Is the eastern monarch population continuing to decline?

Introduction

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.

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.

Acknowledgements

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.

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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. doi.org/10.1088/1748-9326/10/4/044003.

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. nature.com/articles/s41467-020-18045-z.

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. doi.org/10.1073/pnas.2101084119.

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. doi.org/10.1007/BF01015180.

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. doi.org/10.1111/icad.12646.

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. climatexas.tamu.edu/files/ClimateReport-1900to2036-2021Update

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. doi.org/10.1111/j.1752-4598.2012.00196.x.

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. doi.org/881 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. doi.org/10.1111/icad.12687.

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. doi.org/10.1093/aesa/sav055.

Russell, E. W. B. 1983. Indian Set Fires in the Forests of the Northeastern United States. Ecology, Vol. 64, #1 (Feb): 78–88. doi.org/10.2307/1937331.

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. doi.org/10.1007/BF01639002.

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. oupress.com/9780806140377/forgotten-fires

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. doi.org/10.3389/fevo.2020.00264.

Taylor, O. R. 2004. Status of the population. Monarch Watch Update, 16 February 2004.Monarch Watch, Lawrence, Kansas. monarchwatch.org/update/2004/0318.html#4.

Taylor, O. R. 2021. Monarch population crash in 2013
monarchwatch.org/blog/2021/06/11/monarch-population-crash-in-2013/

Taylor, O. R. 2023A. Monarchs: Weather and population sizes in the past
monarchwatch.org/blog/2023/07/21/monarchs-weather-and-population-sizes-in-the-past/

Taylor, O. R. 2023B. Monarch populations during the Dust Bowl years
monarchwatch.org/blog/2023/07/17/monarch-populations-during-the-dust-bowl-years/

Taylor, O. R. 2023C. The Western monarch puzzle: the decline and increase in monarch numbers
monarchwatch.org/blog/2023/05/29/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.
monarchwatch.org/blog/2023/10/13/species-status-assessment-and-the-three-rs

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. doi.org/10.1088/1748-9326/aa7637.

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. doi.org/10.3389/fevo.2020.00043.

Monarch Watch One-Day Fundraiser Today!

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!

Monarch Population Status

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 (monarchwatch.org) 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, kbaum@ku.edu
• Orley “Chip” Taylor, Founding Director, Monarch Watch, chip@ku.edu
• Monarch Watch, monarch@ku.edu, +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 (https://monarchwatch.org/blog).

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

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.

Monarch Watch Update January 2024

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 monarchwatch.org/subscribe/

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 https://monarchwatch.org/1day

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 https://monarchwatch.org/about

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. https://shop.milkweedmarket.org

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: https://monarchwatch.org/free-milkweed-restoration

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: https://monarchwatch.org/free-milkweed-schools-nonprofits

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 https://monarchwatch.org/tagging

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 https://monarchwatch.org/tagging ) 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 https://monarchwatch.org/tagging

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: https://monarchwatch.org/waystations

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 https://monarchwatch.org/waystations/registry

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 https://monarchwatch.org/share

1. Main submission form at https://monarchwatch.org/share/submit
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 https://monarchwatch.org/share/photos
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 share@monarchwatch.org 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).

Name:
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 https://monarchwatch.org/share regarding their origin and use. Thank you!

8. About This Monarch Watch List

Monarch Watch ( https://monarchwatch.org ) 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 https://monarchwatch.org/donate 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
https://monarchwatch.org

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Monarchs now ranked as ‘endangered’ in Canada

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 (monarchwatch.org/blog/2023/07/21/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.

2023 Monarch Watch summary

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 monarchwatch.org/about

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 monarchwatch.org/share

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!

Sincerely,

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 (monarchwatch.org/subscribe), join our email discussion list (monarchwatch.org/dplex), visit our blog (monarchwatch.org/blog), and follow us on Facebook, Instagram, and X. To donate to Monarch Watch, please visit monarchwatch.org/donate

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!

Species Status Assessment and the three r’s

When species are being considered for listing under the Endangered Species Act (ESA) by the Fish and Wildlife Service (FWS), a Species Status Assessment (SSA) is usually prepared. This assessment is based on the available science, and in some cases, the opinions of scientists that work closely with that species. At the core of the assessment are the three r’s: resilience, redundancy and representation. Resilience refers to data that may or may not support 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.

