Monarch Watch Blog

Monarch Population Status

25 February 2021 | Author: Jim Lovett

World Wildlife Fund Mexico in collaboration with CONANP and the Monarch Butterfly Biosphere Reserve (MBBR) announced the total forest area occupied by overwintering monarch colonies today. Nine (9) colonies were located this winter season with a total area of 2.10 hectares, a 26% decrease from the previous season (2.83 ha):

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

WWF release (in spanish): Menor presencia de mariposa Monarca y aumento de la degradación en los bosques donde hiberna

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Insect Population Dynamics

19 January 2021 | Author: Chip Taylor

Insect Population Dynamics:
Potential fecundity, realized fecundity and reproductive success

I’ve mentioned realized fecundity from time to time in my posts to the Monarch Watch Blog. It’s a subject that gets little attention perhaps because it is more of a hypothetical deductive construct than a measurable outcome of the interaction between a female (or cohort of females) and the immediate environmental context in which reproduction occurs. Yet, there is ample evidence that realized fecundity needs to be understood if we are to understand how monarchs, pollinators and invertebrates in general deal with average weather conditions, substantial deviations from long-term norms, extreme weather events and xenobiotics.

As you may recall from earlier discussions, realized fecundity for most insects is defined as the lifetime number of eggs oviposited. This number is distinguished from potential fecundity, which is the realized fecundity plus any eggs or well-developed oocytes that remain at death. These values are distinguished from reproductive success which is defined by the number of offspring that not only reach the adult stage but reproduce themselves. There is a presumption that higher realized fecundity leads to higher numbers of progeny reaching the adult stage and successfully reproducing. While there are no expectations that there is a linear relationship between realized fecundity and reproductive success, realized fecundity is the base such that low values are likely to stifle, while high values more effectively enable, population growth. In short, if we want to understand how populations respond to environmental conditions, we have to start with realized fecundity.

Studies of reproduction in lab cultures have been used to assess the differences between realized fecundity, potential fecundity and reproductive success. While we can’t easily make those distinctions in the field, we can make some strong inferences based on how populations respond to environmental conditions. For example, when the mean June–August temperatures are 2°F or higher above the long term mean, monarch populations decline. Why is that the case and how is that result related to realized fecundity and reproductive success?

To answer these questions, I try to think about the impact of temperatures on all actors in the play. We can postulate that as temperatures increase, monarch metabolism increases, and with that, there is an increased demand for water and carbohydrates from nectar to maintain bodily functions, including egg and sperm production, and the functioning of neuroendocrine and accessory glands. However, meeting these demands becomes increasingly difficult as temperatures increase since nectar secretion declines at higher temperatures and flowering duration shortens with both declining if the high temperatures occur during drought conditions. In addition, milkweeds experiencing physiological stress mature more rapidly and quality, as measured by nutrient content and percentage of usable proteins, probably decrease as well. In many plants, secondary plant products evolved to deter herbivory tend to increase during periods of stress further diminishing their palatability to herbivores. In other words, there can be a cascade of negative effects after temperatures significantly exceed long-term averages, effects that can be amplified if droughts occur simultaneously. These conditions could impact both adult and larval monarchs. The lifespan of adult monarchs, capacity to reproduce and number of hours of activity could be reduced. The latter due to the tendency for monarchs to seek shelter when temperatures are in the 90s. These conditions likely result in a lower number of eggs laid per female lifetime and thus a reduced realized fecundity for generations experiencing these conditions. It follows that reproductive success could also decline during these conditions if larvae reduce feeding at times when the temperatures are extremely high or the host plants are physiologically stressed. Any such interactions that affect plant quality and larval feeding success or developmental rate of larvae would have a negative effect on population growth.

When thinking about realized fecundity, we need to be careful to distinguish between individual and cohort or generation outcomes. In the spring, as monarchs returning from Mexico have reached Lawrence, I’ve made an effort to catch and dissect a few female monarchs to assess their reproductive condition. Most monarchs reaching eastern Kansas in late April are battered and torn and barely able to fly and can sometimes be seen crawling from plant to plant to lay eggs. Upon dissection most of these females contain fewer than 10 eggs with none developing in the ovaries and an almost completely depleted fat body. These end-of-life females appeared to have maxed out their reproductive potential. While this was true for the monarchs I caught, to what extent was this true of the entire cohort moving north in those years? We don’t know. But what about other years? In 2012 and 2017, overwintering female monarchs reached eastern Kansas in early April in excellent condition and full of eggs (see “Monarch Population Status” (5-11-2017)). Rather than laying most of their eggs in Texas and southern Oklahoma, these monarchs moved rapidly to the north and distributed their eggs over a broader range of latitudes than in most years. Massive numbers of eggs were laid in eastern Kansas in both 2012 and 2017, which would seem to be a good thing, yet, the winter counts that followed showed that the population had declined in each case.

If we assume that these cohorts of females also maxed out their reproductive potential, did the more northerly distribution of eggs have a role in determining the size of the migratory population and overwintering numbers? Probably. A more northerly distribution of eggs appears to reduce reproductive success and slow population growth in several ways. First, moving into northern latitudes too soon can mean that females are searching for milkweeds that have yet to emerge, second, due to a shortage of newly sprouting milkweeds, too many eggs can be laid per milkweed shoot to support all the developing larvae and third, lower average temperatures in more northerly latitudes slow development. Slowing development has the effect of exposing larvae for longer periods to predation and parasitism while increasing the mean age to first reproduction. The latter is probably the most important effect. It is a basic tenant of demography that populations with the shortest age to first reproduction increase most rapidly. With monarchs, any generation that takes longer to develop has a negative effect on the size of next generation. With only three generations per year, if monarchs start the year with a delayed mean age to first reproduction, it is almost impossible to reach numbers typical of average conditions by the end of the season.

We also need to factor in extreme weather events such as catastrophic mortality due to winter storms in Mexico, massive fires that kill the breeding population, floods and periods of extreme heat. To those natural causes of mortality, we can add mowing when larvae are present, insecticide drift from crops into areas with milkweeds and nectar sources and other sorts of chemical contamination. Mortality during or after the migration due to storms, etc., has the effect of reducing reproductive success the following year by reducing the number of monarchs that have the potential to reproduce in the spring. The other sources of mortality mentioned have an impact on the reproductive success of that particular generation, which, if severe, is likely to negatively affect the growth of the next generation. The impact of all these causes of mortality needs further study. We know little about the survival of monarch adults and larvae when temperatures exceed 110°F for a number of days. To these considerations, we can add mortality caused by predators and parasites. Again, these causes of mortality affect the number reaching the adult stage and therefore the potential reproductive success of that generation. Predation and parasitism appear to vary over generations as well as regionally and from year to year making it difficult to assess the importance of these factors as determinants of overall population growth.

