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Population has not rebounded from all-time low. We must take action now to save the western monarch migration.


Expert Contacts

Emma Pelton, Conservation Biologist—Western Monarch Lead, Xerces Society for Invertebrate Conservation

(971) 533-7245 [email protected] 

Sarina Jepsen, Director of Endangered Species and Aquatics Program, Xerces Society for Invertebrate Conservation

(971) 244-3727 [email protected]

PORTLAND, Ore., January 23, 2020—The Xerces Society today announced that the number of monarch butterflies overwintering in California remains at critical levels for the second year. The monarch population during the 2018–19 winter was an all-time low. Unfortunately, this year’s Western Monarch Thanksgiving Count numbers are no better.

The total number of monarchs counted this year was 29,418. Although this is 2,200 more than last year, it comes as a result of greater survey effort, with volunteers visiting more sites. There is no meaningful difference between the western monarch population this year and last.

In addition, in both years the population has been less than 30,000 butterflies, the threshold below which the migration may collapse.

“We are disappointed by the numbers of year’s Western Monarch Thanksgiving count,” said Emma Pelton, the Xerces Society’s Western Monarch Lead. “We had hoped that the western monarch population would have rebounded at least modestly, but unfortunately it has not. The silver lining is that the population didn’t shrink any further. There are still thousands of monarchs overwintering along the coast, so we can take heart that it’s not too late to act.”


Why are there so few monarchs?

For decades, monarchs in the West have been in decline because of loss of habitat, including destruction of their California overwintering sites and loss of both milkweed for caterpillars and flowering resources to fuel migration. They are also impacted by climate change and pesticide use.

Recent research by the Xerces Society working with researchers at Washington State University, Tufts University, University of Nevada at Reno and elsewhere identified two of the best strategies to improve the odds of recovery: protection and restoration of overwintering habitat; and increasing the availability of early emerging native milkweeds, especially in California, where the monarchs to leave the overwintering sites breed. These activities comprise a major focus of the Xerces Society’s current western monarch conservation strategy.


All remaining overwintering sites need protection

Overwintering sites remain largely unprotected in California, legally and in practice. In the past five years, at least 21 overwintering sites—20 of which were actively used by monarchs—have been significantly damaged or destroyed by human actions. This adds to the tally of a further 20 or more sites which have been lost since 1990. Monarchs return to the same sites—even the same trees—each fall. They need intact overwintering habitat, which provides a very specific microclimate and protection from winter storms.

The trees that monarchs use are being removed or extensively trimmed as housing developments are built, by utility companies, and for other reasons, even on public lands and in conservation areas. While extensive investments are being made to restore the monarch’s breeding habitat in California, it is imperative that overwintering sites be protected from further destruction if we hope to recover this butterfly.

“We must protect all remaining overwintering sites in order to save our monarchs,” said Sarina Jepsen, director of the Xerces Society’s Endangered Species and Aquatics Program. “This is an urgent issue that needs to be addressed by federal, as well as state and local government in California.”


Urgent need for early season flowers and milkweed

It is vital that we invest in increasing restoration of early emerging native milkweeds, especially in the coastal hills and the Central Valley of California, areas where the first monarchs that leave the overwintering sites breed. Restoration sites should include early season milkweeds such as woollypod (Asclepias eriocarpa), California (A. californica) and heartleaf milkweed (A. cordifolia) as well as other native flowering plants such as coyotebrush (Baccharis spp.). Farmers, managers of roadsides, natural areas and parks as well as the public can all help with this effort. The Xerces Society is working across California to provide education and technical assistance to help people successfully source and plant these important resources.


We must kick our pesticide habit

Pesticides (both insecticides and herbicides) are implicated in decline of monarch butterflies as well as other butterflies across California and the country. More pesticides are now used globally than at any time in human history. Millions of pounds of pesticides are used in both agriculture and in urban and suburban areas in California. A recent study by the Xerces Society and the University of Nevada at Reno found multiple pesticides in milkweeds from all land use types including farm edges, natural areas and urban and suburban yards. They were even found where there was no known pesticide use. Buying produce that is organic or from farms that limit pesticide use (like Bee Better Certified) and eliminating pesticides for cosmetic uses in landscaping would help monarchs and other pollinators.


Nonnative milkweed threatens monarchs

Though well intentioned, gardeners who plant tropical milkweed may be doing more harm than good. A growing body of research shows that tropical milkweed (Asclepias curassavica) can interrupt monarch migration and spread disease—and the effects will only become worse in a warming climate. Tropical milkweed bought from nurseries also can contain residues of pesticide in amounts that can harm monarchs. Planting native milkweeds, where appropriate, which naturally die back in the fall and planting nectar plants is a much better alternative to help monarchs.


Climate change is changing everything

In recent years, California has suffered catastrophic fires and severe weather precipitated by the climate crisis. Both lowering carbon footprints and adopting nature-based climate solutions such as restoring climate change-ready habitat for pollinators and other wildlife are needed to maintain biodiversity in California. There are climate-smart solutions for all landscape types and it is vital that urban and suburban residents, farmers and natural areas managers all take action.   


We must take action now!

It is time to take action for monarchs. Gardeners can plant climate-smart habitat for pollinators and give up pesticides. Farmers can plant climate-adapted hedgerows and minimize pesticide use. Natural area managers can restore habitat with monarchs in mind. Roadside managers can encourage early season milkweed and flowering resources across California. Local governments can protect overwintering sites and eliminate the use of pesticides. The State of California can pass laws that protect all overwintering sites and encourage monarch conservation. The federal government can list the monarch butterfly under the US Endangered Species Act so we can protect and restore habitat for future generations.

“Without immediate action I fear we will lose these animals from the western landscape,” said Scott Black, executive director of the Xerces Society. “With them, California will also lose out on tourism in places like Pacific Grove and, across the West, we will lose the ability for our children to experience the majesty of the monarch migration.”  




Read more about the Thanksgiving count in a blog by Emma Pelton,

Learn more about helping western monarchs:

Learn more about Xerces’ Western Monarch Thanksgiving Count:

Download the data from 23 years (1997–2019) of western monarch counts at

Contribute sightings of monarchs and milkweeds to the Western Monarch Milkweed Mapper:, or through the special effort to get sightings in California this spring: Western Monarch Mystery Challenge:

Learn more about monarch conservation nationwide:

Xerces is partnering with Ink Dwell studio to educate and inspire people to take action for monarchs. Read more in an article in Wings magazine or at



The Xerces Society is a nonprofit organization that protects the natural world by conserving invertebrates and their habitat. Established in 1971, the Society is a trusted source for science-based information and advice and plays a leading role in promoting the conservation of pollinators and many other invertebrates. We collaborate with people and institutions at all levels and our work to protect bees, butterflies and other pollinators encompasses all landscapes. Our team draws together experts from the fields of habitat restoration, entomology, plant ecology, education, farming and conservation biology with a single passion: Protecting the life that sustains us.

To learn more about our work, please visit or follow us @xercessociety on Twitter, Facebook or Instagram.



[Note: A revision was made at 10:20 a.m. on 1/23/2020. In the sixth paragraph, "University of Washington" was corrected to "Washington State University."]