production, you have to know how to manipulate the growth of the colonies in the spring: that is, to bring the numbers of bees in each colony to the maximum number at the time the flowers provide the greatest amounts of nectar. Since colony development is strongly correlated with the seasonal progression of flowering (phenology), which in turn is influenced by temperature and moisture, the goal is to manage each colony in concert with the sequence of flowering to provide the best shot at maximizing honey production. I used to tell the students that each spring is a challenge, in effect a series of experiments, in which beekeepers have to apply their knowledge of bee biology and management skills for each colony with what they can deduce from the temperature and moisture patterns during the spring that determine plant growth and flowering. And so it is with monarchs. Each year is an experiment, or series of experiments, with numerous hypotheses, during which I try to match what I know about monarchs with the progression of the seasonal conditions that influence both monarch behavior and plant growth. As a beekeeper, my hypotheses were often off the mark and I have been off the mark about monarch projections as well, but that’s alright. The idea is to learn from one’s mistakes.

To make projections for each fall migration and overwintering population, I start with the numbers of monarchs measured at the overwintering sites in Mexico. Next, I focus on overwintering mortality, followed by the spring conditions that prevail as monarchs move northward from the overwintering sites to the milkweed areas in south and central Texas, and then the conditions in the South Region (Texas, Oklahoma, Louisiana, Arkansas, Kansas) during the growth of the first generation in March and April. That is followed by attention to the conditions during the period from 1 May-9 June that allow (or don’t allow) first-generation monarchs to reach the northern breeding grounds. Summer temperatures along with the seasonal distribution and amounts of rainfall are also in focus when estimating the fall and winter numbers.

The above provides the context for a number of hypotheses or projections concerning the coming migration and the opportunities to tag monarchs this fall. First, this should be a GREAT tagging season. It will certainly be as good as the 2015 season and probably better. The overwintering numbers should match or exceed the 4.01-hectare population measured in the winter of 2015-2016 (see Monarch Population Status from February). Further, several fall monitoring sites (Peninsula Point, MI; Long Point, ONT and Cape May, NJ) are all likely to record much higher numbers of monarchs than in recent years. Specifically, the migration through Cape May has the potential to be stronger than any migration since 2012. While the numbers at Cape May will probably not be as high as 2012, they are likely to rank within the top ten seasonal averages in the 25 years of that program. Fall monarchs should be abundant in the Upper Midwest from the eastern Dakotas east to Wisconsin and Illinois with good numbers present from Michigan through Ohio as well. Production of monarchs should also be higher than it has been for many years for all of the Northeast from New York and Pennsylvania through Maine. The Mid-Atlantic region hasn’t been heard from in recent months, but the flow south and southwest through that region by monarchs originating further north should present some good opportunities for tagging in that region as well. Taggers located south of the northern breeding areas, particularly those located in Kansas, Oklahoma and Texas, should also have a greater opportunity to tag monarchs than in recent years.

In sum, this looks to be a good year for monarchs – with a stronger migration in most regions and a good prospect that the overwintering population will increase from the 2.91 hectares of last year to 4 hectares or better this coming winter.

Monarch Population Status

Those of us who are educators, and who follow monarchs closely, are being educated by the monarchs themselves this spring. The movement and behavior of monarchs returning from Mexico has been unprecedented. I’ll save the details for a longer Status of the Population that will be posted online at a later date but for the purpose of making the point of how the monarchs are schooling us, I’ll briefly summarize the important points here.

The overwintering population was just 2.91 hectares. That’s a relatively small population. Yet, more returning monarchs have been reported this spring than for any previous overwintering population including many that were much larger.

Monarchs moved into central Texas after the 12th of March in good numbers and advanced at a rapid rate to the north and northeast, reaching Oklahoma a bit earlier and in larger numbers than seen in most years. This advance into Oklahoma continued in late March and early April, resulting in many sightings of egg dumping (multiple eggs on single plants). Evidently, large numbers of monarchs had reached northern Oklahoma before the 4th of April, but no further due to colder weather in Kansas and Missouri. On the 4th of April, we received a report of clustering monarchs on a ridge top near Bixby, OK (see “Spring roosting: A rare event” at monarchwatch.org/blog/2017/04/11/spring-roosting-a-rare-event/). This clustering may have been the result of storms that were moving through the area at the end of the day. Small spring clusters have been reported before, but the observers in this case reported that 1200-2000 monarchs had clustered in a series of pine trees on this hilltop. That was unprecedented. No one has reported seeing that many monarchs in one place that far north in the spring. Some monarchs lingered at this site through the 6th.

