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Record Low Number of Overwintering Monarch Butterflies in California—They Need Your Help!

By Katie Hietala-Henschell and Emma Pelton on 17. January 2019
Katie Hietala-Henschell and Emma Pelton

We urge you to join us and our colleagues in the western monarch science and conservation community in taking meaningful, swift action to help save western monarchs.

Working at a conservation nonprofit means that we often come across bad news, but the results from this winter’s Western Monarch Thanksgiving Count left us shocked: An all-time record low of 28,429 monarchs at 213 sites.

This number is an 86% drop from the previous count done at Thanksgiving 2017, when 192,668 monarchs were counted at 263 sites (comparing only the sites monitored in both years)—and a dizzying 99.4% decline from the numbers present in the 1980s (Schultz et al. 2017). In short, only one of every 160 monarchs present in the 1980s exists today.


This graphic shows that the western monarch population is 1/160 the size it was in the 1980s.


The Western Monarch Thanksgiving Count began when concerned scientists and citizens started counting overwintering monarchs 22 years ago—worried that monarch numbers were dropping. This long-term community-science effort continues to provide critical information that is used to track the size of the western monarch population. These are the monarchs that overwinter in coastal California, with smaller numbers in Arizona and northern Baja, Mexico (this is a separate migration from monarchs in the eastern US that head to Mexico). Only through the participation of so many dedicated volunteers can we continue to be able to capture the status of the California overwintering population and document this precipitous decline.

This year’s low estimates were foreshadowed by reports of low numbers of the western monarch breeding population observed during the summer in western states and preliminary Thanksgiving count data. The drop between the 2017 and 2018 counts may be attributable to late-season storms and a severe wildfire season in California and elsewhere in the West. And while this year’s numbers are alarming, the real issue is the longer-term decline of the butterfly due to stressors such as habitat loss and degradation (including nonnative plants), pesticides, and climate change. There are also other pressures on the migratory cycle of the monarch that we still have yet to fully study or comprehend.

There are no quick fixes to solve all these large and complex forces, but we can still take actions NOW to help save the western monarch population. Research into monarch losses is active and ongoing, but the depth and abruptness of the recent declines means that we need to act now based on the available evidence. The western monarch population may collapse completely if we wait until all of the answers are fully in focus. Urgent action is crucial because research has suggested that a population as low as the one we have seen this year may result in a partial or total collapse of the western monarch migration.


A graph shows that, although the amount of overwintering sites being monitored has increased in the past eleven years, the amount of monarchs observed during that time has dropped significantly.
Although the amount of overwintering sites being monitored has increased in the past eleven years, the amount of monarchs observed during that time has dropped significantly


In an effort to save the western monarch migratory population, the Xerces Society developed the Western Monarch Call to Action, a set of rapid-response conservation actions that, if applied immediately, can help the western monarch population bounce back from its extremely low 2018–19 overwintering size. We recognize and support longer-term recovery efforts in place for western monarchs such as the WAFWA plan and MJV implementation plan. This call to action, however, identifies steps that can be done in the short-term (the next few weeks or months up to one year), to avoid a total collapse of the western monarch migration and to set the stage for longer-term efforts to have time to start making a difference.

The Xerces Society is taking action for monarchs across the United States, with a special focus on restoring breeding and overwintering habitat for the western population in California. We are pushing for protection for overwintering sites and working with partners to restore overwintering habitat near the coast.

Also, working with farmers, natural area managers, California cities and others, we are planting and restoring habitat across the Central Valley—a key breeding and migration area for monarchs. In the last 18 months, we have restored 20 miles of hedgerows on farms, and in the coming year, we will be adding another 10 miles to further re-connect habitats. These hedgerows provide essential nectar sources, milkweed for breeding, and unsprayed refuge.

Xerces staff are working with the USDA-Natural Resources Conservation Service Plant Materials Centers in California and Idaho to conduct planting trials of milkweed and monarch nectar plants to develop best practices for establishing these plants.

Saving the western monarch migration is not something that we at the Xerces Society can do alone. We must change our landscapes to give monarchs a fighting chance to find nectar, have enough milkweeds for breeding, and complete their annual migration across the western states to return to secure overwintering sites in California next fall. There are steps that can be taken by anyone in any place. We urge you to join us and our colleagues in the western monarch science and conservation community in taking meaningful, swift action to help save western monarchs.


A monarch clings to a tree trunk in this dimly-lit scene.
There is still time to save western monarchs and their magnificent migration, but we need to act—quickly, decisively, and together. (Photo: Xerces Society / Candace Fallon)


Top 5 Actions to Help Save Western Monarchs

The five actions listed below offer our best chance to recover western monarch populations. Here, we only mention the most urgent steps to be taken under each of the five actions, steps that should be taken in the next few weeks. To see what steps need to be taken during the next 12 months and to find information and guidance to help you act, please visit our Save Western Monarchs page.


1. Protect and manage California overwintering sites.

We need to halt the destruction of overwintering habitat. In the next few months, we need to work at local, regional, and state levels to ensure that overwintering sites in California have sufficient legal and enforced protection.


2. Restore breeding and migratory habitat in California.

The primary focus for habitat restoration should be the Coast Range, Sacramento Valley, and the foothills of the Sierra Nevada—areas critical to producing the first generation of monarchs in the spring. If you are in California, plant nectar sources, especially flowers that bloom in the early spring (February–April), and native milkweed, especially species which emerge earliest and are already at the seedling or transplant stage. These actions can be done right now to support monarchs that will be leaving overwintering sites in the coming weeks. Refer to our Milkweed Seed Finder to locate a native milkweed vendor near you.


3. Protect monarchs and their habitat from pesticides.

We need to halt all cosmetic use of pesticides. Seek out non-chemical options to prevent and manage pests in your garden and landscaping. We need to push to suspend the use of neonicotinoids on the commercial production of milkweed plants.


4. Protect, manage, and restore summer breeding and fall migration monarch habitat outside of California.

Monarchs spread out across the western states, seeking breeding areas. For the butterflies to return to their overwintering sites next fall, we need to identify existing monarch habitat and protect it from destruction, and then in the months ahead manage these areas in way that minimizes harm and restore monarch habitat.


5. Answer key research questions about how to best aid western monarch recovery.

The most immediate need is for people in California and Arizona to collect observations of monarchs and milkweeds, especially in the early spring (February–April), the period in which monarchs leave the overwintering sites and year-round breeding sites. In the weeks and months ahead, we also need eyes looking out for monarchs across the rest of the West, in particular, in New Mexico, Colorado, Utah, Wyoming, and Montana. Please contribute this data to the Western Monarch Milkweed Mapper.


How Xerces Can Help You

Saving western monarchs is a big task, and we all need to work together. Xerces is here to help you.


Thank You

Thank you to all the Western Monarch Thanksgiving Count volunteers and regional coordinators whose dedication makes understanding the population’s status possible.


Additional Resources

Learn more on our Save Western Monarchs Page.

Check out our best management practices for western monarchs here.

Learn more about the Xerces Society’s overall monarch conservation program here.

Keep an eye on the #SaveWesternMonarchs campaign on FacebookTwitter, and Instagram for further tips and updates—and spread the word! Download and share the graphics below! Email [email protected] if you require a different format.


This graphic introduces the situation with western monarch declines.


This graphic shows the 1:160 ratio between the current western monarch population and the historic population.


This graphic shows that the current western monarch population is the size of Monterey, whereas the historic population was the size of Los Angeles.



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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