Xenobiotics could also have an impact on population development. Xenobiotics are man-made chemicals that are both intentionally and inadvertently widespread in the environment. Although different from stressors associated with weather, chemical stressors could have similar effects – subtle, sublethal effects, that reduce reproductive success. While we tend to think of insecticides, herbicides and fungicides as probable agents in insect declines, there are literally hundreds of other widespread compounds that could be acting as single agents or synergistically with other compounds in ways that could affect realized fecundity. All that would be required is an interaction that causes a slight increase or decrease in metabolic rates. As mentioned, higher metabolic rates could lead to shorter life spans with lower reproductive output, while lower metabolic rates could lead to longer generation times, slower egg maturation, less reproductive activity and ultimately slower population growth. Metabolic rates are but one example as to how trace amounts of man-made compounds could be affecting invertebrates. Such compounds could affect the nervous system in ways that alter key functions such as the ability to produce gametes or respond to environmental stimuli in a manner that interferes with the ability to locate host plants or locate nest sites.

Realized fecundity can also be affected by the spatial distribution of resources. It takes energy to move through the environment in search of resources, and it follows that the costs associated with finding resources, let’s say nectar and host plants, are a function of the spatial distribution and abundance of those resources. In the context of the present-day conditions, involving mega cities, intensive farming and reduction of roadside vegetation through mowing or herbicides, it’s clear that monarchs are dealing with an increasingly fragmented environment. It is likely that fragmentation requires more time and energy for monarchs to find the needed nutrients and host plants to maximize their reproductive potential. How these conditions affect monarchs is not known, but it’s reasonable to expect there is a cost. To appreciate the landscape monarchs must traverse to find milkweeds and nectar sources in the Midwest, you need to drive across central Illinois, Iowa or Minnesota in mid-summer. The fragments with few or no milkweeds and nectar plants are huge. I’ve made those trips, and if my car ran on nectar rather than gasoline, even if an ounce of nectar was equal to a gallon of gas, I certainly couldn’t have completed those trips. It’s not easy being a monarch, and it’s getting harder.

It should be clear that everything I’ve just described for monarchs applies to honey bees, bumble bees, solitary bees, other pollinators and most other insects. I can envision scenarios based on the above that account for population declines of all of these organisms.

For an additional discussion dealing with monarch population dynamics, please see

Those readers interested in taking a deeper dive into population dynamics will find the following Wikipedia entry helpful:

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ESA listing decision for the monarch

15 December 2020 | Author: Chip Taylor

In a press release today, the U.S. Fish and Wildlife Service announced its decision with respect to the petition to declare the monarch a “threatened” species under the Endangered Species Act:

“After a thorough assessment of the monarch butterfly’s status, the U.S. Fish and Wildlife Service (Service) has found that adding the monarch butterfly to the list of threatened and endangered species is warranted but precluded by work on higher-priority listing actions. With this decision, the monarch becomes a candidate for listing under the Endangered Species Act (ESA), and its status will be reviewed each year until it is no longer a candidate.”

When asked to respond to this decision, my immediate response was the following:

“The warranted but precluded decision for monarchs is the right one at this time. It acknowledges the need for continued vigilance due to the numerous threats to the population while emphasizing the need to continue support for programs that create and sustain habitats for monarchs.”

“Warranted” in the above means that monarchs should be considered threatened due to the near- and long-term threats to the population. Stated another way, monarchs are vulnerable to falling below what biologists have identified as an extinction threshold, a low number from which the population is unable to recover. The term “precluded” means that among the long list of species whose populations are threatened or endangered, monarchs are less at risk than others at this time. Effectively, this places monarchs on a watch list in which favorable outcomes in the form of an increase in population numbers could result in removal from threatened status or negative trends that could result in regulations and further measures to protect the species. This ruling also means that monarchs are not subject to regulations at this time and that funding is insufficient to support monarch conservation. It follows that, in the near future at least, habitat restoration will have to be funded by the private sector.

There are many threats to the monarch population, including habitat loss, fragmentation of habitats, loss of nectar resources, widespread use of herbicides and pesticides, excessive mowing and climate change. From my point of view, the most serious near-term and long-term threats to the monarch population involve climate change. That effect can already be seen in the West. Temperatures have been increasing in the West at an alarming rate with significant consequences for the western monarchs that appear to have fallen below the extinction threshold for that region. In an earlier Blog post, I presented a preliminary analysis of the temperatures and monarch numbers along the California coast during the winter months (see “Monarchs and climate in the West“). Briefly, that analysis shows that overwintering sites are disappearing in the southern counties with an increasing proportion of the overwintering population being found in more northerly counties. These changes appear to be due to increasing temperatures during January–February along the coast. The changes in the mean temperatures during the growing season since 1901 to 2020 are shown in Figure 1 and the overall pattern of temperature changes per decade for the entire United States is shown in Figure 2. (I will provide further explanation for Figure 2 in another Blog article). Extreme temperatures, mean temperatures that are well above the long-term average, together with drought stress, appear to account for the rapid monarch decline in the West.

A rapid decline could occur in the East as well, if the overwintering population is decimated by a winter storm and followed by unfavorable conditions during the growing season such as those in 2012. I’m concerned about the winter storms in Mexico. These storms are a real and immediate threat to the longevity of the monarch migration. Temperatures in the mid-Pacific have increased, resulting in warm, moisture-rich weather systems that sweep eastward toward the Americas in the winter months. In the last two decades those weather systems have entered central Mexico in mid-winter which, when they hit the mountains, result in heavy rains, sleet, snowfall and freezing temperatures that have killed 50–70% of the overwintering monarchs. There have been 4 such events in recent years: 2002, 2004, 2010 and 2016. Fortunately, all of these events have occurred when the population was robust enough such that the numbers of survivors were sufficient to reestablish a substantial population in the spring. Still, you can see the impact of the 2004 and 2016 winter kills on the size of the population the following year. If there is a winter kill at the 70% level that hits an overwintering population of less than two hectares, it will be years before the population recovers – and it may not, if other unfavorable events such as an extremely warm March and summer, e.g. 2012, follow.

Long-term, we will lose the monarch migration due to increases in March temperatures in Texas, increasing summer temperatures in the Upper Midwest, warmer than average temperatures that delay the fall migrations, an increase in drought conditions in the South Region during the fall, and higher than average temperatures at the overwintering sites in Mexico UNLESS we significantly reduce greenhouse gasses. That said, there will be monarchs in the future, but the populations will be local, limited to southern latitudes and mostly non-migratory.

Yes, I know, the above scenario is pretty grim, but it is a reality we have to deal with. So, the question becomes: what are we going to do to sustain the monarch migration? To me, it’s clear. We have to do all we can to restore and sustain monarch habitats, and we have to support initiatives that favor the reduction of greenhouse gases.

Figure 1. Growing season mean temperatures for California in 30-year intervals starting in 1901. Note that while mean temperatures have increased from 68.4°F to 70.9°F, most of that increase (1.4°F) has occurred in the last 30 years.

Figure 2. Rate of temperature increase (°F) per decade during the growing season, 1975–2020. The rate remains unchanged for those areas with growing seasons that start earlier.

Press Release: U.S. Fish and Wildlife Service Finds Endangered Species Act Listing for Monarch Butterfly Warranted but Precluded

Full report: U.S. Fish and Wildlife Service. 2020. Monarch (Danaus plexippus) Species Status Assessment Report. V2.1 96 pp + appendices.

USFWS: Assessing the status of the monarch butterfly

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Monarch Watch Update November 2020

30 November 2020 | Author: Jim Lovett

This newsletter was sent via email to those who subscribe to our email updates.

Greetings Monarch Watchers!

Here’s a brief update as we head into the holiday season – stay safe!