The weather changed on the 7th and from 7-9 April strong south and southwesterly winds and favorable temperatures allowed monarchs to expand the leading edge of the returning population from the Kansas/Oklahoma border well into Nebraska, a distance of 300 miles, in three days. I’ve looked at all the first sightings data posted via Journey North and I don’t recall anything comparable to that expansion in those records. While the expansion was impressive, the number of monarchs in this wave was also remarkable.

These monarchs were ahead of the milkweeds in most of Kansas, Missouri, Nebraska and Iowa. Milkweed that had just emerged in burned over grassland sites, in the heat islands of cities and towns, and in some gardens, were quickly found by females who deposited large numbers of eggs on the few plants available. Egg dumping was the rule, allowing the collection of hundreds and hundreds of eggs and larvae – again, unprecedented numbers for these latitudes for this time of year. The eggs and larvae were collected to save both the milkweed plants in gardens and the monarchs from predators. We collected well over 500 eggs and larvae with a minimum of effort. We also monitored a number of sites with large number of eggs and larvae that were not collected. Nearly all of the latter disappeared.

I kept watch on a special cohort of larvae that were relatively protected from predators to monitor their developmental rate. Those larvae were from eggs laid on the 9th and 10th of April. They are 29-30 days old at this writing (9 May) and most will pupate over the next three days. At emergence, most will be 45 days old. That’s a long generation and that’s not good. Shorter generation times are better for a number of reasons.

Monarchs resulting from the premature, ahead of the milkweed push, resulting from the winds of 7-9 April, will arrive late to the northern breeding grounds. In effect, these monarchs will lose a generation.

In 2000, there was a somewhat similar earlier push into Kansas and other northern sites. That didn’t work out well. The overwintering population that year was only 2.83 hectares, down considerably from the 9.05 hectares from the previous overwintering population.

So, what does all of this foretell for this year’s migration and overwintering population? Frankly, it doesn’t look good. We could be looking at another decline such as seen in 2000, but it is really too early to make predictions. We will have to assess the number and timing of first generation monarchs that move into the northern breeding areas later this month and into early June. If those numbers are low, the population is certain to decline. Moderate numbers and summer temperatures that are 1.5F above normal could offset the loss of reproduction associated with the “too far north too soon” scenario that has played out this spring.

Spring roosting: A rare event

At 6:32PM on Tuesday (4 April) I received the following message from a landowner I know near Bixby, in northeastern Oklahoma.

“Looking at hundreds of monarchs right now on the pine trees down by our gate. I assume they blew in with the storms. It’s amazing!!”

My response was “Are you just trying to get me to call you? Or, are you seeing something that should be documented six ways from Sunday? If real, that is a first. REALLY!!!!”

You could tell I was excited.

I then went on to say that, if there were indeed hundreds of monarchs on the property at this time of year, it was remarkable, even extraordinary and a sight that may never have been reported.

I subsequently contacted Elizabeth Howard. Elizabeth, as most of you know, manages Journey North which has been recording first sightings of monarchs returning from Mexico since 1997. My question to Elizabeth was “In all the records of first sightings over the last decade and more, have you ever received a report of spring clustering that involves hundreds, perhaps thousands of monarchs?” Elizabeth answered “No we haven’t had clustering reports before other than this one of 50 in Tamaulipas:
learner.org/jnorth/sightings/query_result.html?record_id=1487466914”

I was pretty sure Elizabeth’s answer would be no, at least not in the United States. So, over and over again, I pressed my colleague to get pictures, estimate numbers and to document the event as thoroughly as possible. Credibility is important. I’ve been there. I saw a mountain lion once just a mile from my house, but the ground was frozen and there were no tracks or other evidence. So, to this day, I only mention the event when I’m with those who believe in and want to hear mountain lion stories.
Back in Oklahoma it was a dark and windy night but monarchs kept coming into the pine trees and did so until last light. The winds were from the south and most of the clusters formed on the north side of the pine trees. The clusters were small and scattered. Some clusters formed in isolated pines but no clusters were found on the neighboring oaks or other tree species.

