- Author: Kathy Keatley Garvey
Where do Western monarchs go after leaving their overwintering sites along coastal California in February?
An observation: They didn't stop in the spring or summer to deposit eggs on any of our four species of milkweed in our Vacaville pollinator garden.
Spring? Zero. Zilch. Nada.
Summer? Zero. Zilch. Nada.
Fall? Yes.
Why not spring and summer? Did the monarchs passing through Vacaville opt for "a better habitat" in the cooler Pacific Northwest and beyond (British Columbia)?
"I wish I knew," commented UC Davis distinguished professor emeritus Art Shapiro, who has monitored the butterfly populations of Central California since 1972 and maintains a research website, Art's Butterfly World.
Beginning in September, as many five monarchs a day began fluttering into our garden. Some laid eggs.
To date, we've spotted some 20 eggs and caterpillars.
"This is generally consistent with the pattern we've seen in previous years," said UC Davis Department of Entomology and Nematology professor Louie Yang, who researches monarchs. "Even in Davis, we've been seeing more caterpillars in the late summer/fall. I think this is probably because some are stopping to lay eggs on the return migration, and the fall population is much larger than the spring migration population. Looking very carefully, we did also see eggs in the spring each year, but very few of them developed into large caterpillars." See the Louie Yang et al, research paper, "Different Factors Limit Early- and Late-Season Windows of Opportunity for Monarch Development," published in July 2022 in the journal, Evolution and Ecology.
The availability of food resources, such as tropical milkweed (Asclepias curassavica) that can overwinter in warmer climates, doesn't deter them from migrating, said UC Davis emeritus professor Hugh Dingle of the Department of Entomology and Nematology. Dingle, an internationally known expert on animal migration who has studied monarchs for more than two decades, said: "Migration and the diapause that accompanies it in the fall are determined by shortening photoperiod and temperature (warm temps can override short days hence the issue with climate change)."
Said UC Davis professor Elizabeth Crone of the Department of Evolution and Ecology: "Monarchs may behave similarly in spring, but the spring population is probably much smaller than the fall one, so they are less likely to happen across your garden. Our estimate is that the population increases 2-3x each generation (so it's about 100-200x larger in Fall than Spring), then resets each year due to mortality during Fall migration and overwintering. There is some research from Sonia Altizer's lab in Georgia showing that monarch butterflies that encounter milkweeds during fall migration will leave reproductive diapause and breed. It is unknown whether these monarchs are effectively lost from the migratory population, or whether they or their offspring (the caterpillars in your yard) will continue on to the overwintering sites."
"The egg-laying females you are seeing now are likely migrants that have eschewed reproductive dormancy for reproduction," says entomologist David James, an associate professor at Washington State University who researches migratory monarchs. "This has probably always happened to some extent but is likely more significant now because of warmer falls."
"The lack of activity in summer in Vacaville was probably a function of most of the population having dispersed further east and north, maybe more than usual? They surely did pass through Vacaville in spring on their way north but clearly didn't stop to use your milkweeds. It does seem that some years they are more prone to frequent stopping/oviposition on their way north and east, yet in others they just keep flying. There's evidence that the latter was the case this year... with as many migrants making it to BC as to Washington... Normally they stop in Washington and only a handful make it to BC."
"The many mysteries of monarchs," James added.
James is the author of a newly published book, The Lives of Butterflies: A Natural History of Our Planet's Butterfly Life (Princeton University) with colleague David Lohman of the City College of New York. The book, released in the UK on Oct. 3, 2023, will be available in the United States starting Jan. 9, 2024.
Irish scientist Éanna Ní Lamhna recently interviewed the WSU entomologist in a podcast on RTÉ, or Raidió Teilifís Éireann. The book, she said, "showcases extraordinary diversity of world's butterflies, while exploring their life histories, behavior, conservation and other aspects of these most fascinating and beguiling insects." (See Bug Squad blog)
Listen to the butterfly podcast here: https://www.rte.ie/radio/radio1/clips/22294525/
Meanwhile, are you seeing fall breeding and egg-laying in your garden? We have for more than a decade, with some monarchs eclosing in November and December.
- Author: Kathy Keatley Garvey
He points out that he is a Lepidopterist but "not a monarch specialist."
Shapiro's 10 monitoring sites stretch from the Sacramento River Delta through the Sacramento Valley and Sierra Nevada mountains to the high desert of the Western Great Basin. The largest and oldest database in North America, it was recently cited by British conservation biologist Chris Thomas in a worldwide study of insect biomass.
