Monarch Watch Blog

Monarch population development in 2024: Part 2

23 May 2024 | Author: Chip Taylor


The report that follows is a rough attempt to assess the prospects that the monarch population will recover from the historically low number of hectares recorded for all the overwintering sites last winter (0.9ha). As you may recall, in Monarch population development in 2024: Part 1, there were no clear signs in the data that the population would increase, decrease or remain relatively the same. There were both positive and negative signs. The timing of the return from Mexico was early relative to most years. Early establishment of the population is favorable, and in this case, it led to a long oviposition period in Texas at a time when the temperatures favored rapid development of eggs, larvae and pupae. The negative signs were that the numbers returning to Texas in March were not only lower than those of last spring but were lower than those in the spring of 2013, a recolonization that resulted in the lowest overwintering number in the record.

We are now another month into the breeding season, and the picture is becoming a little clearer, and a bit more positive. In this report, I will examine more of the first sighting data for this spring and will compare these data with those from other years. In addition, I will illustrate one way of assessing how the movement of first generation into the northern latitudes over the next six weeks determines the size and geographic distribution of the fall migratory population.

The stage specific model I’m developing is based on the premise that the number and timing of adult monarchs entering a stage together with the weather and sometimes, but more rarely, the role of predators, parasites and pathogens, determines the number of adult monarchs entering the next stage (or generation). The challenge is to identify data that defines timing and number along with inferences about the effects of weather. Such inferences are derived from a less-than-ideal understanding of how temperatures and soil moisture affect monarchs and the plant resources they depend on. Comparisons of weather and outcomes over the last 30 years help define these relationships. Since seasonal dynamics often determine the abundance of predators and parasites that in turn affect monarch numbers, it is possible to infer greater or lesser monarch mortality due to these factors under some conditions. Data are always better than inference, but inference can be useful if an inferred cause and effect relationship is consistent through time.

The narrative that follows is based on the timing and number of monarchs returning from Mexico, the weather, and in this case, a real possibility the survival of monarch eggs and larvae was higher in March compared to most years due to a relatively low number of predators and parasites. The data for 2024 will be compared with those of 2013, a recolonization that was followed by the lowest overwintering number in the record and 2014, a year of recovery from the all-time low.

Timing, numbers and weather

The temporal distributions for first sightings in March and April are shown in Figure 1. The numbers sighted for 2024 are a bit lower than the number tallied for 2013 but, given the dependency of sightings on weather and probably weekends when more observations are made, these records are similar. The difference is the earlier arrival of monarchs in March this year than in 2013. Earlier arrivals should be beneficial for a number of reasons as discussed below.

Weather, in this case temperature, is a factor in determining both the mean age to first reproduction for the first-generation cohort and the length of exposure to predators and parasites. Above average March temperatures in Texas can be favorable unless daytime highs and southwesterly winds enable monarchs to move too far north too soon as in 2012 and 2017. Moving into areas where the temperatures are lower in subsequent weeks, or before the milkweed has emerged, has a negative effect on population growth. The comparison of temperatures for March and April of 2024 and 2013 (Table 1) doesn’t explain the late arrival distribution in 2013 but does support the premise that lower temperatures slowed the growth of the population that year.

Figure 1. Distribution of first sightings in Texas in March and April by 5day intervals for the years indicated. 65% by 20 Mar 2024 vs 39% for 2013; Totals 96 vs 113.


Table 1. Deviations from average temperatures (F) in March and April for Texas and Oklahoma in 2024 and 2013.

Temperature mediated latitudinal egg distribution

The concept indicated by this heading is based on the observation that temperature mediates the northward movement of monarchs and therefore the latitudinal distribution of eggs by females returning from Mexico. Whether the distribution of eggs into more northerly latitudes is beneficial or not depends on the temperatures that follow the interval during which most of the egg laying occurred. If the females advance too far north in April, as they did in 2012 and 2017, colder temperatures at higher latitudes can slow the development of immatures and slow the development of the population. In contrast, movement and egg laying by females into areas that experience warmer than average temperatures result in faster development of eggs, larvae and pupae and faster population growth. More rapid development also reduces exposure to predators and parasites and therefore higher average rates of reproductive success per female.

As you can see in Table 1, the temperatures in 2024 in March and April were higher for both Texas and Oklahoma while the comparable temperatures for 2013 were near or lower than the long-term average. The low temperature in April 2013 in Oklahoma likely lengthened the development of the first generation which contributed to the later colonization of the summer breeding ground north of 40N as seen in Figure 2. The influence of temperature on the latitudinal distribution of females and eggs is evident in the strong contrast between 2024 and 2013. The total March/April first sightings for Texas and Oklahoma was 159 and of these 40% were in Oklahoma. In 2013, the respective total was 122 of which only 4% were in Oklahoma.

Have monarchs benefited from a temporal disconnect between predator and parasite populations and their prey?

Surviving as a population, and sometimes even as a species, involves consistently producing more offspring than are lost to predators, parasites and sometimes pathogens – the consumer species. There is usually some sort of quasi balance between the prey and those that feed them such that the prey seldom attain outbreak numbers. But that does happen, and in the case of some butterflies, the cause appears to be a factor (or factors) that reduces the consumer numbers. Relative to the prey species, the consumer species tend to have longer breeding cycles, fewer generations and lower reproductive rates. Low numbers in the consumer populations mean that the prey lose fewer offspring, and with high reproductive rates, their populations can grow rapidly outpacing the growth of the consumer populations. These conditions can lead to massive “outbreaks” that often involve emigrations and migrations by species that are generally “held in check” by consumers. A clear example of this dynamic occurred in the spring of 2012 when 16 species of butterflies common to Texas disbursed or migrated northward through Kansas and beyond. In the case of red admirals (Vanesa atalanta), massive numbers created headlines along the path as they migrated well into northeastern Canada.

This multispecies outbreak in Texas followed the historic seven-month drought in 2011 that ended in Sept of that year. Seven months of rain followed. It’s likely that the drought knocked back the predators and parasites by the end of the drought and that they did not recover their numbers in the cooler months that followed. The rains, however, allowed the vegetation to recover including that of the host plants of a number of butterfly species such as false nettle – Boehmeria cylindrica – the main host for the red admiral in southern latitudes. Evidently the combination of lush host plants and low numbers of predators and parasites allowed the red admirals to build up rapidly in February and March leading to the migration in early April. Similar conditions, but less severe, and slightly different, occurred this spring. In January, two sweeps of freezing temperatures that extended well into Mexico probably reduced predator and parasite numbers over wide areas. Those events were followed by widespread rainfall and good plant growth, and once again, red admiral numbers soared leading to a rapid expansion of the population well into Canada and the northern states in the first three weeks of April.

Since many of the consumer species that attack red admirals also feed on monarch larvae, it’s reasonable to hypothesis that the welfare of the red admiral population is a positive sign that monarch larvae suffered fewer losses to predators in March than is usually the case. Further support for this hypothesis became apparent later in April through reports of three other Texas butterflies (buckeyes, American painted ladies and orange sulfurs) moving north in greater than typical numbers. Thus, it seems likely that monarchs have also benefited from a temporal disconnect between predator and parasite populations allowing the production of a larger than expected (based on first sightings alone) first generation – a generation that is rapidly colonizing the summer breeding areas north of 40N at this writing (3 May).

Colonization of the summer breeding area by first generation monarchs in May and early June

The offspring of the monarchs that return from Mexico start emerging and moving northward in mid to late April. This migration by first generation monarchs continues until the 12th of June at 50N. Directional flight ceases at that time (Note 1.). Once again, the timing and number of monarchs arriving at latitudes north of 40N (and across the longitudes from west to east) by the 10th or so of June largely determines the size of the migratory population in the fall. In 2013, few monarchs were sighted before the 20th of May across all longitudes and the overall number arriving was low (Table 2). This late start to summer breeding led to a small migratory population and the lowest overwintering number recorded to date (0.67ha). In 2014, the numbers returning from Mexico were higher and the conditions for the development of a large first generation were more favorable. These conditions led to a larger migratory population and a significant increase in the overwintering numbers (from 0.67ha to 1.13ha). As of the 2nd of May this year, the colonization of the northern latitudes is off to a good start with at least 22 recorded north of 40N relative to only 2 in 2013, 1 in 2014 and even 3 in 2018 – the year with the largest population in recent years (6.05ha) (Fig 3A, B, C, D). An additional 40 sightings were recorded through 7 May making the recolonization this year one of the three earliest in the 24year record. If the arrival of first-generation monarchs continues at this pace for the next two weeks, there is a strong possibility the overwintering population will more than double this coming winter (Table 3). Still, it’s early and there are a lot of “ifs” to consider.

Table 2. Distribution of first sighting in 10day intervals across longitudes quadrants (Q) from west to east for 2013, 2014 and 2018. The fourth quadrant (70W-65W) is not shown due to the low number of sightings. The timing and number of first sightings is critical. Low numbers and percentages in the first 20 days of May are associated with low migrations while high numbers sighted during the first 20 days of May usually signal large numbers of fall migrants.


Table 3. Number of hectares in the previous winter for the year designated followed by the number of first sightings in Texas in March and April and the total first sightings for all areas as of the 2 of May. The number sighted north of 40N before 2 May along with the number sighted after 2May are indicated. The percentage of all sightings recorded for 1 May through 9 June are given for 2013 and 2014. The 62 sightings north of 40N for this year through 7 May represents an early recolonization by a relatively large number of first-generation females. These data were gleaned from Journey North. Where necessary, duplicate records and sightings from MX, CA and AZ and those with non-monarch images were subtracted from the raw totals.


Figure 3. A. (below left) 2 May 2013 N=214 OW=0.67 B. (below right) 2 May 2014 N= 313 OW=1.13


C. (below left) 2 May 2024 N=359 OW=? D. (below right) 2 May 2018 N=644 OW=6.05


What can go wrong after the spring migrations end in June?

I have examined the weather conditions for the breeding season and migration since 1994. During the last 30 years, the population increased from one year to the next during 14 years and declined in 16. Two factors during the summer breeding season appear to determine population growth while two factors during the migration appears to influence the number of monarchs reaching the overwintering sites in Mexico.

For the breeding season, the temperatures and rainfall during June through August for the Upper Midwest are usually close to the long-term averages (22/30 = 73%), but there have been extremes conditions that appear to have reduced the size of the fall migration and the overwintering numbers. These negative conditions and the years in which they occurred are listed below. The years tallied below are from a spreadsheet that is the basis for the next Blog article – “The curvilinear monarch”.

Droughts and or extremely high temperatures from June through August in the Upper Midwest: 1995T, 2003P, 2012TP, 2020T, 2023P.

Extremely low summer temperatures: 2004 and 2009.

During the fall migration, extreme conditions such as droughts in Texas and higher than average September temperatures are both associated with lower numbers of monarchs reaching the overwintering sites. These events are common having occurred in 18 of the last 30years (60%). There have been only 13 years in the last 30 in which neither of these extreme events occurred, the population increased in 9 of these years but declined in 4 apparently due to other strong negative events. The frequency of years with high temperatures in September appears to be increasing.

Droughts in TX in October: 1999, 2000, 2011, 2015, 2019, 2022, 2023.

Higher than average temperatures from the start of the migration in early August at 50N to the end of September as the migration enters OK: 1998, 2002, 2004, 2005, 2009, 2013, 2015, 2016, 2017, 2018, 2019, 2023.

Looking forward, there is a good chance the population will increase during this breeding season and migration from an overwintering population 0.9ha to over 2ha – if the conditions from June through October are close to the long-term average. Negative events occur in about 60% of the years and the incidence of such events is increasing. It is often the strength of a negative event that determines the difference between one year and another.


This report would not have been possible without the long record of first sightings reported to Journey North under the direction of Elizabeth Howard and later Nancy Sheehan. Janis Lentz assisted with the tabulation of the first sightings and Jim Lovett assisted with the layout and posting of this text.

Note 1. Those readers interested in why monarchs “appear” to abandon directional flight in the early summer might find the following post interesting and challenging:

Note 2. For a discussion of how low temperatures in May and early June can limit the number of first-generation monarchs reaching Canada, please see:

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Jennie Brooks of Lawrence, Kansas: Her early contributions to monarch science

20 April 2024 | Author: Chip Taylor

by Chip Taylor, Founding Director, Monarch Watch

It is easy to forget how we came to know what is known today about monarchs. Our understandings of how the world works often have long and convoluted histories that include fundamental misunderstandings, unsupported interpretations and sometimes unintended consequences. These paths to discovery occur within a background of political history, prior knowledge, cultural biases and economic conditions – and so it was, and is, with monarchs.

