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.

Monarch Population Status

World Wildlife Fund Mexico in collaboration with SEMARNAT and CONANP and the Monarch Butterfly Biosphere Reserve (MBBR) announced the total forest area occupied by overwintering monarch colonies. Thirteen (13) colonies were located this winter season with a total area of 2.91 hectares:

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 – temporada 2016-2017

FWS/NRCS Conservation Plan

Restoring habitat for any species is complicated and requires a great deal of thought and lots of research to establish best practices. The following “plan” and set of guidelines was issued last Friday (13 January) under the title

This report is long and complicated. It’s 107 pages! The message is mostly tailored to agency personnel and land managers rather than the general public. That said, it is intended to show what the respective agencies are committed to doing to sustain the monarch migration. Frankly, the document needs an executive summary.

I haven’t read the entire document but skimming various sections suggest that some of the take home messages should be:

1) plant regionally appropriate native milkweeds wherever possible within what might be loosely called the milkweed/monarch corridor – although they don’t use that term.

2) follow best practices for restoration in your area

3) add nectar plants to restoration sites in seed mixes or as plugs

4) maintain restored sites

5) develop partnerships

6) minimize the use of insecticides and limit the use of herbicides as much as possible (it’s common to use herbicides in the first step of restoration to eliminate introduced and sometime invasive species and other vegetation that might interfere with the establishment of the desired seedlings or plugs).

7) monitor plantings to establish their success

8) monitor the use of restored sites by monarchs and pollinators (I didn’t see specific protocols for that topic in this doc but that will be a goal of other programs).

This report is based on long discussions and research that establishes the background for how monarchs got to the point where we have to focus on habitat restoration to sustain the migration. The text contains numerous sections dealing what is known about monarch biology, population dynamics, climate influences and habitat needs. An extensive bibliography is provided at the end of the text.

Read the full report here:
Monarch Butterfly Conference Report 2016 (107-page PDF, 10MB)
www.fws.gov/savethemonarch/pdfs/MonarchConferenceReport2016.pdf

Why monarchs need Monarch Waystations

Our interstates are populated with gas stations, restaurants, rest stops and other resources needed by travelers. These fueling stations for both vehicles and people are waystations for those of us that migrate across the country. We rely on these resources, but what would happen if these fueling sites weren’t reliable? Let’s suppose your task is to drive/migrate on I-35 from the Texas/Mexico border to Duluth, MN – a distance of 1300 miles. Now suppose that there is a breakdown in fuel delivery in some places, massive and widespread blackouts in others that keep the gas from being pumped and the restaurants closed and that, as a traveler, you have no idea where the gaps in service are located. What would you do? Would you leave the interstate or trust that you would find resources somewhere ahead? If you gambled that there was gas ahead, that might work, but it might not, and you might find yourself stranded on the roadside, along with thousands of other cars and trucks whose drivers also gambled that there was fuel ahead. Millions of cars and trucks use I-35 each day and, if this scenario developed suddenly, tens of thousands of vehicles could become stranded.

Now suppose you are a monarch butterfly and you are driven to migrate north in the spring across a landscape parallel to I-35 in which there are abundant resources in the form of milkweeds and nectar sources in some areas but big, really big, gaps with no milkweeds or nectar plants in other areas. How would these gaps (ecologists call them fragments) affect monarchs? Would some starve? Would females simply lay fewer eggs? The answer to both questions is probably yes. That said, we have no quantitative data on this point, only anecdotes, assumptions, models* and more questions. How is the pace of the migration, mortality, and egg laying rate compromised by the lack of resources? Are the effects large or small? The fact is that we know very little about the physiological capacity of monarchs, but surely they have limitations. I get 52 miles per gallon with my Prius. How many sips of nectar are needed for a monarch to cover the same distance or lay an average number of eggs in a day? Stated another way, monarchs have daily resource needs. In short, they need fuel and they need patches of milkweeds for oviposition. Ultimately, what we need to know is how total reproductive output (also known as realized fecundity) is affected by large gaps in the landscape that lack resources.