The next morning it was cool and overcast and the monarchs weren’t moving. My colleague tried to take pictures of the clustered monarchs. It was difficult since the clusters were high in the trees and the monarchs blended in with the pine cones and were nestled deeply within the pine needles. The best picture is below. If you look closely, you can see 8 monarchs.

Although most of the monarchs were in a row of pines, others were found in pine trees scattered over 2-3 acres. The first estimate on Wednesday morning suggested that there were roughly 500-1000 monarchs in the trees. Later, after a more thorough search over a slightly larger area, the estimate grew to 1200 to perhaps as many as 2000. (I should say at this point that the latter estimate was made by someone who routinely works with large numbers of butterflies).

The weather was pretty iffy at this location throughout the day on Wednesday. There were strong winds from the north and the temperature grudgingly inched up to 60F with a few intervals of sunshine. In spite of the winds and low temperatures, some monarchs were seen puddling and others seemed to be leaving the area. Yet, it looked as if some would remain for another night and that’s what happened. This morning (6 April) roughly 150 monarchs remained in the area.

This event raises lots of questions. Data from first sightings and first eggs as reported to Journey North would seem to suggest that monarchs fan out and become highly dispersed as they move into the United States from Mexico. There is no literature, and there are no observations, that I’m aware of that would suggest 2000 monarchs would converge on a small parcel of land as far north as northeastern Oklahoma to form overnight clusters.

This event followed a series of storms that moved into Oklahoma from Texas. Winds associated with these storms were variable with some from the WSW raising the possibility that the weather patterns and the habit of monarchs to ride tail or quartering winds caused them to converge and to seek refuge at a site that offered protection from the winds. We will try to dig into the weather data to see if we can learn more about the conditions preceding and during this event.

During fall migration, if you follow the flight of single monarchs that are looking for a roost site at the end of the day, one after another can be seen headed in the same direction, and along what appears to be the same path, usually toward the highest feature on the horizon. That behavior often takes them to trees at the tops of hills. The site of these observation was also on a hilltop. Fall or spring, clustering high in trees in refuge sites on hills has the effect of protecting monarchs from freezing temperatures. It’s possible that this phenomenon occurs from time to time but goes unobserved because few of us would think of looking for spring clusters on hilltops.

Two other points are worthy of mention. While many of the monarchs appeared to be in good condition, others were quite worn and tattered. There was no way to determine the sex ratio but the clusters were composed of both males and females.

As I was finishing this text, I received an email from my colleague written at 6:54 saying that 10 monarchs are in the process of forming a cluster on one of the pines. Spring monarchs in the trees three nights in a row. That’s amazing. It’s totally out of my experience.

ADDENDUM

The Weather and Assumptions

Before diving into the weather data, it’s useful to remind ourselves about the basic assumptions as to how monarchs interact with physical factors. Our assumptions are as follows:
1) Monarchs don’t fly at night
2) They are progressively dispersed in the spring as they move in a generally northeasterly direction in the United States
3) They advance using powered flight
4) When possible, they take advantage of tail and quartering winds to move NE.
5) They don’t advance into strong head winds unless there are areas where wind speed is low at ground level
6) They don’t fly in heavy rain
7) The minimum temperature for flight is close to 50F in full sunlight
8) The most rapid advances occur when temperatures exceed 65F with quartering winds from the SSW, SW and WSW.

There are observations and opinions but very little data that pertain to these assumptions, but let’s press on.

The data below are summaries of the times, temperatures, wind speed, wind direction, precipitation and cloud cover for the greater Tulsa, OK area (that includes Bixby) for 2-5 April 2017.