Shapiro records his research on his website at http://butterfly.ucdavis.edu/.
At the Bohart Museum open house, his topics included the research that he co-authored, "Understanding a Migratory Species in a Changing World: Climatic Effects and Demographic Declines in the Western Monarch Revealed by Four Decades of Intensive Monitoring" (Anne Espeset et al), published in Oecologica in 2017. Professor Matthew Forister of the University of Nevada, one of his former graduate students, is among the co-authors.
The abstract: "Migratory animals pose unique challenges for conservation biologists, and we have much to learn about how migratory species respond to drivers of global change. Research has cast doubt on the stability of the eastern monarch butterfly (Danaus plexippus) population in North America, but the western monarchs have not been as intensively examined. Using a Bayesian hierarchical model, sightings of western monarchs over approximately 40 years were investigated using summer flight records from ten sites along an elevational transect in Northern California. Multiple weather variables were examined, including local and regional temperature and precipitation. Population trends from the ten focal sites and a subset of western overwintering sites were compared to summer and overwintering data from the eastern migration. Records showed western overwintering grounds and western breeding grounds had negative trends over time, with declines concentrated early in the breeding season, which were potentially more severe than in the eastern population. Temporal variation in the western monarch also appears to be largely independent of (uncorrelated with) the dynamics in the east. For our focal sites, warmer temperatures had positive effects during winter and spring, and precipitation had a positive effect during spring. These climatic associations add to our understanding of biotic-abiotic interactions in a migratory butterfly, but shifting climatic conditions do not explain the overall, long-term, negative population trajectory observed in our data."
Handout. "When I was asked to participate in this event, it got me thinking…" Shapiro began in his monarch comments handout.
"My group did an analysis of the Monarch vis-à-vis climate in a 2017 paper (Espeset et al.,, DOI: 10.1007/s00442-01607600-1) None of my group is a Monarch specialist, and that includes me. Since 1999 I have done counts of all butterfly species at 4 Valley sites (Suisun, West Sacramento, North Sacramento and Rancho Cordova) using standard “Pollard walk” methods, slightly modified. As a result we have a quantitative picture of Monarchs in breeding season... Such data are very rare. Population estimates of Monarchs are typically based on the overwintering (non-breeding) aggregations and we know from published material that what breeding-season data exist routinely diverge from the overwintering data. That is, trends in population size as measured by overwinter animals are not routinely reflected in the summer numbers. There can be a variety of explanations for this. To me the most likely is that as a very mobile species, the Monarch may breed in different places in different years, so that a monitoring program like mine, based on a limited number of fixed, Intensively-monitored sites, is unlikely to capture this stochasticity in where Monarchs breed. I am attaching the overwintering estimates from the Xerces Society. Direct quantitative comparisons are inappropriate, but you can judge how well the local trends match them just by eyeball (until we develop a convincing statistical approach to the problem!)
"My assignment for today forced me back to the original data for my Valley sites. The actual data are reproduced on the attached sheets. It is immediately evident that:
- There is very high variability in Monarch numbers among years at all sites, but
- There are short-term trends that may be associated with climatic fluctuations, in particular drought, and
- Among my sites, Suisun has had the highest counts, partly but not entirely reflecting coastward migration from farther inland early in the season, but these high numbers have effectively disappeared—perhaps reflecting a systematic change in migratory trajectories, and
- Rancho Cordova has very consistently had the lowest counts, with little year-to-year variation compared to other sites..
"My interest is now piqued and I am going to go with this. From 1972 to 1998 at all sites, and from 1972 to date at our 5 mountain sites, monitoring was on a presence/absence basis only because there are too many species to Pollard-count simultaneously. But the seasonal distribution of the Monarch is still easily extracted. We know Monarch breeding seasonality has changed over the 50-year time span of this study. We also have devised and published methods to use presence-absence data (“day-positives”) as a crude proxy for population trends. This is perhaps a good moment to revisit the Espeset et al. paper and try to get into the specific components of Monarch trends. Suggestions are welcome!" (amshapiro@ucdavis.edu)
Shapiro, who joined the UC Davis faculty in 1971, continues his research. The author of the book, Field Guide to Butterflies of the San Francisco Bay Area and Sacramento Valley Regions, he has studied more than 160 species of butterflies in his transect.
