Monarch Watch Blog

Gardening for monarchs in the age of COVID-19

19 March 2020 | Author: Chip Taylor

We appear to have entered a new era of uncertain duration, one possibly characterized by waves of reinfection by Covid-19. Yet, we must carry on with monarch conservation – somehow.

We are in new territory. Our lives will change in many ways. Social distancing and quarantines will ground many of us, confining us to our properties yet giving us time to garden for monarchs. By adding milkweeds and nectar plants to our gardens, while waiting for the virus to subside, we can contribute to the health of monarch and pollinator populations. Why not? Gardening gets you out of the house, it’s good therapy, you’ll be in a virus-free environment, the exercise will be good for you and your actions will have a positive impact.

Through our partner nurseries, we have milkweed plugs of many species available for much of the country. For those of you in Texas and Oklahoma, we will be able to ship in April. Why not order a flat today for yourself or your house-bound friends?

Visit our Milkweed Market: monarchwatch.org/MilkweedMarket

For those who already have milkweed, or have no space to plant your own, you can donate to Monarch Watch in support of our Free Milkweeds for Restoration program to help get milkweeds into the ground.

Donate to Monarch Watch: monarchwatch.org/donate/

Chip Taylor
Monarch Watch

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Monarch Population Status

13 March 2020 | 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. Eleven (11) colonies were located this winter season with a total area of 2.83 hectares, a 53.22% decrease from the previous season (6.05 ha):

monarch-population-figure-monarchwatch-2020
Figure 1. Total Area Occupied by Monarch Colonies at Overwintering Sites in Mexico.

WWF release (in spanish): La mariposa Monarca redujo en un 53% su ocupación en los bosques mexicanos de hibernación


Why overwintering numbers were lower this year
Chip Taylor, Monarch Watch Director

In my November 2019 “Monarch Population Status” blog post (Why overwintering monarch numbers will be lower this year) I outlined my reasons for expecting lower monarch numbers.

I finished the article with a summary of bullet points which made sense to me given the data at hand at the time:

Population growth
• Less than optimal egg distribution in March and April
• Later recolonization of the Upper Midwest
• Low monarch production in Iowa and maybe western portions of the upper Midwest
• Lower summer temperatures than in 2018

Migration
• Late migrations are associated with lower numbers reaching Mexico
• Droughts are associated with lower numbers reaching Mexico
• High numbers in the northeast do not translate to high overwintering numbers
• Northeast butterflies take too long to migrate southwest

In the text that follows, I will elaborate on these points.

Conditions were less favorable for population growth in 2019 than in 2018. Although the temperatures in March 2019 were near the long-term average, monarchs still moved too far north too soon with many laying eggs at latitudes with cooler weather. With cooler temperatures, the immatures develop more slowly, and the overall effect is to produce a first-generation cohort with an older average age to first reproduction. Growth rates of populations decrease as age to first reproduction increases. Because most first-generation monarchs migrate north in May and early June, the conditions during that time period are critical. In 2019, those conditions – mostly lower temperatures — delayed the recolonization of the summer breeding area north of 40°N. Delayed arrivals can ripple through the rest of the breeding season, resulting in a late migration.

Reports we receive during the summer alert us to booming populations, but silence from areas that are normally productive can be informative as well. Last August we heard about large numbers of monarchs in several areas of the northeast, especially coastal Maine and parts of Wisconsin and southeast Minnesota, but there was silence from, or reports of low numbers from, the western portion of the Upper Midwest. Summer temperatures can be important with both extreme high or low temperatures leading to population decreases (see Monarchs are an enzyme – Part 1). Populations grow well with summer temperatures close to the long-term mean, and that was the case in 2019. However, they grow even better when temperatures are a couple of degrees above normal as they were in 2018.

While conditions for growth of the population weren’t as favorable in 2019 as they were in 2018, the two biggest factors that appear to account for the lower numbers this winter are the lateness of the migration and the drought in Texas. Both late migrations (Taylor, et al. 2019) and droughts (Saunders, et al. 2019) have been associated with lower overwintering numbers. In the earlier post to the blog, I commented on the extreme lateness of the migration in September which I attributed to long periods of high temperatures north of Kansas that inhibited migratory flight. Although there have been a few late migrations through Kansas, since the late 1980s, the two-week-late passage of monarchs in 2019 was absolutely the latest to date. Although we have no way to be certain, hot dry weather probably takes a toll on the monarchs. Longer migrations in terms of the number of days in flight likely add to this attrition. As the migration moved into Texas, nectar was in short supply due to the drought (Figure 2).

U.S. Drought Monitor, Texas, 2019-10-15
Figure 2. U.S. Drought Monitor, Texas 15 October 2019.

Because Texas and northeast Mexico share weather patterns in addition to a border, it’s likely that monarchs continued to experience drought conditions as they entered northeastern Mexico. If so, the drought could have taken a considerable toll of the monarchs with low lipid reserves. However, how much drought monarchs experienced in Mexico in October isn’t clear. The end of the migration monarchs we sampled here in Lawrence, Kansas were both smaller than average and substantially below average in mass and thus ill-prepared to reach Mexico.

In the earlier text, I predicted that the overwintering number would be 4.7 hectares. Having made that claim I pointed out that:

I will be both right and wrong. I will be right about the size of the overwintering population relative to that of last year (6.05 hectares). The number this year will be lower. That’s been clear since late March and early April. I’ll explain why it will be lower below. The question I’ve been wrestling with is how much lower will the number be this winter. That’s where I’ll be wrong. I’ll never hit that number precisely. There are too many variables.

Given the numbers tallied by the World Wildlife Fund Mexico for the total hectares for 2019–2020 (2.83), where I was right and where I was wrong is clear to all. I’ll keep working at it.

References
Saunders, S. P., Ries, L., Neupane, N., Ramirez, M. I., Garcia-Serrano, E., Rendon-Salinas, E., and Zipkin, E. F. (2019). Multi-scale seasonal factors drive the size of winter monarch colonies. PNAS 116: 8609-8614. doi.org/10.1073/pnas.1805114116

Taylor, O.R., Lovett, J.P, Gibo, D.L., Weiser, E.L., Thogmartin, W.E., Semmens, D.J., Diffendorfer, J.E., Pleasants, J.M., Pecoraro, S.D., and Grundel, R. (2019). Is the timing, pace and success of the monarch migration associated with sun angle? Frontiers Ecology Evolution. published: 10 December 2019 doi.org/10.3389/fevo.2019.00442

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Why monarchs are an enzyme – Part 3

6 March 2020 | Author: Chip Taylor

Why monarchs are an enzyme – Part 1
Why monarchs are an enzyme – Part 2

In Part 2 of this tutorial on monarch demography, I dealt with realized fecundity and age to first reproduction with the promise that the next topic would be reproductive success. Realized fecundity, as you may recall, is the total number of offspring produced relative to the potential reproductive output. For monarchs and most insects, that means the total number of eggs laid per female lifetime. Reproductive success represents the proportion of those offspring (eggs) that hatch and mature to reach the adult stage. Some might argue that reaching the adult stage isn’t the stopping point. Rather, the end point for defining reproductive success should be the number of offspring that survive to reproduce themselves. Indeed, when it comes to monarchs, it is not enough to talk about the number of monarchs produced in the last generation, the end point for success is the number of offspring that survive the migration, the overwintering stage and the return migration to reproduce in the spring in the southern United States. So, while maximizing the number of eggs laid is an important aspect of population growth, we need to consider all the mortality that follows the egg laying process together with the condition of newly emerging adults.

Once returning monarchs reach Texas, we need to consider the conditions for monarch reproduction in the spring in terms of realized fecundity. Those conditions can be favorable or limited. Limited egg production can be sufficient to produce a large cohort of larvae and eventually adults – IF – the fire ant population is low but insufficient when fire ants are abundant. Even when realized egg laying is high, fire ants can limit reproductive success, thus curbing population growth. To understand this dynamic, we need to know what influences the size and number of fire ant colonies. It’s rainfall. Rainfall governs plant growth, the development of insects that feed on the plants and more. In other words, the abundance and diversity of prey allows fire ant colonies to grow and to produce queens that produce more colonies. Droughts, especially long droughts, reduce fire ant numbers, and cool temperatures reduce their foraging rates. Recovery from droughts requires rainfall and warm temperatures.