Lincoln Brower detailed how we came to understand the migration and biology of the monarch in a 1995 paper entitled “Understanding and misunderstanding the migration of the monarch butterfly in North America, 1857-1995.” The story starts with the writings of naturalists and lepidopterists in the mid 1800s, the start of entomology as a science and later a period in which the public became interested in natural history. The account eventually leads to the recruitment of volunteers by Fred and Nora Urquhart to answer the question of where monarchs spend the winter – a quest that led to the “discovery” of overwintering sites in Mexico by Ken and Cathy (now Trail) Brugger. It’s a fascinating tale best understood if the reader reflects on the general state of knowledge in those times and the conditions of travel and communication. The pace of change was slower then.

Although I knew much of the monarch backstory, I was surprised to learn from Brower’s text of Jennie Brooks, a Lawrence, Kansas resident, who in 1907, was the first person to publish a detailed description of the formation and breakup of an overnight monarch roost, the first to photograph a monarch cluster and the first to propose that monarchs overwintered in Mexico. I could relate. I knew Jennie’s neighborhood and having lived in Lawrence since 1969; I had seen many over-night monarch roosts. Having founded Monarch Watch in 1992, and after reading Brower’s article, I came to realize that in a sense I was following Jennie’s lead while validating her hypothesis with the aid of thousands of monarch taggers.

I was brought back to thinking about Jennie Brooks recently by Jeanne Klein, a retired KU professor, who volunteers as a Master Gardener at Monarch Watch’s Monarch Waystation #1. She researches and writes about Lawrence history and came across Jennie Brooks’ connection to monarchs and many natural history writings. Jeanne has written a long account about Jennie. The section that deals with monarchs is included here.

Jennie Brooks and Monarch Migrations in Lawrence, Kansas
by Jeanne Klein

Jennie Brooks (1853-1934), a part-time resident of Lawrence, Kansas from 1905 to 1910, was a devoted nature lover and prolific magazine writer. In mid-September 1906, she experienced a miraculous sight in the expansive front yard of her home at 1300 Haskell Ave. As she wrote, “I had been only three days in Kansas, and, lo! a migration of butterflies.” From 4:00 p.m. until after 6:00 p.m., she observed, described, and detailed swarms of monarch butterflies fluttering among milkweed plants and then hanging from the lower branches of elm, maple, spruce, and pine trees in the yard. Having decided to spend the night outdoors, she continued to study the monarchs’ behaviors and, at dawn, saw “fully two thousand wings [rise up] through the highest treetops, to the south—to the south! . . . [and all the way] to Mexico.” In this way, Jennie Brooks became the first person to theorize that monarch butterflies migrate to Mexico, as detailed in her touted 1907 article, “A Night with the Butterflies.”1


As Lincoln B. Brower wrote in 1995, her essay “was the first detailed description of the monarch’s clustering behavior during the fall migration. She combined elegant prose, high quality observation, counts of monarchs in the cluster, and actual experimental manipulation. No one before or since has so fully documented watching the quiescent monarchs all night long, their reaction to the rising sun, cluster break-up, and resumption of the southward migration.”2 Mrs. Maria Martin, her African American domestic servant, also witnessed this migration with Miss Brooks and declared, “‘Dat ain’t nothin’ new, Missy! I dun seed ’em a power o’ times swingin’ in de trees by de run!”3

Thrilled by her experience, Brooks consulted Francis H. Snow, a long-time professor of natural history and former chancellor of the University of Kansas. She astonished him by bringing him two monarchs. Back in 1875, Snow had catalogued 77 species of butterflies found in Douglas County, although apparently, he had not located nor listed monarchs by their Latin name, Anosia (now Danaus) plexippus, in the Nymphalidae family. He did however find their look alike mimic, the Archippus or Viceroy butterfly, that also feeds on milkweed plants.4 To satiate her demand for more knowledge, Snow and his biology students supplied Brooks with numerous books, including one by Samuel H. Scudder, who had named and described monarchs in 1875.5

Three years later, Brooks’ brief sketch, “A Butterfly Flitting,” recounted a second migration of monarchs in her yard in mid-September 1909. By regarding them as “distinguished visitors,” she considered their selection of her cedar tree “a mark of special favor.” Again, she included photographs taken at night with her Kodak camera and a flashlight on the same cedar (Eastern juniper) tree.6


Jennie Brooks’ unique discoveries about monarchs’ fall migrations and her detailed accounts of their behaviors in Lawrence, Kansas deserve to be more widely known and credited by Monarch Watch enthusiasts across North America and Mexico. Each time you see a flitting monarch butterfly in the fall, remember Jennie Brooks and imagine monarchs’ extraordinary migrations “to the south—to the south!”

© Jeanne Klein 2024

1. Quoted in “A Night with the Butterflies,” Harper’s Monthly June 1907: 108-11. This article is available online in her book, Under Oxford Trees (Cincinnati: Jennings and Graham, 1911), at details/underoxfordtrees00broo/page/10/mode/2up.

2. Quoted in Lincoln B. Brower, “Understanding and Misunderstanding the Migration of the Monarch Butterfly (Nymphalidae) in North America, 1857-1995,” Journal of the Lepidopterists’ Society 49(4), 1995: 312.

3. Quoted in Jennie Brooks, “Migration Among the Butterflies,” Western Christian Advocate, June 5, 1912: 14, her third article on monarchs.

4. F. H. Snow, “Catalogue of the Lepidoptera [butterflies and moths] of Eastern Kansas,” Transactions of Kansas Academy of Science 4 (1875), 29-63. The Dyche Museum of Natural History does have one of Snow’s monarch specimens (#1561197) in its entomology collection found in the county with no date. The mention of milkweeds as a host for the viceroy is incorrect. The larvae feed on willows and cottonwoods.

5. In her 1907 article, Brooks quoted from Scudder’s Frail Children of the Air: Excursions Into the World of Butterflies (New York: Houghton Mifflin, 1895), 53-55. Carl Linnaeus, the first author to consistently use binomial nomenclature, described the monarch in the 10th edition of his Systema Naturae in 1758.

6. “A Butterfly Flitting,” Country Life in America, August 1, 1911, 48. Her second photograph was published in Howard J. Shannon, “Insect Migrations as Related to Those of Birds,” Scientific Monthly 3(3) (Sept., 1916): 238. Note that this photograph was published upside down. The Lawrence World (January 30, 1909) reported that Brooks discussed “The Butterflies” for the local Review Club, “which appeared in a recent McClure’s Magazine,” but this article has not been found.

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Monarch population development in 2024: Part 1

2 April 2024 | Author: Chip Taylor

As most of you reading this know, the estimate of the number of monarchs overwintering in Mexico this past winter was a mere 0.9hectares, the second lowest in the record that began in 1994. Low numbers have again triggered concerns about the viability of the eastern monarch migration and given rise to a number of questions. Why did the population decline from 2022 to 2023? Will the population recover? How long might recovery take? What is the extinction threshold for the eastern monarch population? These are just a few of the relevant questions. In various posts to this Monarch Watch Blog, I have pointed out that monarch numbers have been low at many times in the past and have recovered. In fact, they are remarkably resilient due to their high reproductive rate and ability to find even scarce host plants and nectar sources. I have claimed that, as a species whose numbers are driven by weather, all that monarchs need in the coming months and years is favorable weather. Since we are in a period in which temperatures and droughts appear to be increasing, my assurances have not quieted concerns. To be sure, there is no way to control the weather, but I’m getting closer to understanding how weather influences the development of the monarch population each year. In the following text, I’m going to describe three data-based “tells” that I have been using to determine how well the population is developing each year. These indicators only suggest whether the population will increase or decrease. There is no precision here, but even knowing trends that provide an indication of outcomes is useful.

Early season indicators of population development

I use three indicators, the timing and number of monarchs reported in Texas from 1-30March, total monarchs reported in Texas in March and April and the total monarchs reported N of 40N for all longitudes from 100W to 65W. This report covers the first interval. The second report will follow in early May and the third in mid-June. The first two reports only feature sightings in Texas since the I-35 corridor is the gateway for monarchs to reach the Upper Midwest, the area that produces the majority of monarchs that reach the overwintering sites each winter. How the population develops in Texas in March and April has a significant impact on the size of the fall population.

About the data

The data represent sightings of adult monarchs from Journey North and iNaturalist data sets. In the case of Journey North, “vetting” the data required elimination of double and triple entries for what appeared to represent a single butterfly (N>10). iNaturalist records required the elimination of many images of eggs, larvae and pupae. Some images were not included in the counts since they appeared to represent reared monarchs. Records with good photo resolution indicated that 12-19% of the butterflies had recently emerged and surely had not originated from the overwintering colonies in Mexico. In the records for 2024, the origins of the newly emerged monarchs are not clear since few monarchs appeared to have survived the two January cold fronts with freezing conditions that swept into Texas and even northern Mexico. No attempt was made to eliminate these butterflies from the counts since it was impossible to assign a number of the images as either new or old. Duplicate entries appear to be a minor problem for both data sets. The data for Journey North are summarized in Table 1.

Table 1. The relationship between first sightings in Texas, total first sightings in March and April and the percentage of first sighting in March to the mean temperatures in March and the number of days with temperatures >70F.


The good news

Let’s start with the good news. In the 1-30March period, 84% of the first sightings reported to Journey North occurred by the 20th (Figure 1). That’s early relative to all other years from 2010-2023, except 2012 (Figures 2 and 3). Early arrival favors population development since it assures, in most years, that there is a long oviposition interval before the monarchs push on to Oklahoma and beyond. The higher temperatures early in March also favor more rapid development of larvae and the possibility of outpacing the growth of the populations of the many parasites and predators that prey on monarch eggs and larvae.

Early arrival also favors a Texas-biased latitudinal egg distribution profile. Population growth is favored when the majority of eggs are laid at the lower latitudes where the temperatures are warmer, as pointed out above. You can imagine the egg distribution as a decay function where the tail of the distribution is long or short depending on the distance monarchs advance in March and April. In this case, population growth is favored when the tail on that distribution is short since the warmer temperatures assure that the first-generation cohort will have a lower average age to reproduction than a distribution that extends into colder regions and longer development times. That distribution has a short tail this year. There were only 4 first sightings in Oklahoma in the Journey North records as of the 28th of March and 9 during the following two days. March temperatures were closer to the long-term averages this year than in many recent years.

Figure 1. Distribution of March and April first sightings for 2024, in progress. Data from Journey North.

Figure 2. Distribution of March and April first sightings for 2013 and 2015. Data from Journey North.

Figure 3. Distribution of March and April first sightings for 2012 and 2023. Data from Journey North.

The latest rabbit hole

I have fallen into many a rabbit hole in the course of trying to understand weather and monarchs. Here is the latest one – the relationship of the sightings of monarchs returning from Mexico to temperatures, specifically to the number of days in which the temperatures reach at least 70F. The choice of 70F is arbitrary. I could have chosen any number between 68-72 and would have obtained similar results, but 70F works because that temperature and higher puts monarchs on the wing and visible to observers. The following graphs (Figure 4) represent the March temperature records for Dallas, Texas for the years indicated. The Dallas records were obtained from Weather Underground since that site provides daily and monthly records. The means shown for Dallas in Table 1 are similar to the monthly means for the state of Texas. The number of days with temperatures above 70F for the month and for just the first 10 days of March are also shown in Table 1. The differences between the years with higher-than-average March temperatures, 2012, 2023 and 2024, and those with lower-than-average temperatures, 2013 and 2015, are striking. Temperatures have an effect on the percentage of the March-April first sightings recorded in March (2012 and 2023 vs 2013 and 2015) Table 1.

Figure 4. Graphic representations for the March temperatures in Dallas for the years indicated (see Table 1). Source: Weather Underground: Historical Weather

The bottom line


As shown in the data assembled here, March temperatures are important for several reasons. First, they determine the timing of the recolonizations across the latitudes represented in Texas, they influence that rate of egg development and the growth of larvae and lastly, March temperatures retard or enable colonization of more northerly latitudes.

The numbers

There are two questions about the number of first sightings at this point: were fewer monarchs sighted in the first thirty days of March this year compared to last year? and how do the numbers compare with the first sighting to this point in 2013? It is reasonable to expect the numbers sighted this year vs last year to be lower due to the relative size of the respective overwintering populations (2.21ha vs 0.9ha). As expected, the numbers reported to iNaturalist are lower with 266 in 2023 and 199 in 2024 or 75% this year relative to last. The iNaturalist differences are much smaller than expected. Chuck Patterson of Driftwood, Texas reported similar results. Each of the last two years Chuck and his wife have counted each monarch seen and each egg found on their daily walks in March. The totals were 61 in 2023 and 34 (56%) this March and the egg count was 541 vs 461 (85%). So that’s clear, the numbers are down from last year, but are higher than expected due to the differences between the overwintering numbers. But how to the numbers this year compare to those of 2013, the year with the lowest overwintering numbers? To answer this question, we only have data from Journey North. Here the record is less clear because, as shown in Table 1 and in Figures 1-4, the first sightings in March are strongly influenced by temperature with high temperatures early in the month resulting in early sightings and colder temperatures, as in 2015, delaying the arrivals, or at least the sightings. If we compare the first sightings for 2024 vs 2013, it’s 74 vs 64, but that difference is so small it could simply be due to how temperatures influenced the number of sightings. We will have to wait to see if the number at the end of April is similar to the to the 113 total reported in 2013. Even if the final number is lower, the early arrivals this year and the longer oviposition period in Texas might offset the effects of lower numbers arriving from Mexico. Demography is complicated. Stay tuned.