Daily summaries and interpretation

2 April. The temperatures ranged from 59-64F, winds were light and generally from the SE, overcast conditions prevailed with three periods of light rain. Monarch activity was probably light. Wind speed and direction probably had little impact on the amount and direction of flight. These were suboptimal conditions for advancing to the northeast and, it’s likely monarchs did not advance but remained where they were.

3 April. The temperatures ranged from 57-71F with temperatures from 66-71 through the afternoon. Winds were predominantly from the west but shifting a bit to the WNW toward the end of the day. Wind speed ranged from 9-15mph. While the day began as overcast there was a progression to mostly cloudy, partly cloudy and scattered clouds as the day progressed.
With these afternoon temperatures, wind speeds and directions, monarchs should have been on the move. Further, with quartering winds from the W and WNW, the net direction, or vanishing bearing, of monarchs in flight on the afternoon of the 3rd should have been to the ENE. In other words, monarchs from central OK would have been “pushed” towards the Tulsa area – IF, the underlying assumptions are true.

4 April. The temperatures ranged from 55-71F with temperatures ranging from 66-71F for the afternoon. Winds started from the N but shifted to the NE and ENE for most of the day but variable from the N and NW for the last hour of the day. Except for one brief period, winds ranged from about 11 to nearly 20mph. The skies were characterized as overcast, mostly cloudy, scattered clouds with periods of light rain and thunderstorms in the last hour and a half of the day. Under these conditions monarchs would have experienced quartering winds from the NE and ENE much of the day with the possible outcome of being “pushed” slightly to the NW. Just the opposite of what may have happened on the 3rd. In addition, with the advent of the thunderstorms and dropping temperatures after 5:30, directional flight should have declined and shifted to finding safer harbor for the night. This scenario is consistent with sightings of monarchs seeking shelter in pine trees after 6PM.

5 April. Temperatures ranged from 49 – 63F through the day. Winds were from the NW, N, NNW most of the day with wind speeds ranging from 18-32mph until 4PM but dropping somewhat in the last two hours of the day. Although some monarchs were observed puddling and leaving the pines at various times on the 5th, it is unlikely that those that left progressed very far given the head winds. It seems probable that most simply moved to other protected locations.

So, where does this leave us? How is it that 1200-2000 monarchs that probably overwintered came together in one small patch on a hilltop in northeastern Oklahoma? I won’t claim to know, but the data seem to be consistent with the hypothesis that prevailing winds caused monarchs moving through eastern Oklahoma to converge over a two-day period and to seek shelter in a place that offered some protection from unsettled conditions at the end of the second day.

Table 1. Hourly weather and observations for Tulsa, OK area (includes Bixby, OK) for 2-5 April 2017

For additional discussion on a similar spring migration observation, please see “A chance meeting and perhaps some insights on the spring migration” which is a reposting of a message sent via our Dplex-L email discussion list back on 1 May 2000.

New Monarch Watch Citizen Scientist Project

Monarch Watch is seeking the immediate assistance of hundreds of monarch enthusiasts (citizen scientists) in collecting observations of monarchs in their area during the spring and fall. This project is an attempt to assemble quantitative data on monarch numbers at critical times during the breeding season. The data from these observations will be used to assess their value in predicting trends in the population.

Update: A Frequently Asked Questions section has been added to the end of this article.

BACKGROUND

Why do we need a “monarch calendar” and your help recording monarch numbers?

The decline in monarch numbers over the last 15 years has inspired numerous attempts to define critical factors that explain the inter-annual variation in monarch numbers. The data sets used for these analyses have had a variety of limitations which have either been ignored or underappreciated by the authors of a number of publications. The truth is that much of the data that is available is too general and does not adequately represent important aspects of the biology that underlies the development of the population each reproductive season.

There are numerous gaps in our knowledge and some of these gaps can be addressed if we can convince a large number of monarch enthusiasts (citizen scientists) to record the number of monarchs they see each day and what the monarchs are doing, along with general information about the physical conditions associated with each observation.

