By Kathy Keatley Garvey, UC Davis

UC Davis community ecologist  Louie Yang, professor of entomology, UC Davis Department of Entomology and Nematology, was one of 12 invited scientists nationwide who delivered a presentation during the two-day Monarch Butterfly Summit, held recently at the Capitol in Washington D.C. and organized by Sen. Jeffrey Merkley of Oregon.

It was a gathering of science experts and policymakers to share science and conservation actions to help the declining western monarch population. The scientists discussed the natural history of the monarch (Danaus plexippus), its population status, habitats and barriers to conservation success.

“It was a great group of folks working hard to connect science and policy to improve monarch conservation,” Yang said. “It was a privilege to part of it.’

During the summit, the Department of the Interior announced a $1 million award to the National Fish and Wildlife Foundation’s (NFWF) Monarch Butterfly and Pollinators Conservation Fund, and the U.S. Fish and Wildlife Service (USFWS) announced a Pollinator Conservation Center.

Last year two bills to support the Monarch Action, Recovery, and Conservation of Habitat (MONARCH) Act and the Monarch and Pollinator Highway Act were proposed; and if passed, these acts would support a variety of initiatives focused on monarch research and conservation.

Sen. Merkley organized the summit in collaboration with the Department of the Interior. Officials attending included Secretary of the Interior Deb Haaland; Sen. Ron Wyden of Oregon; Sen. Alex Padilla of California; Cong. Jimmy Panetta of California; Assistant Secretary for Fish and Wildlife and Parks (USFWS) Shannon Estenoz; and U.S. Fish and Wildlife Service  Director Martha Williams.

In addition to Professor Yang, three other scientists affiliated with UC Davis gave scientific presentations:

  • Professor Matt Forister, the Trevor J. McMinn Endowed Professor in Biology, Foundation Professor, at the University of Nevada, Reno. He holds a doctorate in ecology (2004) from UC Davis where he studied with major professor Art Shapiro, distinguished professor of evolution and ecology
  • Elizabeth Crone, professor and population ecologist at Tufts University and a UC Davis collaborator who recently completed a six-month sabbatical at UC Davis.
  • Sarina Jepsen, director of the Xerces Society’s Endangered Species and Aquatic Program, who holds a master’s degree (2006) in entomology from UC Davis. She studied with major professor Jay Rosenheim, distinguished professor of entomology.

Others giving scientific presentations were Amanda Barth, Western Monarch and Native Pollinator Working GroupWendy Caldwell, executive director, Monarch Joint VentureRyan Drum, wildlife biologist, USFWS; Wayne Thogmartin, quantitative ecologist, U. S. Geological Survey;  Cat Darst, wildlife biologist, USFWS, Cheryl Schultz, professor, Washington State University, Pullman; Sarah Hoyle, pesticide program specialist policy lead, Xerces Society for Invertebrate Conservation; and Francis Villablanca, professor, California Polytechnic State University, San Luis Obispo.

“Senator Merkley has been a champion for conservation since he entered the senate,” blogged Scott Hoffman Black, executive director of the Xerces Society. “Mace Vaughan and I have worked with his staff in the past on improving pollinator provisions in the Farm Bill, and I have had the pleasure of meeting with him several times.  He is also very interested and worried about western monarchs.  Sarina, Jennifer Hopwood Emma Pelton, and I worked with his staff on the Monarch and Pollinator Highway Act (which passed but is awaiting funding) and the Monarch Action, Recovery, and Conservation of Habitat Act of 2021 (or MONARCH Act).  Sarina also met with him at Pismo Beach to see overwintering monarchs during this past year.”

“The Senator convened the Monarch Butterfly Summit to elevate the conservation issues that western monarchs face, and to include policy makers in work sessions to identify solutions,” Black noted. “Working closely with the USFWS and Xerces, Senator Merkley ensured that issues like pesticides, the availability of early emerging native milkweeds in the spring breeding areas, loss and degradation of western monarch overwintering sites, and other important issues would be highlighted throughout the meeting.  Sarina and Sarah did an amazing job representing Xerces – not only in their talks, but in the working groups.”

Black wrote that the event “raised the profile of western monarchs. One participant that came up to me enthusiastically and said, ‘This was incredible.  I have been working on monarchs for decades and never expected to come to a meeting where three U.S. Senators [Merkley, Padilla-CA, Wyden-OR] a congressperson [Panetta-CA] and the Secretary of Interior [Deb Haaland] come to talk about western monarchs!'”

“We hope will lead to additional focus on key priorities for recovering the western monarch population, such as the essential need to protect overwintering sites and invest in their restoration, and the need to scale up the production of early-emerging native milkweeds, such as Asclepias californica, to support the first generation of monarchs in the Priority 1 Restoration Zone and a focus on protecting habitat from insecticides that can harm monarchs.”

In a news release, the U.S. Department of Interior noted: “In the 1980s, more than 4.5 million monarchs overwintered along the California Coast. Currently, the western overwintering population has declined by more than 95 percent. In 2020, western monarch numbers dropped to all-time lows when only 1,900 overwintering monarchs were observed. In 2021, biologists and the public alike were greeted with the news that monarch numbers were heading in the right direction with approximately 250,000 monarchs estimated at overwintering groves along the coast of California.”

“There is no single cause for the extreme multi-decade drop in the western monarch butterflyoverwintering population numbers,” according to the Department of Interior, which aims to play “a central role in how the United States stewards its public lands, increases environmental protections, pursues environmental justice, and honors our nation-to-nation relationship with Tribes.

“Multiple factors have contributed to the long-term decline, including habitat loss and degradation in overwintering groves and breeding areas, pesticides, and the effects of climate change, including drought, increased storm frequency and severity, and temperature extremes,” the news release related. “As with many insects, monarch populations likely fluctuate in response to changes in temperature, precipitation, and other environmental factors. Conservation efforts are focused on an all-hands-on-deck collaborative approach, engaging a broad array of partners to enact large and small-scale conservation efforts for the benefit of monarchs and their habitats. Outcomes from this week’s summit will further contribute to the conservation of this iconic species.”

On July 21, the International Union for Conservation of Nature (IUCN), which works in the field of nature conservation and sustainable use of natural resources, listed the migratory monarch on its Red List of Threatened Species (Endangered). It is not yet listed as endangered by the U.S. Fish and Wildlife Service, but is listed (as of Dec. 15, 2020) as a candidate. (See more on the monarch butterfly on the USFWS website.)

Monarch-Milkweed Interactions.

Professor Yang recently authored newly published research investigating wild monarch-native milkweed interactions in rural Davis over a three-year period that yielded three key findings in the search for what factors constrain monarch development.

“First, we documented early and late seasonal windows of opportunity in the wild, migratory western monarch population,” the UC Davis professor said. “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.”

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. Among them were 107 high school students and a K-12 teacher, 18 UC Davis undergraduate students,  three graduate students and two post-graduate researchers.

“This study collected a high-resolution temporal dataset on milkweed-monarch interactions during the last three years prior to the precipitous single-year population decline of western monarchs in 2018,” Yang said. He organized and led a 135-member team, all co-authors of the paper, “Different Factors Limit Early- and Late-Season Windows of Opportunity for Monarch Development,” published in the journal  Ecology and Evolution. (This document is open access at

Other monarch research from the Yang lab is pending publication.