- Author: Kathy Keatley Garvey
Western monarchs are now settling in their overwintering sites along coastal California, but the iconic butterflies showed up in force at the Bohart Museum of Entomology's recent open house--in the form of specimens, photographs, books, maps and displays.
Some 650 visitors arrived to talk to the scientists, see the displays, and take home native milkweed seed packets, provided by community ecologist Louie Yang, professor of entomology, UC Davis Department of Entomology and Nematology (ENT-NEM). Yang shared seeds of narrow-leafed milkweed, Asclepias fascicularis.
Statistics show that the overwintering population of western monarchs along coastal California has declined by more than 99 percent since the 1980s, according to the Xerces Society for Invertebrate Conservation, but the population has been showing a mini-boom in recent years. Scientists blame habitat destruction, pesticide use, and climate change as the primary causes of the decline.
Scientists participating in the open house were:
- UC Davis distinguished professor emeritus Art Shapiro of the Department of Evolution and Ecology, who has studied butterfly populations in central California since 1972 and maintains a research website, Art's Butterfly World.
- UC Davis emeritus professor Hugh Dingle, a worldwide authority on animal migration, including monarchs. He is the author of Migration: The Biology of Life on the Move (Oxford University Press), a sequel to the first edition published in 1996. (See news story on the ENT-NEM website.)
- UC Davis professor Louie Yang, who does research on monarchs and milkweed and has been featured nationally. (See news story about his work.)
- UC Davis professor Elizabeth Crone of the Department of Evolution and Ecology, formerly of Tufts University, who researches monarchs. (See news story about the declining monarch population on the ENT-NEM website.)
In addition, the Bohart Museum showcased monarch photography by Larry Snyder of Davis and Kathy Keatley Garvey of ENT-NEM.
Yang and Crone were among the 12 nationally invited scientists who delivered presentations during the two-day Monarch Butterfly Summit, held last year at the Capitol in Washington D.C. and organized by Sen. Jeffrey Merkley of Oregon, During that summit, the Department of the Interior announced a $1 million award to the National Fish and Wildlife Foundation's Monarch Butterfly and Pollinators Conservation Fund, and the U.S. Fish and Wildlife Service announced a Pollinator Conservation Center. (See news story)
In another project, Yang organized and led a three-year study of wild monarch butterflies and milkweed in rural Davis. The project, funded by two of Yang's National Science Foundation grants, involved UC Davis, Davis Senior High School and the Center for Land-based Learning, Woodland. The 135-member team included 107 high school students, a K-12 teacher, 18 UC Davis undergraduates, three graduate students and two postgraduate researchers.
"This study collected a high-resolution temporal dataset on milkweed-monarch interactions during the three years prior to the precipitous single-year population decline of western monarchs in 2018,” Yang said. From 2015 through 2017, the team monitored the interactions of monarchs, Danaus plexippus, on narrow-leafed milkweed, A. fascicularis, planted in December 2013 on city-owned property.
“This study has three key findings,” Yang related. “First, we documented early and late seasonal windows of opportunity in the wild, migratory western monarch population. Second, our data suggest that early and late seasonal windows were constrained by different factors. Third, climatic and microclimatic variation had a strong effect on the timing and importance of multiple factors affecting monarch development. Broadly, we hope that this study contributes to a more temporally detailed understanding of the complex factors that contribute to year-to-year variation in monarch breeding success.” (See news story on ENT-NEM website)
In February of 2022, Yang appeared on Science Friday, National Public Radio, in an interview titled "How Long Will California's Butterfly Boom Last?"
Hugh Dingle. Professor Dingle, an internationally known expert on animal migration, has researched animal migration for some 50 years. In the last two decades, he has focused on monarch butterflies. National Geographic featured him in its cover story on “Great Migrations” in November 2010. LiveScience interviewed him for its November 2010 piece on “Why Do Animals Migrate?”
Dingle says:
- "There is not enough tropical milkweed planted to have much influence (see the amount of A. syriaca and A. fascicularis throughout the American West not to mention various other species like A. erosa, cordifolia, californica, etc.) Yes, there are parasites on A. curassavica as there are on ALL milkweeds."
- "There are populations of monarchs that are doing just fine feeding exclusively on A. curassavica (e.g. on many Pacific Islands, such as Guam where I have studied them."
- "Migration and the diapause that accompanies it in the fall are determined by shortening photoperiod and temperature (warm temps can override short days hence the issue with climate change). There is no significant influence of food plant."
