Tag Archives: Asclepias syriaca

NEW STUDY BY MONARCH WATCH CHIP TAYLOR REFUTES “MIGRATION MORTALITY” AS THE MAJOR REASON FOR THE DECLINE OF THE MONARCHS

Female Monarch depositing egg on Common Milkweed (Asclepias syriaca)

Evaluating the Migration Mortality Hypothesis Using Monarch Tagging Data

Frontiers in Ecology and Evolution

August 7, 2020

Authors:

Orley Talor, Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS, United States

John M. Pleastant, Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA, United States

Ralph Grundel, U.S. Geological Survey, Great Lakes Science Center, Chesterton, IN, United States

Samulel D. Pecoraro, U.S. Geological Survey, Great Lakes Science Center, Chesterton, IN, United States

James P. Lovett, Monarch Watch, Kansas Biological Survey, University of Kansas, Lawrence, KS, United States

Ann Ryan, Monarch Watch, Kansas Biological Survey, University of Kansas, Lawrence, KS, United States

The decline in the eastern North American population of the monarch butterfly population since the late 1990s has been attributed to the loss of milkweed during the summer breeding season and the consequent reduction in the size of the summer population that migrates to central Mexico to overwinter (milkweed limitation hypothesis). However, in some studies the size of the summer population was not found to decline and was not correlated with the size of the overwintering population. The authors of these studies concluded that milkweed limitation could not explain the overwintering population decline. They hypothesized that increased mortality during fall migration was responsible (migration mortality hypothesis). We used data from the long-term monarch tagging program, managed by Monarch Watch, to examine three predictions of the migration mortality hypothesis: (1) that the summer population size is not correlated with the overwintering population size, (2) that migration success is the main determinant of overwintering population size, and (3) that migration success has declined over the last two decades. As an index of the summer population size, we used the number of wild-caught migrating individuals tagged in the U.S. Midwest from 1998 to 2015. As an index of migration success we used the recovery rate of Midwest tagged individuals in Mexico. With regard to the three predictions: (1) the number of tagged individuals in the Midwest, explained 74% of the variation in the size of the overwintering population. Other measures of summer population size were also correlated with overwintering population size. Thus, there is no disconnection between late summer and winter population sizes. (2) Migration success was not significantly correlated with overwintering population size, and (3) migration success did not decrease during this period. Migration success was correlated with the level of greenness of the area in the southern U.S. used for nectar by migrating butterflies. Thus, the main determinant of yearly variation in overwintering population size is summer population size with migration success being a minor determinant. Consequently, increasing milkweed habitat, which has the potential of increasing the summer monarch population, is the conservation measure that will have the greatest impact.

Introduction

Since the late 1990s, the monarch butterfly, Danaus plexippus, population has declined significantly based on measurements made at the Mexican overwintering grounds (Brower et al., 2011; Semmens et al., 2016). Identifying the cause or causes of the decline is important in order to focus conservation measures appropriately. Two explanations for the decline in the size of the overwintering population dominate the literature. The first, known as the “milkweed limitation” hypothesis, posits that the decline in the number of milkweed host plants in the major summer breeding area in the Upper Midwest of the U.S. (Figure 1) has led to a reduction in the size of the migratory population (Pleasants et al., 2017). The second, known as the “migration mortality” hypothesis, posits that the resources and conditions during the fall migration have declined resulting in an increase in mortality during the migration and a decline in the overwintering population (Agrawal and Inamine, 2018).

Figure 1. All wild-caught butterflies tagged from north of 40° latitude and east of 100° longitude were included in the study. This area includes the region we are calling the Midwest, encompassing the area from 40 to 50° latitude and 80 to 100° longitude (outlined in red) and the region we are calling the Northeast, encompassing the area from 40 to 50° latitude and 65 to 80° longitude (outlined in blue). What we are calling the Total Area is the Midwest and Northeast combined. The NDVI values (Saunders et al., 2019) come from the region that encompasses the area from 30 to 40° latitude and 90 to 105° longitude (outlined in green). The dark blue square indicates the location of the overwintering colonies. Butterflies were tagged in other sectors besides the Midwest and Northeast but those data are not included in this study.