This report would not have been possible without the assistance of the many citizens who have reported their sightings and visual records to Journey North and iNaturalist. The administrators and funders of both programs have done a marvelous job of providing data that can be used to answer the many questions that linger about monarchs and other wildlife. The Journey North records assembled by Elizabeth Howard and continued by Nancy Sheehan represent both stability and change over the last 26 years. It is a remarkable archive. iNaturalist is relatively new, but by virtue of photographs and a large number of qualified identifiers together with a remarkable website, it is destined to document much of the change that tracks the responses of wildlife, including many lesser-known species, to the coming changes in weather and climate.

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Is the eastern monarch population continuing to decline?

29 March 2024 | Author: Chip Taylor


The question posed in the title is important. Evidence of a continuous decline could lead to regulations and restrictions in accordance with the Endangered Species Act (ESA) while evidence of stable numbers would indicate that regulations are unwarranted. In fact, monarch numbers did decline substantially from overwintering hectares in the double digits in 1995-1996 to the all-time low of 0.67 hectares in 2013 (Figure1). The question at this time however is whether the population is continuing to decline. The 2013 low led to a petition to the Department of Interior to declare the monarch endangered. In 2020, after delays and a lengthy Species Status Assessment (SSA), the Fish and Wildlife Service (FWS) declared the monarch to be threatened. However, actions and regulations were precluded based on current numbers and the needs of other endangered species. Subsequently, the threatened status in the United States, and the apparent assumption that the decline recorded 1995-1996 to 2013 was ongoing, led the IUCN to declare the monarch endangered in 2022. However, in 2023, the ICUN downgraded the monarch status from endangered to vulnerable, as the result of an analysis by Meehan and Crossley (2023) that clearly indicated the population had not declined measurably in the last 10 years.

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

In this text, I will review the changes in monarch numbers from 1994 to the present and will address whether the population is continuing to decline. I will end with an outlook for the next two decades based on current trends in the weather.

How we got to this point

In an effort to keep this text brief, and to lead as directly as I can to the question posed in the title, I’m going to start with several questions and answers (my answers). First, have monarch numbers declined by 85%? Yes, if we accept that the numbers measured from 1994-1996 represent a long-term average. However, that is unlikely. The size of the overwintering monarch population is largely determined by weather and extreme events, as shown by the crash due to an April freeze deep into Texas in 1997 that led to a decline from 18.19ha to 5.77ha, and the drought in 2000, a decline from 9.05ha to 2.83ha. What the numbers from 1994-1996 tell us is that in the 1990s, and for some unknown number of years earlier, there was enough habitat to enable large populations to develop when conditions were favorable. Actually, conditions favored population growth in all three of those years, the only three consecutive years of positive growth in the 30-year record (Taylor, in prep). In fact, the conditions for population growth in 1996, were the most favorable in the 30-year record and the resulting population was the largest to be measured (18.19ha) (Taylor, in prep). We can also ask why there were no populations as large as those in 1995 (12.16ha) and 1996 (18.19ha) in subsequent years. Was it because of weather and mortality related to the migration that caused the population to decline or was it due to habitat loss? It’s clear that in the 1990s there was enough habitat to enable the development of large populations when conditions were favorable; however, the decline in 1997 (5.77ha), the failure to increase in 1998 (5.56ha) followed by the increase in 1999 (9.05ha) and the crash in 2000 (2.83ha) occurred while there was an abundance of monarch habitat. The ups and downs through these years can all be attributed to weather and not loss of habitat. These and other examples, make it clear that monarch numbers are largely driven by weather irrespective of the amount of habitat available. Subsequently, it became clear that monarch numbers had begun to decline starting in or before 2004-2005. The consistently low numbers in years that followed led to a focus on the loss of habitat associated with the adoption of herbicide tolerant corn and soybean crop lines as responsible for lower population numbers (Brower, et al., 2012, Brower, Taylor and Williams, 2012). Weather, as the driver of numbers, wasn’t part of the conversation until the 2011 drought in Texas, the extreme March temperatures in the spring of 2012 and the crash of 2013.

The above examples show us that to fully understand monarch numbers through the years, we have to track the effects of weather on the growth of the population and the success in reaching Mexico against what is known about the distribution, abundance and quality of monarch habitat. This applies especially to the conditions in the Upper Midwest, the area that produces the largest number of monarchs that reach the overwintering sites.

The monarch annual cycle – a stage specific approach

To parse out the possible effects of habitat loss and weather, we have to identify what happens during each stage of the annual cycle. The “health” of the monarch population is based on measures of the areas in the oyamel forests in Mexico that contain clustered monarchs. The overwintering period extends from November to late March. The colonies of clustered monarchs are thought to be fully formed by mid-December, and the colonies are measured at that time.

The numbers, in hectares (ha) of occupied forest, for the last 30 years are shown in Figure 1. To understand the increases and decreases in these numbers, we need to follow the population through six stages: 1) overwintering, 2) the 600-800mile return from late February to April to Texas, 3) the production of the first generation in March and April, 4) the colonization of the northern breeding area in May through early June, 5) the production of the second and third generations during the summer months and finally 6) the migration in September-October. Weather events in each of these stages determine the number of monarchs that enter the next stage. In the winter months (S1), and the return to Texas in the spring (S2), weather has an impact on adult survival. During the breeding season from March-September both weather and habitat determine adult numbers and reproductive success (S3-5). In simple terms, the population increases in the breeding season and declines from the end of the last summer generation (S6) until the initiation of the next breeding season.

Effects of weather

The effects of weather on overwintering numbers, during migrations and through the breeding season, have been summarized in other articles in this series (Taylor, 2023 A, B, C, D and in prep). Briefly, in the breeding season, increases are strongly associated with conditions that are close to the long-term averages during each stage from March through September. Decreases are associated with elevated March and September temperatures, extreme high or low temperatures during the breeding season, droughts during the migration or breeding season, catastrophic winter mortality, and, in one instance (1997), an April freeze that extended into Texas. The effects of weather can be seen through the entire 30-year record. There are two trends in this record that are worrisome, the increases in the March temperatures in Texas and elevated September temperatures during the fall migration north of 35N. In the case of the March temperatures, higher than average temperatures have a negative impact on the growth of the population due to the tendency of monarchs to disperse too far north too soon. Above average September temperatures are associated with slower migrations with fewer monarchs reaching the overwintering sites (Taylor, et al., 2020). Looking ahead, an increase in the frequency and severity of droughts in Texas (Nielsen-Gammon, et al., 2021) will also limit the number of monarchs reaching the overwintering sites.

Loss of habitat

There have been a number of studies dealing with the decline in monarch habitat that started in the 2000s. Most have focused on the loss of milkweeds in row crops (corn and soy) due to the adoption of herbicide tolerant crop lines (Pleasants, 2017, Pleasants and Oberhauser, 2013). Less attention has been paid to the loss of habitat that followed the adoption of the renewable fuel standard (RFS) in 2007 (Faber, et al., 2012, Lark, et al., 2015, Lark, et al., 2020, Lark, et al., 2022) and even less to the amount of habitat loss that has occurred in the last 10 years. Through this 30-yr period the acres devoted to corn and soy have increased from 140million acres to 180million acres (Table 1) and much of the grain production in the Upper Midwest was shifted to grassland areas somewhat to the southwest (Faber, et al., 2012, Lark et al., 2015). Loss of milkweed/monarch habitat due to development, mostly suburban sprawl, increased during this period until the housing/banking crisis of 2008 but began to pick up again after 2011 (Houston Housing Starts). How much monarch habitat was lost to development throughout this period is difficult to estimate but was probably significant. The American Farmland Trust puts the loss of farmland during the period from 2012 to 2017 at 14.3million acres (New Census of Agriculture Shows Decline in Number of America’s Farms, Farmers, and Farmland). It is likely that much of the more than 2million per year loss was, and continues to be, due to the sprawl surrounding the cities in the Upper Midwest and the Ohio Valley. In the South Region, the city of Houston provides an extreme example of the expansion that occurred broadly in the United States before 2008. In 2007, 37,568 new single-family homes were added in the greater Houston area. That’s about 12,000 acres without accounting for multi-family units, roads, schools, churches, etc. Habitat losses associated with HT crop adoption and the growth of corn acreage that followed implementation of the RFS are summarized in Table 1.


Table 1. Running averages for three, five and seven year intervals are summarized for overwintering numbers for 1994 – 2023. “Change” refers to the change in the number of hectares from one year to the next with gains highlighted in green and losses in pink. Corresponding corn and soybean acreages and corn prices are included for reference. Note the shift in corn and soybean acreage in 2007. Habitat losses due to the adoption of HT crops may have ranged from 70-100million acres while losses that followed the adoption of the RFS were roughly 17-24million acres. Additional habitat losses are not listed due to their complexity. Row crop acreage increased from 140 to 180 million from 1994-2022.

Habitat fragmentation

The loss of habitat due to HT crops, the RFS, urban sprawl, herbicide use along roadsides and other causes has come with a cost. It has resulted in the creation of large fragments of the landscape that lack nectar sources and host plants. The effect has been to increase the distance between the remaining resource patches. Because there are only so many hours for foraging and egg laying each day, and so many active days in the life of female monarchs, increased distances mean increasing search times, greater stress and reduced egg laying efficiency (Crone and Shultz, 2022, Fisher and Bradbury 2021, Grant, et al., 2018). Although there are no measures of these costs, they are easily envisioned by taking a car trip through the Midwest in June and measuring the distance between, and abundance of, nectar sources and milkweed patches. Or, you can zero in on landscape use with Google Earth. Should you do so, try to imagine the landscape as a tall and mixed grass prairie in the early 1800s, the habitat that supported monarchs for thousands of years. The fact that monarchs persist in this man-made environment, with massive empty fragments, is a testament to their adaptability and therefore the “representation” that is key to the Species Status Assessment used to determine an ESA designation (Taylor, 2023F).

Modifications of the landscape for agriculture and development have broken the connectivity that previously existed in the prairies. This process is ongoing. It follows, that to sustain the monarch migration, we will need to restore much of this connectivity, especially in the Upper Midwest and Ohio Valley that produce the largest number of monarchs that reach Mexico.

Origins of monarchs that reach Mexico

Prior to Native Americans and Europeans, eastern monarchs were a species of the tallgrass and short grass prairies. Their present distribution is much broader, ranging from Saskatchewan to the Maritimes in Canada and from the Front Range in the Rockies to the east coast. Common milkweed, Asclepias syriaca, an early successional species, rapidly colonizes disturbed soils and likely increased in abundance as Native Americans used fire to open up the landscape for hunting and the production of crops (Russell, 1983, Stewart et al., 2002). These activities, that ranged from Minnesota to the east coast, likely led to an increase in monarchs east of the grasslands (Brower,1995). Monarchs were known to the earliest settlers as the “King Billy”, a name taken from William of Orange, the King (1689-1702) at the time. Their occurrence in the late 1600s signals the presence of common milkweed and open areas in a forest climax region. As settlers opened up the landscape further, it is likely that both milkweeds and monarchs became even more abundant in the east (Brower, 1995). Thus, although the original distribution of the monarch is not known, it is likely that human activities have played a role in the distribution and abundance of monarchs for thousands of years. In this history, it’s probable that humans have both extended and reduced monarch habitats as the use of the land has changed over the centuries. This dynamic continues.

Remarkably, whatever the original distribution, tagged monarchs have been recovered from every 5×5 latitude/longitude sector east of the Rockies in which more than 400 monarchs have been tagged (Taylor, et al., in prep). These recoveries have included monarchs tagged in the Maritimes, a previously forested area, that probably had no monarchs before early settlers began opening up the landscape. While these records demonstrate the monarchs’ remarkable ability to respond to changes in the distribution of milkweeds, it remains a butterfly of what was originally the tall and mixed grass prairies as indicated by recoveries of tagged monarchs. Preliminary analysis of the recoveries of tags recovered in Mexico shows that about 70% of the monarchs reaching Mexico were tagged between longitudes from just west of Madison, WI to the middle of the Dakotas (90W to 100W). Another 20% were tagged from western Pennsylvania to just west of Madison (80W to 90W). The recoveries from the Maritimes to western PA to (65W to 80W) totaled about 10% (Taylor, et al., in prep). From these results, and other analyses (Thogmartin, et al., 2017), it’s clear that sustaining the monarch migration will require protection and restoration of nectar and milkweed resources in the Upper Midwest and the Ohio Valley.