My bottom line is this – it’s not only the abundance of resources in some areas but how resources are distributed across the entire landscape used by monarchs. The vast prairies and grasslands that were once the home for monarchs (and many other migratory species as well) have been replaced by farms and rangeland, cities large and small, and their attendant sprawl. And while there are abundant resources remaining for monarchs in some areas, there are also large – very large – gaps and these gaps with no waystations are the very reason for Monarch Watch’s Monarch Waystation Program. Our intention has always been to encourage people to create resources that fill these gaps. In the West, the earliest trains required waystations to take on coal and water to keep going and the Pony Express had waystations so riders could change horses every twenty miles or so. Monarchs also need waystations, just as we need them along our interstate highways.

*The models developed by Myron “Meron” Zalucki and colleagues suggest that increased fragmentation results in a significant loss in egg laying (realized fecundity). See references.

NOTES AND MAPS
The Monarch Waystation program began in the spring of 2005. The program began slowly with only 395 habitats (sites) added to the registry in 2005. The number of habitats added through 2012 remained modest and averaged only 823 per year. However, beginning in 2013, as the extent of the monarch decline became more widely known, the number registered per year jumped rapidly. In 2016, 2869 habitats were added to the Monarch Waystation Registry.

An interactive map and complete listing of habitats that have been registered as Monarch Waystations can be found via the Monarch Waystation Registry (monarchwatch.org/waystations/registry/). The map allows you to zoom in to specific cities or regions and view approximate locations of Waystations in your area. Since Monarch Waystations are mapped only by zip code (for privacy), the number of sites in specific areas are likely to be under-represented (i.e., a single map point may represent several nearby habitats).

Here is a current screenshot of the map:

Brenda Dziedzic kindly sorted and assembled the numbers of Monarch Waystations for each state:

REFERENCES

Habitat loss
For texts and references dealing with habitat loss, please visit the following Monarch Watch Blog posts.

Is the monarch decline due to an increase in mortality during the fall migration?
monarchwatch.org/blog/2016/11/02/tagging-results-and-the-monarch-decline/

Monarch Butterfly Recovery Plan: Part two
monarchwatch.org/blog/2015/12/01/creating-a-monarch-highway/

Monarch Butterfly Recovery Plan
monarchwatch.org/blog/2014/03/25/monarch-butterfly-recovery-plan/

Monarch Population Status
monarchwatch.org/blog/2014/01/29/monarch-population-status-20/

Monarchs and the spatial distribution of resources
Zalucki, M. P. and Rochester, W.A. (2004). Spatial and temporal population dynamics of monarchs down under: Lessons for North America. In K.S. Oberhauser and M.J. Solensky (Ed.), The Monarch Butterfly 1 ed. (pp. 219-228) Cornell University Press, UK: Comstock Publishing Associates.

Zalucki, M. P., Parry, H. R. and Zalucki, J. M. (2015) Movement and egg laying in Monarchs: to move or not to move, that is the equation. Austral Ecology, 1-14. doi:10.1111/aec.12285

Zalucki, Myron P. and Lammers, Jan H. (2010) Dispersal and egg shortfall in Monarch butterflies: what happens when the matrix is cleaned up?. Ecological Entomology, 35 1: 84-91. doi:10.1111/j.1365-2311.2009.01160.x

Milkweeds for Monarchs in 2017

Milkweeds for Monarchs in 2017 – please order now.

Monarchs need milkweeds. These plants are the sole food sources for monarch larvae and if there are no milkweeds there are no monarchs. Our mission at Monarch Watch is to do whatever we can to facilitate the planting of milkweeds to replace the enormous number of milkweeds that have been lost over the last 15 years due to the adoption of herbicide tolerant (HT) crops, the production of ethanol from corn (the renewable fuel standard – RFS), excessive mowing and use of herbicides and suburban sprawl.

We have three programs designed to get milkweeds planted through much of the United States: 1) the Milkweed Market, through which milkweed plugs can be purchased at low cost; 2) the Free Milkweeds for Restoration program underwritten by donors; and 3) the Free Milkweeds for Schools and Non-Profits. The latter program allows us to provide milkweeds for monarch and pollinator gardens at schools and sites maintained by non-profits.