Resilience and redundancy are somewhat similar in that both assessments address evidence of the ability of a species to respond to external factors such as weather events, diseases, or the actions of predators or competing species. Representation seems to be more difficult to assess since it depends on a known history of adaptability which is often lacking. Similarly, evidence of the role a species plays in the ecological processes of the environment in which it resides is also difficult to assess. Representation would seem to rely quite often on subjective assessments rather than quantitative data. For example, what is the role/contribution (value) of an herbivorous insect that is one of many species that feeds on a particular plant, but whose main contribution is as a food item for foliage-gleaning wasps and birds? How is that judged? As a practical matter, it is quite difficult to assess how the presence of a species fits into the ecological mix in a particular environment. Still, it’s possible to define species that are host specific as lacking in adaptability if their host is removed from the environment by disease or other factors. Weevil and moth species, and perhaps many other insects, were lost as the result of the blight that killed the American chestnut (Anderson, 2017). This is an example of co-extinction. Co-extinction is likely to apply to most of the 300 species of insects that use ash trees as their hosts. Many will become extinct due to their inability to adapt to other hosts as their host ash trees (18 species) are eliminated by the introduced Emerald Ash Borer (Horne, et al., 2023). These will be silent extinctions. There will be no SSAs or clamor of any kind to save these species.

So, how do the three r’s apply to monarchs? As I have pointed out in previous articles, monarchs are remarkably resilient (Taylor, 2023A, B). The assessments of how monarchs have responded to weather events over the last 29 years have been used to ask how monarch populations might have been affected by extreme weather in the past. This approach led to two articles. One examined the probable responses to the most extreme weather events in the record that dates from 1895 and the other examined the likely outcomes of the extreme conditions during the dust bowl years from 1927–1936 (Taylor, 2023A, B). In both cases, there were several years in which it was likely that the population was as low or much lower than it was in 2013 (0.67ha). In all of these examples, monarchs recovered, again demonstrating the resilience of the species. Since many of the extremes were greater than any recorded in the last 29 years, it could be argued that these recoveries demonstrated adaptability to the climate and therefore a degree of representation. As for the last 29 years, there are numerous examples of recoveries from extreme weather events, e.g., the decline from 1999 (9.05) to 2000 (2.83) due to the drought in 2000 and the subsequent recovery in 2001 (9.35). There were similar declines and recoveries from 2003–2005 (11.12 – 2.19 – 5.92), 2008–2010 (5.06 – 1.92 – 4.02). Multiple factors were involved in the declines recorded in 2004 and 2009 (Taylor, in prep). There was also the big crash from 2011-2015 that began with the 7-month drought in Texas in 2011. In that case, the numbers, starting with 2011, were 2.89 – 1.19 – 0.67 – 1.13 – 4.01. There were significant increases in the population in each of the two years following the low (0.67) in 2013. For reference to the overwintering numbers see Figure 1. For an account of the decline and recovery from 2011–2015, see Taylor, 2021. A long explanation for what happened in the Western monarch population in the fall of 2020 with only 1,899 found at overwintering sites, to the following fall when 247K were counted can be found at Taylor, 2023C. This account represents another example of the resilience of the monarch population.

As to redundancy, which refers to the ability of a species to recover from catastrophic events, monarchs have that ability. In the last 29 years, the population has recovered from three El Niño related winter weather events that killed 75% of the butterflies in January of 2002, 70% killed in two January–February storms in 2004 and 40% in an early March storm in 2016 (Brower, et al., 2004, Brower, et al., 2017, Taylor, 2004). The severity of those storms was reflected in the post storm recovery of Monarch Watch tags from dead monarchs. These tags had been applied the previous fall migration. While tag recoveries typically number 400–600, the tags recovered after these storms numbered 3,331, 3,127, and 1,798 respectively. The monarch populations were lower in the year following each of these events (2002, 2004, 2016) but increased again in 2003 and 2005 and decreased only slightly from 2016 to 2017 (2.91 – 2.48). Thus, in each case, while the catastrophic mortality was severe, the population recovered in the second year or the following year. These are remarkable examples of the ability of the monarch population to recover following episodes of mass mortality.