So, what do you suppose might happen if there was a long drought before monarchs returned to Texas in March with temperatures that were substantially below the long-term mean? My guess is that milkweeds, being perennial and deep-rooted, would emerge while other vegetation would lag with the result that milkweeds would be “apparent” to returning females allowing them to maximize the number of eggs laid. At the same time, due to lower numbers because of the drought, predation and foraging* by fire ants would be reduced, resulting in what ecologists have referred to as “ecological release.” Has this scenario ever happened? Yes, indeed. Those may well have been the conditions in 1996**, the year of the largest overwintering population in the record (18.19 hectares). There had been a lengthy drought that extended into the spring of 1996, and the mean temperatures for March of that year were -3.2°F below average. It’s easy to imagine that these conditions produced a large cohort of first-generation monarchs that moved into the Upper Midwest. That was before the widespread adoption of herbicide-tolerant crops, and milkweeds were still abundant in corn and soybean fields. That year, the fall migration was spectacular, and overwintering monarchs were reported at colony sites that hadn’t been used by monarchs in years. The net increase in the population from 1995–1996 was 5.58 hectares (12.61 to 18.19). That number prompted me to see if there were other increases as large in the record, and there is one.

From 2000 to 2001 the population increased from 2.83 to 9.35 hectares – an amazing 6.52 hectares! Hmm, what were the conditions in the spring of 2001? Get ready. There had been a severe drought in 2000 (Figure 1), which evidently had an impact on the number of monarchs reaching the overwintering sites that fall (a decline from 9.05 to 2.83).


Figure 1. U.S. Drought Monitor, TEXAS 11 October 2000.

The effects of that drought on fire ants probably carried over into the spring of 2001 (Figure 2) due to cooler than average temperatures (-1.2°F, October – February) that limited colony growth and reproduction.


Figure 2. U.S. Drought Monitor, TEXAS 20 March 2001.

Though rainfall had been well above average during that interval (15.37 inches vs 4.95 for 1996) effectively eliminating the drought, the mean March temperatures were -3.0°F below average once again. Since lower than average temperatures tend to limit most egg laying by returning monarchs to Texas, it’s probable that this egg laying also produced a large cohort of first-generation monarchs that moved north in May due to low fire ant numbers. The greater increase in 2001 vs 1996 may have been due to higher mean temperatures in May (+2.4°F vs -2.8°F) and the summer (+1.5°F vs -0.5°F) that more strongly favored population growth than in 1996. Again, in 2001, there was still an abundance of milkweeds in corn and soybean fields in the Upper Midwest. Those are the only two spring drought and low temperature scenarios in the record. This similarity is a discovery. I had never compared these years before. But there is one other drought to consider, that of 2011 (Figures 3 and 4).


Figure 3. U.S. Drought Monitor, TEXAS 18 October 2011.


Figure 4. U.S. Drought Monitor, TEXAS 20 March 2012 .

The dynamics were different in the spring of 2012. Instead of cool temperatures, the mean March temperature was +6.8°F. The vegetation had rebounded somewhat from the drought of the previous season. In 2011 there had been a seven-month drought (rainfall of 4.06 inches from February through August) – a drought of historic proportions that changed the landscape due to the death of hundreds of millions of trees. The drought ended in September and was followed by seven months during which rainfall exceeded the long-term average (20.44 inches). There were several results of this shift from drought conditions to warm and wet that pertain to monarchs and the points made earlier and in Part 2. First, the fire ants, which had declined during the drought had not yet rebounded by March of 2012. Second, the high March temperatures and favorable winds allowed the returning monarchs to expand their distribution rapidly with the result that large numbers of overwintering monarchs were recorded north of 40N in late April and early May (see Journey North first sightings for 2012). They arrived too far north too soon. For monarchs, this meant that reproduction in Texas was minimal in contrast to years with cooler temperatures, and, by distributing eggs further north into areas with cooler temperatures, it meant that age to first reproduction for the entire returning female cohort was much older than normal – a negative for population growth. Mean age to first reproduction was likely one of the factors that accounted for the decline from 2.89 hectares in 2011 to 1.19 hectares in 2012. This outcome, in contrast to that of 1996 and 2001, suggests that cooler March temperatures result in high rates of egg laying in Texas which favors population growth, especially when the fire ant population is low. So, if fire ants were down in the spring of 2012, was there evidence of “ecological release” that spring as well as in 1996 and 2001? The answer is yes.

There was a massive migration northward of other butterfly species that spring. Conditions for the development of butterfly populations were favorable yielding large numbers of dispersing butterflies which I attributed to “ecological release.” Starting with an abundance of red admirals in the first week of April, I recorded the arrival of 16 species of butterflies in eastern Kansas that originated from Texas. The numbers were like nothing I had ever seen. All species were extremely abundant relative to their usual numbers. The red admiral migration was so spectacular that it created headlines as far north as Toronto***. I prepared a slide show and gave talks about the uniqueness of this event which was likely due to low fire ant numbers, as well as those of other predators and parasites. Part of this dynamic is due to the fact that predators and parasites have lower reproductive rates than their prey or hosts.

The point of this discussion is that predation can have a major impact on reproductive success. We can add other predators, parasites (Tachinids) and pathogens (O.e., etc.) to that list, but there are other factors to consider such as density dependence (too many larvae per plant), milkweed condition, latex production that traps first instar larvae and extreme physical conditions that affect survival of immatures and even adults during the migration. Understanding the impact of each of these factors on reproductive success and how they vary regionally and from year to year, along with variation in realized fecundity and age to first reproduction, will help us understand inter-annual variation in monarch numbers.

*Fire ants appear to require surface temperatures of at least 80°F (27°C) to forage.

**Although there is no Drought Monitor map for March of 1996, that drought is well represented in the literature (see references).

***Sample headlines included the following:

“Canada’s butterfly migration is largest on record”
300 million red admiral butterflies estimated from Windsor to New Brunswick
CBC News Posted: May 16, 2012 5:12 AM ET

“Southern Ontario sees ‘irruption’ of red admiral butterflies”
Published on Saturday April 21, 2012

“Red Admiral Butterfly Invasion Update: Some Will Settle In NYC!”
The great butterfly migration: Unnoticed by most, Red Admiral silently invades N.J.
Published: Friday, May 11, 2012, 8:02 AM

“Syracuse hit by swarm of butterflies”
Published: Thursday, May 03, 2012, 9:20 PM

“Red Admiral, ‘Butterfly of Doom,’ population explodes in NY Special”
By Victoria N. Alexander May 5, 2012 in Science
(Abundant the year the Russian Tsar Alexander II was assassinated.)

“The Migration Event Of The Week Wasn’t Birds, It Was Butterflies!”
Salmon Creek Tree Swallow Project, May 5, 2012

References

Allen, C. R.; Epperson, D. M.; and Garmestani, A.S., “Red Imported Fire Ant Impacts on Wildlife: A Decade of Research” (2004). Nebraska Cooperative Fish & Wildlife Research Unit — Staff Publications. Paper 31. digitalcommons.unl.edu/ncfwrustaff/31

Brown, W. O. and R. R. Heim, Jr. Drought in the United States: 1996 Summary and Historical Perspective. 1997. digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1038&context=droughtnetnews

Lu, Y., Wang, L., Zeng, L. and Y. Xu. 2012. The Effects of Temperature on the Foraging Activity of Red Imported Fire Ant Workers (Hymenoptera: Formicidae) in South China. Sociobiology 59(2):573-584.

NOAA. Update on Drought Conditions in the Southern Plains and the Southwest. 1996. www.cpc.ncep.noaa.gov/products/special_summaries/96_3/


Suitable Habitat for Imported Fire Ant Colonization Under Natural Rainfall and Irrigated Conditions. USDA APHIS.

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Monarchs and climate in the West

25 February 2020 | Author: Chip Taylor

Many months ago, I received a request to be a keynote speaker at a Monarch Summit in California. I accepted the invitation with some reluctance realizing that most of the audience wouldn’t be interested in what I had to say about the eastern monarch population. In addition, I knew almost nothing about what was happening in the West. I had purposefully ignored the West for several reasons. First, I had plenty to do trying to manage Monarch Watch and understand what was happening in the East. Second, I was generally ignorant about the dynamics of the Western population, and third, there always seemed to be a lot of conflict in the West that wasn’t exactly inviting. Further, a number of colleagues had begun publishing papers on monarchs and habitats with milkweeds in the West. Nevertheless, no longer being as smart as I was when younger, I decided to determine if I could learn anything new about the Western monarch population by applying what I know about how the eastern monarchs respond to seasonal conditions. My first approach was to examine the inter-annual variation in monarch numbers in the West relative to monthly and seasonal averages in temperature and precipitation. In other words, I wanted to determine if linked seasonal conditions, or weather, explained any of the year to year variation. They do, sort of, but that’s another story that will require more study. What I want to deal with in this piece is how weather led me to climate, and it’s the climate story I want to tell since that story is critical to understanding what is happening to the Western monarch population and what might happen to monarchs in the near future.