At the start of this project, we won’t ask participants to record behavior or physical conditions (temperatures and wind speed and direction) but a few observations and notes along those lines might be useful in targeting conditions most favorable for monarch activity. The pivotal latitude is 35N (e.g., Oklahoma City). If the observer is located at a latitude less than 35N (i.e., “South”), we need the number of monarchs seen each day during the following two periods: 10 Mar-30 Apr and 1 Aug-25 Sep – 52 days & 56 days = 108 days total. If the observer is located at a latitude greater than 35N (i.e., “North”) the observation periods are 1 Apr-20 Jun and 15 Jul-20 Aug – 81 days & 37 days = 118 days total.

The first period in the south covers the interval during which the overwintering monarchs arrive in Texas and Oklahoma and points to the east. We need to capture a better estimate of the number of monarchs in this region that arrive from Mexico each year. This starting number has not been captured effectively. The second interval in the south captures the arrival of pre-migration monarchs from the north as well as potential local reproduction during this time. In the north, the first interval will capture some of the returning monarchs early in that period but is more likely to chronicle the arrival of first generation monarchs migrating north to the summer breeding grounds. The second period in the north should capture the relative intensity of the reproductive activities of monarchs during the period in which most of the eggs are laid that become the adults that populate the migratory generation later in August and September.

To provide meaningful data, we need to recruit hundreds of volunteers to record what they see.

INSTRUCTIONS FOR CITIZEN SCIENTISTS

Here is what we need you, as citizen scientists, to do:

1. Register as a participant in this project by providing your name, location (including latitude and longitude), and email address via the form at

To determine your geographic coordinates, please use any of the following sites (or others) to enter your city, state/province, and zip/postal code and retrieve your latitude and longitude in decimal form (e.g., latitude: 38.95 longitude: -95.27 for Lawrence, KS 66045).

2. Record every monarch seen in your location for specific periods depending on your latitude. To keep these records all one has to do is to list the number of monarchs seen each day in which seeing a monarch was a possibility. If you were outdoors and saw none, record a zero (0). On the other hand, if there was no opportunity to make any observation due to work or vacation, etc., leave that date record blank. There will often be days when monarchs can’t be active due to weather conditions (e.g., low temperatures, extreme overcast, heavy rainfall). These intervals, if long enough, can also impact population growth. A “W” (for weather) should be entered for each of these days.

We have provided some sample files below that you can use to log your observations but exactly how you do it is up to you. Here are some suggestions: spreadsheets (Excel, Numbers, Google Sheets, etc.), printed calendar sheets (or just a calendar), calendar applications on your computer or phone, notebooks, notes or other text files on your computer or phone. Please feel free to use whatever is easiest and most comfortable for you to log your daily observations of monarch numbers.

Please note: The records for each time period should only reflect the numbers of monarchs seen on any specified day within 50 miles of your home location. If you wish to report monarchs seen at a location other than your home location (specifically, at a different latitude) please use another datasheet as this should be submitted separately.

3. Submit your data to us at the end of the observation period via an online form. We will provide a link to the submission form at a later date via the email address you give us when you register. The form will be very simple; all you will need to do is enter your name and location (including coordinates as you do when you register) then you will be presented with the appropriate time period form to enter your data for each day.

We will assemble the calendar records for each period and region then provide summaries online once we have a chance to analyze the data.

Please register for this project and start logging your observations today! Thank you in advance for your assistance – if you have any questions or comments about this project, please contact us at monarch@ku.edu

SAMPLE FILES (for logging observations)

Spreadsheets (Excel format; can be imported into other applications)
2017-spring-south.xls
2017-spring-north.xls
2017-fall-south.xls
2017-fall-north.xls
sample-data.xls (partially completed sheet for reference)

Blank Calendar Sheets (to print)
2017-spring-south.pdf (Apr 2017)
2017-spring-north.pdf (Apr-Jun 2017)
2017-fall-south.pdf (Aug-Sep 2017)
2017-fall-north.pdf (Jul-Aug 2017)
You can also create custom calendars via www.timeanddate.com

FREQUENTLY ASKED QUESTIONS

Preamble

We’ve received a number of questions about our Monarch Calendar Project. We’ve tried to summarize these questions and, through the answers, clarify how we’d like you to record the data.

