Launched in 1997, the Xerces Society’s Western Monarch Thanksgiving Count celebrates its 25th year of community science with a surprising and remarkable outcome: 247,237 monarch butterflies observed across western overwintering sites, an over 100-fold increase from last year. However, the population remains more than 95% below its size in the 1980s, when low millions were observed most years.
This year’s total both amazed us with the monarchs’ ability to bounce up from a record low and underscores the importance of ongoing conservation efforts to recover the western monarch butterfly population.
Graph of total abundance estimates with number of sites monitored from 1997-2021 (c. The Xerces Society for Invertebrate Conservation 2022).
Summary 2021 Thanksgiving count findings
Despite the challenges of conducting community science during yet another pandemic year, Thanksgiving Count volunteers surveyed 283 overwintering sites, 30 more sites than last year and an all-time record high in volunteer effort since the inception of the count. The 2021 Thanksgiving Count total of 247,237 illustrates a considerable rebound from 2020’s all-time low of less than 2,000 monarchs, which was preceded by two years of less than 30,000 monarchs. Thanks to our volunteers and program partners, there are now 25 years of Thanksgiving Count data demonstrating that western monarchs have undergone a significant decline estimated at more than 95% since the 1980s.
Bay Area: Where monarchs chose to overwinter this season was geographically skewed a little further south than usual. Typically, the central coast hosts the majority of monarchs, with the San Francisco Bay Area hosting a significant number as well. However, this year it was notable that many sites in the Bay Area had few or no monarchs. Less than 600 butterflies total were counted at overwintering sites stretching from Mendocino in the north all the way down through San Mateo County. Over 100 butterflies were counted at only two sites in the northern range: the San Leandro Golf Course in Alameda County and along Alder Road in Marin County.
Central Coast: More monarchs were found starting in Santa Cruz County with over 1,000 counted at both Natural Bridges State Park and Moran Lake. In Monterey County, the city of Pacific Grove celebrated the return of approximately 14,000 monarchs to their sanctuary, and there were thousands at other sites in Big Sur. San Luis Obispo County had over 90,000 butterflies reported at its overwintering sites, including the California State Parks-managed Pismo Beach Butterfly Sanctuary which had the second highest count at an overwintering site this season at 20,871 butterflies. The county with the most monarchs was Santa Barbara County, with over 95,000 monarchs reported. Santa Barbara County also hosted the largest site this year, a count of just over 25,000 butterflies at a private property.
This season's western monarch butterflies cluster in Pismo State Beach Monarch Butterfly Grove (Photo: Lisa Damerel)
Ventura and Los Angeles Counties: Moving further south, monarchs were found in numbers unseen since the early 2000s. Ventura County contained a total of nearly 19,500 butterflies and had several stand-out sites, including Arundell Barranca with over 7,700 butterflies. Ventura has not seen an excess of 19,000 monarchs since the 2001 Thanksgiving Count, which totaled 28,465 butterflies. In Los Angeles County, volunteers reported over 4,000 butterflies, the highest Thanksgiving Count in that area since 2000. Regional volunteer coordinator for Los Angeles County, Richard Rachman, expressed his excitement after surveying a newly discovered overwintering site in Hermosa Beach, Los Angeles: “I was really excited to see for myself the clusters at Hermosa Beach… because they’re located in the downtown area – very urbanized with only a narrow greenway of trees. Walking up, I was just taken aback at the sheer volume of monarchs, it really says what sustainable urban planning can do to protect biodiversity.”
Southern California and Inland: Overwintering sites in Southern California counties such as San Diego and Orange had smaller numbers, as is typical for this area. One exception was Huntington Central Park’s amphitheater site in Orange County, which surprised Orange County volunteer coordinator Bob Allen and volunteers with 147 monarchs. The Saline Valley Monarch Count reported over 800 butterflies at inland sites in the Saline Valley of Inyo County, California, and the Southwest Monarch Study reported over 100 monarchs overwintering in Arizona.
Thanks to public tips, monarchs were also discovered roosting in five new locations this season: three sites close together in San Luis Obispo County and two sites in Los Angeles County. Counts from these five new sites totaled over 7,000 butterflies. This is a reminder that reports from the public are incredibly valuable. Additionally, with the help of Los Angeles regional volunteer coordinator Richard Rachman and long-time Thanksgiving Count volunteer Eleanor Laney, we are expanding the use of iNaturalist to follow up on monarch observations from the public.