Milkweeds and monarchs

Although monarch larvae are known to feed on about 30 of the more than 70 species of milkweeds known to occur in the United States and Canada, the eastern migration is largely dependent on three of these species, Asclepias syriaca, A. viridis and A. asperula. In fact, it is probably safe to say that there would be no eastern migration without these three species. All three are abundant and widespread, but their most import attribute is their ability colonize disturbed sites and to persist in spite of attempts to eliminate them through mowing and herbicides. Their ability to replace themselves sets them apart from most species in the genus. The vast majority of milkweed species are unable to colonize disturbed sites and none of them, aside from the three mentioned, are both widespread and abundant. Many species persist as small, scattered populations in sites with relatively little disturbance.

The reestablishment of the monarch population in the United States and Canada each spring involves a two-step process (Cockerel, Malcolm and Brower, 1993, Malcolm, Cockerel and Brower, 1993, Flockhart, et al., 2013). Monarchs return to Texas in March and early April. Females seek out milkweeds on which to lay eggs. Most of these eggs are laid on A. viridis, the most common milkweed in Texas and Oklahoma. Many are also laid on A. asperula that is also abundant in portions of Texas west of I-35. Most of the returning adults die by the end of April, and about that time, the earliest offspring of these monarchs begin their migration northward. The first-generation females in this cohort mate and lay eggs as they move north with most eggs being laid on A. viridis in Texas, Oklahoma and even southern Kansas. As they move further into Kansas, A. viridis declines with the predominant host plant becoming A. syriaca north of 40N, the main summer breeding range. The dependence on common milkweed as the host for the summer generations is almost complete. Seiber, et al., 1986, and Malcolm et al., 1993 using cardenolide signatures specific for milkweed species found that 85% and 92%, respectively, of monarchs obtained from overwintering sites had fed on A. syriaca as larvae. Malcolm et al., 1993, also showed that 84% of the first-generation monarchs that colonized the Upper Midwest had fed as larvae on A. viridis. Clearly, without an abundance of A. viridis and A. asperula in Texas in March and April there would be little in the way of a first generation and therefore an infinitely small migratory generation in the fall – if there was any at all. So, it is not just A. syriaca that we need to sustain and restore in the Upper Midwest and Ohio Valley, we also need to protect and restore A. viridis and A. asperula in Texas, Oklahoma and Kansas.

Milkweed limitation vs migratory mortality hypotheses

The reduction in monarch numbers over the last two decades has given rise to two competing hypotheses about the cause of the decline. One is based on the observation that milkweeds have declined due to the adoption of herbicide tolerant (HT) row crops. This assessment has been termed the milkweed limitation hypothesis (Pleasants and Oberhauser, 2013). The presumption is that there is a link between the amount of habitat and the number of monarchs that reach Mexico. Stated more directly, fewer milkweeds mean fewer monarchs. The second interpretation comes from a series of mid-summer butterfly counts from eastern Illinois through the Ohio Valley that appear to show no decline in monarch numbers over many years (Crossley, et al., 2022, Inamine, et al., 2016, Ries, et al., 2015). These observations have led adherents to maintain that the population has declined due to events that occur during the migration or shortly after the monarchs reach the overwintering sites (Agrawal, 2019, Agrawal and Inamine, 2018). This hypothesis is termed the migration mortality hypothesis. A presumption in this case is that milkweed is not limiting in that females are able to locate enough plants to fulfill their reproductive potential. Proponents of the milkweed limitation hypothesis maintain that the summer counts fail to account for the loss of milkweeds from the intensely farmed areas of the Upper Midwest that followed the adoption of herbicide crop lines (Taylor, et al., 2020, Pleasants, et al., 2024). Those that maintain that the summer population has not declined argue that the reduction must be due to losses during the migration (Agrawal, 2019, Agrawal and Inamine, 2018). In effect, one side is arguing that milkweeds can be relatively abundant and widespread yet limiting due to massive fragmentation while the other argues that milkweed is so abundant that it can’t possibly be limiting. Early on in this discussion neither side considered other factors that determine the size of the population in a given year or through time. There is also a question about monarch production vs the area in which the summer counts were obtained. The majority of monarchs that reach the overwintering sites in Mexico originate from the Upper-Midwest (west of 90W, Taylor et al., in prep), the summer counts were obtained in lower production areas to the east of the Upper-Midwest, e.g., from 90-89W.

There are two questions that need to be dealt with in this debate. First, can a host plant be abundant and widespread and limiting at the same time? The answer is yes, and it has to do with fragmentation and the ability of monarchs to find diminished resources in a progressively fragmented landscape (Crone and Schultz, 2022, Fisher and Bradbury, 2021). Fragmentation surely has a cost. As search time, energy expenditure, and wing ware increase, realized fecundity is likely to decline. Our perception of the abundance and distribution of milkweeds and nectar sources is unlikely to align with how a monarch perceives those resources (Grant, et al., 2022). The second question deals with why the summer populations fail to track the general decline in monarch numbers. The butterfly counts that were used to indicate a disconnect between summer and winter numbers spanned a period before the adoption of herbicide tolerant (HT) corn and soybeans as well as the years after their use had largely eliminated milkweeds from these row crops.

A recent analysis of the same data showed that, while summer counts conducted during the interval before milkweed were eliminated from row crops (1994 -2005) were not correlated with winter numbers, those obtained after the elimination of milkweeds (2006-2021) from croplands were correlated with winter numbers (Pleasants, et al., 2024). The message here is that by including all years in the analysis, Crossley, et al., 2022 had combined data from a period during which milkweed was declining rapidly with a range of years in which habitat loss was minimal. This result also supports the assessment prior to the elimination of milkweeds in row crops that these “habitats” accounted for “most” of the monarchs that were produced in the Upper Midwest (Oberhauser, et al., 2001).

Questions about the number of monarchs in some counts can be approached in another way. In theory, if we know what has happened during every stage from the winter to the development of the second generation, especially if we know the timing and number of monarchs returning to Texas together with measures of the timing and numbers of the first-generation monarchs arriving at summer locations, we should be able to predict the relative size of the summer population. Indeed, a preliminary analysis suggests that this is possible since the number of sightings reported to Journey North of first-generation adults in the Ohio River Valley by mid- June is correlated with the mean temperature for May, p = 0.023, (Taylor, in prep).

Further, the possibility, indeed the likelihood, that declines in the distribution and abundance of milkweeds and increases in mortality during the migration both account for lower numbers in Mexico is not treated in detail. The loss of milkweeds is well established, and it is also clear that higher than average September temperatures in the Upper Midwest and Northeast (Culbertson, et al., 2021, Taylor, in prep.) and droughts (1999, 2000, 2011, 2019, 2022, 2023) (Taylor, et al., 2020, Hobson, et al., 2023) during the fall migration are associated with lower numbers reaching the overwintering sites in Mexico. However, knowing how many monarchs reach Mexico is only part of the story since the number returning from the overwintering sites to Texas in the spring is determined by the conditions during the winter months (Taylor, in prep) and the temperatures and abundance of nectar along the 800-mile pathway most monarchs use to reach the milkweed areas in Texas. In fact, the numbers returning from Mexico in March are often lower (2012 -2013) and sometimes higher (2013-2014) than would be expected from the overwintering counts (Taylor, 2021). The point here is that to understand the overwintering numbers, or those at any time during the year, we need an approach that links all the consequential events during the annual cycle.

How much habitat remains?

To further monarch conservation, we need to know a great deal about the distribution and abundance of the three milkweed species A. syriaca, A. viridis, A. asperula that play the greatest role as hosts for the population each year. These data need to be linked with what is known about the geographic origins of monarchs that successfully reach the overwintering sites in Mexico. The regions (Upper Midwest, Ohio Valley) where milkweeds are most used by monarchs are priority areas for restoration. In addition to tagging data, first sightings recorded by Journey North, egg and larval counts by the Monarch Larval Monitoring Project (MLMP), and surveys for adult abundance help define these priority regions. Beyond that, it is helpful to know the maximum size that a population can attain under the most favorable conditions. The presumption here is that the distribution and abundance of milkweeds sets a limit, or cap, on the number of monarchs that can be produced from a region under the most favorable conditions. Comparing conditions during population development each year allows us to define the metrics associated with both increases and decreases (Taylor, in prep). The conditions that occur during the most productive years tell us two things: the upper limit that can be supported by the available milkweed and what defines the most favorable conditions. Further, comparing conditions among all years (1994-2023) shows that larger numbers of monarchs were produced under similar conditions (1994-2003) when more milkweed was present. These observations support the milkweed limitation hypothesis, and they tell us that, at present, even under conditions similar to those of the early period, it is impossible for populations to reach the numbers of the early 90s given the current distribution and abundance of milkweeds.

The future status of monarchs: The listing

The Fish and Wildlife Service is under court order to establish whether there is sufficient evidence to confer protected status to the monarch butterfly based on provisions in the Endangered Species Act (ESA). The range of options includes not warranted, warranted but precluded (the current status), threatened 4d, and endangered. Under a threatened 4(d) ruling, FWS can customize prohibitions and regulate activities as it deems appropriate for a species under consideration. The range of potential prohibitions are listed in Section 9 of the ESA.

The decision will largely depend on how trends in the data are interpreted, the perceived imminent threats to the population, and the presumption that the migratory population would NOT be able to recover from a series of extreme events and would therefore become extinct. In practice, the decision should be based on the best available data-based science and not speculation. In general, such decisions are preceded by a Species Status Assessment (SSA). This assessment includes a literature review and usually the opinions of experts. It’s centered around what are known as the three r’s: resilience, redundancy and representation. Resilience refers to the ability of the species to respond to stochastic (random) events. Redundancy represents an assessment of the ability of a species to respond to catastrophic mortality. Representation seems to have two interpretations: the ability of a species to adapt to long-term changes in the environment and/or the species’ role in the ecological processes in the range it occupies (Taylor, 2023F). For reasons that are not clear, none of these criteria were assessed in detail in the SSA used as the basis of the threatened but precluded status for monarchs issued in 2020 (Fish and Wildlife Service, Monarch SSA, 2020). Yet, at the time of the SSA, there was ample evidence that supported each of the three r’s for monarchs (Taylor, 2023F). Monarchs are a resilient species with a high reproductive rate that is well adapted to recover from extreme climatic events and catastrophic mortality. It’s clear that monarchs have recovered from low numbers many times in the past (Taylor, 2021, 2023, A, B, C, F).

The depth and quality of the assessment is important since the pending decision and the attendant assumptions and prohibitions, will have consequences that are likely to involve agricultural interests, pesticide regulations, landowners, government sponsored restoration programs, conservation efforts led by NGOs and corporations as well as citizens and even educational programs. This decision will have a far-reaching impact.

An underlying assumption in the Endangered Species Act is that regulations limiting harvest (take), protecting habitats, or managed propagation followed by releases, which have led to the restoration of a number of vertebrates, will also work for monarchs and other invertebrates whose numbers are determined by weather. That’s not likely. Threatened 4(d) prohibitions and regulations will surely be ineffective in this case and could have unintended consequences.

Monarch numbers now and in the coming decades

The low number of hectares of overwintering monarchs in 2013 (.67ha) was a shock. At the time, knowledge of monarch demography was minimal, and there was no understanding of why the population was low and no prior record of recoveries from low numbers. In the West, monarch numbers went from lows in 2018 (27,721) and 2019 (29,429) to only 1849 in California in 2020, a number that was believed to be below the extinction threshold for that population. Both populations recovered rapidly. By 2015, the overwintering numbers in the East measured 4.05 hectares, a remarkable recovery in just two years. In the West, the low winter count in 2020 led to >247K in the fall of 2021 (Taylor, 2023C). In retrospect, the recoveries from low numbers in both the East and West indicate how little we knew at that time about the factors that determine monarch numbers from one year to the next. There was an overreaction in both cases. Recoveries from both lows indicate that there is enough habitat to support 6-7 hectares of overwintering monarchs in the East (6.05ha in 2018) and at least 350K monarchs in the West when conditions are favorable.

In the immediate future and perhaps into the next two decades, the population will be relatively stable since it is not presently on a continuous downward trend as it was from 2000-2006. Meehan and Crossly (2023), using a statistical approach, pointed out that the decline in numbers in the East over the last 29 years progressed at an uneven rate and concluded that the population has not decreased measurably over the last 10 years. This pattern can also be seen in the 3, 5 and 7-year running averages in Table 1. The running averages as of 2023, are similar to those of 2013-2015, Table 2. Although the numbers reported for the winter of 2023-2024, were low (0.9ha), and therefore alarming, this number is within the range of variation (0.7-6.5ha) we might expect over the next two decades. As mentioned earlier, and in several of the Monarch Watch Blog texts, monarchs have gone through many ups and downs in the past and there are reasons to be confident that they will recover again – IF weather allows and IF the collective “WE” sustain and restore the resources that monarchs require.

Table 2. Running averages from 2013-2015 compared with 2023.