Did you know that there is a difference between how the terms weather and climate should be used? Lots of folks don’t – including politicians and some scientists. Weather is defined as the state of the atmosphere at a place and time as regards heat, dryness, sunshine, wind, rain, humidity, barometric pressure and cloudiness. In other words, it’s what is happening now or forecast to occur in the near future. On the other hand, climate represents the long-term average of weather over a period of 30 years or more. Another way to think about the difference is that weather is a snapshot in time while climate represents past events whose trends might inform us of both future weather events and long-term changes.

The transition from thinking about how weather might explain year to year variation in monarch numbers to the potential impact of long-term climatic changes in California produced a number of surprises. Let’s start with the main breeding season. The mean temperatures for the 5-month period from May through September for California are summarized for the last 30 years in Figure 1.


Figure 1. California average temperature May–September. Modified from ncdc.noaa.gov/cag/

The trend line shows temperatures increasing through this 30-year period. Although the long-term trend from 1895 to 2019 shows an increase of 0.2 degrees per decade, the mean for the last 30 years shows an increase of 1.63 degrees or 0.54 degrees per decade. Added to that figure are the 30 year means and rates of increase per decade for AZ, the NW and UMW (Upper Midwest), with the latter showing the lowest rate of change. It’s clear from these data that the West is heating up faster than the Upper Midwest, in fact, faster than the rest of the lower US. That result is sobering, but the real shocker is what has happened along the California coast over the last 20 years (Figure 2).


Figure 2. Average temperature January–February in four counties in California. County locations shown in Figure 4. Modified from ncdc.noaa.gov/cag/

Figure 2 displays both the long-term mean and the mean for the last 20 years for January–February for 4 counties from Marin in the north to San Diego in the south. The differences range from +1.7°F for Marin County to +2.4 degrees (.85–1.2 degrees/decade) for San Diego County. Wow! That’s an incredible rate of increase over such a short period. When I saw those numbers, I asked what might be happening at the overwintering sites. It had been rumored that monarchs were moving progressively northward to overwinter. I looked for references where this interpretation had been published but found nothing. So, I decided to dig into the Thanksgiving Day Count Database maintained by the Xerces Society. The result of my partial analysis is shown in Figure 3.


Figure 3. Changing distribution of overwintering monarchs in California.

Since many new overwintering sites had been added to the Thanksgiving counts after 2011, sites added after 2011 were excluded from my tabulation to avoid biasing the interpretation. As you can see in Figure 3, the number of sites and the number of butterflies in the southernmost counties (San Diego, Orange, and Los Angeles) has declined to almost nothing while the counts in Marin, the most northerly county, indicate that there has been a significant increase in the proportion of the overwintering population in that county from 1998 to that of 2015–2018. Although these results indicate that sites are being lost in southern counties, and that monarchs are progressively moving northward to overwinter, these trends deserve a more in-depth analysis by someone broadly familiar with the monarch overwintering in California.

map of California counties
Figure 4. Map of counties in California. Starred counties referenced in Figure 2.

So, what might be happening in the southern most counties? The temperature data for San Diego County in January and February (Figure 2), and the preceding months*, may signal that it is simply too warm for monarchs to form clusters, or stay in them, resulting in progressive movement northward to cooler locations. If this interpretation is correct, what can we expect in the future if mean January-February temperatures continue to increase at 0.80 degrees, or greater, per decade? We don’t want to go there, do we? We don’t want to think about it, but the reality is that, by the end of the next decade, mean temperatures could be 50.8–51.0°F for all counties along the California coast. Such temperatures could further limit the ability of monarchs to successfully overwinter in traditional sites. Would monarchs move inland to cooler overwintering sites or continue moving northward along the coast in search of the temperatures and cluster sites that favor overwintering? That’s a good question. Folks familiar with coastal and inland conditions in January and February might be able to answer that question. I can’t.

The loss of overwintering sites and lower numbers of monarchs through the winters in the southern California counties raises another question. What about spring recolonization? With fewer overwintering butterflies, recolonization of the southern areas of California and Nevada will be limited further contributing to the decline of monarchs in those areas, a decline that could move northward as it continues to warm along the coast. At the same time, monarchs overwintering further north would be closer to the summer breeding grounds in the Northwest. That might be beneficial since the limited isotope data reported by Yang, et al (2015) suggests that, at present, roughly 50% of the overwintering monarchs originate from that region.

As to why the mean temperatures along the California coast are rising so rapidly, you can blame it on the increase in temperatures in the Pacific, and if you ask why those temperatures are increasing, point your finger at yourself and at the system that has failed to curb the emission of greenhouse gases (CO2, methane, nitrous oxide) that trap heat energy – 90% of which is absorbed by the oceans.

*November–December mean temperatures for San Diego County increased from 53.5°F (the long-term mean) to 55.0°F from 1990–2019 or 0.5°F per decade.

References
Office of Environmental Health Hazard Assessment
https://oehha.ca.gov/epic/impacts-physical-systems/coastal-ocean-temperature
Yang, L.H., Ostrovsky, D., Rogers, M. C., and J.M. Welker. 2015. Intra‐population variation in the natal origins and wing morphology of overwintering western monarch butterflies Danaus plexippus. Ecography 39:998-1007.

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Why monarchs are an enzyme – Part 2

25 February 2020 | Author: Chip Taylor

See Why monarchs are an enzyme – Part 1 posted earlier this month.

What the heck is realized fecundity/fertility and why is it important?

A term I mention from time to time in my talks is realized fecundity. Add to that, I might mention fertility, reproductive success and age to first reproduction. I first encountered these terms when taking an ecology course in graduate school in the late 1960s. There was a unit in the course that dealt with demography – birth and death rates, stable age distributions and factors leading to declines or growth of populations. Among these lessons were a few exercises designed to inform the students of factors that most strongly influenced population growth. The two that stood out were realized fecundity and age to first reproduction. Both are key to understanding population growth in monarchs and inter-annual variations in the sizes of the population at the end of the growing season.

When assessing population growth, the focus is on females. Each monarch female has a potential to produce offspring – a maximum number of eggs that could be laid given the size of the female, the fat body carried over from the larval stage, it’s inherent fitness as defined by its genes, etc. Total lifespan is a factor as well. There are only so many wing beats and degree days per life time. These are all intrinsic factors, that is, properties of each female. Realized fecundity deals with extrinsic factors that have the effect of limiting the number of eggs laid by a female in her lifetime. The list of extrinsic factors is long and involves both physical factors such temperature, precipitation, and wind speed as well as biological factors that include plant quality, nectar availability, number of and fertility of mates, predators, etc. In addition, we need to consider that there may be a cost in terms of eggs not laid due to search time required to find suitable host plants and nectar sources. Search time involves habitat fragmentation which I may get to in other posts.

A basic tenant of population growth is that populations with a short age to first reproduction grow faster than populations in which reproduction is delayed. When talking about monarchs, age to first reproduction can be defined as the interval from when an egg is laid until a female that has developed from that egg lays her first egg. That interval can be as short as 30 days (4 egg, 12 larva, 10 pupa, 4 mating to first egg) and at least as long as 50 days in the spring. This range is due to differences in the temperatures experienced throughout the developmental period. In other words, the temperatures experienced throughout development determine age to first reproduction. As we will see, the distribution of eggs across the latitudes in the spring has a big role in determining age to first reproduction and therefore population growth.