The representation/adaptability/ecological role for monarchs is more nuanced. To some extent monarchs are pollinators and to another they are food for other species, but these roles are minor in the sense of representation. Monarchs cannot be described as a keystone species. In another sense, they are vulnerable since they are dependent on milkweeds as hosts for their larvae. Thus, if there are no milkweeds, there are no monarchs. Further, they show little capacity to explore alternative hosts in the Apocynaceae. Fortunately, milkweeds are diverse and widespread and monarchs are sufficiently adaptable to utilize at least 30 of the more than 70 species of milkweeds in the United States. A counter to concerns about habitat loss is our ability to propagate and restore milkweeds in habitats from which they have been extirpated. In the sense of representation, monarchs are adaptable, in that, if we create habitats, they will find them. Further, monarchs which were originally a species limited to the Americas, are now a pan-tropical species having adapted to a wide range of subtropical and tropical habitats following the introductions of several milkweed species. These examples surely speak to adaptability.

Curiously, though the three Rs are at the core of SSAs, they are only mentioned in passing in the SSA of 2020 (FWS, 2020, see pp 12-13). There was no discussion or analysis of how these criteria applied to monarchs even though all of the evidence outlined above was readily available at that time (except for the recovery in the West from 2020 to 2021). The data cited above, and more, should surely be incorporated into the SSA being prepared for the pending listing decision.

The silent partner in the push to have monarchs regulated is their cultural value. They are an iconic species. Their migration is remarkable. They are a species of wonder with a remarkable capacity to traverse a continent. Their beauty, and accessibility, along with charisma, generate emotional responses like no other insect. They are part of our heritage and reminders that we are the stewards of their fate being that we dominate the landscape and how it is used or misused. Biologically, they are an extraordinary example of the drive to survive and reproduce. Much remains unknown of how they respond to the physical cues in the environment and how those cues are processed in a manner that leads to behavioral responses. They are a model species for this research area. None of these considerations can be part of the SSA, yet they heighten the concerns about the need to sustain the monarch migration.

References

Anderson, R. S., 2017. Co-extinction: The Case of the American Chestnut and the Greater Chestnut Weevil (Curculio caryatrypes). https://nature.ca/en/co-extinction-and-the-case-of-american-chestnut-and-the-greater-chestnut-weevil-curculio-caryatrypes/.

Brower, L. P., Williams, E. H., Jaramillo-Lopez, P., Kust, D. R., Slayback, D. A., and Ramíerz, M. I. (2017). Butterfly Mortality and Salvage Logging from the March 2016 Storm in the Monarch Butterfly Biosphere Reserve in Mexico. Amer. Entomol. 63, Issue 3, 151–164.

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

Fish and Wildlife Service. Monarch Butterfly Species Status Assessment (SSA) Report. September 2020. https://www.fws.gov/media/monarch-butterfly-species-status-assessment-ssa-report

Horne, G. M., R. Manderino, S. P. Jaffe. 2023. Specialist Herbivore Performance on Introduced Plants During Native Host Decline. Environmental Entomology, Volume 52, Issue 1, February 2023, Pages 88–97, https://doi.org/10.1093/ee/nvac107

Taylor, O.R. 2004. Status of the population. Monarch Watch Update, 16 February 2004.Monarch Watch, Lawrence, Kansas. http://www.monarchwatch.org/update/2004/0318.html#4.

Taylor, O. R., 2021. Monarch population crash in 2013
https://monarchwatch.org/blog/2021/06/11/monarch-population-crash-in-2013/

Taylor, O. R., 2023A. Monarchs: Weather and population sizes in the past
https://monarchwatch.org/blog/2023/07/21/monarchs-weather-and-population-sizes-in-the-past/

Taylor, O. R., 2023B. Monarch populations during the Dust Bowl years
https://monarchwatch.org/blog/2023/07/17/monarch-populations-during-the-dust-bowl-years/

Taylor, O. R., 2003C. The Western monarch puzzle: the decline and increase in monarch numbers
https://monarchwatch.org/blog/2023/05/29/the-western-monarch-puzzle-the-decline-and-increase-in-monarch-numbers/

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

Monarch Watch Update September 2023

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Greetings Monarch Watchers!

A brief update this time around as we wrap up our fall events and begin to think about catching our breath – fall is a busy time for us, as you can imagine. If you have contacted us recently and not yet received a response, thank you for your patience!

Included in this issue:
1. Summary of Monarch Watch Fall Events
2. Monarch Watch Tagging Kits
3. Submitting Tag Data
4. Monarch Calendar Project
5. Send us your photos, videos, stories, and more!
6. About This Monarch Watch List

1. Summary of Monarch Watch Fall Events

As the monarch migration continues, we are wrapping up our local fall events and want to thank everyone who visited us in person or otherwise participated in our events and activities. It is extremely gratifying to see so many people enjoying what we do and to hear how their experiences with monarchs have enriched their lives. We couldn’t do what we do without the support and participation of all of the Monarch Watchers out there, so THANK YOU!