Although there are reasons to be optimistic, there are trends in the data that are of concern. Higher than average March and September temperatures are strongly associated with years in which the population declines. Both have negative effects. High March temperatures allow monarchs to advance into higher latitudes where mortality due to late frosts kill eggs and larvae. The lower temperatures also lead to longer periods of development and older mean age to reproduction for the first-generation cohort. These effects reduce the rate of population growth. High temperatures in September slow the exodus from the northern latitudes since monarchs reduce flight when temperatures exceed 86F. High temperatures also shorten flowering periods and perhaps the availability of nectar for late monarchs. Whatever the interaction, these high temperatures are associated with years during which numbers are lower. Another concern involves a trend in higher temperatures in September and October in southern latitudes (<35N). At some point, it is likely to become so warm that larvae developing at these latitudes will no longer be able to enter diapause and migrate. Given these trends, together with habitat losses due to intensive land use and the growth of our cities and towns, monarch numbers will gradually decline unless habitat restoration more than matches the annual loss of habitat. There is no doubt, it’s up to us to maintain the Eastern monarch migration.


The views and interpretations in this text have been shaped by conversations with many colleagues and by numerous data sets large and small provided by citizen scientists. Many insights have been gained through our tagging program at Monarch Watch. The latter has involved thousands of taggers and assistance of many. Through all of these efforts I have been ably assisted by Jim Lovett, Ann Ryan and Dena Podrebarac and many others. John Pleasants has patiently listened or read many of my views and has offered statistical advice on many occasions. My approach to monarch demography, which I only touch on in this text, is derivative of a graduate course in Insect Ecology I took at the University of Connecticut more than 60 years ago.


Agrawal, A. A., and Inamine, H. 2018. Mechanisms behind the monarch’s decline: Migratory failure may contribute to the dwindling of this iconic butterfly’s population. Science 360:1294-1296.

Brower, L. P. 1995. Understanding and misunderstanding the migration of the monarch butterfly (Nymphalidae) in North America: 1857-1995. J. Lepidopterists Soc. 49, 304–385.

Brower, L. P., Taylor, O. R., Williams, E. H., Slayback, D.A., Zubeita, R. R. and Ramirez, M. I. 2012. Decline of monarch butterflies overwintering in Mexico: is the migratory phenomenon at risk? Insect Conserv. Divers, 5: 95-100.

Brower, L. P., Taylor, O. R. and Williams, E. H. 2012, Response to Davis: choosing relevant evidence to assess monarch population trends. Insect Conserv. Divers, 5: 327-329.

Cockrell B. J., Malcolm S. B., Brower L. P., 1993. Time, temperature, and latitudinal constraints on the annual recolonization of eastern North America by the monarch butterfly. Pp. 233–251 in Malcolm, S. B., Zalucki, M. P., eds. Biology and Conservation of the Monarch Butterfly. Natural History Museum of Los Angeles County, Science Series 38. link

Crone, E. E. and C. B. Schultz. 2022. Host plant limitation of butterflies in highly fragmented landscapes. Theoretical Ecology 15(17).

Culbertson, K. A., Garland, M. S., Walton, R. K., Zemaitis, L., and V. M. Pocius. 2021. Long‐Term Monitoring Indicates Shifting Fall Migration Timing in Monarch Butterflies (Danaus plexippus). Global Change Biology.

Faber, S., Rundquist, S. and T. Male. 2012. Plowed Under. Report. Environmental Working Group. pp 1-12.

Fish and Wildlife Service. Monarch Butterfly Species Status Assessment (SSA) Report. September 2020.

Fisher, K. E., and S. P. Bradbury. 2021. Influence of habitat quality and resource density on breeding-season female monarch butterfly Danaus plexippus movement and space use in north-central USA agroecosystem landscapes. J. Applied Ecology,

Flockhart, D.T. T., Wassenaar, L. I., Martin, T. G., Hobson, K.A., Wunder, M.B. and D. R. Norris. 2013. Tracking multi-generational colonization of the breeding grounds by monarch butterflies in eastern North America. Proc. R. Soc. B 280,20131087.

Grant, T.J., Perry, H. R., Zalucki, M. P., and S. P. Bradbury. 2018. Predicting monarch butterfly (Danaus plexippus) movement and egg-laying with a spatially-explicit agent-based model: The role of monarch perceptual range and spatial memory. Ecological Modelling 374:37-50.

Hobson, K. A., Taylor, O., Ramírez, M. I., Carrera-Treviño, R., Pleasants, J., Bitzer, R., Baum, K. A., Mora Alvarez, B. X., Kastens, J., and J. N., McNeil. 2023. Dynamics of stored lipids in fall migratory monarch butterflies (Danaus plexippus): Nectaring in northern Mexico allows recovery from droughts at higher latitudes. Conserv Physiol 11(1): coad087;

Inamine, H., Ellner, S. P., Springer, J. P., and Agrawal, A. A. 2016. Linking the continental migratory cycle of the monarch butterfly to understand its population decline. Oikos 125, 1081-1091.

Krannich, J. M. 2006. A Modern Disaster: Agricultural Land, Urban Growth, and the Need for a Federally Organized Comprehensive Land Use Planning Model. Cornell Journal of Law and Public Policy. 16 (1): 57.

Lark, T. J., Salmon, J. M. and H. K. Gibbs. 2015. Cropland expansion outpaces agricultural and biofuel policies in the United States. Environmental Research Letters. 10(4): 044003.

Lark, T. J., Spawn, S. A., Bougie, M. and H. K. Gibbs. 2020. Cropland expansion in the United States produces marginal yields at high costs to wildlife. Nature Communications, 11, 4295.

Lark, T. J., Hendricks, N. P., Smith, A., Patese, N., Spawn-Leea, S.A., Bougie, M. et al. 2022. Environmental outcomes of the US Renewable Fuel Standard. Proc. Nat. Acad. Sci., 119, e2101084119.

Malcolm, S. B., Cockrell, B. J., and L. P. Brower. 1993. Spring recolonization of eastern North America by the monarch butterfly: successive brood or single sweep migration? Pp. 253–267 in Malcolm, S. B., Zalucki, M. P., eds. Biology and Conservation of the Monarch Butterfly. Natural History Museum of Los Angeles County, Science Series 38. link

Malcolm, S. B., Cockrell, B. J. and L. P. Brower. 1989. Cardenolide fingerprint of monarch butterflies reared on common milkweed, Asclepias syriaca L. J Chem Ecol 15, 819–853.

Meehan, T. D. and M.S. Crossley. 2023. Change in monarch winter abundance over the past decade: A Red List perspective. Insect Conserv. Divers. 1–8.

Nielsen-Gammon, J. S., Holman, A., Buley, S., Jorgensen. J., Escobedo, C., Ott, J., Dedrick, J., and A. Van Fleet. 2021. Assessment of Historic and Future Trends of Extreme Weather in Texas, 1900-2036: 2021 Update. Document OSC-202101, Office of the State Climatologist, Texas A&M University, College Station, 44 pp.

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

Pleasants, J. 2017. 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 Conserv. Divers. 10, 42-53. 10.1111/icad.12198.

Pleasants, J., Thogmartin, W.E., Oberhauser, K.S., Taylor, O.R. & Stenoien, C. 2024. A comparison of summer, fall and winter estimates of monarch population size before and after milkweed eradication from crop fields in North America. Insect Conserv. Divers. 17(1), 51–64.

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

Russell, E. W. B. 1983. Indian Set Fires in the Forests of the Northeastern United States. Ecology, Vol. 64, #1 (Feb): 78–88.

Seiber, J. N., Brower, L. P., Lee, S. M. et al. 1986. Cardenolide connection between overwintering monarch butterflies from Mexico and their larval food plant, Asclepias syriaca . J Chem Ecol 12, 1157–1170.

Stewart, O. C., Lewis, H. T. and M. K. Anderson (eds.). 2002. Forgotten Fires: Native Americans and the Transient Wilderness. Norman, OK: University of Oklahoma Press. 364 pages.

Taylor, O. R. Jr., Pleasants. J. M., Grundel, R., Pecoraro, S. D., Lovett, J. P. and A. Ryan. 2020. Evaluating the Migration Mortality Hypothesis Using Monarch Tagging Data. Front. Ecol. Evol. 8:264.

Taylor, O. R. 2004. Status of the population. Monarch Watch Update, 16 February 2004.Monarch Watch, Lawrence, Kansas.

Taylor, O. R. 2021. Monarch population crash in 2013

Taylor, O. R. 2023A. Monarchs: Weather and population sizes in the past

Taylor, O. R. 2023B. Monarch populations during the Dust Bowl years

Taylor, O. R. 2023C. The Western monarch puzzle: the decline and increase in monarch numbers

Taylor, O. R. 2023F. Species Status Assessment and the three r’s. Monarch Watch Blog.

Taylor, O. R. 2024. The curvilinear monarch: How weather drives the numbers of monarch butterflies (in prep).

Thogmartin, W. E., López-Hoffman, L., Rohweder, J., Diffendorfer, J., Drum, R., Semmens, D., Black, S., Caldwell, I., Cotter, D., Drobney, P., Jackson, L., Gale, M., Helmers, D., Hilburger, S., Howard, E., Oberhauser, K., Pleasants, J., Semmens, B., Taylor, O. and R. Wiederholt. 2017. Restoring monarch butterfly habitat in the Midwestern US: ‘All hands on deck.’ Environmental Research Letters 12: 074005.

Thogmartin, W. E., Szymanski, J, A., and E. L. Weiser. 2020. Evidence for a Growing Population of Eastern Migratory Monarch Butterflies Is Currently Insufficient. Frontiers in Ecology and Evolution 8:43.

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Monarch Watch One-Day Fundraiser Today!

6 March 2024 | Author: Jim Lovett

Today only! Help Monarch Watch climb to the top of the leaderboard again and get more milkweed in the ground by making a donation of any amount during this special one-day fundraising event, through midnight tonight. Thank you for your support!

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Monarch Population Status

7 February 2024 | Author: Monarch Watch

The WWF-Telmex Telcel Foundation Alliance, in collaboration with the National Commission of Natural Protected Areas (CONANP), the National Autonomous University of Mexico (UNAM), and the Monarch Butterfly Biosphere Reserve (MBBR), announced the total forest area occupied by overwintering monarch colonies today. Nine (9) colonies were located this winter season with a total area of 0.90 hectares, a 59.3% decrease from the previous season (2.21 ha). This is the second lowest number counted to date – the lowest was 0.67 ha during the 2013–2014 overwintering season.

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

Report: Areas of forest occupied by the colonies of monarch butterflies in Mexico, during the 2023-2024 overwintering period

WWF story: Eastern migratory monarch butterfly populations decrease by 59% in 2024

Note: The WWF-TELMEX Telcel Foundation Alliance collaborates with CONANP to systematically monitor the hibernation of the Monarch since 2004, and they join the Institute of Biology of the National Autonomous University of Mexico (UNAM) to analyze changes in forest cover in the area core of the Monarch Butterfly Biosphere Reserve in order to have scientific bases that support the implementation of conservation strategies for the benefit of the species, ecosystems and human beings.

MEDIA ADVISORY: Monarch Watch experts at KU available to discuss today’s announcement of low numbers in monarch butterfly population

Today authorities in Mexico City announced that the size of the eastern monarch butterfly population that overwinters in Mexico is the second smallest on record. The numbers are so low that few monarchs will be seen this coming summer in many parts of the U.S. and Canada.

WWF-Telmex Telcel Foundation Alliance, in collaboration with the National Commission of Natural Protected Areas (CONANP), the National Autonomous University of Mexico (UNAM), and the Monarch Butterfly Biosphere Reserve (MBBR), announced the total forest area occupied by overwintering monarch colonies as 0.90ha; a 59.3 percent decrease from the previous season (2.21ha).

This is the second lowest number of hectares counted to date. The lowest was 0.67 ha during the 2013–2014 overwintering season. A chart produced by Monarch Watch at the University of Kansas and posted to the Monarch Watch Blog shows the total forest area occupied by overwintering monarch colonies annually since the winter of 1994–1995.

Two Monarch Watch experts on the eastern monarch butterfly migration are available to discuss with reporters the low population numbers and their implications. Orley “Chip” Taylor founded Monarch Watch in 1992 and Kristen Baum is the organization’s new director – see Monarch Watch: About Us for bios.

Monarch Watch ( is an education, conservation and research program based at the University of Kansas within the Kansas Biological Survey & Center for Ecological Research. To arrange an interview with Taylor and/or Baum for further comments, please use the following contact information:

• Kristen Baum, Director, Monarch Watch,
• Orley “Chip” Taylor, Founding Director, Monarch Watch,
• Monarch Watch,, +1 785 864 4441

Reporters may use comments from the following Q&A with Taylor and Baum.

Q: Was this news expected?

Taylor: This news is a shock to all who follow monarchs. The depth of this decline is beyond our experience, and the implications for the future of the monarch migration are surely of concern. However, populations have been low in the past. This count does not signal the end of the eastern monarch migration.