We are accepting applications/orders for all three of these programs at this time. Please visit the following links:

Milkweed Market: monarchwatch.org/milkweed/market/

Free Milkweeds for Restoration Projects: monarchwatch.org/free-milkweeds

Free Milkweeds for Schools and Non-Profits: goo.gl/forms/pfdn8iy01n38mhuf2

Growing milkweeds is a lengthy process that begins in December with estimates of the number of milkweeds needed for each region of the country. Although we try to anticipate demand, it’s a bit of a guessing game. If we overestimate demand, plants go to waste and that’s costly and, if we underestimate demand, customers are disappointed.

Please place your orders or complete your applications now to help us match supply with demand in the coming season.

Our program to distribute Free Milkweeds for Restoration has been supported by contributions from corporations, non-governmental organizations (NGOs) and individuals. This past season, with the assistance of these contributions, we distributed 171,000 milkweeds. We would like to do the same in 2017 but need more support. If you are interested in supporting this program, please donate through the donation link at monarchwatch.org/donate/ and specify that your gift is for restoration.

Thank you from the Monarch Watch Team,
Chip Taylor
Angie Babbit
Dena Podrebarac
Ann Ryan
Jim Lovett
Matt Tucker

In Pursuit of a Little History – A Retraction

Mea culpa is a Latin phrase that means “through my fault” and is an acknowledgement of having done wrong. The expression is used also as an admission of having made a mistake that should have been avoided. In other words, I messed up and should have known better. So, what am I confessing to? The publication in the 1998 Monarch Watch Season Summary of an article entitled “In Pursuit of a Little History” (pages 24, 25 & 50) and it is with these notes that I wish to retract this publication and to declare that all statements therein should forever be ignored. I also wish to apologize to Cathy Brugger, as she was then known, and now as Catalina Trail, for the publication of this article.

Catalina and I have been communicating about the article for several months. She has had several specific objections to the content such as not having met the “guide” mentioned in the article and NOT being led to the monarch colony on Cerro Pelon. She feels that the latter point specifically diminishes her role in the discovery of the first monarch colony by those not native to the area. In addition, I made the mistake of telling the story mostly from the standpoint of Ken Brugger thus ignoring Catalina’s leading role in the discovery of the monarch colonies. On 2 January 1975 Catalina and Ken hired a local person (not a guide) to help them carry their equipment and supplies up the mountain side since they expected to spend nearly the entire day exploring the mountain. Catalina and Ken came upon their first colony on Cerro Pelon that day at a location known as Carditos. Finding the first colony was a major achievement. The search had been long and hard with many days on holidays and weekends spent exploring likely locations throughout this mountainous region. Failures on many searches, although discouraging, surely led to insights and maybe a bit of intuition. The bottom line is that we owe a debt of gratitude to Catalina and Ken Brugger along with their partners Fred and Nora Urquhart for their persistence and dedication – an effort that solved one of the major biological puzzles of our time. Further, these discoveries made the world aware of the magnificence of one of the world’s most amazing migrations. Thanks, Catalina, and thanks to your team for opening our eyes to this extraordinary force of life.

Catalina has been interviewed many times over the last several years. The story of the discovery of the monarch overwintering colonies and her role in this effort has been well defined in these write-ups. Here are links to several articles with notes that relate to the above comments:

Trail said she and Brugger had hired a local “so we wouldn’t be alone” and routinely hiked 18 kilometers a day over the skirt of the mountain and back to their camper or inn at day’s end.

Finally, on January 2, 1975, the couple came upon Cerro Pelón, a dramatic high elevation summit that spills into an arroyo, or dry streambed. “That’s when we saw them,” recalled Trail.

The location hosted what seemed to be a Monarch butterfly superhighway and fir trees laden with millions of the roosting creatures. Occasional dead butterflies littered the forest floor.

Trail was first to the site. Brugger and their helper (you can see him behind Catalina in one of the above article’s photos) brought up the rear with food, water, and gear, including a camera that snapped the photographs reprinted in this story:

“Trail is the only living founder of three people present at the “discovery” of the site where millions of Monarch butterflies roost each winter.”