While I used the potential egg laying capacity of individual females to introduce this topic, we need to consider females as a group or cohort to determine the impact of extrinsic factors at the population level. So, what are the conditions that would enable a cohort of females to achieve a high-level egg laying or, conversely to reduce egg laying? I’ve examined the weather conditions during the annual cycle for the eastern monarch population for every year since 1994. That analysis has yielded lists of factors that favor and do not favor monarch population growth (Tables 1 and 2). As you go down the list in each of these figures, you will note that a number of the factors listed, such as winter mortality or survival as monarchs migrate north from the overwintering sites into Texas in March, have to do with losses that ultimately define cohort size. Some unknown portion of that mortality may be due to the condition of the butterflies that arrived at the overwintering sites in the fall. For example, butterflies that experienced drought, either during development as a larva or during the migration itself, are more likely to die during the winter and migration north than butterflies that developed and migrated under more favorable conditions. Further, it is probably the case that the potential reproductive capacity of female cohorts arriving in Texas varies from year to year. It should be noted that both nectar and water availability during both the winter and the spring exit from Mexico play a role in survival during these periods.


Table 1. Optimal conditions for population growth.


Table 2. Negative conditions.

Once the cohort of returning monarchs reaches the milkweed rich areas of Texas (12-15 March), realized fecundity and age to first reproduction becomes important. Conditions favoring egg laying include temperatures that are less than -1.5°F below the long-term average, abundant emerging milkweeds, adequate nectar and water, moderate winds and relatively low precipitation from 15 March to 15 April. The lower than average temperatures extend the life of the females (lower number of degree days) but also have the effect of limiting northward movement. The net effect of lower temperatures is that most eggs are laid in Texas and southern Oklahoma where it is relatively warm allowing the immatures to grow rapidly – thus reaching reproductive age in a minimum number of days. In contrast, with warmer temperatures females continue moving north laying their eggs at latitudes with cooler temperatures. The effect is to produce offspring with longer ages to first reproduction at these latitudes and to increase the average age to first reproduction for all offspring produced by the cohort arriving from Mexico. The importance of where eggs are laid by returning females and age to first reproduction is supported by the observation that in all four years with mean temperatures of less than -1.5°F for March in Texas, the populations grew from one year to the next. However, the populations declined in 9/11 years during which temperatures were greater than 1.9°F above the mean. One of the two years with high mean March temperatures in which the population increased was 2018 (+5.4°F). In other years with similar high temperatures, the returning monarchs moved northward into Oklahoma, Kansas and sometimes Nebraska, but not in 2018. This unusual dynamic was due to a low that settled over north Texas and southern Oklahoma in late March. Temperatures were low enough during this period to keep monarchs confined to central Texas well into April*. Thus, egg laying was largely confined to Texas where warmer than average temperatures accelerated the development of the immatures. The result was a large cohort of first-generation monarchs that migrated northward in May, a cohort with a low and therefore favorable age to first reproduction. This combination of warm conditions favoring rapid development of immatures yet cold that largely restricted egg laying to Texas in March and into early April has only occurred once since 1994. Yet, it was one of the major factors that contributed to the increase in monarch numbers from 2017 (2.48 hectares) to 2018 (6.05 hectares).

Up to this point I’ve just hinted at how realized fecundity can be modified by extrinsic factors. Let’s consider drought, high temperatures and extended periods of rainfall. There are other factors, but these cases will provide examples of how deviations from optimal conditions can influence population growth.

Summer droughts affect monarchs, nectar sources and host plants. Monarchs need water which is usually obtained from nectar or dew during the summer, and both are scarce in droughts. In addition, monarchs need the carbohydrates (and amino acids) found in nectars to fuel flight, egg development and egg laying, etc. Lack of water and nectar can result in fewer eggs laid and even shorten life span for a reproductive cohort. Higher than average temperatures (>+2°F) can have similar effects. Plants develop faster resulting in shorter flowering intervals, often with lower nectar production and more rapid senescence, the latter making the milkweeds less attractive to females for oviposition. Again, adult life span is reduced at higher temperatures. Rainfall, if prolonged over several days, or any weather that restricts flight and egg laying for a number of days, also reduces realized fecundity. There are only so many degree days in the life of an adult monarch (530)**, time is ticking, and, as pointed out in Zalucki and Rochester (2004), there is no recovery from lost opportunities to lay eggs.

If you have been able to follow this tutorial, it should be apparent how deviations from optimal conditions in terms of realized fecundity are the basis for the stage-specific model I’ve mentioned in previous posts to this Blog. But, it’s not the only factor. We need to consider reproductive success as well. Beyond that, we need to discuss how populations recover from a series of negative conditions that have significantly reduced the size of reproductive cohorts.

*Although the optimal temperatures that allow returning monarchs to move northward are not known, it’s clear that advances are limited when temperatures are less than 70°F.

**The estimated number of degree days (530) represents a life span of roughly 3-4 weeks for reproductive monarchs under average summer conditions (Zalucki and Rochester, 2004). Longer life is possible during periods with daytime temperatures in the 60s. Shorter life spans are expected when temperatures exceed 90°F.

Reference
Zalucki, M.P. and W.A. Rochester. 2004. Spatial and temporal population dynamics of monarchs down under: Lessons for North America. In The Monarch Butterfly: Biology and Conservation, eds., Oberhauser, K. S. and M.J. Solensky. pp. 219-228.

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Give to Monarch Watch today via One Day. One KU. fundraising campaign

20 February 2020 | Author: Jim Lovett

Help Monarch Watch continue its mission – our Free Milkweeds for Restoration Projects and Free Milkweeds for Schools and Nonprofits programs need your support.

Your generous support today via the University of Kansas’ One Day. One KU. fundraising campaign will help us restore habitat for monarchs and other native pollinators. Specifically, your donation will be used to:

• administer free milkweed grants to schools and nonprofits

• provide milkweed plants for school gardens created and maintained by grantees

• provide milkweed plants for large-scale restoration projects

Monarch Watch Director Chip Taylor will match all gifts, up to $2,000. Double the impact of your gift today!

Give to Monarch Watch today via One Day. One KU.

Thank you!

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Grasslands, birds, monarchs, pollinators and more

11 February 2020 | Author: Chip Taylor

The world has been changing rapidly, but the changes are such that most of us aren’t aware of what has changed or what is missing.

As an ecologist, I’m alert to change but, like most people, I often miss the indicators. Crows are down. The numbers aren’t what they used to be. Did you notice? I did but well after I should have. Crows and other corvids declined due to their susceptibility to West Nile Virus. I anticipated that the numbers would recover once the virus had run its course. They did, somewhat, but the numbers are not what they were before West Nile, and now they may be declining for other reasons.

What about other birds? Did you catch the headlines in September announcing the results of a study of bird population numbers in the United States over the last 50 years? The numbers have declined by 29% or 2.9 BILLION birds! The biggest losses, a negative 53% (>700 million) occurred, in 31 grassland species. Wow! That’s staggering, and these results give rise to many questions. Why were the losses highest across the vast grasslands that dominate areas east of the Rockies in the United States and Canada to eastern Illinois? What factors contribute to these losses? Probable causes include loss of habitat, fragmentation, neonic insecticides, herbicides and mowing. Of these, there are data on habitat loss due to the intensification of land use in agriculture and the continuous march of development. While it is likely that the other factors contribute significantly to habitat loss and losses of specific species, attaching specific numbers or even assessing which is the most important isn’t possible at this time.

Land use changes have been hard to track often resulting in long lags in reporting. Recently, the urgency of knowing what is happening in real time has resulted in more rapid updating providing us with a better measure of conversion rates each year. The impact of the Renewable Fuel Standard (RFS) on land use was a shocker. The publication of a report entitled “Plowed Under” by Faber et al. in 2012 indicated that nearly 24 million acres, an area nearly the size of Indiana, had been converted from one land use classification to another from 2008 through 2011. Subsequently, Lark et al (2015) showed that 77.7% of that acreage involved the conversion of grassland to cropland. Another report from the Lark team in 2018 indicated that over 10 million acres of grassland had been converted to crops from 2008-2016. The Plowprint Report by the World Wildlife Fund in 2018 indicated that another 1.7 million acres were converted to cropland in 2017. The bottom line is that grasslands are being lost at an average rate of more than a million acres per year.

What is less clear is how much habitat is being lost to development in grasslands. It’s probable that these losses are also in the range of a million acres a year. Further, some losses may not be accounted for. In many areas in the Midwest, growers have reduced the distance from the edge of the field to the edge of the road, leaving only low diversity grass filled margins.

There is no doubt that the grasslands are in decline and we are losing birds, but does it matter? It does. The loss of grasslands signals that we are not only losing birds, but also pollinators, monarch butterflies, small mammals and the raptors and other predators that feed on them. Further, without the pollinators, we will lose both plant and insect diversity further eroding the connections that sustain these ecosystems.