As a reminder, if you would like to receive periodic email updates from Monarch Watch, please take a moment to complete and submit the short Google Form at

1. Monarch Population Status —by Chip Taylor
In recent years, I’ve written extensively about the development of the monarch population from early March through September, often ending with predictions about the size of the overwintering population. My observations and comments have been few this year because there just hasn’t been much to say. The pattern of recolonization and population development from March to early June was modest at best in the Upper Midwest and disappointing in the Northeast. Recolonization was followed by a hot summer (June–August) in both the Upper Midwest (2.7°F above average) and the Northeast (3.2°F above average). Mean summer temperatures greater than 2°F in the Upper Midwest are usually associated with low numbers of migrants and a decline from the previous year in overwintering numbers. Spring and summer conditions, including the quantity and quality of host and nectar sources available, determine the number of migrants.

In terms of production, the best reports of monarch numbers late in the summer were from west of 90°W (west of Madison, Wisconsin) and mostly north of Iowa. That’s a small area of high productivity relative to most years.

To get a better sense of the size of the migration each year, Jim Lovett, who compiles the tagging data, began keeping notes on tagging success in 2018. Although the data for this past tagging season is still arriving, the preliminary information suggests that taggers were less successful this year. For example, when asked if they had used all their tags, 33% said yes last year to only 26% so far this year. We’ll have more statistics to share in future updates.

There were some good things underway this fall. The migration was not late, as it was last year, and there was no shortage of nectar this year due to a drought in Texas and northeast Mexico. Both the lateness of the migration and the Texas drought were factors that contributed to the low numbers of migrants reaching the overwintering sites in Mexico last year. Monarchs were more or less on time this year with conditions more like those seen in the mid 1990s than seen in recent years. They also arrived in late October in time for the Day of the Dead (November 1–2).

Overall, my expectation is that survival of monarchs using the central flyway should be relatively high this year. Still, the numbers at the overwintering sites will be relatively low. I’ll be surprised, and pleased, if the total population measures over 2 hectares. That said, my record shows that I tend to underestimate the count.

2. Restoring milkweeds for monarchs
Our mission is to sustain the monarch migration and that means restoring milkweeds to landscapes from which they have been eliminated or creating new locations for milkweeds.

We work with 5 partner nurseries to distribute 2- to 4-month-old milkweed plugs for restoration and garden projects in most of the continental U.S. These plants can be used for 1) restoration projects through our free milkweed program, underwritten by generous donors, 2) through our free milkweeds for schools and non-profits, another program supported by donations or 3) purchased directly through our Milkweed Market.

Since 2010, we have distributed over 1 million milkweed plugs through these programs. Six-hundred thousand of these plants have been planted in restoration sites of 2 acres or more since 2015. Milkweeds have also been distributed to over 950 schools and non-profits. Many private and public gardens with milkweeds have been created and registered as part of our Monarch Waystation program as well. Monarchs, pollinators and many species that share the same resources benefit from these efforts. You can contribute to monarch conservation by planting milkweeds or donating to support these efforts.

Free Milkweeds for Habitat Restoration on sites of 2 acres or more

Free Milkweeds for Schools and Non-profits

Milkweeds for Private or Public Gardens and other projects (pre-orders begin in January)

Donate to Monarch Watch (GivingTuesday is December 1st!)

3. Submitting Tag Data
Thousands of you have already submitted your 2020 season tag data to us by mail or via our online submission form – thank you! If you haven’t submitted your data yet (from any season) please review the “Submitting Your Tagging Data” information on the tagging program page then send us your data at your earliest convenience via the Tagging Data Submission Form.

Complete information is available at if you have questions about submitting your data to us and we have conveniently placed a large orange “Submit Your Tagging Data” button on our homepage at that will take you directly to the online form.

There you can upload your data sheets as an Excel or other spreadsheet file (PREFERRED; download a template file from or a PDF/image file (scan or photo).

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

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

We rely on private contributions to support the program and we need your help! Please consider making a tax-deductible donation. Complete details are available at or you can simply call 785-832-7374 (KU Endowment Association) for more information about giving to Monarch Watch.

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

Thank you for your continued interest and support!

Jim Lovett
Monarch Watch

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Monarch coloration, milkweed toxins, and predation by birds

5 November 2020 | Author: Chip Taylor

This text is both a preamble and addendum to the “Monarch Fallout and A Predator Story” blog article posted recently by Brad Guhr of the Dyck Arboretum (republished below, with permission).

Predation by birds has been offered as the explanation for monarchs’ aposematic coloration. This contrasting orange and black color combination is thought to be a feature that effectively advertises the toxic cardiac glycosides (also called cardenolides) sequestered in the tissues of adult butterflies from the milkweeds consumed during the larval stage. This interpretation is strongly supported by the experiments and numerous analyses conducted by Lincoln Brower and his colleagues. Among these tests were feeding experiments with caged naïve blue jays. Young jays, that had never seen a monarch, would unhesitatingly eat one when it was first presented as a food item. Within a short interval, the jays would vomit up the monarch due to the emetic properties of the cardiac glycosides. A picture of this reaction is iconic (see “The Case of the Barfing Blue Jay“), having graced the pages of Scientific American and many a biology textbook. The jays thereafter refused to eat monarchs when presented among food items. This learning by experience, though some monarchs are consumed in the process, is said to provide monarchs, as a population, with a degree of protection from bird predation since birds, being highly visual, recognize the contrasting colors and, after a feeding experience, subsequently avoid feeding on monarchs or perhaps all species displaying these colors. Indeed, observations of birds feeding on monarchs, other than the black-backed orioles and black-headed grosbeaks that prey on monarchs clustered in the oyamel fir trees in Mexico, are rare.

Yet, now and then, we hear of instances in which observers have reported seeing scissor-tailed flycatchers and Mississippi kites feeding on monarchs during the migration. Unlike blue jays, that stopped eating monarchs after one experience, the scissor-tails and Mississippi kites appear to be undeterred by the cardiac glycosides in the monarchs. Still, the stories that reach us have always been fragmentary. The following blog article created by Brad Guhr, of the Dyck Arboretum, in Hesston, KS, and the wing collection assembled by Karen and Dick Fulk, describe an instance of intense predation by 5 immature Mississippi kites on migratory monarchs that had taken temporary shelter within the grounds of the arboretum.

Monarch Fallout and A Predator Story
By Brad Guhr on Oct 07, 2020

Monarch Fallout
It happened again in 2020. The convergence of the peak of the September monarch southerly migration over Southcentral Kansas was met by a strong south wind, causing a “fallout” of monarchs at the Dyck Arboretum. Rather than waste energy fighting the headwind, monarchs find a place of refuge to rest and sip nectar. I would estimate that I’ve seen this phenomenon happen five times in the Arb since 2005 and this year’s was the most memorable for a few different reasons including big numbers, fallout location, and a predator story.

Monarchs in the Hedge Row at Dyck Arboretum, 9/20/2020 – Photo by Gerry Epp

Big Numbers
The monarch numbers I observed on Monday, 9/21/2020 seemed to me to be more stunning than I can ever remember. I estimated conservatively in a report to Journey North, there were at least 500 monarchs resting in the Arboretum that day. But after giving it more consideration and talking to a local monarch tagger, Karen Fulk, I wonder if that number was more accurately in the thousands.