Q: Why is the population so small this year?

Taylor: Monarch numbers are at a near all-time low because of drought conditions last fall that extended from Oklahoma deep into central Mexico. Droughts reduce flowering and therefore nectar production, and monarchs need the sugars in nectar to fuel the migration and to develop the fat reserves that get them through the winter.

Q: Will monarchs recover?

Taylor: Catastrophic mortality due to extreme weather events is part of their history. The numbers have been low many times in the past and have recovered, and they will again. Monarchs are resilient.

Q: What can people do to help monarchs recover?

Baum: To recover, monarchs will need an abundance of milkweeds and nectar sources. We need to get more milkweed and nectar plants in the ground, and we all need to contribute to this effort.

More information about the low population numbers can be found on the Monarch Watch Blog (

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Background on the relationship of overwintering monarch numbers in 2023-2024 to the extreme drought in October and November 2023

7 February 2024 | Author: Monarch Watch

The text and graphics below are intended to provide the background needed to understand why many of the monarchs in the 2023 fall migration failed to reach the overwintering sites in central Mexico. This is a story of biology, weather and geography as well as the resource supply chains that support the monarch migration. This is not a scientific analysis. That is underway.

What is the monarch butterfly’s annual cycle?

The eastern monarch population overwinters in Mexico. Monarchs that survive the 5month winter begin moving north at the end of February/beginning of March with the leading edge of spring migrants reaching Texas in the second week of March. The returning females lay eggs on native milkweeds through March and April with most dying by the first of May. The offspring of the returning monarchs begin to emerge in late April. These butterflies migrate northward to colonize the northern breeding areas. It is the reproduction in these northern areas, usually two more generations, that produces third and fourth generations that migrate in the fall. The pattern of the north to south movement is represented on the map in Figure 1.


Figure 1. Spring and fall migration map showing stages.

How can you predict monarch overwintering numbers?

For the purpose of developing a model that predicts overwintering numbers, the annual cycle of monarchs is partitioned into six overlapping stages: 1) overwintering in Mexico from November to April, 2) migrating back to the United States from late February to April, 3) breeding from March to May by returning monarchs, 4) first generation recolonization of the summer breeding areas north of 40N, 5) summer breeding from May to September and 6) migration to the overwintering grounds in Mexico from August to December. The time intervals represented by each stage are shown in Figure 2.


Figure 2. Stages in the annual cycle.

This stage-specific approach represents an attempt to understand/estimate the numbers of adult monarchs at the start of each stage, to define the weather conditions during the stage and to assess how those conditions determine the birth and/or death rates that establish the number of adults entering the next stage. The analysis used to predict whether a population in a specific year will increase or decrease starts with the timing and number of monarchs arriving from Mexico in March (stage 2) and following that the outcomes are compared among years to see if similar metrics result in similar outcomes. 2023 is the most similar to the conditions of 2012, which was the second lowest wintering population (1.19hectares). However, 2023 is different from 2012 because of the drought in Texas in 2023 which suggested even lower numbers in the winter of 2023.

How do weather patterns influence monarch numbers?

Monarch numbers are a function of the weather conditions that determine reproductive success and mortality. Reproductive success itself is determined by the abundance, distribution and quality of host plants (milkweeds) and nectar resources which are also influenced by weather conditions. Predators, parasites and pathogens also limit population growth, and these sources of mortality are also enhanced or limited by weather. The influence of weather on all components in this system allows us to both explain and predict population numbers from one stage to the next. This overall influence of weather tells us that the only way to sustain monarchs is to maintain and restore the milkweed and nectar resources monarchs require. That dictum applies to vulnerable pollinators and insects in general. Given that we can’t change the weather, we must maintain habitats for vulnerable insect species.

How do changing climate trends influence monarch numbers?

The development of the population each year is strongly influenced by March temperatures. These temperatures determine the timing of the arrival of monarchs in Texas as well as the rate of egg laying and larval development, and therefore, the size of the first generation. These effects follow through the breeding season and usually determine the size of the fall migration. The temperature record for Texas from 1895 to 2023 is shown in Figure 3.


Figure 3. Average March temperatures for Texas from 1895-2023. Climate at a Glance Statewide Time Series

There are three trends in these records: the high variation from year to year that ended around 1974, the damped variation from 1975 to perhaps 1994 and the progressive increase in temperatures from 1994 to the present. The mean temperatures increased during these intervals from 1895-1974 = 56.1, to 1975-1993 = 57.7 and 1994-2023 = 58.6. The recent rate of increase is 1.3F per decade. Note the five periods of 2-3 years in succession with extreme cold March temperatures. Such temperatures delay recolonization by monarchs returning from Mexico and recolonization of the summer breeding area north of 40N. These conditions would have led to smaller migrations and lower numbers overwintering in Mexico.

Why and when do monarchs migrate in the fall?

Tens of millions of monarch butterflies migrate from eastern North America to Mexico each fall to overwinter in the high elevation oyamel fir forests of the Transvolcanic Range of central Mexico. Monarchs are unable to survive freezing temperatures and those breeding in temperate regions must escape to moderate climates to reproduce the next season.

The fall migration begins in early August in the north (Winnipeg) and in September at mid latitudes. The migration progresses at a pace of 25-30 miles per day, although individual butterflies often fly further during periods when conditions are favorable. Because not all monarchs join the migration at the same time and some advance faster than others, it takes the migration 25-30 days to pass through a specific area. Monarchs generally begin arriving at the overwintering sites in Mexico in late October a few days before the Day of the Dead (1-2 November). Most monarchs originate from the Upper Midwest from locations more than 1500 linear miles from the overwintering sites. The duration of the migration appears to be 2-2.5 months but can be longer.

How and when are monarchs counted on the overwintering grounds in Mexico?

The 13 overwintering sanctuaries located within the “Monarch Region” in central Mexico are visited twice per month starting in December. For each colony observed, GPS (global positioning system) coordinates are recorded. The area occupied by each colony is calculated by locating the tree that is farthest up slope and then recording the direction and distance from that tree to the trees around the edge of the colony. The formal report from the authorities includes a table with the size of the colony at each sanctuary. The combined total across all the sanctuaries is reported as the size of the overwintering population. The report from 2022-2023 is available and the most recent report will be posted soon.

2022-2023 Report: Area of forest occupied by the colonies of monarch butterflies in Mexico during the 2022-2023 overwintering period

Why are resource supply chains important?

The monarch annual cycle involves two phases, a period of births and population growth and a period of migration and wintering during which the population declines. Population growth rates are linked to the abundance, distribution and quality of resources and weather. The biological resources in this case involve milkweed host plants for larvae, and nectar for adults that is used to fuel flight and reproduction. In recent decades, it has become apparent that land use and weather largely define the distribution and abundance of the resource base that monarchs require. The intensive use of landscapes has increased fragmentation and eliminated the resources monarchs need. In a word, this is a supply chain problem. There are now big gaps in the resource base and that is limiting population growth (Crone and Schultz, 2022).

During the migration and wintering phase, monarchs are dependent on nectar and water. Nectar provides the sugars that are converted to fats (lipids) that monarchs require during the winter as well as water that is lost due to respiration. During the winter, the fats are broken down into a sugar known as trehalose that is used to fuel metabolic processes. This breakdown releases some “metabolic water”, but the quantities are evidently too low to replace water lost due to respiration, requiring monarchs to seek water sources when the temperatures are high enough for flight.

The availability of nectar along the entire migration route is critical. Again, it’s a supply chain problem, a supply chain in the form of fall flowers that is becoming increasingly fragmented. It’s also a supply chain that breaks due to droughts. And it’s the droughts that extended from southern Oklahoma and Texas all the way to the overwintering sites in Mexico that largely account for the low numbers of monarchs that reached the overwintering sites this past fall (Figures 4, 5). Monarchs entering Mexico from Texas in October encountered severe to extreme drought conditions along almost most of the pathway to the overwintering sites (Figure 6). In effect, they encountered a dearth of nectar required to fuel flight and develop fat reserves as well as the water in nectar needed to replace the water lost to respiration. It’s likely these conditions resulted in massive losses as monarchs continued to move south toward the overwintering sites. This interpretation is supported by the results of a recently published paper on the fat (lipid) levels in migratory monarchs from Canada to the overwintering sites (Hobson et al., 2023). There was a drought in Texas in 2019 that extended into northeastern Mexico. The lipid levels were low in monarchs collected in these areas in 2019, but increased and were effectively restored as monarchs passed through the mid-elevation sites in Mexico and approached the overwintering area (Figure 7, Table 1). There was no drought in these mid-elevation areas in 2019. The data from the monarchs reaching the overwintering sites in 2020 and 2021 also indicated that lipid levels had increased from the time they left Texas until they reached the overwintering area. Again, there were no droughts in central Mexico in 2020 and 2021. A conclusion from the Hobson et al., 2023 paper was that “The increase in mass and lipids from those in Texas to the overwintering sites in Mexico indicates that nectar availability in Mexico can compensate for poor conditions experienced further north.” It follows that the absence of nectar in mid-elevation areas in 2023 due to the extreme drought in October and November contributed to the low number of monarchs at the overwintering sites.


Figure 4. This drought monitor map for mid-October shows the extreme and exceptional drought conditions as monarchs migrated through Oklahoma and Texas and into Mexico. Map courtesy of NDMC via U.S. Drought Monitor.

Figure 5. The leading edge of the monarch migration reaches Mexico during the first week of October with some monarchs reaching the overwintering sites by the end of the month. Monarchs continue to arrive at the overwintering sites through the first week of December. The three drought monitor maps from mid-October to mid-November indicate the occurrence of severe and extreme drought conditions along most of the pathway from South Texas to the overwintering sites. Extreme drought characterized the mid-elevation sites that usually are the last source of nectar for monarchs before they reach the overwintering sites. Map courtesy of Mexico Drought Monitor.


Figure 6. Spring first sightings reported for Mexico to Journey North. These records suggest monarchs use two pathways (coastal and inland) to reach the breeding grounds in Texas and beyond. Records and observations suggest that monarchs use the same pathways to return to the overwintering sites in the fall. The coastal pathway is the weaker of the two pathways. In the spring, and sometimes in the fall, the temperatures can be too high and nectar availability too low for easy movement through this area. The inland pathway is longer (about 800miles vs 600miles). Much of this pathway hugs the mid-elevation contours where the temperatures are milder. From January 2023 Monarch Population Status (Taylor, 2023A).


Figure 7. Monarchs were obtained for lipid analysis from these seven marked sites in Mexico in 2019. All samples were obtained along the main fall and spring migratory pathway.

Table 1. The data for the seven sites in Figure 7 – five mid-elevation sites and two overwintering sites in Mexico. (Hobson et al., 2023).


How many monarchs are there in a hectare?

The sizes of overwintering monarch populations are a function of the summation of all the areas of oyamel fir trees occupied by clustered monarchs. The areas are given in hectares (2.47 acres per hectare) with the mean number of monarchs per hectare estimated to be 21.1 million (Thogmartin et al., 2017). Using this estimate, each twentieth of a hectare would be about 1 million monarchs and a tenth of a hectare about 2 million. A million sounds like a large number of monarchs, but it isn’t given the loss that occurs during the winter and return migration. Further, the land area to be recolonized each season is massive. Comparing the first sightings of monarchs reported to Journey North this spring in Texas with the numbers and timing of arrivals over the last 23 years (when Journey North started) will provide out next measure of the status of the population.

What does the low count mean for the future of monarchs?

Unfortunately, the numbers are so low that few monarchs will be seen this coming summer in many parts of the United States and Canada. Several things will be key for developing the largest possible population during the breeding season in 2024. First, a maximum number of the remaining monarchs have to survive the rest of the winter and the return migration to Texas. But there is more, the timing of the monarchs reaching Texas will need to be favorable along with the temperature and precipitation that favor reproduction (Taylor, 2023B).

Despite the low numbers, this count does not signal the end of the eastern monarch migration. Populations have been low in the past, perhaps even lower. Based on what we know about how the monarch population responds to weather, a review of weather records back to 1895 suggests there were several 2-3year periods during which overwintering populations were probably extremely low due to cold temperatures or high temperatures and droughts (Figure 3) (Taylor, 2023C, 2023D).

The bottom line is that the eastern monarch migration is down but not out. Monarchs are resilient and will recover (Taylor, 2023E, 2023F) The pace of the recovery won’t be as fast as the six-fold increase we saw from 2013 to 2015 (0.67ha to 4.01ha), but monarchs will increase (Taylor, 2021). The year-to-year increases will be determined by the weather and the number of milkweeds and nectar plants first in Texas and Oklahoma and then in the northern breeding areas and throughout the rest of the monarch’s breeding range. Monarchs need an abundance of milkweeds and nectar sources, and we need to make that happen for monarchs to recover.

Why do we need to maintain resource supply chains for monarchs?