Elizabeth Crone. Crone focuses her research on population ecology, "especially of plants and insects, and plant-animal interactions. Specifically, I am interested in how environmental changes translate to changes in population dynamics in animals. I was also one of the first ecologists to use generalized linear mixed models to parameterize stochastic population models." She co-authored "Why Are Monarch Butterflies Declining in the West? Understanding the Importance of Multiple Correlated Drivers," published in 2019 in Ecological Applications, Ecological Society of America.
Art Shapiro. Professor Shapiro shared several handouts, including "Comments on Monarchs." He co-authored research (lead author Anne Espeset and six other colleagues) titled, "Understanding a Migratory Species in a Changing World: Climatic Effects and Demographic Declines in the Western Monarch Revealed by Four Decades of Intensive Monitoring," published in Population Ecology.
"None of my group is a Monarch specialist, and that includes me," Shapiro wrote in the handout. "Since 1999 I have done counts of all butterfly species at 4 Valley sites (Suisun, West Sacramento, North Sacramento and Rancho Cordova) using standard 'Pollard walk' methods, slightly modified. As a result we have a quantitative picture of Monarchs in breeding season over 14 years. Such data are very rare. Population estimates of Monarchs are typically based on the overwintering (non-breeding) aggregations and we know from published material that what breeding-season data exist routinely diverge from the overwintering data. That is, trends in population size as measured by overwinter animals are not routinely reflected in the summer numbers. There can be a variety of explanations for this. To me the most likely is that as a very mobile species, the Monarch may breed in different places in different years, so that a monitoring program like mine, based on a limited number of fixed, Intensively-monitored sites, is unlikely to capture this stochasticity in where Monarchs breed."
Over the last 50 years, "Suisun has had the highest counts (of monarchs), partly but not entirely reflecting coastward migration from farther inland early in the season, but these high numbers have effectively disappeared—perhaps reflecting a systematic change in migratory trajectories."
Also at the open house, entomologist Jeff Smith, who curates the Bohart's Lepidoptera collection, and colleague Greg Kareofelas showed visitors drawers of monarch and other butterfly specimens.
Two origami monarchs, the work of UC Davis alumnus Kevin Murakoshi of Davis and a gift to the Bohart Museum, drew special attention. Murakoshi earlier crafted origami praying mantises, ticks and bed bugs for Bohart Museum open houses.
One of the books displayed at the open house was UC Berkeley professor Noah Whiteman's newly published work, "Most Delicious Poison: The Story of Nature's Toxins--from Spices to Vices" (Little Brown Spark, Oct. 24, 2023) It includes information on the toxicity of milkweed.
The Bohart Museum, directed by UC Davis distinguished professor Lynn Kimsey, is located in Room 1124 of the Academic Surge Building, 455 Crocker Lane, UC Davis campus. It is the home of a global collection of eight million insect specimens. It also houses a live "petting zoo" (including Madagascar hissing cockroaches, stick insects and tarantulas) and a gift shop.
- Author: Kathy Keatley Garvey
We haven't had a cat since our 16-year-old tuxedo, Xena the Warrior Princess crossed the Rainbow Bridge in March of 2016. She sported a butterflylike marking on her left leg.
Monarch butterflies fascinated her. They brought out "the princess" instead of "the warrior" in her.
If you don't have a cat or a feline pollinator partner, plant milkweed and you'll get another kind of 'cat, the larvae of monarch butterflies, Danaus plexippus.
Today we have several 'cats on our tropical milkweed, Asclepias curassavica, in our Vacaville garden. None this year on our narrowleafed milkweed, A. fascicularis; showy milkweed, A. speciosa; or butterfly weed, A. tuberosa.
If you want to learn more about monarchs, their life cycle, milkweed and other related topics, attend the Bohart Museum of Entomology open house on Saturday, Nov. 4 from 1 to 4 p.m. in Room 1124 of the Academic Surge Building, 455 Crocker Lane, UC Davis. The theme is "Monarchs" and scientists will be there to answer your questions.
The event is free and family friendly and a great opportunity to learn more about D. plexippus.
The scientists will include:
- UC Davis distinguished professor emeritus Art Shapiro of the Department of Evolution and Ecology, who has studied butterfly populations in central California since 1972 and maintains a research website, Art's Butterfly World.