Loaded with three backpacks and sturdy walking sticks, Brugger, Trail and Kola set off at 4 a.m. on Thursday, Jan. 2, 1975, on the trail bike. They met up with a local man whom they’d hired and tied their packs onto his uncle’s horse. Their equipment included three cameras, canisters of film, topo maps, water, food and notebooks.

As to why I chose to write the story in question, all I can say in my defense is that I was misled and more than a bit naïve and gullible. Mea culpa.

Tagging results and the monarch decline

Introduction

The authors of three recent papers dealing with the decline in monarch numbers at the overwintering sites in Mexico have proposed that the decline is due to increased mortality during the migration or the establishment of the overwintering population (Badgett and Davis, 2015, Inamine, et al., 2016, Ries, et al., 2015). While Ries, et al. (2015) suggest that increased mortality during the migration could account for the decline, they acknowledge that other factors could be involved. Badgett and Davis (2015) are more certain of this interpretation, to quote – “we interpret the disconnect between the size of the migratory cohort at Peninsula Point and the overwintering population to be the result of mortality incurred during the migratory journey”. Similarly, from Inamine, et al. (2016) “our results are consistent with failed migration or re-establishment at the overwintering grounds impacting the population decline in Mexico.” These statements are nothing more than speculation, and no data are offered in these papers in support of this supposition. Reviewers of these manuscripts and editors of the respective journals should have challenged these unsupported statements, particularly since this speculation is used in the papers by Badgett and Davis (2015) and Inamine et al. (2016) to challenge the view, well supported by data, that the loss of milkweed and breeding habitat is the cause of the monarch decline.

Unfortunately, unsupported claims have a way of becoming facts (especially in press releases and news reports). Decisions with regard to monarch conservation should be based on data and not on unsupported speculation. This brings us to the question: Are there data that support or refute the supposition that mortality during the migration has increased over the last decade? Our tagging data are relevant to this question.

Because this text is written as a blog article, we will start with a brief summary of the results followed by a discussion. The sections that follow include background information on the tagging program along with a discussion of the dynamics of tag recovery and a section dealing with the analysis. For those interested in a quick read, we suggest reading the summary together with a scan of Figures 1-3. This text is being rewritten for publication.

Summary

The following analysis is based on tags applied to the wings of over 1.2 million monarchs over an 18-year period.

1) A significant positive association exists between the numbers of monarchs tagged each fall and the sizes of the subsequent overwintering populations (Figure 1). The tagging represents both a broad sampling area and an extended time period and, as such, is a more realistic measure of the population than population estimates obtained at peninsulas and regionally-limited butterfly counts. The migratory population is tagged over much of the area east of the Rockies (Figure 2). Tagging is conducted annually for a 2.5-month period as the migration progresses toward Mexico.

2) The data from 1998 to 2015 show no systematic decline in the proportion of tags recovered each year (Figure 3).

3) Some of the possible factors influencing variability in the tag recovery rate among years are:

1. Higher or lower numbers surviving the migration
2. Higher or lower mortality during the winter months
3. Accessibility of the searchers to the dead monarchs
4. Higher and lower off-site mortality
5. The effect of high or low density understory on recovery rates
6. Number of people searching for tags.

4) The tagging data are strongly correlated with the number of hectares of overwintering monarchs. This relationship establishes that there is no “disconnect” between late summer and overwintering populations. In contrast, the data sets used by Badgett and Davis (2015), Inamine, et al., (2016), and Ries, et al., (2015), which represent a small monarch source population (Peninsula Point, MI) and regionally-limited butterfly counts (OH and IL), are not correlated with overwintering numbers. Given the tagging results, it’s clear that the data sets used by these authors are inadequate measures of the late summer and migratory monarch populations. It follows that the conclusions, and speculations, based on these data are unjustified.

Figure 1. Number of monarchs tagged each year vs. the size of the overwintering population for the years 1998-2015. R² = 0.5476, p = 0.0004

Figure 2. Distribution of >220,000 monarch tags to >2250 recipients in 2015.

