Monarch Watch Blog

Monarch Population Status

11 February 2017 | Author: Jim

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

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FWS/NRCS Conservation Plan

17 January 2017 | Author: Chip Taylor

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

Monarch Butterfly Conference Report
A collaboration of the
Natural Resources Conservation Service and the
U.S. Fish and Wildlife Service
December 2016

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)

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Why monarchs need Monarch Waystations

4 January 2017 | Author: Jim

Why monarchs need Monarch Waystations
(and habitat restoration)

Chip Taylor and Jim Lovett

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.

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 ( 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:



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?

Monarch Butterfly Recovery Plan: Part two

Monarch Butterfly Recovery Plan

Monarch Population Status

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

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Milkweeds for Monarchs in 2017

27 December 2016 | Author: Jim

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:

Free Milkweeds for Restoration Projects:

Free Milkweeds for Schools and Non-Profits:

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 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

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In Pursuit of a Little History – A Retraction

5 December 2016 | Author: Chip Taylor

“In Pursuit of a Little History”
Monarch Watch Season Summary 1998

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:

Austin woman remembers finding monarch sanctuary

Q & A: Catalina Trail, founder of the Monarch butterfly roosting sites

Founder of the Monarch Butterfly Roosting Sites in Mexico Lives a Quiet Life in Austin, Texas

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:

Historic Gathering of Those Who Located Monarch Butterfly Roosting Sites Draws Crowd of 200

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

Maiden of the Monarchs: Discoverer of butterfly wintering site breaks decades of silence to tell her story.

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.

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Tagging results and the monarch decline

2 November 2016 | Author: Jim

Is the monarch decline due to an
increase in mortality during the fall migration?

Chip Taylor, Jim Lovett and Ann Ryan
Monarch Watch, Kansas Biological Survey, University of Kansas, Lawrence, KS


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.


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)


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.,, 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.


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.


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%.


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.


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:

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. 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.

You may download this text as a PDF file.

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Monarch Population Status

14 September 2016 | Author: Jim

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).

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Monarch Population Status

7 July 2016 | Author: Chip Taylor

As most of you know, the summer of 2015 produced a strong migration and a relatively large overwintering population (4.01 hectares). To place this population growth in context, let’s review the last several years. The population declined following each of the three growing seasons from 2011-2013. There were aspects of each season that account for these declines. For example, the temperatures from March through August in 2012 were warmer – actually hotter – than for any year going back to 1895. Monarchs arrived in the northern breeding area in good numbers in early May but altogether too early, and the hot/dry summer that followed dried up milkweeds and nectar sources leading to a significant decline in the migration and the overwintering population. In 2013, a cold period during the first three weeks of May restricted movement of the first generation monarchs produced in Texas and Oklahoma into the northern breeding range resulting in a much later than normal recolonization of this region. This pattern also led to a decline, with the lowest overwintering population on record (0.67 hectares). Conditions were somewhat better in 2014 and the population increased to 1.13 hectares in spite of the low numbers of overwintering monarchs returning to the South region.

If you go back through the older Monarch Population Status reports, you will see that I was excited about the prospect of the population increasing in the spring of 2015. Later in the summer I dialed back my expectations when I didn’t receive the positive reports I was expecting. Then, in the critical period from 20 July to 10 August, when most of the eggs are laid that produce the fall generation, a significant number of reports and observations suggested that the population would increase substantially. Still, I was cautious and predicted overwintering numbers of less than 3 hectares. I missed by a hectare or more. Going back over all the data I look at to come up with these estimates, I see where I made my mistake. I underestimated the number of monarchs arriving in the northern breeding area in May and early June. The starting numbers were larger than I realized and I never picked up on that, hence my underestimate of where the population was headed. Being wrong is part of the process and is ok as long as I learn from my mistakes.

This leads me to the end of June prediction for 2016. Unfortunately, in the words of Yogi Berra – “It’s like déjà vu all over again.” Meaning that all the data to this point in time suggest that this year will be a repeat of 2014 with a significant decline in the migration and the overwintering numbers. While the overwintering population may not be as low as 2014 (1.13 hectares), the overwintering numbers for 2016 are unlikely to exceed 2 hectares. Summer temperatures throughout the breeding area are projected to be close to normal and that should favor population growth. There are no extreme conditions on the horizon though local droughts could impact the population in some areas. The problem this year seems to be the low numbers of first generation monarchs moving north in May and early June. As best I can tell, these numbers are quite similar to those reported in 2014.

First sightings reported to Journey North for Texas in March and April were lower than normal this spring with numbers closer to 2013 than 2014 and, while it is difficult to make strong inferences from first sightings, they do provide an indication of how many monarchs are returning from the overwintering sites in Mexico. The lower numbers this spring may reflect the mortality that occurred at the colony sites as a consequence of the sleet storm that occurred from the 8-9th of March. Although some monarchs had left the colonies before the storm, many remained. Mortality estimates varied from observer to observer and from colony to colony with the highest rate of mortality being 50% for El Rosario, the colony with the greatest number of monarchs. We will never have a comprehensive assessment of the impact of this weather event but it does appear to have been significant.