Karen’s many years of efforts to tag monarchs in Hesston has her keenly in touch with monarch phenology and migration patterns. She reports that the peak of migration through south central Kansas is usually between 9/22 and 9/27. This year, however, she started seeing an uptick in numbers when a cold front and north wind jump-started the southerly monarch migration a bit earlier.

Karen usually tags 300 annually during the fall migration. This year, Chip Taylor at Monarch Watch, knowing that migration numbers were higher this year, suggested that Karen start with 500 tags. She was able to apply most of those 500 tags when the fallout began Friday 9/18/2020 through Sunday 9/20/2020. Arboretum member, Gerry Epp, further documented this event by posting photos of the fallout on his Facebook page, 9/20/2020.

Monarchs on Seven Son Flower at Dyck Arboretum, 9/20/2020 – Photo by Gerry Epp

Fallout Location
With some repetition now in seeing these fallouts occur in the same place, I want to give some thought to why they congregate where they do at Dyck Arboretum. Karen usually tags at three places in Hesston based on the ability to catch and tag the maximum number in one place, and Dyck Arboretum is where she does the majority of her work. She estimated that 95% of her tagging this year happened at the Arboretum, based on seeing the greatest number of butterflies here.

I would hypothesize that they repeatedly congregate in the small 1/8th-acre area at the Arboretum amphitheater/pinetum for three reasons. One, they are seeking protection from the elements of wind and heat. This is about energy conservation. By escaping the wind and congregating in large groups on the north side of the dense hedge row of Osage orange trees, they are finding a microclimate that is cooler, more humid, and less turbulent than they would find on the south side.

Monarchs on Seven Son Flower at Dyck Arboretum, 9/20/2020 – Photo by Gerry Epp

Two, this location is next to a number of nectar sources. Why not rest where you can eat/drink too? Nearby native plant beds and a reconstructed prairie had a timely profusion of flowering from many species of the genera Helianthus (sunflower), Solidago (goldenrod), Symphotrichium (aster), Liatris (gayfeather), Eryngium (eryngo), and Heptacodium (seven son flower).

Three, a number of white pines in this location may resemble the trees of the Oyamel fir forests in Mexico. I don’t have any proof of this theory, but it seems plausible to me.

Predator Story
The newest wrinkle of this monarch fallout experience was the side story of five immature Mississippi kites. They were probably migrating with the monarchs and decided also to not fight the strong south wind. For a day and a half that I observed, this hungry bunch of pentomic predators took advantage of an abundant food supply. They hung out in the top of one of the white pines and took turns swooping through the monarch clouds to easily catch a snack.

Mississippi Kite Eating A Monarch at Dyck Arboretum, 9/22/2020 – Photo by Janelle Flory Schrock

Sometimes they missed catching their target, but usually, these agile insect catchers snagged their prey. Typically they would return to their perch to eat their catch, but sometimes they would eat in flight or “on the wing” as I hear experienced birders say. At one point, I counted approximately 120 monarch wings that had fluttered down to form what I’ll call a monarch confetti debris field. At four wings per monarch, that represented the carnage of about 30 monarchs. However, a number of wings had already been collected by onlookers, so it is not unreasonable to think that the number of monarchs preyed upon were double or triple what I saw.

Monarch Wings at Dyck Arboretum, 9/20/2020 – Photo by Brad Guhr

Monarch Toxicity
This predator behavior was a surprising observation. Monarch larvae eat milkweed and sequester in the mature butterfly wings and exoskeleton the milkweed toxins called cardiac glycosides. These heart poisons can seriously affect vertebrate predators, including birds, and often cause them to vomit and subsequently avoid eating them further. However, these young kites not only ate monarchs all day Monday, but they continued their feeding frenzy the next morning. Either their stomachs weren’t too adversely soured, or the calories needed to continue this migratory journey were simply too important.

A Google literature review turned up no articles mentioning this habit of Mississippi kites eating monarchs. However, a follow-up conversation with University of Kansas Professor, Brad Williamson, helped me understand that this observation is not so irrational. He explained that the monarch population is not 100% toxic.

“The individual toxicity depends a lot on the particular milkweed species that hosted the larval stage. Asclepias syriaca (common milkweed) and Cynanchum laeve (honeyvine milkweed) are not nearly as toxic as A. verticillata (whorled milkweed). There is an entire range of toxicity and it makes for some great mathematical modeling questions–just how much toxicity (percent toxic) in the population is necessary for protection for the entire population? How much metabolic costs are there for monarchs trying to process highly toxic host plants? Turns out that only 25-40% of the population being toxic confers protection for the remaining population.” (I will include below a bibliography on monarch toxicity that Dr. Williamson provided if any of you are interested as I am in learning more about this topic.)

There were a lot of interesting biological and ecological issues at play here with these monarchs and kites. It was just one more interesting natural history story with subplots to be observed by those of us living in the Monarch Flyway. Until I’m able to one day witness the hundreds of millions of monarchs wintering in the the Oyamel forests of central Mexico, I am completely content having a front row seat to this fascinating migration phenomena right here in Kansas.

Monarch butterflies observed at the Monarch Butterfly Biosphere Reserve in Michoacán, Mexico.
Video by Beatrix Amstutz, February 7, 2020.

Plant Milkweed
To assist the monarchs and their annual migration, plant milkweed host plants and other native nectar plants for adults. Check out our annual spring and fall Flora Kansas native plant sales.

Articles on Monarch Toxicity
Brower, L. P., and C. M. Moffitt. “Palatability Dynamics of Cardenolides in the Monarch Butterfly.” Nature 249, no. 5454 (1974): 280–283.

Brower, Lincoln P. “Avian Predation on the Monarch Butterfly and Its Implications for Mimicry Theory.” The American Naturalist 131 (1988): S4–S6.

Brower, Lincoln P., and Susan C. Glazier. “Localization of Heart Poisons in the Monarch Butterfly.” Science 188, no. 4183 (1975): 19–25.

Brower, Lincoln P., Peter B. McEvoy, Kenneth L. Williamson, and Maureen A. Flannery. “Variation in Cardiac Glycoside Content of Monarch Butterflies from Natural Populations in Eastern North America.” Science 177, no. 4047 (1972): 426–429.

Fink, Linda S., and Lincoln P. Brower. “Birds Can Overcome the Cardenolide Defence of Monarch Butterflies in Mexico.” Nature 291, no. 5810 (1981): 67–70.Malcolm, S. B., and L. P. Brower. “Evolutionary and Ecological Implications of Cardenolide Sequestration in the Monarch Butterfly.” Experientia 45, no. 3 (1989): 284–295.

Malcolm, Stephen B. “Milkweeds, Monarch Butterflies and the Ecological Significance of Cardenolides.” Chemoecology 5, no. 3–4 (1994): 101–117.

Malcolm, Stephen B., Barbara J. Cockrell, and Lincoln P. Brower. “Cardenolide Fingerprint of Monarch Butterflies Reared on Common Milkweed, Asclepias Syriaca L.” Journal of Chemical Ecology 15, no. 3 (1989): 819–853.