The milkweed limitation hypothesis is supported by data showing that in the early 2000s the majority of monarch production came from common milkweed, Asclepias syriaca, in corn and soybean fields in the Midwest (Oberhauser et al., 2001) and that the abundance of those milkweeds declined precipitously due to glyphosate herbicide use in those fields (Pleasants and Oberhauser, 2013; Flockhart et al., 2015; Pleasants et al., 2017; Thogmartin et al., 2017a; Saunders et al., 2018). The loss of the milkweeds from corn and soybean fields began in the late 1990s with the adoption of glyphosate-tolerant crops. Milkweeds had been nearly eliminated from these fields by 2006 (Pleasants, 2017). During this period, an estimated 71% of the monarch production potential of milkweeds on the Midwest landscape was eliminated, amounting to 25 million hectares of agricultural habitat that no longer had milkweeds (Pleasants, 2017). The subsequent decrease in the availability of milkweed is thought to have limited the size of the summer breeding population. Support for this hypothesis comes from the pattern of decline in milkweed availability that parallels the decline in the size of the overwintering population (Pleasants et al., 2017). Further support comes from the strong correlation between yearly late summer Midwest monarch egg production and yearly overwintering population size (Pleasants and Oberhauser, 2013; Pleasants et al., 2017).

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WHERE HAVE ALL THE BUTTERFLIES GONE?

In thinking about where have all the butterflies gone, I am reminded of the poignant song written by Pete Seeger “Where Have All the Flowers Gone,” which although a song about the futility of war, sums up much about the environmental impact of habitat loss. Without wildflower habitat, there will be no pollinators of any sort.

Where have all the flowers gone?
Long time passing
Where have all the flowers gone?
Long time ago.

Buckeye and Seaside Goldenrod

Where have all the butterflies gone? Different species of butterfly populations fluctuate from year to year. For example, some years you may see far greater numbers of Buckeyes, the next year not so much. That same year you may hardly see any Tiger Swallowtails but will the following.

That being said, everyone must realize that every year there are fewer butterflies than the year before. Butterflies thrive in meadows, the very same topography that is the easiest to build upon. Every time a new house or shopping mall is built on a meadow, we decrease not just butterfly habitat, but a whole community of wildlife habitat.

In the above photo you can see a Monarch with a Black Swallowtail flying overhead. This stunning patch of wildflowers and nectar plants was sited in Gloucester at a prime spot for Monarchs to rest and refuel after migrating across Massachusetts Bay. The new home owners ripped out most of the wildflowers and planted the site in a more formal style, with non-native perennials and shrubs. At this location, I would often see Monarchs, Tiger Swallowtails, Black Swallowtails, Painted and American Ladies, Sulphurs, and many other species. That is no longer true.

Tiger Swallowtail drinking nectar from Joe Pye-weed at the same wildflower patch, no longer in existence.

Butterfly and bee populations are declining overall, not only because of habitat loss, but because of the unbridled use of herbicides and pesticides in agriculture and home lawn care.

Butterflies are especially sensitive to fluctuations in weather, and also to overall climate change. This year we had a long, cold wet spring. The inclement weather is continuing, too, from a butterflies perspective, because although we are seeing some warmer temperatures the past few days, it has mostly been rainy, foggy, or overcast. Butterflies thrive during long stretches of sunny, hot weather. Their wings don’t work very well in the damp and cold. Because of global climate change, we have seen a seven percent increase in precipitation worldwide.

One of the best years I have ever seen for dozens and dozens of species of butterflies, including Monarchs, in the Northeast, was the summer and fall of 2012. That year, we had a warm winter followed by a warm spring, then a warm, dry summer, and a long, warm Indian summer. It was butterfly bonanza that summer and autumn!

Adding to people’s concern is the fact that last year, there was an abundance of spring rain that in turn created an extraordinary wildflower bloom in Texas, which got all the butterflies off to a good start. In 2019, we were seeing Monarchs as early as early June, which was very unusual for Cape Ann. Folks are comparing this year to that of 2019, however, 2019 was not an average year.

Monarchs are a case unto themselves. Their spring and summer numbers largely depend upon an additional variety of conditions, including how successful was the previous year’s autumn migration, whether or not there were nectar providing wildflowers on their northward and southward  migrations, and wind and weather conditions all along their route, from Canada to Mexico.

Note the bar graph in that the eastern population of the Monarchs plummeted by half, according to this year’s spring count by the World Wildlife Fund Mexico.

Particularly in the northeast, the wind patterns during the Monarchs spring northward migration matter tremendously. My friend Charmaine at Point Pelee, in southern Ontario, which is 49 degrees latitude (we are 43 degrees latitude) has been raising and releasing Monarchs for over a month now, while most of us on Cape Ann have only seen a smattering. The Monarchs moved this year in a straight northward trajectory. If the wind does not blow from west to east during some part of their northward migration, far fewer will end up along the eastern shores.