We need a better way of predicting the fall migration and the size of the overwintering population. This project is an attempt to capture three aspects of the seasonal dynamics of the monarch population that will help us understand how the population develops through the breeding season. Specifically, we are trying to obtain data (with your help) that will provide information on the relative numbers of monarchs seen after first sightings in most areas of the country. In addition, we are seeking data on the number of monarchs seen during the last egg laying periods in the north and south. Lastly, records of the weather-related events, as indicated by the Ws on the data sheets, may indicate times and regions during which weather had a negative impact on the population.

Thanks for your willingness to participate in this project. We appreciate your help. As you can see, from the scope of the project, the only way to obtain these data is through the cooperation and commitment of a large number of citizen scientists such as yourself. Again, we appreciate your help and we are looking forward to receiving your data.

Questions and Answers

1. When should I start my calendar?

The idea is to keep the record keeping as simple and as accurate as possible. Here are some suggestions:
• Start with your first sighting
• Start when you find the first eggs
• Start when monarchs and/or eggs have been sighted in your area
• Start only when sightings are reasonable given your latitude.

2. How do I make counts? Suppose I see a monarch six times in my garden during a day do I count that as six butterflies or one?

The rule here has to be to use common sense and be conservative. Egg laying females in the morning and patrolling males in the afternoon will often return to the same patch over and over on a given day. If during the sightings, the observed butterfly appears to be the same color, size and condition, count it as a single butterfly. Females are darker than males and male/female behavior is different. Careful observations should help you distinguish one butterfly from another. However, if you are uncertain, be conservative and record the lower number.

3. What if I am in an area in the northern part of the range where monarchs are seldom seen before 20 June?

Actually, we want to confirm that monarchs aren’t seen above certain latitudes until after the 20th of June. Please indicate that to be the case, if true, and only record data for the critical egg laying period from 15 July to 20 August. This directive is likely only to apply to a few of you who report sightings from 46N or further north.

4. What if I work during the week and can’t make observations? Or, do I have to observe for a certain length of time on a given day to record a number seen or a zero?

We expect the opportunity to observe will vary greatly for each observer over the calendar period and that some observers will, by virtue of opportunity, activity or lifestyle, see more monarchs than others. That’s fine. We want to capture relative numbers over large areas and long time periods for multiple years. Don’t worry if you don’t see monarchs or don’t spend a lot of time looking for them. Just record what you see and, if you think there was a good opportunity to have seen a monarch and didn’t, just record that day as a zero. If you had no opportunity to observe, that’s a blank. We expect more blanks and 0s with some Ws (for “weather” – see #7 below) than actual numbers sighted on nearly all the data sheets.

5. If I raise and release monarchs, do I count those?

The short answer is no. We are trying to record the dynamics of the wild population.

6. What about species that are easily confused with monarchs?

Yes, there are species that are sometimes confused with monarchs, most commonly the viceroy and the queen. In flight, the viceroy flies closer to the ground than monarchs and frequently lands on the ground. It is also less likely to visit flowers. However, when on flowers, viceroys and queens can be easily mistaken for monarchs. Monarchs are larger than both of these species. All we can tell you here is to learn your butterflies, observe closely and do your best.

7. When should I record a W for weather? What weather conditions limit monarchs?

Low temperatures (mid 60s and lower), extremely high temperatures (95 and higher), extreme overcast, rain, and high winds can completely stop monarch activity. When that happens, please record a W for weather. The Ws are important. There is no reproduction during a W – no mating, no egg laying and, if the temperatures are low, larval development slows down as well. Monarchs can get off to a good start and then be slammed by weather that shuts down reproduction. We need to capture that. Five consecutive days of low temperatures and rain can have a strong negative impact on a population that can easily be missed if projections are based on mean monthly temperatures. We aren’t really concerned about the weather before monarchs arrive. If necessary, we can capture weather data from “Weather Underground” for the periods prior to the arrival of monarch in any region.

8. Does this project apply to Hawaii, Southern California or Florida or other continuously breeding populations?

No, it doesn’t. Continuously breeding populations are found in Florida, some regions along the Gulf Coast, Southern California, Hawaii and numerous Pacific Islands. It’s probable that some or all of these populations cycle with the seasons and this should be captured. However, that will require a different protocol.