Figure 3. Proportion of tags recovered by year, 1998-2015 (2001 and 2003 excluded due to extreme weather events). R² = 0.002, p = 0.87 (NS)

Discussion

The data sets and analysis used by Badgett and Davis (2015), Inamine, et al. (2016) led them to conclude that there is a disconnect between the year to year numbers recorded by observers at Peninsula Point, MI (Badgett and Davis, 2015) or NABA summer butterfly counts (Inamine, et al, 2016) and overwintering numbers. “Disconnect” refers to the fact that neither count predicted or was correlated with the overwintering numbers. Failure to find the expected connection led the authors of both papers to speculate that the reason for the decline had to lie with increasing mortality during the migration. No data were offered in either paper in support of this speculation. The idea that mortality has increased during the period of the decline, roughly from 2005 to the present, is not supported by the tagging data.

The numbers of monarchs tagged each year are strongly correlated with the size of the overwintering populations, R² = 0.5476, p = 0.0004 (Figure 1). These data constitute direct evidence that the size of the late summer monarch population is related to the size of the overwintering population. In contrast to data cited by Badgett and Davis (2015) for Peninsula Point, a relatively small source area representing western Ontario and the Upper Peninsula of MI and the NABA summer butterfly counts from Ohio and Illinois analyzed by Inamine et al., (2016) and previously by Ries, et al., (2015), the tagging represents sampling of the population over much of the area east of the Rockies as the monarch migration progresses southward over a 2.5-month period from mid-August to November (Figure 2).

In this analysis we’ve made a distinction between the total number of tags recovered from those tagged in a given year and the rate (percentage/proportion) of recovery of all tags applied in a given year, the latter being the total recovered divided by the total number tagged. The total recoveries are positively related to the total hectares of monarchs reported in each year as well as the total area occupied by monarchs at El Rosario. This result is expected since recovery is likely a function of the proximity of tagged monarchs to a population of searchers. Analysis of the rates of recovery of tags shows that there was no significant change in the rate of recovery from 1998 through 2015 (Figure 3). This result indicates that mortality during the migration has not increased over the last 18 years.

Given the lack of evidence of an increase in mortality during the migration, the question becomes: How can we account for the so-called disconnect between the data from Peninsula Point (Badgett and Davis, 2015) and the midsummer NABA butterfly counts (Inamine, et al. 2016, Ries, et al. 2015) and the overwintering numbers reported in Mexico? The authors in each case accepted the respective data bases as representative of the larger population in spite of a substantial body of evidence defining the loss of milkweeds in row crops and the loss of milkweed-containing habitat in the Upper Midwest, the area known to produce most of the monarchs that reach Mexico, as the major causes of the monarch decline (Faber, S., et al., 2012, Flockhart D. T. T., et.al., 2015, Hartzler, R. G. 2010, Lark, T.J., et al., 2015, Pleasants, J. M. and Oberhauser, K. S. 2013, Wassenaar, L. I. and Hobson, K. A. 1998, Wright, C. K. and Wimberly, M. C. 2013). Wouldn’t it be wiser to reverse the questions in each case and ask why the Peninsula Point and NABA data are out of sync with the larger data sets on monarchs, milkweeds and habitat loss, since the data representing these factors are strongly correlated with the size of the overwintering population in Mexico? The expectation that population counts on peninsulas or from specific regions of the breeding range should correlate with the overwintering numbers in Mexico rests on the assumption that the conditions that lead to the establishment and development of the breeding population each year are uniform for all regions of the country. That assumption simply isn’t true. Recolonization and climate vary sufficiently across the breeding range within and among years to account for the so-called disconnect between population assessments from limited areas and the overwintering numbers (Saunders, et al. 2016). Stated another way, the timing of colonization across the northern breeding range and the biotic and physical factors the growing populations experience result in regional differences in the production of monarchs. We need to integrate these regional differences in population development to fully understand the year to year numbers in the fall migration. Further, we need to know the relative contribution of monarchs originating in each region to the overwintering population. The tagging data speak to that point as well but that will come later.