Monarchs and Seaside Goldenrod

All is not lost. I am 90 percent certain we will soon be seeing some of our migratory and non-migratory local populations, we just need some good weather. They are later than usual, but not gone entirely.

For so many more reasons, I am hopeful for the future of wildlife and their habitats and see such tremendous, positive change. Despite the current administration’ s extremely harmful stance against the environment, many, many individuals and organizations are gaining a deeper appreciation about the importance of habitats and taking positive action. Many have made it their life’s work. These individuals and organizations are creating wildlife sanctuaries and conserving existing habitats. If the Monarch is declared an endangered species, that will surely bring an added awarenesses and increased federal spending for protecting and creating habitats.

How can you help species such as the Monarchs, which in turn will help myriad species of other butterflies and pollinators)? Plant wildflowers! Both Marsh and Common Milkweed for their northward migration, and lots of nectar-rich later summer blooming wildflowers for their southward migration, including New England Aster, Smooth Aster, Purple-stemmed Aster, Seaside Goldenrod, and Canada Goldenrod.

Monarchs and New England Aster

TWELVE NATIVE MILKWEEDS

Did you know that there are over two hundred species of milkweed (Asclepias) found around the world? Seventy different species are native to North America.

Milkweeds, as most know, are the host plant for Monarch Butterflies. A host plant is another way of saying caterpillar food plant. Monarchs deposit eggs on milkweed plants. Some milkweeds are more productive than other species. For the Northeast region, the most productive milkweed is Common Milkweed (Asclepias syriaca). The second most productive is *Marsh Milkweed (Asclepias incarnata). What is meant by productive? When given a choice, the females choose these plants over other species of milkweed and the caterpillars have the greatest success rate. In our own butterfly garden and at at my client’s habitat gardens, I grow both side-by-side. The females flit from one plant to the next, freely depositing eggs on both species.

This fun chart shows some of the most common species of milkweeds found in North American gardens. *Swamp Milkweed is another common name for Marsh Milkweed.

 

KIM SMITH MONARCH BUTTERFLY PROGRAM FOR KIDS AT THE SAWYER FREE LIBRARY

Come join us Wednesday morning from 10am to 11am at the Sawyer Free Library where I will be sharing Monarch fun with young people. We have art activities, as well as eggs, caterpillars, chrysalides, and possibly a butterfly or two emerging on the day of the program. I hope you can join us!

This program is held in conjunction with the Cape Ann Reads exhibit currently on view at the main floor of the Sawyer Free.

2019 has been an amazing year for Monarchs. We got off to a very early and fantastic start, but then with a wave of cool rainy weather the Monarch movement slowed considerably. Despite the slow down, we’ve had at least two subsequent waves come through for a total of three broods this summer. Hopefully this will translate to a great 2019 migration followed by strong numbers at the Monarch butterfly’s winter sanctuaries at Michoacán and the state of Mexico.

The eggs we see now on milkweed plants are the super generation of Monarchs that will travel to Mexico!

The photos show the Monarch caterpillar becoming a chrysalis. When ready to pupate, the caterpillar finds a safe place and spins a silky mat. He inserts his last pair of legs into the silky mat and hangs upside down in a J-shape for about a day. Biological developments that began when the caterpillar first emerged are in high gear now. The caterpillar’s suit, or exoskeleton, splits along the center line of the thorax and shrivels as the developing green chrysalis is revealed. The last photo in the gallery shows the moment when the old skin is tossed off.

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MONARCH EGGS UPDATE

Dear Friends,

There has been more interest than anticipated in Monarch eggs. Thank you to everyone for writing!

At present, Jane has over 100 caterpillars in her kitchen terrariums. These will become butterflies within the month, and each female that emerges will lay between 300 to 700 eggs. I’ve compiled a list of everyone who left a comment. We are thrilled and grateful readers are so interested in helping raise Monarchs this summer. I will contact all as soon as Jane has a new batch of freshly laid Monarch eggs.

In the meantime, I am going to type up some FAQs. I also suggest using a glass rectangular fish tank/terrarium, with a fitted screen top, for rearing the caterpillars. If you don’t have one, they are available at our local pet stores. Also, a package of cheese cloth. Along with a plentiful supply of milkweed, that’s all you will need.

Thank you again and we’ll be in touch. ❤

MONARCH BUTTERFLY EGGS FREE FOR THE TAKING!

A friend with a lovely garden just loaded with milkweed would like help this summer raising Monarchs. She is located in the Annisquam area. Last year Jane had so many eggs and caterpillars, she had a real time of it trying to take care of all. This year promises to be as good as, if not better than, last year.