To sustain the monarch migration, we need maintain the supply chain resources that monarchs depend on during their annual cycle. That means large scale restoration of milkweeds and nectar sources during the breeding season and migration as well as sustaining the integrity of the forests in which they overwinter in Mexico.

What can people do to help?

Monarchs need milkweeds and nectar plants. We need to get more milkweeds and nectar plants in the ground, and we all need to contribute to this effort. There are many resources available to support the creation and management of monarch habitat. For example, you can create or register a Monarch Waystation, and help others do the same. You can also request free milkweed for large-scale restoration projects or for gardens for schools and educational non-profits, or you can order a flat of milkweed plants from our Milkweed Market. Many other organizations have resources and programs to support these efforts, such as the Natural Resources Conservation Service, Farmers for Monarchs, Monarch Joint Venture, the Pollinator Partnership, the Xerces Society, and many more.

People can also contribute to monarch community science projects, such as Journey North. Submitting your first sightings of monarchs to Journey North will help us understand the status of the population this spring. You can also submit monarch nectar plant observations to the Xerces Society. The Monarch Joint Venture maintains a list of community science projects focused on monarchs and milkweeds.


Crone EE, Schultz CB. 2022. Host plant limitation of butterflies in highly fragmented landscapes. Theor Ecol 15, 165–175.

Hobson KA, Taylor O, Ramírez MI, Carrera-Treviño R, Pleasants J, Bitzer R, Baum KA, Mora Alvarez BX, Kastens J, McNeil JN. 2023. Dynamics of stored lipids in fall migratory monarch butterflies (Danaus plexippus): Nectaring in northern Mexico allows recovery from droughts at higher latitudes. Conserv Physiol. 2023 Nov 24;11(1):coad087.

Taylor OR. 2021. Monarch population crash in 2013. Monarch Watch Blog.

Taylor, OR. 2023A. Monarch Population Status. Monarch Watch Blog.

Taylor OR. 2023B. Monarch numbers: dynamics of population establishment each spring. Monarch Watch Blog.

Taylor OR. 2023C. Monarch populations during the dust bowl years. Monarch Watch Blog.

Taylor OR. 2023D. Monarchs: Weather and population sizes in the past. Monarch Watch Blog.

Taylor OR. 2023E. Why there will always be monarchs. Monarch Watch Blog.

Taylor OR. 2023F. Species Status Assessment and the three r’s. Monarch Watch Blog.

Thogmartin WE, Diffendorfer JE, López-Hoffman L, Oberhauser K, Pleasants J, Semmens BX, Semmens D, Taylor OR, Wiederholt R. 2017. Density estimates of monarch butterflies overwintering in central Mexico. PeerJ 5:e3221


News reports

Drought in northern Mexico brings water shortages and social unrest

Mexico in Numbers: Drought

Background information on monarch biology

Monarch Watch: Monarch Butterfly Press Materials

Monarch Watch Blog articles

Taylor OR. 2023. Monarch numbers: trends due to weather and climate. Monarch Watch Blog.

Taylor OR. 2023. The pending decision: Will monarchs be designated as threatened or endangered? Monarch Watch Blog.

Other links

Climate at a Glance Statewide Time Series

Farmers for Monarchs

Journey North: Monarch Migration & Milkweed Phenology Project

Journey North: Monarch Sightings

Mexico Drought Monitor

Monarch Watch

Monarch Watch: Free Milkweed Programs

Monarch Watch: Milkweed Market

Monarch Watch: Monarch Waystation Program

Natural Resources Conservation Service: Monarch Butterflies

Monarch Joint Venture: Downloads and Links

Monarch Joint Venture: Monarch Community Science Opportunities

Pollinator Partnership: Monarch Resources

U.S. Drought Monitor

Xerces Society: Monarch butterfly Conservation

Xerces Society: Monarch Nectar Plant Observations

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Monarch Watch Update January 2024

31 January 2024 | Author: Jim Lovett

This newsletter was recently sent via email to those who subscribe to our email updates. If you would like to receive periodic email updates from Monarch Watch, please take a moment to complete and submit the short form at

Greetings Monarch Watchers and Happy New Year to all!

Each and every one of you is an important part of our team and we are very thankful for everyone who supports us through donations, participation in our programs, and other activities that serve our mission to sustain the monarch migration. As we’ve said before, we need to get more plants in the ground – specifically milkweeds and nectar plants that support the breeding population and fall nectar plants that support the migration. The challenge is substantial and difficult to navigate but we must do what we can counter the threats to monarchs and their habitat. We all can create Monarch Waystations, restore habitats, and inspire stewardship in the younger generations. These actions represent our mission at Monarch Watch, and we are grateful for your continued support. We hope you will be with us again this year!

If you have not yet seen our 2023 Monarch Watch Summary, I encourage you to check it out via the Monarch Watch Blog when you have time – after reading this important update, of course 🙂

Included in this issue:
1. Monarch Watch One-Day Fundraising Event
2. Monarch Watch Welcomes a New Director
3. Monarch Population Status
4. Monarch Watch Milkweed Programs
5. Monarch Tag Data & Recoveries
6. Monarch Waystations
7. Send us your photos, videos, stories, and more!
8. About This Monarch Watch List

1. Monarch Watch One-Day Fundraising Event

Monarch Watch will again be featured in the University of Kansas’ annual One Day. One KU. 24-hour fundraising campaign which will take place on Thursday, February 15th this year. The event will provide an opportunity for Monarch Watchers all over the globe to come together and show their support of our program. As you may know, we have topped the departmental challenge leaderboard for the last three years, bringing in the greatest total number of gifts of any unit at KU during this event. This is extremely gratifying but not only that – it demonstrates to the entire KU community the substantial reach of our program (well beyond our city, state, and country boundaries) and the incredible support we receive from all of you.

We hope to top the chart once again this year and we need your help! Our 3-yr average number of gifts for this event is 592 and we would love to meet or beat that number. Several Monarch Watchers have stepped up to provide matches or challenges to make your donation go even further. Donations of any amount are appreciated and will push us closer to our goal.

This year, gifts will help get more milkweeds in the ground via our free milkweed programs (described below). Please plan to visit us on Thursday, February 15th to give and we will also email you the direct link on the day as a reminder. Please spread the word about this opportunity and thank you for your interest and continued support!

Additional information about this year’s campaign is available at

2. Monarch Watch Welcomes a New Director

Dr. Kristen Baum, well known for her work on monarchs and pollinators, is now the Director of Monarch Watch. She comes to us from Oklahoma State University, where she was a professor in the Department of Integrative Biology for more than 18 years.

Kristen’s monarch research focuses on the effects of land use and management practices on the distribution and abundance of monarchs, milkweeds, and monarch-parasite interactions. She also has a long-term project focusing on the wing size, body weight, sex ratio, and OE infection status of fall migrants in Oklahoma. She has served on numerous state, regional and national working groups to support conservation efforts for monarchs and other pollinators.

The Monarch Watch Directorship will be supported in part by the Chip and Toni Taylor Professorship in Support of Monarch Watch, an endowment fund established in 2022 when Chip announced that he would be stepping away from the day-to-day operations of Monarch Watch to focus on writing and other projects:

“When close to retirement, I realized that the program was reaching at least 100,000 people a year and that it simply had to continue. I’m pleased to be able to turn the directorship over to Kristen Baum. Kristen is an outstanding scientist, a dynamic and experienced leader with a strong research program. She also has an outstanding record as an adviser to developing scientists.” – Chip Taylor, Founder and Director Emeritus of Monarch Watch

Kristen is excited to join the Monarch Watch team:

“Under Chip’s leadership, Monarch Watch has developed an international reach through research, education and on-the-ground conservation efforts that have benefited the monarch butterfly, as well as other pollinators and wildlife. I’m honored to have been selected to lead Monarch Watch and build on these efforts that have been decades in the making. It has been interesting to learn more about Monarch Watch and I continue to be amazed by Monarch Watch’s reach and impact. There are a lot of behind-the-scenes activities that I think you would be interested in learning more about as well, and we will look for more ways to share these with you soon.” – Kristen Baum, Director of Monarch Watch

You can learn more about Kristen at

3. Monarch Population Status

Eastern Monarch Population
Several key metrics linked to the development of the monarch population and success of the migration suggest that the overwintering numbers may be lower than last year. We expect the official report of the monarch numbers in Mexico to be released in the coming weeks and we will send a brief update at that time with a summary and analysis (and post via the Monarch Watch Blog as well) – stay tuned!

Western Monarch Population
A total of 233,394 butterflies across 256 overwintering sites were counted in the annual Western Monarch Count. This is lower than last year’s count but similar to that in 2021. From a Xerces Blog post about this season’s count: “One highlight was a visitor at the Pacific Grove Monarch Sanctuary in Monterey County, California, spotted a butterfly that had been tagged by the Southwest Monarch Study in northern Utah, meaning it had traveled over 700 miles.”

For additional discussion about historical Western monarch population numbers, please see Chip’s The Western monarch puzzle: the decline and increase in monarch numbers posted to the Monarch Watch Blog last year.

4. Monarch Watch Milkweed Programs

All hands on deck! Plant milkweed for monarchs! Great pollinator habitat includes native milkweeds. Milkweed is the host plant for the monarch butterfly and a nectar source for many other insects. Invite monarchs to your habitat, large or small, with milkweeds from Monarch Watch. Please help us spread the word by sharing widely.

Monarch Watch Milkweed Market

Native milkweeds for gardens or habitat are available for purchase from our Milkweed Market. The minimum purchase is one flat of 32 plants (58 for Texas). If your space is too small for 32 milkweeds, share with your neighbors! Not available in all areas.

Free milkweed for habitat restoration projects

Monarch Watch will once again be distributing free milkweeds for planting in large-scale habitat restoration projects in 2024. Since this program began in 2015, 840,000 milkweeds have been distributed and planted in restored habitat throughout much of the monarch breeding range. To qualify, applicants must have a minimum of two acres (one acre or less in California) to restore to natural, native habitat, and have a management plan in place. Milkweeds are awarded on a first come, first served basis, so apply early. Those awarded free milkweeds need only pay shipping/handling, which is modest compared to the value of the plants. For more information and to apply, please visit:

Free milkweed for schools and educational non-profits

Butterfly gardens are a great educational tool! Schools and educational nonprofits may apply for a free flat of native milkweeds for a public garden. Single flats of 32 plants (58 for Texas) will be distributed to recipients in the spring. The application can be found here:

5. Monarch Tag Data & Recoveries

Many of you have already submitted your 2023 season monarch tag data to us via mail, our online submission form, or our mobile app – thank you! If you haven’t submitted yours yet (even for previous years) please do so at your earliest convenience. Please review the “Submitting Your Tagging Data” information on the Tagging Program page at

There is a large “Submit Your Tagging Data” button on our homepage that will take you directly to the online form. There you can upload your data sheets as an Excel or other spreadsheet file (PREFERRED; download a template file from ) or a PDF/image file (scan or photo). You may also record and submit your data via the Monarch Watch mobile app (iOS & Android).

If you have any questions about getting your data to us, please feel free to drop Jim a line anytime via JLOVETT@KU.EDU

As a reminder, tag recoveries from Mexico are typically reported to us in February/March and posted in April/May, as soon as everything has been verified. Tag recoveries within the U.S., Canada and northern Mexico are typically reported online in February. Once updated, you will be able to check your tag codes against the lists published on the Tagging Program page at

6. Monarch Waystations

To offset the loss of milkweeds and nectar sources we need to create, conserve, and protect monarch butterfly habitats. You can help by creating “Monarch Waystations” in home gardens, at schools, businesses, parks, zoos, nature centers, along roadsides, and on other unused plots of land. Creating a Monarch Waystation can be as simple as adding milkweeds and nectar sources to existing gardens or maintaining natural habitats with milkweeds and nectar plants. No effort is too small to have a positive impact.

Have you created a habitat for monarchs and other wildlife? If so, help support our conservation efforts by registering your habitat as an official Monarch Waystation today!

Monarch Waystation Program:

A quick online application will register your site and your habitat will be added to the online registry. You will receive a certificate bearing your name and your habitat’s ID that can be used to look up its record. You may also choose to purchase a metal sign to display in your habitat to encourage others to get involved in monarch conservation.

As of 4 January 2024, there have been 46,102 Monarch Waystation habitats registered with Monarch Watch!

You can view the complete Monarch Waystation Registry and a map of approximate locations via

7. Send us your photos, videos, stories, and more!

We are always looking for monarch photos, videos, stories and more for use on our website, on our social media accounts, in our publications, and as a part of other promotional and educational items we distribute online and offline to promote monarch conservation and Monarch Watch.

There are several ways you can send us your favorite files (please only submit your own materials) and all of the methods below are accessible via

1. Main submission form at
This is the form we prefer you use as it is the most comprehensive and allows you to provide complete information.

2. Quick uploader for photos and videos at
Note that this method does not allow you to include contact or other information.

3. If you have issues using either of the tools above you may also email your submission to us at but please include everything we ask for on the main form by copying/pasting the information below into your email message (or use it as a guide).