- UC Davis emeritus professor Hugh Dingle, a worldwide authority on animal migration, including monarchs. He is the author of Migration: The Biology of Life on the Move (Oxford University Press), a sequel to the first edition published in 1996. See news story on the UC Davis Entomology and Nematology website.
- UC Davis professor Louie Yang, who does research on monarchs. Due to parental duties, he may be able to attend only the last part of the open house. See news story about his work.
- UC Davis professor Elizabeth Crone of the Department of Evolution and Ecology, formerly of Tufts University, who researches monarchs. See news story about the declining monarch population on the UC Davis Entomology and Nematology website.
The Bohart Museum houses a global collection of eight million insect specimens, plus a living insect petting zoo (Madagascar hissing cockroaches and stick insects, among others), and a insect-themed gift shop. UC Davis distinguished professor Lynn Kimsey has directed the Bohart Museum, founded in 1946, since 1990.
- Author: Kathy Keatley Garvey
It's Wednesday afternoon, Nov. 1 and a female monarch butterfly flutters into our Vacaville pollinator garden.
Me: "Welcome Ms. Monarch! Aren't you a little late for the migration?"
Ms. Monarch: "No, I'm just a late bloomer,. so to speak. I'm heading to Santa Cruz to join my buddies for the winter and then we'll return in February. Right now, I need some nectar, a little flight fuel, to make it to Santa Cruz, if you don't mind."
Me: "Help yourself, Ms. Monarch. Right now we have several plants blooming, including Mexican sunflower, tropical milkweed, zinnias, blanketflower, catmint, roses, foxgloves, and evening primrose. One of your sisters passed through here Oct. 21 and she laid eggs on the tropical milkweed, Asclepias curassavica. She ignored the native milkweed, Asclepias fascicularis, and the other natives we planted."
Ms. Monarch: "Thank you for giving us a choice."
Me: "You're welcome. But watch out for the spiders and praying mantises."
Ms. Monarch: "Hope they won't catch me!"
Me: "I'll check to see where they are. No, don't see them, but that doesn't mean they're not there."
Ms. Monarch, sipping nectar on the tropical milkweed: "This is delicious. You don't mind if I stay 'n sip, sip 'n stay, or awhile?"
Me: "We planted it for you and your brothers and sisters. Well, for other insects, too, like honey bees and syrphid flies, but mainly for you. There's talk, you know, about being endangered."
Ms. Monarch: "Will my sister's eggs survive?
Me: "Well, between the spiders, ants, wasps, lady beetles and milkweed bugs, we can't promise. Hey, even monarch caterpillars will eat the eggs. But we do know this: only 5 percent of the eggs make it to adulthood. So, the odds aren't good. Oops, gotta go. 'Bye for now."
Bohart Museum Open House on Saturday, Nov. 4
Want to talk to a scientist about monarch butterflies? Then you'll want to attend the Bohart Museum of Entomology open house on Saturday, Nov. 4 from 1 to 4 p.m. in Room 1124 of the Academic Surge Building, 455 Crocker Lane. Scientists will be there to answer your questions.
The event is free and family friendly and a great opportunity to learn more about Danaus plexippus.
The scientists will include:
- UC Davis distinguished professor emeritus Art Shapiro of the Department of Evolution and Ecology, who has studied butterfly populations in central California since 1972 and maintains a research website, Art's Butterfly World.
- UC Davis emeritus professor Hugh Dingle, a worldwide authority on animal migration, including monarchs. He is the author of Migration: The Biology of Life on the Move (Oxford University Press), a sequel to the first edition published in 1996. See news story on the UC Davis Entomology and Nematology website.
- UC Davis professor Louie Yang, who does research on monarchs. Due to parental duties, he may be able to attend only the last part of the open house. See news story about his work.
- UC Davis professor Elizabeth Crone of the Department of Evolution and Ecology, formerly of Tufts University, who researches monarchs. See news story about the declining monarch population on the UC Davis Entomology and Nematology website.
- UC Davis postdoctoral fellow Aramee Diethelm of the Elizabeth Crone lab. She holds a doctorate from the University of Nevada, Reno. Both her Ph.D. and postdoctoral work are on monarch butterflies.
The Bohart Museum houses a global collection of eight million insect specimens, plus a living insect petting zoo (Madagascar hissing cockroaches and stick insects, among others), and a insect-themed gift shop. UC Davis distinguished professor Lynn Kimsey has directed the Bohart Museum, founded in 1946, since 1990.