If you would like Monarch eggs and information on how to take care of the eggs and caterpillars, please comment in the comment section, and we will provide you with Monarch babies!

Raising Monarchs with kids is the best!

 

MONARCH BUTTERFLY FILM UPDATE

A very brief update to let all our Friends know that work is progressing on my documentary Beauty on the Wing: Life Story of the Monarch Butterfly. The new footage from this year’s magnificent migration in Mexico has been added. My amazing team, Eric and Kristen, are plugging in the newly recorded voice over.

For the next several weeks, I’ll be planting my client’s pollinator gardens and getting them underway for the summer. After mid-June, we’ll be back in the editing studio with Eric and Kristen finessing the color correction and audio, with plans for a mid-summer release. Happy Butterfly Days!

Tree-top view – standing at the top of the mountain looking down into the valley below. All the orange bits and flakes in the trees are Monarchs.

In early March, the native wildflower White Snakeroot (Ageratina altissima) was at bloom in Cerro Pelon and the Monarchs couldn’t get enough of it!

So many Monarchs this early in the season portends a possibly great summer for butterflies in our meadows and gardens. It’s the perfect time of year to plant Common Milkweed (Asclepias syriaca) seeds and many of our local nurseries carry Marsh Milkweed  (Asclepias incarnata) plants. These two species are the most productive for Monarch eggs and caterpillars in our region.

Monarchs mating in a patch of Common Milkweed.

Monarch drinking nectar from Common Milkweed florets.

Female depositing egg on Marsh Milkweed foliage.

The milkweed we grow in the north supports spectacular migrations such as the one that took place this past winter of 2018-2019.

AMAZING!!! MONARCH BUTTERFLIES HAVE ALREADY ARRIVED TO CAPE ANN

There are Monarchs on Cape Ann, and they are laying eggs!!! Check your milkweed Friends! This is nearly a month earlier than usual.

Jane Danekis had a female several days ago in her garden on Revere Street and she deposited over 100 eggs on shoots of newly emerging milkweed.

Michele Del Vecchio saw a Monarch at Good Harbor Beach today, too!

Please let us know if you have seen a Monarch recently, and take a snapshot if you can. Thank you 🙂

A Monarch egg is pale golden yellow in color and shaped like a tiny ridged dome. The egg is no larger than a pinhead.

Morgan Faulds Pike spotted a female Monarch nectaring on her lilacs. Photo courtesy Morgan.

Monarch Madness!

Four Monarchs eclosing and nineteen caterpillars becoming chrysalises, all in a day! And we have a new batch of caterpillars, just in time for my program tomorrow morning at the Cape Ann Museum. I hope to see you there!

Many thanks to my friend Jan Crandall for the caterpillars. She has a gorgeous butterfly garden and this morning there were dozens and dozens of caterpillars on her Common Milkweed plants.

Velvet wings drying in the morning sun.

Monarch Conference

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CATERPILLAR CONDO

Caterpillar Condo

Several readers have written to ask how do I manage to have so many Monarch Butterfly caterpillars and chrysalises. The answer is very simple–because we have planted a wonderful little milkweed patch! We grow both Common Milkweed (Asclepias syriaca) and Marsh Milkweed (Asclepias incarnata) side-by-side. Our milkweed patch is planted near our kitchen. When washing the dishes, I can look out the window and watch all the pollinators and fabulous activity that takes place at the milkweed patch.

Several weeks ago, a Mama Monarch arrived and I watched as she gently floated from leaf to leaf, and bud to bud, ovipositing one golden egg at a time. She went back and forth between the Common and Marsh, depositing eggs on both the tender upper foliage as well as the more sturdy lower leaves. I waited for her to leave, but not too long (because the eggs are quickly eaten by spiders) and collected the sprigs with the eggs. I thought I had scooped up about eight eggs and you can imagine our surprise when 19 caterpillars hatched, all within the same day! Female Monarchs like to deposit eggs around the tiny buds of Marsh Milkweed and many of the eggs were hidden within the buds.

Here’s a video of a Mama depositing eggs on our Marsh Milkweed buds. Charlotte was with me that day and we were dancing to the song “There She Goes” as the butterfly was depositing her eggs and it was too perfect not to include in the video.

Our garden is postage stamp size, but I have managed to fill it with a wide variety of songbird, butterfly, bee, and hummingbird attractants. The great majority of plants are North American native wildflowers and shrubs, and we also include a few nectar-rich, non-native, but not invasive flowering plants. Plant, and they will come 🙂

I am super excited to give my children’s program at the Cape Ann Museum on Saturday morning. The program is free and open to the public. I hope to see you there!