Do we want to live in a world without birds and pollinators? The larger question may be, can we? These ecosystems support us. We are dependent on the richness of these environments. The soil is alive. It’s a matrix that supports a complex web of life, and the organisms within it are often connected intimately with the health and well-being of the plant and animal life above. These connections are destroyed or modified through changes in land use and the addition of chemicals in the form of fertilizers and short and long-lived insecticides and herbicides. It’s fair to ask if, collectively, we know what we are doing. What will be the costs of our quest to extract everything we can from grasslands? Is there another dust bowl in our future?

To counter our destructive tendencies, there is a strong movement to restore habitats both broadly and for specific species. The bird study shows that, in contrast to the general decline, waterfowl numbers have increased over the last 50 years. So have eagles, peregrine falcons and a few other species. These successes are due to habitat restoration and protection. There are also attempts to restore grasslands. The challenge is massive. To keep pace with the annual rate of loss, we need to restore more than a million grassland acres a year. That requires dollars, seeds, locations, boots on the ground and more.

Can we maintain or even increase that rate of restoration? Surely, we can. Will we, is the question. I deal with this issue on a regular basis. Monarch numbers have declined by about 80% over the last two decades, and the crash in the population during the winter of 2013–2014 led to a petition to the Department of the Interior to declare the monarch a threatened species.

At Monarch Watch, we have made it our mission to do what we can to sustain the monarch migration. This mission involves getting people, businesses, states and federal agencies to plant milkweeds, the host plants of monarch caterpillars. The task is immense. A major study indicated that 1.4 BILLION milkweed stems need to be planted, mostly in the Upper Midwest, to restore monarch numbers to a level sufficient to buffer the population in the event of extreme losses due to winter storms and other weather events.

We have made a small dent in this number. To date, over 27,000 Monarch Waystations, generally small gardens or restoration sites containing milkweeds and nectar sources, have been created and registered. In addition, working with nurseries, we have facilitated the production and distribution of a million milkweed plugs (small plants) for restoration projects throughout much of the United States. Monarchs are a gateway species. They have charisma and are known to the public, and the public is strongly interested in monarch conservation. By saving the monarch migration through the restoration of grasslands we will save many other species. It’s our mission, but all can contribute. Plant milkweed!


This article was also published in the recent Winter 2019 Wild Ones Journal (Vol. 32, No. 4, pp 26–28).

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Why monarchs are an enzyme – Part 1

10 February 2020 | Author: Chip Taylor

Monarchs are an enzyme or rather a complex set of enzymes that interact with the physical environment in a deterministic manner. In this article, I’m going to argue that the responses of monarchs to physical conditions are determined by their genetic code which defines metabolic processes that are mediated by enzymes and biocatalysts that respond in predictable ways with the physical environment. Enzymes, as you may recall, are mostly proteins that mediate reactions with substrate molecules yielding products that mediate cellular and metabolic processes that sustain life. These processes are rate-limiting which means they are a product of the quantities of the enzymes, the substrates and temperature (and sometimes pH). Since insects, and most invertebrates, are cold blooded, with few exceptions, it is the ambient temperature that governs these reactions and ultimately the responses of the organisms to the physical conditions.

Specifically, I’m forwarding the view that an understanding of the range of responses by monarchs to a variety of conditions will help us understand and predict the inter-annual variation in monarch numbers. While the following may be obvious to some readers, conversations with colleagues suggest that many do not understand or agree with my interpretations. That said, hear me out and see what you think.

The underlying thesis is that the monarch’s DNA defines a set of limits and optima for each monarch as it interacts with the physical and biological environment. I wasn’t great at biochemistry but was impressed by enzyme kinetics and all the cascading results. Enzymes mediate chemical interactions deterministically, and in simple laboratory systems in which quantities of the interacting components are held constant, it is clear that each reaction is defined by temperature and pH with a lower limit or zero point at which no reaction is catalyzed, a rise in activity as temperatures increase, an optimal temperature for interaction with the substrate and then a decline as temperature increases even further to an upper limit where again reaction with the substrate reaches zero (Fig 1).

enzyme curve
Figure 1. A generalized enzyme activation curve. The degree day model for the development of monarch larvae developed by Zalucki (1982) indicates a developmental zero of 11.5°C (52.7°F) at the lower extreme, an optimal temperature of 29°C (84.2°F) and an upper developmental zero of 33°C (91.4°F).

Living systems are complex with lots of enzymatic interactions having different optima and with lots of complex rate limiting interactions as well but, in my view, within the organism, all these interactions are deterministic as opposed to stochastic or random*. If you are with me so far, the argument is that the DNA driven and limited biological engine represented by the monarch functions at rates determined by temperature, light, sometimes humidity, and more rarely the composition of the surrounding gases. There are biological factors such as host plant quality, predators, pathogens and parasites to consider, and all of these respond to physical factors as well. Overall, the response to physical factors, particularly temperature, by all the biological components of the monarch ecosystem appears to be the driver that broadly determines monarch breeding success during a given year. In effect, they determine realized fecundity, a subject that I’ll deal with in Part 2.

It follows that to fully understand inter-annual variation, and to sort out the effects of biological factors, we need to define the deterministic properties of the monarch system. We can call them physical windows within which the organism functions – as an example, imagine a range of temperatures with death due to freezing at one end and death due to extreme heat at the other. Monarchs function between these limits. There is a lower limit for growth and upper limit for growth. These limiting temperatures are known as developmental zeros. For caterpillars, the low point is 11.5°C (52.7°F) and the high point is 33°C (91.4°F). At either of these extremes, caterpillars stop feeding and the metabolic system slows down. If these temperatures are maintained for long periods, the caterpillars will run out of the enzymes, metabolites and blood sugars necessary to keep the systems going and will die. There is an optimal temperature for growth as well. If we find a fifth instar caterpillar in the wild, we can estimate how long it has been a caterpillar, if we know the temperatures the caterpillar has experienced over the last two weeks or more. The calculation is based on a degree day model which, to me, is effectively an enzyme kinetic model. What I’m arguing is that we extend the degree day model to all of the other physical factors to which monarchs are exposed.

Example windows include an ambient light window, a temperature window (for all flight and for the migration specifically – and they are different), a wind speed and direction window (again with variation depending on reproductive vs migratory status), a thermal window for gliding and soaring, an oviposition window, a mating window, an e-factor window (polarization) and a few more.

Basically, we need to know how monarchs spend their days under a variety of physical conditions – the window (time, temp, light, etc.) for oviposition would be one of my first targets. I want to understand the optimization functions in the system.

Over the last 10 years or so I’ve spent many hours trying to assess the impact of physical factors on the yearly growth of the monarch populations. We focused mostly on temperature and the regressions indicated there were strong associations between temperatures in Texas in March and April and the development of the population each year. However, the regressions only explained about 40% of the year to year variation. Clearly, there was something missing. I eventually realized that mean temperatures, or rainfall, or drought indexes, were only surrogates for what was really happening. After plotting data for yet another regression, I recognized that the outcome represented an optimizing function rather than a linear relationship, and that we needed to understand the system in terms of a series of linked optimizations. Once that became clear, it was evident that, if we knew the optima for a variety of factors and could associate those with monarch specific distributions and reproductive output, we could derive a predictive model to explain monarch numbers both regionally and for most of the eastern monarch population. I have been using a crude optimization model for the last several years to predict the population trends. Some of my predictions based on this approach have been short of my expectations and others have been on the mark. It’s an iterative process of learning from my mistakes and successes.

There are many more aspects to this theme such as how this interpretation relates to behavior of individuals with specific genotypes, realized fecundity, population crashes and perhaps even to the insect apocalypse. I’ll provide additional explanations and examples in Part 2.

Here is a departing observation: in 9/11 years during which the mean temperature for March in Texas was greater than 1.9°F above the long-term average the population declined. However, for each of the 4 years with March mean temperatures <-1.5°F, the population increased. What did enzymes and optimization functions have to do with those outcomes? Plenty, as I will explain in Part 2. [Edit: Why monarchs are an enzyme – Part 2 is now online.]

*Monarch populations are defined by stochastic events to be sure but, I will argue that much of the mortality experienced during many of these events is determined by genetic limitations.