The interpretations of the data sets used by these authors have already been challenged (Brower, et al., 2012, Pleasants, et al., 2016). The results of the tagging analysis lend support to the views articulated in these earlier papers that the data from peninsulas (Badgett and Davis, 2015, Davis, A. K. 2011,) and regionally-limited butterfly counts (Inamine et al., 2016, Ries et al., 2015) are not representative of late summer monarch populations.

Background

Each year we issue monarch tagging kits to taggers broadly distributed east of the Rockies. The distribution of those receiving tags in 2015 is shown in Figure 2. Taggers are asked to return their data sheets. The date, location and person tagging each butterfly is logged into a database. Creating the database is a significant task since we receive 2000-5000 data sheets per year. Each tag bears an individual code and the codes are carefully matched to the tagger and the data on returned data sheets. Some taggers fail to return their data sheets with the result that 5-10% of the recovered tags cannot be associated with the date and location of tagging. These data are discarded. The failure to return data sheets also means that the number of monarchs we record as tagged each year is an underestimate. With few exceptions, tags are applied to migratory monarchs from early August to November. Most monarchs are tagged within the “migration window” for each latitude. The migration window is a 30-day period roughly corresponding to a 10-degree shift in the altitude angle (sun angle) of the sun at noon from 57-47 degrees. The leading edge of the migration usually arrives at each latitude close to an altitude angle of 57-56 with nearly all monarchs passing through a particular location when the altitude angle reaches 47 degrees (Taylor and Gibo, unpublished data). In this data set, the numbers tagged per year varied from 106,564 (2001) to 32,667 (2013).

Dynamics of Recovery

As the migration moves S and SW, we are informed of low numbers of sightings and recoveries of tagged butterflies. We will deal with these “domestic” recoveries at a later date. This analysis is limited to the recoveries at the overwintering sites in Mexico. Monarchs usually begin arriving at the overwintering sites in the last few days of October. Conspicuous colonies form by mid-November with tourism beginning at about the same time. Most tags are recovered from dead monarchs found beneath the colonies by guides and ejido members, including children. We estimate that there are 10-40k untagged butterflies for every one that is tagged. Because of the ratio of untagged to tagged, the search time to find a tag typically involves hours of shuffling through dead butterflies to find a single tag. Due to the effort required to find each tag (estimated to be 2-4 hours) and to reward those who recover tags, we purchase tags from guides and residents in late winter each year. Those with tags save them in the hope that they will be present when Monarch Watch (MW) representatives show up to buy tags. Some residents hold on to tags for many years until they have the opportunity to sell them. As a result of this dynamic, there is a long lag in tag recovery. Most tags applied in a given year are recovered over the next 4-5 years. However, it is not uncommon for MW representatives to be offered tags that were applied to fall migrants >10 years earlier. Two tags applied in 2001 and one from 2002 were purchased this past winter.

Because of the lag in recoveries, it is likely that more tags will be recovered for the monarchs tagged during the past five seasons (2011-2015). These additional recoveries will change the slopes of the graphs presented here but will not change the conclusions derived from these data. Similarly, as we continue to clean up this massive data set, it is likely that some numbers will change. Again, there is no reason to expect that such changes will alter the interpretations presented here.

Our tagging program evolved over the years. We started the program in 1992 and used the “alar” tags pioneered by Fred and Nora Urquhart. This method proved to be too difficult for many taggers and resulted in many broken wings. Over the next four years, we used rectangular tags that were applied with glue to the underside of a monarch’s hind wing. This method was also unsatisfactory and, in 1997, we developed the technology (a special adhesive and tool to cut the tags) to produce the circular tags used in most tagging programs today. The circular tags resulted in a substantial increase in recoveries.

Reasons for recovery rates

Although the number of tags recovered for a given year is related to the overall size of the population and to the area the colony occupies at El Rosario, other factors certainly contribute to the rate of recovery. It is likely that survival during the migration is both higher and lower than normal in particular years resulting in either greater or fewer tags at risk of being recovered. Similarly, it’s probable that mortality during the winter is both higher or lower than normal in specific winters, resulting in either higher or lower tag recovery. There are also day to day dynamics and seasonal changes as monarchs seek water or colonies shift in location, both of which can result in off-site mortality where tags are not likely to be found. Other site issues include the density of the understory, with denser cover limiting the ability to spot tags. There are human dynamics as well that include the accessibility of the colonies to the searchers, the shifting population of searchers due to the turnover in guides, the overall number of searchers and the economic conditions that motivate the searchers. Nevertheless, in spite of these sources of variance in the recovery rates, there are no patterns in the data suggestive of a significant decline in mortality during the migration.