Nelson, C. J., J. N. Seiber, and L. P. Brower. “Seasonal and Intraplant Variation of Cardenolide Content in the California Milkweed, Asclepias Eriocarpa, and Implications for Plant Defense.” Journal of Chemical Ecology 7, no. 6 (1981): 981–1010.

Roeske, C. N., J. N. Seiber, L. P. Brower, and C. M. Moffitt. “Milkweed Cardenolides and Their Comparative Processing by Monarch Butterflies (Danaus Plexippus L.).” In Biochemical Interaction between Plants and Insects, 93–167. Springer, 1976.

Zalucki, Myron P., Lincoln P. Brower, and Alfonso Alonso-M. “Detrimental Effects of Latex and Cardiac Glycosides on Survival and Growth of First-Instar Monarch Butterfly Larvae Danaus Plexippus Feeding on the Sandhill Milkweed Asclepias Humistrata.” Ecological Entomology 26, no. 2 (2001): 212–224.

The post Monarch Fallout and A Predator Story appeared first on Dyck Arboretum.

Karen Fulk had been tagging monarchs in the area at the time of this event, and wings of seven of her tagged monarchs were found among the scattering of wings in the area of intense feeding by the Mississippi kites. Curious to learn more, Karen made a search for all the wings she could find. She collected many, but some were evidently collected by others. Still, the collection gives us a rough idea of the total number killed and the sex ratio of those consumed.

Karen gave a quick look at the wings and concluded that the sample represented over 90 monarchs. Since it was of interest to determine the sex of each forewing to determine the sex ratio of the sample, Karen being less certain of those determinations, sent the collection to me.

The results of sorting the wings by sex and left verses right are given below.

Left Right Left Right
Male 37 43 43 36
Female 50 47 28 31

This tabulation suggests that AT LEAST 50 females and 43 males, or 93 in total, were killed and eaten by these birds while the monarchs were roosting in and passing through the arboretum. It would seem that the cardenolides had minimal effect, if any, on the feeding habits of these Mississippi kites. Curiously, I saw no signs of beak marks on any of the wings.

Bag of monarch forewings

Left and right female monarch hindwings

Hindwings of tagged monarchs eaten by Mississippi kites at the Dyck Arboretum 21-22 of September 2020.

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Fast-paced migration this year

9 September 2020 | Author: Chip Taylor

If you are a monarch tagger located north of 35N (e.g. Oklahoma City), tag when you can. This will be a fast-paced migration compared to recent years. If you hesitate, you could miss the opportunity to tag.

Last year we experienced the latest migration in the last 28 years. It was too warm in the Upper Midwest with daytime highs in the 80s and 90s for much of the month. Monarchs prefer to migrate when the temperatures are in the 60s and 70s and that is what is shaping up for the Upper Midwest and much of the northern breeding area over the rest of the month.

Once this cold surge passes after Friday and Saturday, monarchs will be on the move. This migration will be more like those seen in the late 1990s and early 2000s in the northern breeding area. The population will advance at a steady pace into the South region and it is likely that this migration will be more compressed with few stragglers.

Thus, the opportunities to tag will be more limited than over the last 5 warm Septembers. This temperature shift also means that late developing monarchs will be left behind in larger numbers than in recent years. That happens, and there is nothing we can do about it that will affect the number of monarchs reaching Mexico. Monarchs have dealt with these swings in the weather for a very long time.

Enjoy the tagging and thanks for your assistance in helping us all learn more about the monarch migration.

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Monarch displacements and orientation

31 August 2020 | Author: Chip Taylor

Lost and found

In the spring of 2019, I cleaned out my office in Haworth Hall, the main biology building. It was an emotional trip through my 47-year career as a KU faculty member as I sorted through the artifacts that represented my academic and personal history. In the process, I made a number of discoveries that led to recovered memories but also engaged in a few searches for things long lost.

One priority involved the search for an unpublished manuscript that was written about 20 years ago by Sandra Perez and myself. I had been looking for that text since the data therein speaks to some of the recent discussions about monarch orientation. Unfortunately, the manuscript was a no show. Then Covid-19 paid us all a visit this spring, and I had to move my office from Monarch Watch to home. That required a bit of clean-up of the home office to make it more usable – and, you guessed it. I found the Perez/Taylor manuscript in an unmarked folder. I suspect many retired profs have unpublished texts. I have a bunch. Some should have been published and others not. The Perez/Taylor manuscript was reviewed and sent back for revisions. Unfortunately, I don’t have the reviews. For reasons I don’t recall, the revisions were never made and the manuscript wasn’t resubmitted.

The text described the results of two field experiments conducted in 1997 and 1998 involving orientation of displaced migratory monarchs. The results of the first test were clear and informative, but there was a problem with the second experiment due to the fact that it was shortened and possibly influenced at one location by an advancing hurricane. In other words, the two-site comparison we were counting on, that would have given power to the results, whatever they showed, was compromised. In the best of all possible worlds, to achieve the two-site results we wanted, a do over the next migratory season was required, but that wasn’t possible. Below is a link to the manuscript as I found it. It needs a rewrite and a little more context and if we were to do the same set of experiments again, we would do them a bit differently. I’m posting this to the Blog since the data from the first experiment is informative and that of the second is certainly suggestive though not entirely convincing. These experiments should be repeated on a larger scale, this time with more controls and radio tagged or simply tagged monarchs that have been weighed and measured. We hope someone will take up this challenge. At another level, this approach offers an opportunity to trace the physiological (biochemical and genetic) change from one entrained behavioral response to specific environmental cues to another set of cues or signals at new locations. What I’m suggesting is that displaced monarchs go through a reset process, not unlike jet lag in humans. However, unlike humans, in monarchs, the reset duration is temperature dependent.

Link to unpublished manuscript (PDF):
Monarch Butterfly (Danaus plexippus) Migratory Orientation: Regional Differences and Effects of Displacement
Sandra M. Perez and Orley R. Taylor

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Monarch Watch Update July 2020

24 July 2020 | Author: Jim Lovett

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Greetings and welcome to Monarch Watch’s 29th tag season!

As you’ve probably come to expect in the fall, we have a TON of information to share so let’s get to it. This update includes:

1. Monarch Population Status
2. Tagging: then, now and in the future
3. Submitting Tag Data for the 2019 Season
4. Monarch Watch Tagging Kits
5. Tagging Wild and Reared Monarchs
6. Chip in for Monarch Watch in 2020!
7. Grant-Sponsored Free Milkweed Programs
8. Monarch Waystations
9. Collect Milkweed Seed for Monarch Watch
10. Monarch Calendar Project
11. Fall Monarch Watch Events
12. Monarch Rearing, Tagging and Releasing Survey

1. Monarch Population Status —by Chip Taylor
There are a number of ways to assess the development of the summer monarch breeding population that lend some predictability to the size of the migratory population. One can use mid-summer numbers gleaned from surveys conducted by the North American Butterfly Association or eggs per stem counts tallied by the Monarch Larval Monitoring Project, or simply follow the chatter about the numbers of adult monarchs and immatures reported on various social media sites and email lists like Dplex-L. All have merit and all have limitations.