Reference

Zalucki, M.P. (1982), TEMPERATURE AND RATE OF DEVELOPMENT IN DANAUS PLEXIPPUS L. AND D. CHRYSIPPUS L. (LEPIDOPTERA:NYMPHALIDAE). Australian Journal of Entomology, 21: 241-246. doi:10.1111/j.1440-6055.1982.tb01803.x

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Monarch Population Status

17 November 2019 | Author: Chip Taylor

Why overwintering monarch numbers will be lower this year

I’ve had an answer in mind for weeks. It’s been dogging me. The question that’s the basis for this answer has many parts, and not all the parts have come together. It’s as if the answer is disconnected from the question. Some of you will remember Johnny Carson’s skits featuring “Carnac the Magnificent”. In the skit, Ed McMahon hands Carnac a succession of envelopes. Upon receiving each, Carnac holds the envelope to his forehead and announces an answer to the question sealed in the envelope. Carnac then tears open the envelope and reads a silly question that fits an off the wall answer. The absurdity of having an answer before knowing the question was great fun because life seldom works that way. When it comes to monarchs, the questions usually come first. In this case, my answer came first, and the task at hand is to determine if the many part question fits the answer, or not. And so it is with my attempts to predict the size of the overwintering population. It’s a process, part intuition and part data with an emphasis on the later. I’m sparing you the raw data in this account.

As I’ve mentioned in previous posts to this blog, I’m developing a stage-specific model that will allow me to predict the approximate size of the fall migration and the overwintering population. The model has 6 stages: 1) overwintering, 2) the return migration from the colonies to Texas, 3) reproduction by returning monarchs in March and April, 4) the migration north of the first generation in May and early June, 5) the growth of the population during the summer months and 6) the fall migration which I break up into three temporal/latitudinal segments. In addition, I consider regional monarch production, droughts, storms, and other weather events. Having put all of these measures and estimates together, I can tell you two things with certainty – I will be both right and wrong. I will be right about the size of the overwintering population relative to that of last year (6.05 hectares). The number this year will be lower. That’s been clear since late March and early April. I’ll explain why it will be lower below. The question I’ve been wrestling with is how much lower will the number be this winter. That’s where I’ll be wrong. I’ll never hit that number precisely. There are too many variables. The goal is to test the data and the assumptions with an estimate of the total area occupied by overwintering monarchs. The presumption is that, in time, as the model becomes more refined, the predictions will become more accurate. Similar models have been developed to predict salmon and waterfowl numbers.

Pass the envelope, please. Thank you. The answer: 4.7 hectares.

To answer the question “How big will the overwintering population be this winter?” we need answers to many additional questions associated with the different stages and other factors. While not as large as last year, 4.7 is still a good number relative to the recent past. If I’m correct, 4.7 will be the second highest number of hectares since 2008. Although there is a lot of uncertainty in this estimate due to the lack of data on critical measures, it is likely that the area of trees occupied by monarchs will be between 4.3 and 5.3 hectares and will still be the second largest population since 2008. In the following text, I will provide a brief, somewhat sketchy, account of what has happened between the last migration and the one that is just finishing as monarchs continue to arrive at the overwintering sites.

Stages 1 & 2: Overwintering and the migration north from the colonies to Texas
The migration in 2018 was the best since 2006, and the conditions favoring population growth were probably the best since 2001. The weather conditions during the migration were excellent with abundant nectar along the entire migratory route. Texas, which experienced the rainiest September on record, was particularly rich with flowers and therefore nectar when the migration reached those latitudes in October. The last stages of the migration were delayed both in Texas and Mexico due to cold and rainy weather, and the monarchs first appeared at the overwintering sites about a week later than expected based on long-term records. Although the late fall and early winter conditions were said to be a bit warmer than usual, there were no events that appear to have contributed to higher than average winter mortality. In short, the monarchs wintered well. In March, or perhaps the last few days of February, monarchs began moving north toward Texas and the southern U.S. That return also went well with residents of Texas reporting a large number of first sightings to Journey North in March and April. At this point, I’m going to digress into a series of comparisons of the conditions during each stage for both 2018 and 2019 to illustrate why I’m predicting a lower number for the winter population in 2019-2020.

Stage 3: Reproduction by returning migrants in March and April in Texas and the South Region
Although the conditions (temperature and soil moisture) were favorable for population growth during March and April of both years, those for 2018 were better. Due to a dip in the jet stream in late March and early April, most egg laying was confined to Texas in 2018 due to the colder temperatures in North Texas and Oklahoma. Confinement to Texas resulted in a more optimal egg distribution in that it allowed a large proportion of the offspring of returning migrants to mature rapidly due to the warmer than normal March temperatures. I consider this scenario to be more optimal than having eggs distributed further north in March and early April since eggs laid at more northerly latitudes take longer to develop due to cooler temperatures. A basic principle in population biology is that populations with the lowest mean age to first reproduction grow the fastest. Although egg distribution, as inferred from first sightings, was similar in 2019, the temperatures were substantially lower in the critical developmental period resulting in a higher mean age to first reproduction than in 2018. The number of returning monarchs was higher in 2019, and more eggs and larvae may have been produced. However, this advantage could have been offset due to higher levels of fire ant predation since fire ant numbers increase following periods of abundant rainfall.

Stage 4: Migration of first-generation monarchs northward from late April to 10 June
The metric used to represent what happens during this stage is the number of days in May with temperatures above 70°F. Temperatures in this range appear to be associated with flights to the north/northeast and, using this metric, the temperatures in May allowed the population in 2018 to advance into the summer breeding area north of 40°N 7–10 days earlier than in 2019. That said, recolonization in 2019 was quite good with especially high numbers of first sightings reported to Journey North in the north central region (Michigan, Ohio, Ontario). The overall pattern of first sightings for the two years through early June is quite similar. Although the first sightings give us a picture of when monarchs reach each latitude, they don’t tell us the number of monarchs arriving at the northern latitudes. Lack of knowledge of the numbers of first-generation monarchs reaching each latitude or region limits how accurately we can predict growth of the population in June. The determinants of population growth in the northern breeding area are the time of arrival, the numbers arriving and the conditions that allow for an optimal number of hours of oviposition and larval growth. While I can’t compare the numbers arriving in the northern breeding areas in 2018 vs 2019, it does appear that the temperatures during the first two weeks in June in 2018 in the Upper Midwest were more favorable for population growth.

Stage 5: Population growth north of 40 N during June-August
The summer temperatures being 2°F higher than average in 2018 were more favorable for population growth than in 2019. In addition, the growth of the population appeared to be more widespread in 2018. In the Midwest, the highest production seemed to occur from 43–46°N in 2019 with lower than expected production from 40-43°N. From the Midwest, good production extended all the way to Maine including Ontario and parts of Quebec. Monarch numbers appeared to be higher in the Northeast in 2019 than in 2018. Comparing the size of the last generation for these two years has been difficult. While there were numerous reports of “best ever in the last xx years” there were also areas such as Iowa where the population was said to be low. Further, there was total silence about the size of the population from central Minnesota to 100°W in the central Dakotas, normally an area that produced high numbers of monarchs. I followed the number of roosts reported to Journey North almost daily for a clue as to the size of the fall population. The number of roosts were similar, but those of 2019 averaged smaller. Was that meaningful? There are many things that determine roost formation, their size and the probability that they would be observed. After wading through these mixed signals, I finally decided that the last generation and migratory population this fall was lower than in 2018 by perhaps 0.5–0.7 hectares.

Stage 6: The fall migration from early August at 50°N in Canada to 19.5°N in Mexico
The migration typically starts out slowly in the north, often moves a bit more rapidly at mid latitudes and then slows down again as it moves through northeast Mexico to the overwintering sites. It’s usually the case that, as the migration reaches each latitude, there is a wave of monarchs with large numbers the first few days or perhaps a week with monarchs still passing through for the next two to three weeks. I often characterize the migration as a standing wave with a leading crest and a long tail of perhaps 28–30 days as it progresses southward across the latitudes. This year was different. The migration was extremely slow and appeared to be stalled in southern Minnesota and Iowa day after day. We hold our Monarch Watch tagging event at a time that aligns with the peak migration at this latitude year after year. There were virtually no monarchs at the time of our event this year (21 September). They were late and didn’t arrive in our area until the last few days of September—at least two weeks late. And then, what little we saw of the migration blew through the area in a week. If I were to judge the total migration on the basis of what we were aware of passing through Lawrence, I would have to say that this migration was the smallest and weakest I’ve seen since 1992 when we started Monarch Watch. Once the migration moved through our area, it continued to progress south/southwest at a moderate pace with masses evidently moving with a weather front that passed through Oklahoma City on the 5th of October. Again, about 17 days late for that latitude. Monarchs eventually reached Texas without much fanfare about roosts, masses seen, etc. and they seemed to pass through quickly.

