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The Vanishing Butterfly Groves of California

By Emma Pelton on 27. January 2020
Emma Pelton

Action is urgently needed to address the challenges facing monarch butterfly overwintering sites.

With the number of western monarchs overwintering in California at less than 1% of historic levels for the second year in a row, it is obvious that monarchs are vanishing from the state. What’s less obvious, but vitally important to understand, is that the forested groves that the western monarchs call home each winter are also disappearing.

The latest research suggests that the damage and loss of overwintering habitat is one of the primary drivers of the decline of western monarchs. Yet the dominant story of monarch conservation in the United States so far has focused on planting milkweed and other nectar plants; reducing pesticides; and, to a lesser extent, acknowledging the roles of climate change and disease.

When overwintering habitat issues are mentioned, it’s nearly always in regards to the eastern monarchs’ overwintering grounds in central Mexico, where illegal logging continues to be a threat to the butterfly and, sometimes even human rights—as evidenced by the recent disturbing deaths of individuals involved with protecting the monarch forests. Here at Xerces, we are keeping their families and their communities in our thoughts.

We of course need to continue to work to meaningfully support overwintering protections in Mexico. It is also time for the U.S. monarch conservation efforts to bring their energy to bear on the problems facing the California overwintering sites, which still have no meaningful protection from damage or destruction.


In this hand-drawn/hand-painted image, a grove of trees is shown, with a cut stump and a dead monarch with tattered wings in the foreground.
One of the main drivers of the western monarch butterfly’s precipitous decline is the damage to, and loss of, overwintering habitat along the California coast. (Illustration: Xerces Society / Jenni Denekas)



A Brief History of Overwintering Sites in California

There is written documentation of monarchs gathering in coastal California in the late fall and winter since at least 1816. However, coastal tribes were aware of the clusters long before the 1800s. Public enthusiasm for overwintering monarchs and tourism to the sites in California is evident in newspaper accounts starting in the late 1800s and the 1914 book The Butterfly Trees by Lucia Shepardson.

Skipping ahead to 1988, the voters of California showed their support for monarchs by passing Proposition 70, which allocated state funds to buy land that hosted monarch overwintering sites. Several sites were purchased in subsequent years with this funding. Thanks in part to this bond measure, the largest single landowner and manager of monarch overwintering sites today is the California Department of Parks and Recreation.

However, California Parks still own only a small fraction of the more than 400 known overwintering sites in the state. There are many other public owners, spanning federal (including the Department of Defense, National Park Service, and U.S. Forest Service), state (e.g., University of California, California Department of Fish and Wildlife), regional (East Bay Regional Parks District, Cambria Community Services District, and others), and local (e.g., the cities of Pacific Grove and Goleta). Many other sites are privately owned—including by individuals, oil and gas companies, religious organizations, retreat centers, golf courses, and conservation nonprofits. A sizable number of overwintering sites lie across property boundaries, with multiple owners and/or unclear ownership. Many of these sites are also subject to easements including by utilities and transportation entities.

For more perspective, check out this interactive map of overwintering sites. We have spatial files available by request; email [email protected]. This data is also shared regularly with the State’s California Natural Diversity Database.


A large group of monarch butterflies clings to a pine branch, with blue sky in the background. The butterflies with closed wings are a dull orange-brown, resembling dead leaves. The butterflies with open wings are bright orange.
The stunning sight of clusters of overwintering monarchs has been celebrated along the California coast for hundreds of years. (Photo: Xerces Society / Candace Fallon)



Overwintering Habitat Damage and Destruction

Prior to 1990, 38 overwintering sites were documented as destroyed. In the 1990s, 11 more were destroyed in Santa Barbara County. Six other sites were destroyed in the 2000s and early 2010s. These losses are summarized in the “State of the Monarch Butterfly Overwintering Sites in California” report.

Since we published that report in 2016, 21 additional sites have been reported to Xerces as experiencing serious damage or even destruction by human hands—including inappropriate tree trimming and/or tree removal. All but one of these sites are actively used by monarchs. In fact, five of these 21 damaged sites are in the list of the Top 50 Priority Sites for California monarchs.

Of the 21 sites, five have been damaged by excess tree trimming by utility companies. Three sites have been damaged due to development. Some sites were damaged due to city, county, state, conservation nonprofit, and/or other public agency actions. And these 21 represent only the most egregious cases. Many additional sites have faced lesser impacts of minor tree trimming, tree removal, path construction, etc. Wildfire, lack of management, drought, and tree pests have rendered many more sites degraded—some even destroyed. And often, it is a combination of factors. For example:

  • The Woolsey wildfire swept through one of the Top 50 Priority Sites, in Leo Carrillo State Park, in November 2018. Biologists documented the damage, but noted that some of the trees had survived. However, soon after, utility crews came in and cut most of the surviving trees. The site is now a shadow of its former self.
  • Ellwood Mesa in the City of Goleta contains multiple overwintering sites, including a number of Top 50 Priority Sites. Local advocates, the city, and biologists have been working haltingly towards a management plan for almost a decade. Due to a lack of proactive management and recent drought, many of the blue gum eucalyptus trees have died. In 2019, Southern California Edison representatives met with these groups and did a site visit to identify a small number of trees for trimming due to utility line safety concerns. However, when the crews came in, hundreds of trees were trimmed.
  • Trees in or near housing developments have been cut on private properties at multiple sites in Santa Cruz and Santa Barbara counties.
  • A large overwintering site in the Central Coast, owned by the state, was damaged in 2017 when the monarch cluster trees were cut down due to concerns that the roots may damage a water line.
  • Another overwintering site in the Central Coast located within a property set aside for wildlife conservation, was recently heavily trimmed.  
  • Two sites in the San Francisco area which are owned by the federal government have been developed in the past three years.

Besides these 21 damaged sites, several more are under threat due to development. For example, Albany Hill, a popular public park and a Top 50 Priority monarch overwintering site in the East, is at risk. Part of the hill, including some of the trees crucial to providing the right conditions for monarchs, are privately owned. A pre-application for building a housing development was recently submitted to the city.

This may all leave you wondering: Are there no laws to prevent this? The short answer is: Not really. There are some protections for some sites, but it is patchy. Even many sites you would assume are protected because they are on public land have been damaged or destroyed, per the examples above.


This photo shows roadside crews removing trees on a slope.
Wildfire; improper, or lack of, management; drought; and tree pests have rendered many overwintering sites degraded—some even destroyed. Pictured here is tree removal at a monarch overwintering site in Ventura County, 2017. (Photo: Laura Drizd / USFWS)



The Legal Protection that No One Knows about or Enforces

The California Coastal Act of 1976 was passed “to protect, maintain, and, where feasible, enhance and restore the overall quality of the coastal zone environment and its natural and artificial resources.” The Coastal Act protects certain natural resource areas as “environmentally sensitive habitat areas” (ESHA) which is defined as “any area in which plant or animal life or their habitats are either rare or especially valuable because of their special nature or role in an ecosystem and which could be easily disturbed or degraded by human activities and developments” (Public Resources Code §30107.5).

The California Coastal Commission, the agency which turns the Coastal Act into action, considers all monarch overwintering sites within the Coastal Zone to be ESHA. The Coastal Zone varies in width inland from the ocean, ranging from several hundred feet in some urbanized areas to up to five miles in some rural areas. Roughly two thirds of monarch overwintering sites are estimated to exist within the Coastal Zone and numerous sites within recent years have been destroyed or made unusable due to development even though they are considered ESHA.

“According to the Act, ESHA shall be protected against any significant disruption of habitat values, and only uses dependent on those resources shall be allowed within those areas. Furthermore, adjacent development shall be sited and designed to prevent impacts that would significantly degrade those areas (Section 30240 of the California Public Resources Code),” per the Western Association of Fish and Wildlife Agencies (WAFWA) “Western Monarch Butterfly Conservation Plan.

However, the Coastal Act is largely enacted and enforced by Local Coastal Programs (LCPs), developed by local governments to guide development in the coastal zone. One key limitation is that most, if not all, jurisdictions respond to violations of the LCP on a complaint basis. Therefore, unless something is reported to that jurisdiction, they cannot issue a violation and require restoration.


A monarch with closed wings clings to the trunk of a tree in this dimly-lit scene.
The California Coastal Commission, the agency which turns the Coastal Act into action, considers all monarch overwintering sites within the Coastal Zone to be “environmentally sensitive habitat areas” (ESHA). However, protection and enforcement is patchwork, primarily overseen by Local Coastal Programs (LCPs), developed by local governments to guide development in the coastal zone. (Photo: Xerces Society / Candace Fallon)


The larger problem we are facing is that many of these LCPs were adopted before the Coastal Commission considered monarch overwintering sites to be ESHA. Without monarch overwintering sites listed as ESHA by their LCPs, many local jurisdictions believe that overwintering sites cannot be protected as ESHA. Depending on how the LCP was written—if the Coastal Act definition of ESHA is written in the LCP—it is possible that overwintering sites do not specifically need to be listed as ESHA. However, each LCP would need to be evaluated separately. In addition, many jurisdictions interpreting the LCP may not realize that the protection of the overwintering sites is allowed, even though they are not specifically listed.

For instance, in 2017 a U.S. Fish and Wildlife Service (USFWS) biologist witnessed city workers trimming and removing trees at Harbor Boulevard in Ventura County, another of the Top 50 Priority Sites. The issue was reported to their County’s LCP code compliance office. They received the response that a violation could not be initiated because monarch overwintering sites were not listed as ESHA in their LCP. Therefore, no action was taken to stop the work. In fact, additional site damage was noted in 2019.