I prefer to break down the numbers of first sightings north of 40N from 1 May to 14 June as reported to Journey North. I look for two things, the timing of arrival across the longitudes as well as the numbers arriving and I look at how those numbers might have been affected by the numbers of first sightings of returning monarchs from 1 March–30 April. In addition, I ask how the weather might have affected recolonization. To that, I add the forecasts for the mean temperatures for the months of June–August. The result is a prediction each July that is correct more often than it is wrong, but there have been some misses and those are both instructive and humbling.

So, what do these metrics suggest for the coming migration? Actually, the prospects for a reasonably robust migratory population look quite good for the area from central Michigan to 100W in the Dakotas. The numbers from Michigan to the east coast are likely to be lower than for each of the last two years. In terms of the timing of arrivals in the northeast east of Toronto in Canada, and most of northern New England, the recolonization this year was the 6th lowest in the last 21 years. That said, this region has surprised me in the past by producing more monarchs than I expected.

Overall, there should be plenty of monarchs to tag this fall and there is a good likelihood that the numbers this winter in Mexico will be higher than in 2019.

Western Monarchs

The big question for those interested in western monarchs is whether the population will increase from the low numbers each of the last two years. The population in the east bounced back from a low of 0.67 hectares in the winter of 2013–2014 to 4.01 hectares in 2015–2016. That was a remarkable rebound and it’s reasonable that the western population should be able to do the same, right? Maybe and maybe not.

The conditions in the west in terms of the weather extremes, the distribution of milkweeds, etc. are very different from those in the east. Here is what we can say about the west at this point: there is a mix of favorable and not so favorable reports for the west, but generally, there are few reports and that is not a good sign. The good reports involve what appear to be good breeding populations in the vicinity of Prescott, Arizona, and in SE Arizona. Good numbers have also been reported in Salt Lake City and the surrounding area with some reports from Idaho. In contrast, Oregon and Washington have been relatively silent and that is not a good sign. Since a substantial number of the monarchs that arrive at the overwintering colonies along the west coast originate from the Northwest, low production there again this year could mean low numbers during this year’s Thanksgiving Day Counts. Let’s hope things pick up in the west over the next 6 weeks!

2. Tagging: then, now and in the future
Over the years, thousands of taggers have contributed to our tagging database. It is an enormous record and a veritable gold mine of information about how the migration functions. The record represents over 2 million tagged butterflies and lists where, when and by whom each butterfly was tagged. The sex of each butterfly and whether the butterfly was wild-caught or reared, tagged and released is also recorded. The record also includes over 19,000 recoveries at the overwintering sites. We have spent the last several years closely examining these records and the data have been used as the basis for two publications. The first, “Is the Timing, Pace, and Success of the Monarch Migration Associated With Sun Angle?” was published in December 2019 and the second, “Evaluating the migration mortality hypothesis using monarch tagging data”, should be published soon. Two additional papers are in preparation and more are planned.

Briefly, the tagging data have revealed new information on the origins of monarchs that reach Mexico, the timing and pace of the migration, differences among regions due to recolonization and weather, the impact of drought years and many other factors. None of these insights into the dynamics of the migration and the monarch annual cycle would have been possible without the assistance of all those who have so generously donated their time and data to the Monarch Watch Tagging Database (which will ultimately be transferred to a national archive). Yet, in spite of these successes, we are not done; there is more to learn. The climate is changing and monarch habitats are continuing to decline and for these reasons it is likely that the migration will change as well. Continued tagging should enable us to track these changes, and for that, we hope you will continue to tag, to report your data and to generally support monarch conservation by creating habitats for monarchs or helping others do so.

Thanks, and best of luck this tagging season. Please stay safe. Chip Taylor, Director, Monarch Watch

3. Submitting Tag Data for the 2019 Season
Thousands of you have already submitted your 2019 season tag data to us by mail or via our online submission form – thank you! We are still receiving data sheets and if you haven’t submitted your data yet it is not too late. Please review the “Submitting Your Tagging Data” information on the tagging program page then send us your data via the Tagging Data Submission Form.

Complete information is available at if you have questions about submitting your data to us and we have conveniently placed a large “Submit Tagging Data Here” button on our homepage at that will take you directly to the online form.

There you can upload your data sheets as an Excel or other spreadsheet file (PREFERRED; download a template file from or a PDF/image file (scan or photo).

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 Watch Tagging Kits
Monarch tagging is an important tool to help us understand the overall dynamics of the monarch population. Tags for the 2020 fall tagging season are available and we have started shipping them out, ahead of the migration in your area. If you would like to tag monarchs this year, please order your tags soon as they are going fast! Tagging Kits should arrive within 7–10 days but priority will be given to preorders and areas that will experience the migration first.

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 2020 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 – where each purchase helps support Monarch Watch.

2020 datasheets and instructions are also available online at

Tagging should begin in early to mid-August north of 45N latitude (e.g. Minneapolis), late August at other locations north of 35N (e.g., Oklahoma City, Fort Smith, Memphis, Charlotte) and in September and early October in areas south of 35N latitude. See a map and a table with expected peak migration dates at

5. Tagging Wild and Reared Monarchs
The following is an abbreviated version of our “Tagging wild and reared monarchs: Best practices” article posted to our Blog last year. The complete text of the article is available via the link below.

Diving into the data has revealed a number of surprises such as the difference between the probability that a reared monarch will reach Mexico and the probability that a wild–tagged monarch will do so. The recovery rate is higher for wild–caught monarchs (0.9% vs 0.5%) and it is the data from the wild–caught butterflies that tell us the most about the migration. Frankly, for some analyses, we have to set the reared monarch data aside. That doesn’t mean it is not valuable, but its uses are limited.

It should be noted that for tagging data purposes, monarchs captured as adult butterflies should be reported as WILD and adult monarchs reared from the egg, larva, or pupa stage should be considered REARED.

For wild-caught monarchs we need to:
1. increase the number of taggers from western Minnesota and Iowa westward into Nebraska and the Dakotas to give us a more complete understanding of dynamics of the migration;

2. increase the number of wild monarchs that are tagged since these provide the most valuable data; and

3. increase the number of taggers who tag from the beginning of the tagging season in early August until the migration ends. Tagging records for the entire season will help us establish the proportion of the late–season monarchs that reach the overwintering sites. When tagging wild–caught monarchs, many taggers run out of tags well before the season ends. That’s great, but it would help us to know when all tags had been used by indicating this via the online tagging data submission form.

Reared butterflies tend to average smaller than wild migrants. That difference can be reduced significantly if careful attention is given to rearing larvae under the best possible conditions. Large monarchs have the best chance of reaching Mexico, surviving the winter and reproducing in Texas. There are several reasons for this: better glide ratio, better lift with cross or quartering winds, larger fat bodies, more resistance to stress, etc. There are very few small monarchs among those that return in the spring. For those of you who prefer to rear, tag and release, we have a few suggestions:

1. Rear larvae under the most natural conditions possible.

2. Provide an abundance of living or fresh-picked and sanitized foliage to larvae.

3. Provide clean rearing conditions.

4. Plan the rearing so that the newly-emerged monarchs can be tagged early in the migratory season (10 days before to 10 days after the expected date of arrival of the leading edge of the migration in your area).