Analysis

The summaries presented here deal with all records of circular tags applied during the migration as well as tags subsequently acquired in Mexico from 1998 – 2015, exclusive of 2001 and 2003. Circular tags were first used in 1997, and though we began purchasing tags during that year, residents had no advance information, and searching for tags was therefore somewhat limited in the winter of 97-98. The winter of 97-98 was also one of great contrasts, with a freezing event at Chincua that resulted in a small area with dead monarchs said to be two feet in depth to an abandonment of colony sites late in the winter as water sources dried up as a consequence of the extreme drought brought on by the El Niño of that year (Monarch Watch Season Summary 1997, p29). The abandonment of the colony site at El Rosario likely resulted in off-site mortality and lower than expected recovery rates. We excluded 1997 from the analysis for these reasons. The data from the 2001 and 2003 seasons were also excluded from the analysis since severe storms resulted in the deaths of roughly 70% of the monarchs each winter (Brower, et al., 2004, Taylor, 2004). Over 3626 tags were recovered following the January storm in 2002 with 3416 recovered following the storms of early 2004. The records from 1998-2015 represent 14,209 recoveries of more than 1.2 million tagged for an overall recovery rate of 1.18%.

Acknowledgements

We wish to thank Eligio García, Eduardo Rendón, and Lincoln Brower for assistance in locating the reports detailing the number of hectares occupied by monarch each year at El Rosario. Long conversations with John Pleasants helped to clarify statistical issues and how to present the data. We are indebted to Diane Pruden, Debbie Jackson, Gail Morris, Carol Pasternak, Janis Lentz, Sarah Schmidt, Dana Wilfong, Cathy Walters, David Kust and family, and many, many others who helped purchase tags. We are most appreciative of the many donors who have contributed to the tag recovery fund over the years. Hundreds of tags have been purchased by visitors to the overwintering sites and donated to Monarch Watch. Numerous staff members and students have logged and/or managed the data over the last two decades, and recently we have been aided by many volunteers in the process of verifying the records and formatting the data for entry into a larger database. And last, but not least, we wish to thank the tens of thousands of taggers who have so enthusiastically contributed to this project since 1992.

References

Badgett, G. and Davis, A. K. 2015. Population trends of monarchs at a northern monitoring site: analyses of 19 years of fall migration counts at Peninsula Point, MI. Ann. Entomol. Soc. Am. DOI: 10.1093/aesa/sav060: sav060.

Brower, L. P., D. R. Kust, E. Rendón-Salinas, E. García-Serrano, K. R. Kust, J. Miller, C. Fernandez del Rey, and K. Pape. 2004. Catastrophic winter storm mortality of monarch butterflies during January 2002, pp. 151–166. In K. S. Oberhauser and M. J. Solensky (eds.), The monarch butterfly: Biology and conservation. Cornell University Press, Ithaca, NY.

Brower, L. P., et al. 2012. Response to Davis: choosing relevant evidence to assess monarch population trends. Insect Conservation and Diversity 5: 327-329.

Davis, A. K. 2011. Are migratory monarchs really declining in eastern North America? Examining evidence from two fall census programs. Insect Conservation and Diversity doi: 10.1111/j.1752-a4598.2011.00158.x

Faber, S., Rundquist, S. & Male, T. (2012) Plowed Under: How crop subsidies contribute to massive habitat losses. Environmental Working Group report.

Flockhart D. T. T., Pichancourt, J. B., Norris, D. R. & Martin T. G. (2015) Unraveling the annual cycle in a migratory animal: breeding-season habitat loss drives declines of monarch butterflies. Journal of Animal Ecology, 84, 155-165.