Email address:
Do you want to be credited when we use your materials, when feasible?
Name as you would like it to appear in credit:
Description of materials or other comments (for photos and videos this should include an approximate date of capture and location):

Please note that by sharing materials with Monarch Watch you agree to the statements provided at regarding their origin and use. Thank you!

8. About This Monarch Watch List

Monarch Watch ( ) is a nonprofit education, conservation, and research program affiliated with the Kansas Biological Survey & Center for Ecological Research at the University of Kansas. The program strives to provide the public with information about the biology of monarch butterflies, their spectacular migration, and how to use monarchs to further science education in primary and secondary schools. Monarch Watch engages in research on monarch migration biology and monarch population dynamics to better understand how to conserve the monarch migration and also promotes the protection of monarch habitats throughout North America.

We rely on private contributions to support the program and we need your help! Please consider making a tax-deductible donation. Complete details are available at or you can simply call 785-832-7386 (KU Endowment Association) for more information about giving to Monarch Watch.

If you have any questions about this email or any of our programs, please feel free to contact us anytime.

Thank you for your continued interest and support!

Jim Lovett
Monarch Watch

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Monarchs now ranked as ‘endangered’ in Canada

18 January 2024 | Author: Chip Taylor

I started the year with a rant!

While traveling over the holidays, I received an email from Canadian Don Davis on 26 December informing me that “Monarch butterflies are now ranked under Canada’s Species at Risk Act as “Endangered”.” There was no indication of how this decision had been reached or who among the Canadian experts had been consulted. Such decisions have wide ranging effects, and since I’m rather protective about monarchs, and all for accountability, I penned the below on 1 January and hastily posted it to Dplex-L. The following is an improved version of that text. – Chip Taylor, Founding Director of Monarch Watch

These rulings are puzzling. They reveal that there is absolutely no understanding of the factors that determine the number of monarchs that appear in Canada each summer. It’s all about the timing and number of females reaching Canadian latitudes and longitudes from 12 May to 12 June. When monarchs arrive early in that time frame, and in good numbers, the populations are robust if summer conditions allow, and if late, the growth is limited, especially if summer conditions are limiting (low temperatures and/or precipitation). Before that, the number of first-generation monarchs moving north in May is largely determined by the numbers returning from Mexico and the conditions in March and April in Texas and Oklahoma that determined reproductive success by the returning monarchs. Given that reality, there is nothing that Canada can do to increase the timing and numbers of colonizing monarchs. The only thing that can be done is to maintain and restore monarch habitat and hope for favorable weather throughout the annual cycle.

Come to think of it, all of the above applies to the United States as well, doesn’t it? Except that the United States is less vulnerable to unfavorable low summer temperatures. If you go back through the earliest temperature records, which began in the United States in 1895, there were years such as 1915 when it was so cold from March through May that it was unlikely that there was much of a monarch population in either Canada or the United States (Figure 1). Going further into the climatic history suggests that monarch populations in both countries are more robust now than in many periods prior to the 1940s. The interval from 1976 to the present has been more favorable for population development than in earlier decades. Monarch numbers are largely temperature driven (the same for most invertebrates) with the maximum numbers at any time interval determined by the abundance, distribution and quality of the resources that favor reproductive success. Given these relationships, terrestrial invertebrates are more vulnerable to changes in the weather than vertebrates and therefore more difficult to sustain or restore. The Endangered Species Act has had some remarkable successes in the restoration of vertebrates, but given increasing temperatures and more variable precipitation throughout the continent, it seems less likely that endangered status will lead to effective restoration of terrestrial invertebrates such as monarchs and pollinators, and perhaps many temperature-sensitive aquatic invertebrates and fishes as well.

There are near-term and long-term realities when it comes to saving species of concern. In the near-term, to sustain what we can, we must engage in massive efforts to sustain and restore habitats and the resources these species require. At the same time, the long-term realities tell us that we must do all that we can to mitigate climate change.

The following is from a blog post last summer, Monarchs: Weather and population sizes in the past (

Figure 1. Average March temperatures for Texas from 1895-2023.

There are three trends in these records: the high variation from year to year that ended in 1974, the damped variation from 1975 to perhaps 1994 and the progressive increase in temperatures from 1994 to the present. The average temperatures have increased 0.8F per decade since 1975 to 60.14 F vs the long-term (1900-2020) average of 56.3F. Note the five periods of 3-4 years in succession with extreme cold March temperatures. Such temperatures delay recolonization by monarchs returning from Mexico and recolonization of the summer breeding area north of 40N. These conditions would have led to smaller migrations and lower numbers overwintering in Mexico.

On another note. I keep seeing a dramatic shift in the temperature data that starts in the mid 1970s. I haven’t seen anyone comment on that in the climate discussions, but it is suggestive of something of a tipping point, especially for temperate invertebrates.

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2023 Monarch Watch summary

1 January 2024 | Author: Jim Lovett

Season’s Greetings from Team Monarch Watch!

You are an important part of our team as well. Your interest shows that you are aware of the need to sustain the monarch migration, and that means advocacy for all measures that can be taken to increase monarch numbers. Stated simply, we need to get plants in the ground – specifically milkweeds and nectar plants that support the breeding population and fall nectar plants that support the migration. The challenge is substantial and difficult to navigate. The climate is changing; we can see that in the data. March temperatures in Texas are becoming too warm, allowing monarchs to fly too far north too soon. In addition, high September temperatures are slowing the migrations, leading to fewer monarchs reaching the overwintering sites in Mexico. These sites also face threats due to droughts, beetle damage and illegal logging. While there is not much we can do to counter some threats, we can create Monarch Waystations, restore habitats, and inspire stewardship in the younger generations. These actions represent our mission at Monarch Watch, and we are grateful for your continued support.

Monarchs have a remarkable annual cycle – a breeding season in the U.S. and Canada and a non-breeding season as they overwinter for 5 months in Mexico. In effect, every year is the same, yet every year is different due to weather and other factors that influence reproductive success. We have a similar rhythm at Monarch Watch. Winter is spent catching up, writing, and planning for the next season, including our Spring Plant Fundraiser. Late spring and summer we work with nurseries to distribute milkweeds. Fall is all about tagging and public events and later seed collecting and processing followed by planning the number of milkweeds to be grown the next year.

So, while it might be said that each year is the same, they are all different – even more so this year. As you may remember, last year Founding Director Chip Taylor announced that he would be stepping away from the day-to-day operations of Monarch Watch to focus on writing and other projects. We are pleased to announce that the need for a new director has been met. Dr. Kristen Baum, known for her research on monarchs and pollinators, joined us at the end of October and we are still in the process of making the transition. Kristen’s first task as Director of Monarch Watch was to put together a five-year review of our activities. That took some time and a lot of digging into records and memories which enabled Kristen to get up to speed rapidly.

“It has been interesting to learn more about Monarch Watch and I continue to be amazed by Monarch Watch’s reach and impact. There are a lot of behind-the-scenes activities that I think you would be interested in learning more about as well, and we will look for more ways to share these with you soon.” – Kristen Baum, Director of Monarch Watch

You can learn more about Kristen at

Monarch Watch had another busy year:

Monarch Waystations. We added more than 4,200 Monarch Waystations, bringing the total to over 46,000 registered sites. Our minimal target for next year is 50,000. Supporters can help by encouraging others to register and display our signs. If you see a sign in a prominent place, send us a photo – and a photo of your own Monarch Waystation as well! Share via

International Master Gardener Conference. Monarch Watch was a tour destination for the 2023 International Master Gardener Conference this past June. We thank the Douglas County Master Gardeners for their dedication to Monarch Waystation #1 and making it a showcase garden.

One Day. One KU. We won again. Each year after the One Day. One KU. fundraising event the Endowment Association recognizes the University unit that receives the greatest number of donations and each year we win. While we don’t receive the highest dollar amount, we have had more donors than KU Athletics three years in a row. Funds raised during this event support our work to grow and distribute milkweeds. It’s important work, and we invite you to join us again in this effort on February 15, 2024.

Monarch Habitat. We worked with five nurseries to produce and distribute 156,000 regionally appropriate milkweed plugs in 2023. Free milkweeds were sent to 200 schools and non-profits and to those managing restoration projects in the Midwest, Texas, and California. Many were also distributed through our Milkweed Market. We could do much more if there was additional funding to support milkweed production and distribution.

Public Events. Thanks to everyone who joined us for our free public events in the spring and fall. These family events are both fun and informative. This year the tagging event at the Baker University Wetlands Discovery Center attracted over 400 people. It was a great day, and 577 monarchs were caught, tagged, and released. We hope you will join us when we hold these events next year – Spring Open House & Plant Fundraiser (May 11); Fall Open House (September 14); Fall Tagging Event (September 21).

One last thing. On the 2nd of January 1975, Ken and Cathy Brugger came upon a monarch colony at Cerro Pelon, near Zitácuaro, Mexico. Although these colonies were known to local people, Ken and Cathy (now known as Catalina Trail) were the first outsiders to witness and report on this overwintering behavior. A month later, they “discovered” another concentration of monarchs at Sierra Chincua. These findings solved a long-term question about where monarchs spent the winter – a question long pursued by Fred and Norah Urquhart of the University of Toronto. Fred placed an ad in a Mexican newspaper looking for help in locating overwintering monarchs. Ken answered the ad and he and Catalina began a quest to locate monarch concentrations. After the findings were announced, Fred and Ken were widely lauded for the achievement; however, it is now clear that Catalina played a significant role in these discoveries. The “one last thing” in this case is the magnificent feature on monarchs in the January 2024 issue of National Geographic. The article is something of a commemoration of the events in early 1975. The photography by Jaime Rojo is extraordinary and the text by Michelle Nijhuis provides a glimpse of the diverse ways many scientists, conservationists and thousands of individuals are engaged with monarchs. It’s a far cry from the singular efforts by Fred and Norah Urquhart to answer a question that had lingered since the days of C. V. Riley and others in the 1860s. The question for more than 100 years was where and how monarchs spend the winter. Now, a mere fifty years later, the question has become How can we sustain the monarch migration?

Again, thank you for your continued interest and support and we hope you will be with us again this coming year. Best wishes to you and yours for a happy and healthy holiday season!


Chip Taylor, Kristen Baum, Jim Lovett, Ann Ryan, Dena Podrebarac
Team Monarch Watch

To keep up with the status of monarchs and other news, subscribe to our email updates (, join our email discussion list (, visit our blog (, and follow us on Facebook, Instagram, and X. To donate to Monarch Watch, please visit

Looking back and looking forward

In 1992, I started a small monarch tagging project with the help of Brad Williamson, a local high school science teacher. That project attracted the attention of the public and led to the creation of Monarch Watch. Although we characterized Monarch Watch as focused on education, conservation, and research, in the early years, most of our efforts involved educational outreach and research. My thought at the time was that conservation would take care of itself. I was wrong. That became apparent when I received an email from a farmer in Nebraska in 2004 who informed me that the new genetically modified crop lines he had adopted were leading to the loss of milkweeds in his corn and soybean fields and that in turn was reducing the number of monarchs on his farm. Alarmed at this news, I knew we had to shift our emphasis to conservation. Although struggling financially at the time, we decided to start the Monarch Waystation program in 2005. The program has grown, and we now have over 46 thousand registered sites. Once we became more financially secure, we began to work with nurseries to produce milkweeds that could be used in these Monarch Waystations and for restoration. Although educational outreach and research continue, our main focus has become monarch and pollinator conservation. Over the years, we have facilitated the growth and distribution of over 1 million milkweed plugs. We were the first organization to step into this role and are proud of these efforts.

There are many challenges ahead. Our growing population and the intensification of agriculture continue to result in the loss of habitats for monarchs, pollinators, and other species that share these landscapes. Clearly, restoration projects need to increase, and we need to sustain and improve our outreach and research. Confronted with these realities, I realized that I had to assure that Monarch Watch’s role as a leading advocate for monarchs would continue. That meant stepping down as Director of Monarch Watch and finding a way to fund the salary of a new director. The solution was to create an Endowed Professorship at KU with the support of the University and the KU Endowment Association. Fortunately, my wife and I were able to contribute $1.4 million to start the Chip and Toni Taylor Professorship in Support of Monarch Watch and generous contributions received from others have brought us closer to our $3 million goal. The fund allowed the University to initiate a search for the position which resulted in the hiring of Dr. Kristen Baum, and we couldn’t be happier. Kristen is an outstanding scientist with a long history of working with monarchs, pollinators, and grasslands.

People ask me what I will be doing now that I’m retired. I’m not sure what retirement actually means, but I do know I will be contributing to Monarch Watch as long as I can. –Chip Taylor, Founding Director

In order of appearance, photos provided by: Mijeong Baek, Jenny Miner, KBS-CER, Chip Taylor, Chip Taylor, Ann Dean, Ken Brugger, Ann Ryan, and Mei Ling Liu. Thank you!

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