5. Tag the butterflies once the wings have hardened and release them the day after emergence if possible.

6. When it comes to tagging, tag only the largest and most-fit monarchs (see complete article for some guidelines). Records of tags applied to monarchs that have little chance of reaching Mexico add to the mass of tagging data, but do not help us learn which monarchs reach Mexico – unless the measurements, weight and condition of every monarch tagged and released is recorded. There are a few taggers who keep such detailed records and those data can be very informative. If you collect such data and are willing to share it please contact us; do not add this information to the standard tagging data sheet.

As a final note, this text is not a directive. We are not telling you what to do; rather, we are simply providing suggestions that may lead to more successful rearing and tagging efforts.

The expanded version of this article “Tagging wild and reared monarchs: Best practices” is available at

6. Chip in for Monarch Watch in 2020!
Several years ago, we launched our first “Chip in for Monarch Watch” Fundraising Campaign in honor of our director and founder, Chip Taylor (whose birthday happens to be at the end of August, by the way). This campaign offers a chance for Monarch Watchers, colleagues, friends, and family across the planet to show their support for Chip and the Monarch Watch program he brought to life more than a quarter-century ago. It has provided tremendous support for Monarch Watch over the years, through both monetary contributions and kind words. We encourage you to spend a little time reading through the previous donor comments on the Chip in for Monarch Watch page – the connections that are facilitated by monarchs and Monarch Watch are truly extraordinary.

This year’s Chip in for Monarch Watch campaign is now underway – if you are in a position to offer financial support to Monarch Watch (or know someone who might be), please consider making a fully tax-deductible donation of any amount during our 2020 “Chip in for Monarch Watch” fundraising campaign.

Visit for more information or to submit your pledge and tax-deductible donation.

Please be sure to leave your comments, thanks, birthday wishes, etc. for Chip via the Chip in for Monarch Watch Form at

Thank you for your continued support!

Quick Links:

– Chip in for Monarch Watch:

– Chip in for Monarch Watch Form (to leave comments, thanks, birthday wishes, etc.):

– Donate Now via the KU Endowment:

7. Grant-Sponsored Free Milkweed Programs
Monarch Watch is still seeking a few more applications for our very popular grant, Free Milkweed for Schools and Nonprofits. If your organization already has a garden and you want to enhance it with milkweeds, this grant is for you! If your organization doesn’t have a garden at all, but would like to start one, this grant is for you! We award these plants to libraries, schools, nature centers, churches, community gardens, scouting and 4H organizations, master gardeners and much more. Help us meet our annual quota of 6,000 plants so that we can reapply for future funding. We are almost there, with less than 2,000 plants to distribute.

The following map shows the distribution of milkweeds since 2014, all funded through the generous support of the Natural Resources Defense Council:

Apply now for plants that will be shipped in the fall to the eastern United States. California and Texas applicants will receive plants next spring, when we have a new crop. Awardees will receive one free flat of native milkweed plugs! Sorry, private gardens are not eligible for this grant. Previous grant recipients are not eligible.

For complete details about applying for our Free Milkweeds Grants please visit

8. 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. 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!

A quick online application will register your site and your habitat will be added to the online registry (mapped location will be approximate for privacy). 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 24 July 2020, there have been 29,809 Monarch Waystation habitats registered with Monarch Watch! Texas holds the #1 spot with 2,451 habitats and Illinois (2,320), Michigan (2,233), California (1,909), Ohio (1,529), Virginia (1,379), Florida (1,324), Pennsylvania (1,322), Wisconsin (1,304), and Ontario (978) round out the top ten.

You can view the complete listing and a map of approximate locations via

9. Collect Milkweed Seed for Monarch Watch
Monarch Watch is seeking donations of milkweed seed collected from wild populations of native milkweeds in order to maintain our milkweed distribution programs. Milkweeds are beginning to put on seed pods and will continue for the next few months, depending upon your location. We welcome seed donations of one ounce or more, which we pass on to our partner nurseries to grow. Through the Milkweed Market and our free milkweed programs, we then distribute milkweed plugs back to the ecoregion from which the seed was collected.

Generally, our current needs include seed from Texas, Arizona, California, the Midwest, and the eastern/southeastern coastal states. Also, incarnata and tuberosa are always needed from east of Ohio, where they are native. We currently have enough seed from the upper Midwest.

Please visit our seed collecting page for further instructions:

10. Monarch Calendar Project
If you are recording your monarch observations for this project and would like to submit your data for the spring (1st) period please do so using the appropriate form, based on your location:

For locations SOUTH of (less than) 35N latitude (March 15–April 30, 2020) please use this form:

For locations NORTH of (greater than) 35N latitude (April1–June 20, 2020) please use this form:

As soon as the fall period ends for all locations (September 25) we will send out links for submission of that data.

Monarch Watch continues to seek the assistance of hundreds of monarch enthusiasts (citizen scientists) in collecting observations of monarchs in their area during specific periods of the spring and fall. If you would like to participate, all you have to do is: 1. REGISTER (just so we know where you are located and how to reach you), 2. RECORD (keep a record of the number of monarch butterflies you observe each day during the time period dictated by your location) and 3. SUBMIT (at the end of the observation period in the fall we will send participants a link to an online form to submit their observation data).

Complete details and a link to the short registration form are available at

Please note that the fall observation period for those of you in the Southern U.S. runs from August 1–September 25 so you need to start recording your monarch observations! For northern locations (greater than 35N latitude) the fall period runs from July 15–August 20 so recording should be going on now, but it is not too late to join in!

11. Fall Monarch Watch Events
As you might have guessed, our big in-person public events that are held in September each year in Lawrence, KS (Fall Open House and Tagging Event) have been canceled. However, we hope to be able to provide some alternate activities to engage Monarch Watchers. Stay tuned and stay safe!

12. Monarch Rearing, Tagging and Releasing Survey

Do you raise monarchs from eggs, caterpillars or chrysalises? If so, help us understand what techniques monarch enthusiasts, such as yourself, are using when rearing monarchs. We have created a simple survey, here:

Feel free to share this with friends or groups that focus on monarch rearing and/or conservation.

Questions? Comments? Please email Angie at

Thank you!

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

We rely on private contributions to support the program and we need your help! Please consider making a tax-deductible donation. Complete details are available at or you can simply call 785-832-7374 (KU Endowment Association) for more information about giving to Monarch Watch.

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

Thank you for your continued interest and support!

Jim Lovett
Monarch Watch

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Monarch Annual Cycle: Migrations and the number of generations

3 June 2020 | Author: Chip Taylor

monarchs in flight

The monarch annual cycle is quite extraordinary since it involves an overwintering phase that follows a long fall migration, a remigration in the spring and a succession of generations before the start of the next fall migration. This pattern is even more complex since it involves overlapping generations and a total of 4 migrations. Yes, 4 migrations. Further, monarchs breed over a wide range of latitudes with differing temperatures and periods of production. It can be very confusing and there is a lot of misinformation about these patterns in documentaries about monarchs and on many websites. I’ve been trying to sort out the migrations and generations since 1992, and the summary below fits the data that I’ve seen to date. Please be aware, I’m describing overall patterns – average conditions – to which there are exceptions if you look all the data that’s available.

Let’s deal with the migrations first since there is a widespread perception that monarchs take three generations/migrations to reach Canada. That’s not the case. Recolonization of the breeding area requires only two migrations. That’s well-established in the literature and you can see the pattern in the first sightings data posted to Journey North each year. Here is a quick summary:

The first migration
Monarchs leave the overwintering sites starting in late February, a process that can continue into the first week of April. This migration starts to reach Texas in the second week of March. The returning female monarchs move N and NE mating, laying eggs until they die. Most are dead by 1 May with the effective northern limits generally around 37°N.