Some event photos appear on our Facebook page and we plan to share lots more with you soon!

MONARCH WATCH TAGGING EVENT
Last weekend more than 400 monarch enthusiasts joined us at the Baker Wetlands Discovery Center for our annual monarch tagging event. We provided the tags, nets, and instruction then sent taggers out into the field to tag and release monarch butterflies as a part of our long-term mark and recapture program. By the end of the 4-hour event, more than 550 monarchs had been tagged and sent on their way to Mexico.

MONARCH WATCH FALL OPEN HOUSE
Two weeks ago, we welcomed hundreds of visitors of all ages to Monarch Waystation #1 at Monarch Watch headquarters in Lawrence, KS. They made seed balls, took a chrysalis or two home, got their faces painted, watched tagging demonstrations, played with balloon butterflies, enjoyed our garden, experienced monarchs emerging from their chrysalis, tried their hand at origami, discovered braille, learned about monarchs, milkweed, nature and a whole lot more – all thanks to a dedicated group of staff, students and volunteers that Monarch Watch is lucky to have. It was a great day!

CHIP IN FOR MONARCH WATCH
The 2023 Chip in for Monarch Watch fundraising campaign is coming to a close but there is still time to Chip in! If you are in a position to offer financial support to Monarch Watch, please consider making a donation of any amount during our fall campaign.

We encourage you to spend a little time on the Chip in for Monarch Watch page – the connections that are facilitated by monarchs and Monarch Watch are truly extraordinary.

Chip in for Monarch Watch: https://monarchwatch.org/chip

2. Monarch Watch Tagging Kits

Tagging Kits are still available for those of you in southern locations and if you order today, they should arrive within 7-10 days via USPS First Class Mail.

Monarch Watch Tagging Kits are only shipped to areas east of the Rocky Mountains. Each tagging kit includes a set of specially manufactured monarch butterfly tags (you specify quantity), a data sheet, tagging instructions, and additional monarch / migration information. Tagging Kits for the 2023 season start at only $15 and include your choice of 25, 50, 100, 200, or 500 tags.

Monarch Watch Tagging Kits and other materials (don’t forget a net!) are available via the Monarch Watch Shop online at https://shop.monarchwatch.org – where each purchase helps support Monarch Watch.

2023 datasheets and instructions are available online via the Monarch Tagging Program page at https://monarchwatch.org/tagging

Tagging should begin in September and early October in areas south of 35N latitude. See a map and tables with expected peak migration dates and suggested dates to begin tagging on the Monarch Tagging Program page at the link above.

3. Submitting Tag Data

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 https://monarchwatch.org/tagging

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 https://monarchwatch.org/tagging ) 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

4. Monarch Calendar Project

For those of you participating in our Monarch Calendar project for 2023 (complete details and short registration form at https://monarchwatch.org/calendar ), observation Period 2 has ended (the final date being September 25th, for those of you south of 35N). Once you have logged all of your observations using whatever format works for you (spreadsheet, notebook, calendar, etc.), please use the appropriate online form to submit your data to us:

2023 Submission Forms:

SOUTH (latitude less than 35N)
Form for Period 1 (15 March – 30 April): https://forms.gle/wcUEvi1qQhyaQcot8
Form for Period 2 (1 August – 25 September): https://forms.gle/jDvXMbdnsktn1oNF8

NORTH (latitude greater than 35N)
Form for Period 1 (1 April – 20 June): https://forms.gle/tCF26JhaCPYD8Ubm7
Form for Period 2 (15 July – 20 August): https://forms.gle/HDZ4yPMpBpVu9dfh6

You may also use the Monarch Watch mobile app to record and submit your observations. Please see https://monarchwatch.org/app

5. 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 https://monarchwatch.org/share

1. Main submission form at https://monarchwatch.org/share/submit
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 https://monarchwatch.org/share/photos
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 share@monarchwatch.org 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).

Name:
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 https://monarchwatch.org/share regarding their origin and use. Thank you!

6. About This Monarch Watch List

Monarch Watch ( https://monarchwatch.org ) 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 https://monarchwatch.org/donate 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
https://monarchwatch.org

You are receiving this mail because you were subscribed to the Monarch Watch list via monarchwatch.org or shop.monarchwatch.org – if you would rather not receive these periodic email updates from Monarch Watch (or would like to remove an old email address) you may UNSUBSCRIBE via https://monarchwatch.org/unsubscribe

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This e-mail may be reproduced, printed, or otherwise redistributed as long as it is provided in full and without any modification. Requests to do otherwise must be approved in writing by Monarch Watch.