Although Ventura County is currently updating their LCP, and has proposed a variety of specific protections for monarch overwintering sites as ESHA, there is little hope without a statewide effort—either to clarify that overwintering sites are ESHA (whether they are stated or not in LCPs), or to inform the community that they must immediately report any alterations to protected sites.

To read more about the legal status of overwintering sites, refer to The Legal Status of Monarch Butterflies in California (published in 2012), and WAFWA’s “Western Monarch Butterfly Conservation Plan.


Long-Overdue Management Needs

Monarch overwintering sites need more than just protection; they need to be actively managed. This is particularly important as most of these groves are relatively small areas and dominated by non-native blue gum eucalyptus (Eucalyptus globulus) trees. Blue gums in particular need management: Many blue gums at overwintering sites were planted more than a century ago and are nearing the end of their natural lifespan; blue gums are not particularly drought tolerant and many were weakened or killed in recent droughts; and the species is often in the cross-hairs of native plant and wildfire politics. In particular, we have seen a recent uptick in the reports of utilities trimming trees at overwintering sites without consulting land managers.

While monarchs do not need eucalyptus to overwinter—in fact, there are a few all-native-tree overwintering groves!—they are currently the dominant trees in many sites, offer the right microclimate for the butterflies, and are fast-growing. The monarch population is teetering on the verge of collapse and we need all the tools in the toolbox to help the population recover.

Even the second and third most common tree species at overwintering sites—both of which are native—require management. The Monterey pine (Pinus radiata) has suffered severely from disease and many trees have been lost or cut down as a result. Monterey cypress (Cupressus macrocarpa) trees are relatively slow-growing and support monarchs best in mixed-species stands. Suffering from a lack of management for decades, many of the overwintering sites are far from being models of forest health.

Western states have recently—and admirably—been working together to create and work towards a shared vision of western monarch recovery. In the WAFWA 2019-2069 monarch conservation plan, one of the short-term goals is: “By 2029, 50% of all currently known and active monarch overwintering sites will be protected and actively managed for monarchs, including 90% of the most important overwintering sites.” In order to achieve this goal—or better yet, attain protection and management for ALL overwintering sites—we have a lot of work ahead of us.


Monarchs cluster tightly together in a large group on a pine branch on a gloomy, rainy day. Most of the monarchs have their wings closed, showing the dull, orange-brown side that resembles dead leaves. One monarch in the center of this dense cluster has its wings open, seemingly shining against the others, with its bright orange and black coloration.
We need more voices calling for overwintering site protection at the federal, state, and local levels. (Photo: Xerces Society / Carly Voight)



So, What Can We Do?

The beautiful thing about addressing overwintering site protection is that it’s tangible and could happen quickly—if we are lucky. Unlike some of the broader problems facing western monarchs—like the loss of breeding habitat and the impacts of climate change and pesticides—addressing California overwintering site protection is something we can achieve in the near future.

Solutions for meaningful protection could include changes to LCPs, special state or federal legislation, action by the governor of California, and monarchs and their habitats could be listed under California’s Endangered Species Act (CESA). It is important to note that, although the monarch is being considered for listing under the federal Endangered Species Act (ESA), meaningful protection for its overwintering habitat may not be automatic if it is listed—due to weakening of the Act by the current administration.

We need more voices calling for overwintering site protection at the federal, state, and local levels. Show up to your local city council meeting when proposed development is going to destroy overwintering habitat. Find out who owns and manages properties with overwintering habitat in your area. Let them know about the important animals they are sheltering and urge them not to cut the trees. Write your assembly person and state senator. Write your utility. Write your senator. Write your representative. You can find a list of your representatives and their contact information here.

Together, we can make overwintering site protection and management a reality.



On March 2, 2020, city council member Rochelle Nason reported to Friends of Albany Hill that the developer (Trumark Homes) has withdrawn its plans for a housing development on Albany Hill. This update was added to the blog on March 3, 2020.

An earlier version of this blog cited the disappearance of environmental activist Homero Gómez González. Since then, he and Raúl Hernández Romero, a tour guide in El Rosario monarch sanctuary in Michoacán, have both been found dead. We updated this blog on February 7, 2020.


Further Reading

To learn more about how to help western monarchs, check out the Western Monarch Call to Action and This Is How You Can Help.

See to learn more about California overwintering sites and the Western Monarch Thanksgiving count.

Learn more about overwintering site management with the Xerces publication Protecting California’s Butterfly Groves: Management Guidelines for Monarch Butterfly Overwintering Habitat.



As the Xerces Society's western monarch lead, Emma works on the western population of monarch butterflies, including adaptive management of overwintering habitat in California and breeding habitat throughout the western U.S. Emma completed a master's degree in agroecology and entomology at the University of Wisconsin–Madison where her research focused on landscape ecology and an invasive fly that affects fruit crops.

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