9. Why aren’t you asking us to record eggs, larvae and migrating monarchs?

The reason is simple; there are other programs that provide data on these aspects of the life history. Please see the following links if you wish to participate in any of these programs.

First eggs – these sightings can be reported via Journey North (learner.org/jnorth/tm/monarch/SpringWatch.html)

The Monarch Larval Monitoring Project (MLMP) at the University of Minnesota tracks both larvae and eggs (mlmp.org)

Migratory monarchs are tracked by Journey North through sightings of overnight roosts (https://www.learner.org/jnorth/tm/monarch/FallWatch.html)

Monarch Watch’s tagging program captures data related to the size and dynamics of the migratory population (monarchwatch.org/tagging)

Comments on Flockhart et al. (2017)

Comments on Flockhart et al. 2017 by Chip Taylor, Monarch Watch

Regional climate on the breeding grounds predicts variation in the natal origin of monarch butterflies overwintering in Mexico over 38 years

D. T. TYLER FLOCKHART, LINCOLN P. BROWER, M. ISABEL RAMIREZ, KEITH A. HOBSON, LEONARD I. WASSENAAR, SONIA ALTIZER and D. RYAN NORRIS

Full Article: Global Change Biology (2017), doi: 10.1111/gcb.13589

The paper by Flockhart et al. on the climatic factors that contribute to the natal origins of monarchs that reach the overwintering sites in Mexico is interesting to be sure and it’s a valuable contribution to this topic. That said, it’s not a definitive description of the either climatic factors or origins. Most studies of this type have limitations and, in this case, there are a number of issues that need to be resolved. For example, there are limitations to the precision or confidence given to the assignment of any one individual to a specific geographic origin. Each of these assignments can be considered to be a hypothesis based on current knowledge. The addition of a third isotope to the analysis could change the assignments dramatically and the map as well. In addition, there are other data sets that suggest different causal factors and patterns of origin.

As I said, this paper is a foundation, one that needs to be built upon. That will happen if and when the following issues are resolved.

1) A close examination of the data shows that many of the samples were limited to 40 individuals with less than 30 for a given year in three cases. Only 5 of the of the 20 years were represented by 60 or more individuals. Ok, we don’t need to go into the statistical weeds here, and I’m not good at it anyway, but there is a sample size problem here. Relying on samples of 40 or fewer to represent much of a continent for 15 of the 20 yrs is iffy at best. However, as a first step, small samples sizes are understandable since the analysis of each individual is costly (+/-30$ Canadian).

2) As mentioned, the assignment of individuals to specific regions needs to become more precise. Isotope data has a geographic basis determined by carbon isotope profiles (isoclines) across the country as well as hydrogen isoclines that are determined by the amounts and geographic origins of rainfall as influenced by temperature and topography. The latter tends to vary over time. Further, there are sometimes differences within regions that can be attributed to what an organism has fed on. For example, samples from game animals have been analyzed to determine whether or not they have fed on crops. Along these lines, there are unpublished data that suggest there may be differences in the isotope signatures obtained from monarchs within geographic regions that could result in misassignment. Clearly, to further our understanding of geographic origins, a third or perhaps even a fourth isotope will be needed to assign each individual to a specific location.

Modified from Flockhart, et. al 2017.

3) The data and interpretations presented in this paper differ from those obtained by other means. There are at least three cases where monarch counts differ from the isotope data. Here is a short version of my concerns: A) If the number of monarchs counted each year at Cape May is a measure of the production in the northeast, why aren’t years with high or low numbers at Cape May reflected in the isotope data? B) The eggs per stem data from the Monarch Larval Monitoring Project have been shown to be strongly correlated with the overwintering numbers. It can be said to predict the overwintering numbers to a degree suggesting that the upper Midwest (the 38% area on the isotope map) contributes the majority of the monarchs to the overwintering population – a proportion much larger than 38%. C) The isotope map indicates that 12% of the overwintering monarchs originate from the Northwest; western Dakotas, the Prairie provinces and Montana and Wyoming. How can this be the case since this is a region with low numbers of milkweeds and monarchs? Monarchs only appear to reach this region in good numbers when the spring population is robust together with high temperatures in May and June that promote colonization.