Why there will always be monarchs

Last year, the International Union for Conservation of Nature (IUCN) added the monarch butterfly (Danaus plexippus) to its Red List of endangered species. The simplified headlines and accounts that followed this announcement led many people to assume that the monarch is on a path to extinction. What that decision actually targeted was the eastern migratory population that overwinters in Mexico and not the species itself. The assumption that the eastern migratory population is endangered is based largely on the premise that the monarch populations of the mid-1990s (1994-1996) represented the average numbers that could be expected at the overwintering sites each winter. Based on that standard, due to the declines in monarchs in the following decades, many observers declared that the population has declined by 85%.

While the monarch decline from the late 1990s can be attributed to the loss of habitat following the adoption of herbicide tolerant (HT) crop lines as well as the implementation of the renewable fuel standard (RFS) (Pleasants and Oberhauser, 2013, Zuckerman, 2014, Lark, et al 2015, Pleasants, 2017), the loss of habitat due to these changes in agriculture declined after 2012 (Taylor, in prep). Nevertheless, there seems to be the assumption that the population is continuing to decline and that the monarch migration is threatened, possibly endangered and could be lost forever. That premise has been challenged by Meehan and Crossley (2023) who have shown that the population has not declined in the last decade. Indeed, multi-year running averages since 2012 show that the population averages between 2-3ha and is not continuing to decline (Taylor, in prep).

So, what does this mean for the United States? Should the Fish and Wildlife Service declare the monarch threatened or endangered or, given the present numbers and examples of representation, resilience and spatial redundancy, determine that regulatory protection is unwarranted? I favor the latter. In my view, there is nothing to be gained by declaring monarchs threatened or endangered at this time (Taylor, 2023). The “at this time” is key. In the near term, the numbers will certainly vary from year to year, and the prospect of losing the eastern migration may loom from time to time, but the monarch population is remarkably resilient, and the migration will be with us for decades. In the long term (>50 years), due to climate change, the migration will be lost. However, as a species, monarchs will be with us forever. That said, many species are less likely to survive during the coming decades than monarchs. In the following paragraphs, I will outline how the prospect of extinction is related to reproductive rate, specialization and resilience.

There are millions of species on this planet. Some complete their lives in hours while others live thousands of years. For each of these species, continuation from generation to generation depends on continuous successful reproduction by enough individuals to sustain the species. Failure to do so results in extinction. Continuation depends on the reproductive success of individuals that have the capacity to survive and reproduce – adaptations that have been shaped by selection through time. In the simplest terms, the goal for each individual is to replace itself. Some are unfit to do so while others are exceptionally successful. Reproductive rate is the result of long-term selection for numerous traits such as age to first reproduction, the number and size of offspring and more. And all of those traits are influenced by the rate of death prior to reproduction. What selection has produced – for the species that are still with us – is a reproductive rate that offsets the death rates with most species being able to produce an excess of potential reproductive individuals each generation. It is the ups and downs in these excess numbers that we track when trying to assess the status of species of interest. In spite of the shaping of reproductive rates by evolution, there have been intervals in evolutionary history during which change has out-paced the ability of species to evolve or adapt leading to mass extinctions. We are at the beginning of another such period of extinction known as the Anthropocene. Climate change and related human activities during this period seem certain to lead to the extinction of a large number of species that will not sustain their numbers in the face of higher death rates or lower birth rates, or both, associated with these changes.

So, what species will survive, and what species will be lost? We can’t be sure, but it already seems clear that species that are highly specialized, those that live in isolated and unique habitats, and those with extremely low reproductive rates are likely to become extinct in the coming decades. Indeed, some species appear to have already done so, e.g., the golden toad in Costa Rica (Note 1.) Specialization can be adaptive. Selection can favor traits that improve survivorship in a manner that narrows the resource base and habitats in which species reside. It can even result in reproductive modes that rely on the presence of other species, e.g., the emu/quinine/ant/seed dispersal in Australia (Note 2). These specializations can be maladaptive in the face of rapid environmental change. There are a variety of species with these specializations including many butterflies, other insects and even plants. In the case of plants, we have no idea how many involve a relationship with a specific pollinator such that, if the pollinator were to disappear, it would also lead to the loss of the plants themselves due to their inability to produce seeds. There are indications that this may already be happening. Specialists can be left behind during periods of change (Note 3).