In summary, this migration was extremely late. The migratory population also appeared to be compressed with the majority of butterflies moving through each latitude in a matter of days with fewer lagging monarchs than seen in most years. This pattern gives rise to at least two questions: 1) what was the cause of the delay? and 2) what impact will a late migration have on the total number of monarchs reaching the overwintering sites?

The lateness can be accounted for by the higher than average temperatures over a wide area of the Midwest in September and October. Although not precisely determined, we can infer from past migrations that the optimal temperatures for migratory flight range from the mid 60s to mid 70s on days when the winds are favorable. Those conditions were rare from southern Minnesota to southern Oklahoma in September and October. In Kansas and Oklahoma, temperatures for September were the second highest for the 125 years records have been kept. The lateness of this migration is a concern since late migrations are associated with lower numbers of monarchs reaching the overwintering sites.

Another concern is the drought in Texas. Droughts are also associated with lower numbers of monarchs reaching the overwintering sites. A question during this migration is whether monarchs suffered losses given that nectar was scarce in most of Texas south of the Dallas area. Nectar is needed to fuel flight and for monarchs to build up their fat bodies. Although we don’t know whether the population suffered significant losses as it passed through Texas, they appeared to move through the state rapidly. Fortunately, the temperatures in Texas were close to the long-term average over most of the migratory areas. These temperatures allow flight as opposed to high temperatures that tend to slow the migration.

I followed the temperatures and rainfall during most of September and October for northeastern Mexico. The bottom line is that the conditions (flowering, moisture and temperature) appear to be normal for this last leg of the migration.

Ok, let’s get back to the title—”Why overwintering monarch numbers will be lower this year”. Here is a quick summary in bullet points:

Population growth
• Less than optimal egg distribution in March and April
• Later recolonization of the Upper Midwest
• Low monarch production in Iowa and maybe western portions of the upper Midwest
• Lower summer temperatures than in 2018

Migration
• Late migrations are associated with lower numbers reaching Mexico
• Droughts are associated with lower numbers reaching Mexico
• High numbers in the northeast do not translate to high overwintering numbers
• Northeast butterflies are taking too long to migrate southwest

So, there you have it—my rationale for why the population will be lower this winter than in 2018. The number will surely be higher or lower than 4.7 hectares. I hope it’s higher, but I fear it will be lower. For the record, through July, based on an early reading of the data, I predicted a population of about 5 hectares that could trend higher if the summer temperatures were above average. They weren’t.

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Historic Numbers of Monarchs Seek Shelter at Roost Sites in the Lake Erie Region

18 September 2019 | Author: Jim Lovett

Republished with permission of the Southern Lepidopterists Society

Historic Numbers of Monarchs Seek Shelter at Roost Sites in the Lake Erie Region
by Candy Sarikonda

The monarch fallout which occurred during the weekend of September 7-10, 2018 was truly of historic proportion. Thousands of monarchs were reported roosting at numerous sites from Toronto to Chicago, with countless monarchs sheltering from a powerful storm at roost sites in the Lake Erie islands and along Ohio’s Lake Erie shoreline. This once-in-a-lifetime event triggered by remnants of Tropical Storm Gordon sent monarch enthusiasts squealing with delight on social media. The Nor’easter swept through the Lake Erie region during peak fall migration for the monarchs, and sent the monarchs dropping from the sky to seek shelter from the powerful winds and rain that swept through the region.

I raise monarchs from wild eggs I have collected in my northwest Ohio garden. This allows me to be better able to predict the timing and size of the fall migration in my area, based on when my wild-collected monarchs begin to eclose in September. The first week of September 2018 my wild monarchs were eclosing, and I knew peak migration was moving through my area. I carefully watched the weather, and noted the remnants of Tropical Storm Gordon moving through the Lake Erie region. I had also noted reports of large numbers of monarchs being sighted much of the summer and I knew this combination of peak migration, large population size and storm activity had the potential to create large monarch roosts at favored sites in and along Lake Erie. But nothing could have prepared me for just how spectacular this migratory event would be.

I journeyed to South Bass Island in Lake Erie with my mother and children to document the anticipated monarch roosts. We arrived at Catawba Point the afternoon of Friday, September 7th and were stunned to learn that the Nor’easter had already moved in quite fiercely, to the point that the Miller Ferry boat captains were warning passengers that they would likely be cancelling ferry service for Saturday evening and Sunday, due to 10 foot waves on Lake Erie and the storm surge created by the powerful winds. We sought the advice of friends on the island, and decided to still make the journey to South Bass Island, just 3 miles off shore. We had to leave our car on the mainland, and journeyed over to South Bass Island as foot passengers on the ferry.

We arrived on the island and my friend DJ Parker gave us his electric golf cart to use. We headed to our favorite chocolate shop and the downtown area for some lobster bisque. As we ate, I noticed only about a half dozen boats in the harbor, the place seemed empty. VERY unusual for a Friday night, and a bit concerning. I checked the radar, and noted rain was headed our way. So we finished eating and headed back to DJ’s to spend the night


Screenshot of meterorologist Ryan Wichman’s facebook page during storm (Photo by Candy)

My gut instinct told me the monarchs would be at the lighthouse grounds on the southernmost tip of the island. But I did not want to risk my family getting caught in the rain. So my family stayed at DJ’s, and I headed to the lighthouse grounds alone

As I reached the sunflower field next to the lighthouse grounds, I scanned it for monarchs. I saw 4 monarchs still feeding. It was getting a little dark due to sunset and the approaching storm. I knew the monarchs should be roosting, but I did not see any flying toward the usual spot in the trees next to the sunflower field.


CA Regional Weather Server at SFSU 8-IX-2018 satellite image of Gordon

I headed to the adjacent lighthouse grounds, parked, and stood in the driveway watching for monarchs that were flying toward the line of trees. Nothing was happening near the sunflower field. But out of the corner of my eye, through a gap in the trees, I saw 2 monarchs hovering around the other side of the trees (on the lighthouse side). They flitted along the trees, clearly looking for a roosting spot, and I followed them. They flew further down along the trees, I pursued them, and as I rounded the tree line I was greeted with hackberry and maple trees filled with clusters.

I found 1000 monarchs taking refuge at this location on the leeward side of the trees at the South Bass Island lighthouse grounds. This is the largest number I have documented at this site in 5 years, and I have never seen them roost in this particular location on the lighthouse grounds. But it was a perfect location, warm and sheltered from the sustained 20-30 mph NNE winds which were still increasing. I messaged my friend, Darlene Burgess, who does the monarch counts at Point Pelee National Park. She reported 10,000 monarchs were roosting at the tip of Point Pelee. We were excited.

I continued to observe the monarchs before me. The stable flies were biting me like crazy. I could barely stand to take pictures of the roosts.

The things one does to document monarchs.

Determined, I texted Jackie Taylor of the Lake Erie Islands Nature and Wildlife Center, and she joined me at the roosts. Her partner is a ferry boat captain, and she warned me that the ferrymen were now saying they would likely stop ferry service after just a few runs in the morning. I needed to leave the island with my family first thing in the morning, or be forced to stay until Monday.

All night I listened to the winds as my children slept.

We got up early the next morning, ate a quick breakfast, and went with DJ to the lighthouse grounds. As expected, the monarchs were still roosting just after sunrise. A few dozen monarchs would erupt from clusters in bursts to the delight of my family, but then quickly returned to the clusters.

We enjoyed them for a bit, but alas we knew we had to leave. Time was running out to get home safely…


September 8, 2018, South Bass Island monarchs roosting in maple tree (Photo by Candy)


September 7, 2018, South Bass Island, monarchs roosting in maple tree (Photo by Candy)

We arrived home, and I watched the roost reports pour in on Journey North and social media throughout the day on September 8th. DJ Parker texted me to say he had a roost of 100 monarchs for the first time ever, in the trees next to his ice cream shop’s garden near downtown Put-in-Bay on South Bass Island. Another observer on the island reported seeing 100 monarchs in a roost near Park Hotel adjacent to the downtown park. Researchers with Pelee Island Bird Observatory reported on their Facebook page that they were seeing “innumerable monarchs” on Pelee Island’s West Beach beginning 9-9-18, ultimately staying 3 days to ride out the strong winds before leaving their roosts to fly out over Lake Erie. Several observers at Wendy Park, on the Lake Erie shoreline near downtown Cleveland, OH also reported seeing 1000 monarchs roosting in the trees along the leeward side of the main woodlot and other areas of the park, remaining there through September 9th.