Hartzler, R. G. 2010. Reduction in common milkweed (Asclepias syriaca) occurrence in Iowa cropland from 1999 to 2009. Crop Protection, 29:1542-1544

Inamine, H., Ellner, S. P., Springer, J. P. and Agrawal, A. 2016. Linking the continental migratory cycle of the monarch butterfly to understand its population decline. Oikos 000:001–011, doi: 10.1111/oik.03196.

Lark, T. J., Salmon, J. M. & Gibbs, H. K. (2015) Cropland expansion outpaces agricultural and biofuel policies in the United States. Environ.Res.Lett.,10 044003 doi:10.1088/1748-9326/10/4/044003

Monarch Watch Season Summary 1997. p 29.

Pleasants, J. M. and Oberhauser, K. S. 2013. Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. – Insect Conservation and Diversity 6: 135-144.

Pleasants, J. M., Williams, E. H., Brower, L. P., Oberhauser, K. S. and Taylor, O. R. 2016. Conclusion of no decline in summer monarch population not supported. Annals of the Entomological Society of America. DOI: http://dx.doi.org/10.1093/aesa/sav115.

Ries, L., D. J. Taron, and E. Rendón-Salinas. 2015. The disconnect between summer and winter monarch trends for the eastern migratory population: Possible links to differing drivers. Ann. Entomol. Soc. Am. 108: 691–699.

Saunders, S. P., Ries, L., Oberhauser, K. S., & Zipkin, E. F. (2016). Evaluating confidence in
climate-based predictions of population change in a migratory species. Global Ecology and Biogeography. DOI: 10.1111/geb.12461

Stenoien,C., Nail, K., Oberhauser, K. S. 2015. Habitat productivity and temporal patterns of monarch butterfly egg densities in the Eastern U.S. Ann. Entomol. Soc. Am. 108: 670-679.

Taylor, O. R. 2004. Status of the population. Monarch Watch Email Updates. March 2004. http://www.monarchwatch.org/update/2004/0318.html#4. Accessed 4 July 2016.

Wassenaar, L. I. and Hobson, K. A. 1998. Natal origins of migratory monarch butterflies at wintering colonies in Mexico: new isotopic evidence. Proceedings of the National Academy of Sciences 95: 15436- 15439.

Wright, C. K. & Wimberly, M. C. 2013. Recent land use change in the Western Corn Belt threatens grasslands and wetlands. Proc. Natl. Acad. Sci. USA 1104, 134–9.

Addendum to the references

The Inamine et al. (2016) paper was published online in April. The papers below include additional data and analysis that support the hypothesis that the monarch decline is the result of a loss of habitat.

Pleasants, J. 2016. Milkweed restoration in the Midwest for monarch butterfly recovery: estimates of milkweeds lost, milkweeds remaining and milkweeds that must be added to increase the monarch population. Insect Conservation and Diversity (2016) doi: 10.1111/icad.12198.

Stenoien, C., Nail, K., Zalucki, J. M., Parry, H., Oberhauser, K. S., and Zalucki, M. P. 2016. Monarchs in decline: A collateral landscape level effect of modern agriculture. Insect Science. doi: 10.1111/1744-7917.12404.

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Monarch Population Status

It was apparent as early as late May that the migration, and the subsequent overwintering population, was going to be much lower this year than in 2015-2016. The projections outlined in the Blog post of 7 July have largely come true. The one surprise has been the production of late season monarchs in Kansas, Missouri and North Carolina. There have been reports from each state describing sites with large numbers of monarch larvae defoliating patches of naturally occurring milkweeds and in some cases milkweeds in gardens. The numbers of larvae reported by observers in these areas exceed anything reported this season further to the north, where most monarchs are typically produced.

The timing of this production, along with summer observations of low numbers of adult and larval monarchs in these states, suggest a southward movement of reproductive monarchs in late July and early August – a possible manifestation of the little-understood late summer movement southward of monarchs that I’ve dubbed the “pre-migration migration”. How much this more southerly monarch production will contribute to the migration and the overwintering numbers remains to be seen. That said, it still seems likely that the area of trees occupied by monarchs in Mexico this winter will be similar to that measured in 2014 (1.13 hectares).