As to the pollinators, many, especially social and solitary bees, and many wasps, have low reproductive rates. Bumble bees (Bombus) are especially vulnerable. Colonies are started in the spring by a queen that has survived the winter. If the colony grows well during the summer, reproductive males (drones) and females (queens) are produced toward the end of summer. These mate and the mated queens overwinter. However, during the winter losses can be high due to weather conditions and predation by skunks and other predators leaving few to start the population in some years. Nest failure is common following winter and in other cases, especially when resources are scarce, developing colonies produce only a few reproductives or none at all. After two to three years of low queen production and survival, bumble bees can become locally scarce or even locally and regionally extinct. Pockets may remain, and slow recoveries may be possible in some cases if habitats are stable, but that is less likely if resources decline or weather conditions continue to limit reproductive success. And then there is disease. If disease is the main driver of the decline, recovery may not occur with extinction to follow. Solitary bees, most of which are single brooded, also have low reproductive rates and are probably vulnerable to climate change although we know very little about their demography and year to year survival. Solitary bees are responsible for the pollination of many species of plants that are not visited by honey bees and bumble bees. These bees have an important roll in maintaining the integrity of the ecosystems in which they reside. Given the changing conditions, it is likely that many bee species will decline rapidly in the coming decades with significant numbers becoming extinct. Should that happen, there are indications that plant diversity will decline along with insect species that specialize on these plants. Those declines could be followed by declines in birds and other species that depend on the insects and seeds of the plants that are lost. The long-term result of such a negative cascade would be habitats and sometimes entire ecosystems dominated by a small number of species with high reproductive rates and the ability to survive in a broad range of environments. This has already happened in many areas where humans have extensively modified the landscape.

So, what does all of this say about monarchs? In contrast to the species described above, monarchs have a high reproductive rate and they are highly vagile (wide ranging). They are resilient in that they can quickly recover from conditions that led to sharp declines in numbers as we have seen during the recovery from 2013 (0.67ha, the all-time low) to 2015 (4.01) in the East and in the West from 2019 (30K) to 2022 (247K). Whether monarchs will be resilient enough to sustain the migration for the next 50 years is an open question. That will depend on the pace and extent of climate change, but surely, the migration will continue for several decades. However, even if the migration is lost, as a species, monarchs will always be with us (Note 4).

References

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

Meehan, T.D. & Crossley, M.S. (2023) Change in monarch winter abundance over the past decade: A Red List perspective. Insect Conservation and Diversity, 1–8. doi.org/10.1111/icad.12646

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. doi: 10.1111/icad.12198

Pleasants, J. M., and Oberhauser, K. S. (2013). Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conserv. Divers. 6, 135–144. doi: 10.1111/j.1752-4598.2012.00196.x

Taylor, O. R., (2023). The pending decision: Will monarchs be designated as threatened or endangered? Monarch Watch Blog.
https://monarchwatch.org/blog/2023/06/14/the-pending-decision-will-monarchs-be-designated-as-threatened-or-endangered/

Zuckerman, J., 2014 Plowed Under. https://prospect.org/power/plow

Notes

1. Golden toad – This toad, first reported in 1964 from a small rainforest site in Costa Rica was last seen in 1989. It has now been listed as extinct by the IUCN. https://en.wikipedia.org/wiki/Golden_toad

2. There are many species whose reproductive success is dependent on the presence and specific response of another species – sometimes two. One of the more complex three species interactions involve seed dispersal aided by emus and ants in Australia. https://www.indefenseofplants.com/blog/2019/9/30/emus-ants-one-heck-of-a-seed-dispersal-strategy

3. The Emerald Ash Borer, an introduced species from Asia, is decimating 18 species of ash trees over much of the United States. Ash trees are known to be the hosts for 300 insects with about 100 species being Lepidoptera. Among these are species, such as the seed weevil (Thysanocnemis bischoffi ), that specialize on ash trees. Since, there seems to be no natural resistance to the ash borer among most of the ash species, it is likely that the insects that specialize on ash trees, and lack alternative hosts, will become extinct along with their host trees. https://entomologytoday.org/2023/02/07/ash-trees-insects-alternative-host-plants/

4. Monarchs are genetically programed to migrate, and would continue to migrate in the spring and fall as long as populations persist through the winter in southern states.