The low return could well have led to low numbers moving north in May and June but the conditions in the May-June interval were less than favorable for northward movement. Monarchs generally arrived later than normal in the breeding areas with many locations reporting extremely low numbers of sightings or eggs for periods when monarchs are normally present.

Interestingly, there was a 10-day or longer period in the North East during which conditions were favorable for recolonization. I expected monarchs to flow into this area at that time since they have done so in the past under similar conditions but only a few did – suggesting that the number of first generation monarchs moving north was indeed quite low.

My analysis (or guesswork, if you prefer) suggests that the largest numbers of monarchs will be produced from the eastern Dakotas, Minnesota, Iowa, southern Wisconsin and Michigan, northern Illinois with lower production as one moves eastward from Illinois. Numbers will be down in Pennsylvania, New York and most of the East north of Maryland.

Populations at Peninsula Point (Michigan), Long Point (Ontario), Point Pelee (Ontario) and Cape May (New Jersey) will be lower than normal. The numbers at Cape May are likely to be even lower than last year – a year in which the daily census produced a mean number of sighting that was only about a third that of the long term average. Ontario and Quebec are off to a slow start and, even with favorable weather, the fall population is likely to be quite low.

While it is clear that habitat loss is the main factor that accounts for the overall decline in monarch numbers, we need to keep in mind that there is considerable inter-annual variation due to weather conditions that both favor or limit population growth.

My thanks to Janis Lentz for providing summaries of first sightings and to Journey North and their participants for posting their observations.

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Monarch Population Status

4 May 2016 | Author: Chip Taylor

On February 26th, 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. Nine colonies were located this winter season with a total area of 4.01 hectares (up from 1.13 ha last winter; see our February 26th Monarch Population Status post).

Due to an unprecedented rain/sleet storm at the overwintering sites on 8-9 March, the status of the monarch population is uncertain at this time. The storm was accompanied by strong winds that knocked down many trees and buried large numbers of monarchs beneath several inches of sleet. Many froze in place in the trees. There are no firm estimates of the numbers of monarchs that either died or survived this storm. Observers with various backgrounds and experiences visiting different colonies have estimated the losses at 3-50%. Fortunately, many monarchs had already left the area.

Recolonization of the South Region (Texas, Oklahoma, and Kansas) this spring has been slow. The numbers of first sightings recorded by Journey North to date are similar to the numbers reported in 2013, the spring that produced the all-time low number of overwintering monarchs (0.67 hectares) in Mexico. However, first sightings are an imperfect indicator of what to expect for the rest of the season. The conditions in Texas for reproduction by these returning monarchs are key. Successful reproduction in the South Region depends on the temperatures in March-April, the number and distribution of milkweeds and nectar sources, the abundance of fire ants, and other factors. These conditions vary from year to year but have a significant impact on the number of first generation monarchs that move north from this area in May and early June.

The size of this first generation moving north will largely determine the degree to which the population will be able to recover from the losses incurred during the late-winter storm. Right now, based only on first sightings, the overwintering population is likely to be in the 1-2 hectare range. We will have a better sense of how the population is developing later this month. The long-range forecasts for May and early June favor movement northward by the first generation monarchs. The unknown at this point is the number that will be moving north. If the number is low, the overwintering numbers next winter could be close to 1 hectare again. We will post another population status update via our blog in the coming weeks.

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Monarch Population Status

26 February 2016 | Author: Monarch Watch

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 today in Mexico City. Nine colonies were located this winter season with a total area of 4.01 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): Aumenta la superficie ocupada por la mariposa monarca en los santuarios mexicanos

A note from Chip Taylor, Monarch Watch Director

Below you will find links the three status of the population articles I wrote for the Monarch Watch Blog during the 2015 reproductive season. It was clear in May that the population was likely to increase significantly this year (see 6 May 2015 Monarch Population Status article). I backed off a bit in the July post (see 16 July 2015 Monarch Population Status article) due to a poor assessment of the number of monarchs moving north from 1 May to 9 June (we are working to improve this assessment with our own participants and through Journey North). By August it was clear that the earlier assessment/prediction of a significant increase was was probably going to be realized (see 6 August 2015 Monarch Population Status article).

Our methods provide a means of predicting the direction of population change but our ability to predict of the magnitude of change is still at bit shy of where we need to be. But, on that note, I predicted in June that the Cape May numbers would be much lower than the long term average in 2015 – and they were. The numbers at Cape May were only about half that of the long term average.

Interestingly, we had more requests for tags this year than at any time in the last five years. We suspect that the increase was due to the numbers of monarchs people were seeing in the late July – early August oviposition period. A preliminary analysis of returned tagging data sheets indicates that the taggers were more successful than in any year since 2010.

Inter-annual variation is something we are going to have to deal with as best we can. Still, we have to make it clear that it’s the habitat that ultimately limits the size of the population.

It should be clear from the variability in the hectare numbers from year to year and at a time when the habitat is decreasing by 1-2 million acres per year, that the numbers of stems it takes to get a monarch to Mexico is another variable to consider. Far fewer this year than in 2013.

Based on all of the long-range forecasts, 2016 should be another good year for monarchs – if the forecasts are accurate.

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