Volunteer monarch counters Stephanie Turcotte, Shannon Conner, and Natalie Johnston compare notes in Pacific Grove Monarch Butterfly Sanctuary in December 2021 (Photo: Candy Sarikonda).
Why did this happen?
There are more questions than answers as to how and why western monarchs bounced back at the rate they did in 2021. It is unlikely that there is a single cause or definitive explanation for such a complex migratory journey and for a single year’s increase. As butterfly researcher and professor Dr. Cheryl Schultz has put it, “butterflies are bouncy.” Although modeling and analysis of this year’s data is currently underway, it may take several more years of Thanksgiving counts to put this year’s “bounce” in context. The migratory western monarch population has undergone a sustained and significant decline and is now bouncing around in uncharted territory. We do not have much experience with migratory monarch populations when they reach this low level.
Some have suggested that wildfires, resident monarchs, and/or an influx of eastern monarchs could be some of the factors responsible for this year’s uptick. However, it’s important to note that these are hypotheses that, as of yet, lack strong evidence to support them. However, there are some exciting studies underway to better understand the genomics of western monarchs and the impact of resident monarchs. You can read more about a few of the ideas being discussed in a blog “The Bounciness of Butterflies” published this fall and written by Xerces and western monarch researchers.
What does it mean?
Balancing the excitement of the present with the context of the past is challenging but necessary when it comes to discussing western monarch population trends. While the 2021 uptick represents a serious “bounce” up, just a few years ago this count would have been considered deeply concerning. Conservation scientists hope to instill cautious optimism as news of the 2021 Thanksgiving Count circulates.
“This year’s total of nearly a quarter-million monarch butterflies in the West, although a step in the right direction, still indicates a severe population decline,” says Isis Howard, Endangered Species Conservation Biologist for the Xerces Society. “Now more than ever, we have an opportunity to double down on our conservation efforts. Harnessing the momentum of this upswing may be our best chance at aiding western monarchs and other at-risk butterflies.”
With the good news of this year’s Thanksgiving Count, it is important to understand that the western monarch butterfly population may continue to fluctuate, even drastically, over the next several years.
Additionally, the decline of the migratory monarchs isn’t just happening in the West. The eastern migratory population has also declined by approximately 70% since monitoring began in the 1990s. World Wildlife Fund-Mexico typically announces the size of the eastern monarch’s overwintering population in Mexico each February.
How you can help
What we do know is that the 2021 Thanksgiving Count is evidence that the western monarch migration is not gone and our collective efforts can make a difference. Here are a few actions you can take to be part of the solution:
- Plant native milkweed species
- Plant a diversity of nectar plants, ideally native to your area.
- Stop using pesticides, or minimize risk associated with pesticide use.
- Contribute to community science projects that track monarchs, such as the Western Monarch Thanksgiving Count and the Western Monarch Milkweed Mapper.
Visit our website to learn more about monarchs and find additional ways to help.
The Xerces Society has been active in monarch and pollinator conservation in California for decades. Xerces' work has contributed to the restoration of monarch overwintering sites, expanding pollinator habitat on farms, and distributing more than 100,000 pollinator plants to California residents through the Xerces habitat kit program.
A single monarch rests on the floor of an overwintering grove (Photo: Karen Sinclair).
Background on the Thanksgiving Count
The Western Monarch Thanksgiving Count is a volunteer-powered community science effort run by the Xerces Society and count co-founder, Mia Monroe, to count overwintering monarchs. It is centered around the Thanksgiving holiday and this season’s count ran from November 13th to December 5th, 2021. The Thanksgiving Count is designed to collect data on the status of the migratory western monarch population each fall using a standard protocol to estimate the number of butterflies clustered at overwintering sites. (A second count period occurs around the New Year’s holiday; the results of that count will be announced in February).
A huge thank you to the more than 100 dedicated volunteers who collected data at overwintering sites. And, thank you to our western monarch conservation funders, who make this work possible: Bureau of Land Management, California Department of Fish and Wildlife, California State Parks Foundation, California Wildlife Conservation Board, Chantecaille, Google.org, Forest Service International Programs, The Marion R. Weber Family Fund, National Fish and Wildlife Foundation, Natural Resources Conservation Service, San Diego Zoo Wildlife Alliance, The Taggart Saxon Schubert Fund, US Fish and Wildlife Service, and Xerces Society members