September 7, 2018, South Bass Island, monarchs cluster in maple tree (Photo by Candy)


Tagged monarch YUJ012 by Patrick Hogan

September 9th also saw several more reports. Steve Altic on Kelleys Island in Lake Erie reported seeing 200 monarchs at the southernmost tip of the island, roosting in a birch tree about 50 feet from the water’s edge to escape the 25mph winds. A second observer, Bryan Plonski, reported seeing at least 500 monarchs roosting on Kelleys Island from 9-9-18 to 9-10-18, on the west side of trees away from the strong NNE winds. He was delighted, reporting that he had never seen so many butterflies roosting at this site before. The Lake Erie Islands Conservancy reported on Facebook on September 9th, noting monarchs were taking refuge in several island preserves. “Large concentrations of monarchs were found in large trees out of the wind” near Lake Erie on 9-8-18 and 9-9-18, including at Scheeff East Point Preserve and Massie Cliffside Preserve on South Bass Island in Lake Erie and at Middle Bass East Point Preserve on Middle Bass Island in Lake Erie. Video and images of the roosts were posted to their Facebook page on September 9th.


September 10, 2018, Monarchs cluster in dogwood at Ottawa National Wildlife Refuge (Photo by Candy)


September 10, 2018, Monarch cluster in willow at Ottawa National Wildlife Refuge (Photo by Candy)

Reports continued along Ohio’s shoreline. Nothing was more spectacular than the monarch fallout that occurred at Ottawa National Wildlife Refuge in Oak Harbor, Ohio, along the Lake Erie shoreline beginning on 9-8-18.


September 10, 2018, Monarch sips water from its body at Ottawa National Wildlife Refuge (photo by Candy)


Monarchs lined up on the leeward side at Ottawa National Wildlife Refuge (Photo by Jackie Riley)


Roost sizes increased as we neared Lake Erie (Ottawa National Wildlife Refuge) (Photo by Jackie Riley)


Small portion of one of over 70 roosts along a 6 mile trek (Ottawa National Wildlife Refuge) (Photo by Jackie Riley)


Struggling to gain a foothold in the winds (Ottawa National Wildlife Refuge) (Photo by Jackie Riley)


Holding steady on the nearest plant (Ottawa National Wildlife Refuge) (Photo by Jackie Riley)

Refuge staff reported conducting a monarch count from 7-9:30am on 9-9-18, during which they counted 30,000 monarchs roosting in trees along the roads on the park’s Wildlife Drive. Staff reported, “We are experiencing the remnants of Gordon, so we have strong wind pushing off of Lake Erie (16-20mph) creating a Nor’easter. The water levels are pretty high from a combination of rainfall and lake levels over the past 20 hours. Temps are about 60 degrees F with high humidity. The monarchs are roosting on the western side of the trees out of the wind as much as they can be, but they are still bouncing around like crazy. There are pockets of them low in willows and dogwood, but even more towards the tops of cottonwood and maple trees. They were packed in there so tightly that in spots we thought that the leaves had started to change until we had a closer look! There are also monarchs moving over the marshes in the hundreds…Every tree had monarchs on it, from South Estuary Avenue thru North Estuary Avenue and parts of Veler Road and Trumpeter Trail, and a small section of Stange Road. Absolutely incredible.”


Massive roost with many in motion at Ottawa National Wildlife Refuge (Photo by Jackie Riley)

Jackie W. Riley of the Ohio Lepidopterists Society also reported from Ottawa National Wildlife Refuge later that same day (9-9-18). Riley reported viewing monarchs from 2-4:15 pm at the refuge, and at first estimated seeing approximately 2 million monarchs. She later revised her estimate to 200,000 after counting monarchs from over 400 photos she had taken during that 2 hours. Her photos were instrumental in documenting the magnitude of the event. This was truly a remarkable fallout of monarchs, nothing close to this has been seen since 96,000 monarchs were recorded at Point Pelee on September 6, 1993, including two overnight roosts of 7,500 and 3,000 individuals (cited in Wormington, A. 1994. A mass migration of Monarchs at Point Pelee, Ontario. pp. 26-27. In Hanks, A. J. (ed.), Butterflies of Ontario and summaries of Lepidoptera encountered in Ontario in 1993. Toronto Entomologists Association Occasional Publications 27-95.)


Monarchs roosting in Ottawa National Wildlife Refuge (Photo by Douglas Brockway)

Riley reported, “There were many independent roosts, but outstanding were the wooded stretches along the dike roads that held mega roosts with strands of smaller roosts that continued for many yards. Six different dike roads were involved. I was at the refuge the day before (Saturday 9/8/19), and saw NO roosts. However, there were reports of some smaller ones. So, in 24 hours, the roosts went from some, (I think it read a count of 1,000 individuals or more) to the exponential numbers that I saw.”

Riley further stated, “I would guess there were 50 roosts (several dozen). I stopped counting the roosts after the first 12 and figured I was less than one-third the way through the refuge auto-tour. The bulk of the roosts were further north which was the last two-thirds of the tour. Roosts were spread out and thin for the first one-fourth to one-third of the tour…The massive roosts were at one point 100 feet off the lakeshore that had pounding waves and 35mph+ sustained winds. All the monarchs were on the leeward side of the woods that sat between the road and the shoreline. A perfect scenario for them to find shelter immediately coming in off the lake. Weather notes for 9/9/2018: 2 pm-4:15 pm is when I saw them. 63F, 100% sky cover, raining at 4:15pm. Winds over the lake were at least NE 35mph sustained. Winds inside the refuge ranged from NE 10-25 mph depending on location. I believe the overnight temps were in the mid-high 50Fs with rain in the a.m. through 12pm.” Riley noted there were fields of sunflowers and a small amount of goldenrod available for nectaring along the Wildlife Drive.

Notably, Patrick Hogan of Tomahawk Archers and Douglas Brockway of Ottawa National Wildlife Refuge (ONWR) both separately found a tagged monarch at ONWR during the weekend storm. The monarch was tagged with the code YUJ012 and was originally tagged 4 days earlier in Waterford, PA on 9-5-18. This monarch’s likely southwest trajectory along Lake Erie’s southern shoreline, unexpectedly moving west to northwest in the last leg of its flightpath, was likely due to the strong NNE winds moving through the region as Tropical Storm Gordon remnants moved through the area. Doug stated, “I have been coming to ONWR for over 60 years, and never before in my lifetime have I seen this many monarchs.”

By September 10th, the Nor’easter was moving out of the Lake Erie region. The sun emerged and it quickly began to warm up. I had been unable to visit Ottawa National Wildlife Refuge on 9-9-18, but I rushed to the refuge early in the morning on the 10th. It was still rainy and a little cool when I arrived, and the rangers kindly arranged to shuttle visitors out to the monarchs. It continued to warm up as we waited for the shuttle, with light winds around 8-10 mph at times. We left at 10:30am, and air temperatures were 58-62F at that time. Clearly, these temperatures were above flight threshold. As a result, most of the monarchs were gone by the time we reached the roosting sites, with only around 1000 monarchs left, scattered along South Estuary drive. I captured a few dozen photos and it was wonderful enjoying the company of fellow monarch enthusiasts, despite the near constant drizzle. I figured the monarchs would head for fields with large numbers of wildflowers to feed (nectar source). I later found some monarchs in the meadows surrounding the nature center, and a small roost was forming in the line of cottonwood trees across from the barn. But it was clear—the improving weather meant the monarchs would now resume their journey south. Subsequent posts on Journey North and social media indicated the roosts were breaking up throughout the region, and our adventure was over.

The weekend’s historic monarch migratory event was truly a once-in-a-lifetime experience, resulting in cherished memories for years to come. Remarkable. Unforgettable. Historic.


Monarchs roosting in Ottawa National Wildlife Refuge (Photo by Douglas Brockway)


One of the largest roosts observed at the Ottawa National Wildlife Refuge (Photo by Jackie Riley)

Additional photos:
flickr.com/photos/candy__kasey/albums/72157700912789324

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