The second migration
Offspring from the returning migration reach the adult stage mostly in mid to late April and, after a few days needed to fully mature, they begin to migrate N and NE. This generation – the first generation of the season – makes the second migration. These butterflies continue migrating until sometime late in the first week of June. At that point, all directional flight ceases, ending the second migration. By the end of the first week of June, this second migration, or wave of monarchs, has reached most of the areas containing milkweeds, and recolonization is complete or as complete as it can be for a given year.

The third migration
There is no directional movement from the first week of June until sometime in the fourth week of July. In other words, there is a six or seven-week interval during which all flight and reproduction is local. Directional flight for SOME but not ALL monarchs begins in the fourth week of July. These monarchs move S and SW and have been observed to recolonize southern areas from Georgia to Texas that had contained few or no monarchs for the previous two or more months. I had called this migration the “pre-migration migration” in previous discussions. That’s an awkward and confusing term so hereafter I’m going to refer to this migration as the “midsummer migration.” Although we know this migration occurs, we don’t know exactly when it starts or ends or the geographic origin of the butterflies. Judging by observations of directional flight and the arrival of fresh monarchs in areas from which monarchs have been absent, it appears that this migration starts in the fourth week of July and ends in the beginning of the third week of August. How long this migration takes to pass through a particular location is not clear. Reproduction follows the arrival of these butterflies from the North creating some confusion as to the number of generations produced in the South. I’ll get to that later.

The fourth migration
It’s the fourth migration that is well known. It starts at 50°N (Winnipeg) at the end of the first week of August and continues through the fall with the last monarchs arriving at the overwintering sites in early December. This migration is the longest both in terms of distance and time. It also differs from the other three migrations due to the fact that butterflies in this migration do not mate and reproduce during the migration. Nor do they reproduce at the overwintering sites in Mexico.

That monarchs reproduce in Mexico during the winter is another misconception frequently repeated in the media. The overall pattern is this: three migrations involving fast-moving butterflies that mate and reproduce as they expand the range seasonally with an outcome that generally increases monarch numbers and one fall migration that contracts the geographic range during which the population declines due to morbidity and mortality. In effect, there is an eight-month period of reproduction (March–October) that overlaps with an eight-month interval (August–March) during which the population declines. Simply put, there are two migrations going south in summer/fall and two migrations going north in the spring.

When thinking about the duration of a developing generation, it is common to add up the intervals needed for monarch immatures to complete each stage from egg through pupation — and that interval can vary from about 25 to over 50 days depending on temperatures. Egg to adult intervals are generally cited as about 30 days. That’s a good average, but it doesn’t account for a period of maturation females need before mating and egg-laying begins. That interval is also temperature sensitive but probably averages 5 days for monarchs at the northern latitudes. My point is that it’s better to think in terms of egg to egg intervals rather than egg to adult intervals when counting generations, e.g. 35 vs 30 days.

As discussed, first-generation monarchs are offspring from monarchs returning from Mexico. These first-generation offspring mate and lay eggs while moving north. At a particular point, new eggs could be deposited by passing monarchs for several weeks, in effect spreading out the second generation over time and space that later leads to overlapping generations. That’s complicated, and we won’t go there since our purpose is to characterize the general pattern of the number of generations. To do so, it helps to create a simple scenario for different latitudes.

Let’s start with eggs laid by a first-generation female on the 20th of May in northern Iowa. Using the egg to egg interval of 35 days, the second-generation females would begin laying eggs on the 25th of June. Offspring from these eggs constitute the third-generation, and they would be expected to begin egg-laying in another 35 days or around the 30th of July. As the eggs from this third-generation complete development and reach the adult stage, they constitute the fourth or fall migratory generation.

However, if we start our scenario later in Iowa, or start further north, we lose a generation. For example, eggs laid in the Winnipeg area by newly-arriving first generation females, let’s say on the 1st of June, probably wouldn’t reach the adult stage and begin egg-laying until 8 July or later, due to a longer egg to egg interval resulting from lower temperatures at that latitude. Eggs laid by those second-generation females become third generation adults in August that migrate. The message here is that most of the migratory butterflies originating from north of 40°N latitude are third and fourth generation butterflies.

But what about further south? Are there 5th and 6th generation migrants? Probably, but it’s complicated and the numbers are likely few. To explain what might be happening, we have to consider the extent to which there are continuously breeding populations in the South and the impact of the midsummer migrants. There appear to be habitat islands associated with major cities where monarchs survive in low numbers through the summer. It’s conceivable that some of these lineages produce 5th and 6th generation migrants. However, the biggest number of migrants originating from the South in September and October are probably progeny of midsummer migrants that were third generation butterflies. If this is indeed the case, then most of the monarchs originating from the South are fourth generation rather than 5th generation monarchs.

The above description applies to the eastern monarch population. It’s possible, maybe even probable, that what I’ve characterized here for eastern monarchs also applies to the western monarch population. There are many seasonal parallels but there are too many unknowns about western monarchs to know if the annual cycle differs significantly from that of their eastern counterpart.


  • Four migrations annually – two northward and two southward.
  • Most butterflies in the fall migration represent 3rd and 4th generations.
  • Three migrations involve butterflies that are reproductive. Butterflies in the fall migration are non-reproductive.
  • Monarchs DO NOT reproduce at overwintering sites in Mexico.
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Monarch Population Status

1 May 2020 | Author: Chip Taylor

As of yesterday (30 April), the numbers are only 4 and 16 and that’s the way I like ’em. The 4 is the number of sightings of monarchs North of 40°N on the Journey North website. Four is enough, I don’t want to see more than that north of 40°N at this time of year. And the 16, that’s the number of monarchs sighted in Kansas so far this season—and more than half of those were reported in the last 10 days.

What does that mean and why am I happy about those numbers? It means that most of the returning monarchs that produce offspring that colonize the Midwest laid most of their eggs in Texas and Oklahoma, where it is warmer—conditions that allow them to develop faster than they would further north. Further, these numbers tell me there is a possibility that a large cohort of first-generation monarchs will move north of 40°N into the summer breeding grounds in May and early June. That should go well if the long-range forecasts are accurate, especially in the second half of May. The first half of June is forecast to be a bit cooler than normal, and if that comes true, recolonization of the northernmost latitudes could be reduced. All in all, this return recolonization appears to be normal and that’s encouraging.

As many of you may know, the West Coast monarch population has a steep climb to recover from the all-time low overwintering counts of the last two seasons (each less than 30,000). Getting back to the roughly 200,000 overwintering numbers that characterized most of the years prior to 2018 will take favorable conditions for several years. While it is impossible to tell how many monarchs survived the winter to reproduce in the last two months, the numbers of sightings in California reported to Journey North is encouraging. Further, the average temperatures and amounts of precipitation for California were in the near-normal range for March and April combined, and that’s a positive, since previous declines have been associated with extreme high temperatures and droughts for those months. Still, we need to keep our fingers crossed that the Western Monarchs will number more than 30,000 this coming winter.

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