4) The climate analysis does not fit with other data that are known to have a strong impact on monarch production during March and April and later during the summer months. Showing why this is the case will have to wait but this is an issue that also needs to be resolved.

5) And last, but not least, the tagging data has something to say about origins of monarchs that reach the overwintering sites in Mexico. In his post to Dplex-L, Anurag Agrawal assumes that the percentages assigned to each region are equal to production and that area and production and reaching Mexico are linked in a precise way. That’s not the case. The probability of reaching Mexico is a function of origin, but it’s not a linear function. To be a linear function, a certain proportion of monarchs would be expected to reach Mexico in direct proportion to the distance of the starting point to the overwintering sites. For reasons that are not clear, increasing numbers of monarchs need to be tagged at a given latitude for each degree of longitude as one moves eastward. In plain language, more monarchs have to be tagged in the East than in the Midwest for one to reach Mexico. Getting back to the point of geographic production, for 15% of the monarchs reaching Mexico to originate in the Northeast would require production that would be much higher – at least 30% of the total monarchs in a specific migration. This same reasoning and argument applies to the Northwest sector of the isotope map. The 12% and 15% values for these two regions are simply too high.

To clarify my point about differences in recovery rates based on geographic origin, I have included one figure from a preliminary analysis of recoveries obtained following the winter kills at the overwintering sites in the winters of 2001-2002 and 2003-2004. This figure shows the percentage of all monarchs tagged in 2001 distributed over each 5 degrees of latitude and longitude. Note the figure of 25.1% that represents the middle of the corn belt, mostly eastern IA, and all the 5x5s that occur east of 80W (18.3% of all tags applied). The latter represent nearly all of the Northeast and some of the North-Central region. An analysis of the recoveries showed that 33% of the monarchs recovered were tagged in the 5×5 in the center of the corn belt while just 4.6% of the tags were recovered from the area east of 80W. Similar figures were obtained for the tagging and recoveries in 2003-2004 with 32% recovered in the same area of the corn belt and 7.8% from the combined areas east of 80W.

To recap the two years, we are comparing recoveries from areas where 25.1% vs 18.3% of the monarchs were tagged in 2001 and 22.6% vs 18.8% in 2003. The results were similar, with 33% and 32% recovered in the corn belt and 4.6% and 7.8% recovered in the east. This is a striking difference and it strongly suggests that mortality during the migration is much higher for monarchs originating east of 80W. However, before leaving this topic, we have to ask whether the Northeast is underrepresented in the recoveries due to some bias in the tagging. That’s possible. Many of the monarchs in the east are tagged along the coast and the recovery rates for monarchs moving along coast lines are particularly low. Given that potential bias, let’s just compare the inland 5×5 in the east (75-80W, 45-49N) with the corn belt 5×5 for both years. The numbers tagged per recovery were 24 for the corn belt vs 114 for the east in 2001. In other words, taggers had to apply 4.75 times more tags in the eastern 5×5 to have one recovered in Mexico. The difference was not as great in 2003 but those in the east still had to tag 2.2 times more monarchs to have a recovery than their counterparts in the corn belt.

Moving forward, it would be ideal if the isotope data could inform us in greater detail of the natal origins of monarchs that reach Mexico. Such data could be used to more precisely target areas/regions in need of protection and perhaps restoration. This analysis is not quite there yet. At this point, the loss of milkweeds, habitat conversion due to the renewable fuel standard and other factors (see Monarch Watch Blog entries for references), as well as the tagging data, indicate that conservation efforts should focus on what I have referred to as the milkweed/monarch corridor. Based on tagging data, the corridor ranges from 80W to 98W slanting SW through Kentucky, Tennessee and Arkansas and then Texas to the border with Mexico as indicated in the figure below. This figure is similar to one being used by the USFWS to target regions considered to be of greatest concern with respect to monarch conservation.