Western Monarch Conservation Campaign

When monarch butterflies come up in conversation, one usually thinks of the tremendous journey they make between Canada and Mexico east of the Rockies. What people often do not realize is that west of the Continental Divide hundreds of thousands of monarchs also overwinter along the coast of California, traveling from breeding areas as far north as Washington state. Although the western winter roosts are not as large as their Mexican counterparts, these magical places may contain tens of thousands of butterflies. Many of these West Coast sites are open to the public.

In the western United States, monarchs generally migrate no more than a few hundred miles. In the fall, monarchs from an arc of states from Arizona to Washington gather in more than two hundred groves along the California coast, where they cluster for the winter. In the spring, most of these butterflies leave the coast and spread north and east, in search of milkweed to start the cycle again.

Reports from California on the status of overwintering populations of monarchs are concerning. For over a decade, each Thanksgiving, citizen scientists have visited overwintering sites along the California coast to conduct annual counts of overwintering butterflies. These observations have revealed a 50 percent population decline from the long-term average. At some sites, the decline appears to be more severe. For example, at Natural Bridges State Beach near Santa Cruz, the number of butterflies gathering each winter dropped from an estimated 120,000 in 1997 to just 1,300 in 2009. With support from the Monarch Joint Venture, Xerces is working toward the protection and management of monarch overwintering sites in California by:

  • assessing their current condition and compiling all available information,
  • developing and distributing management guidelines,
  • reviewing the laws regulating their management,
  • developing a habitat assessment protocol, and
  • educating the public and land managers on how best to protect these sites.

Milkweed Population Survey

The Xerces Society, with support from the Monarch Joint Venture, has prepared a short web-based survey to gather information about the location of milkweed stands in the western states that potentially serve as important monarch breeding areas. If you know where milkweed grows, we’d appreciate you completing the survey.

You can also help by planting native milkweeds, which support monarch butterflies, native bees, honey bees, and other beneficial insects. Find sources of local, native milkweed seed in your state using our Milkweed Seed Finder.

More Information

For more information on the western monarch migration and the threats currently facing the western monarch population, please read this fact sheet.

For more details on how Xerces is working to protect monarch groves, please read this fact sheet.

Learn about how Xerces is working to restore monarch breeding habitat by increasing the availability of native milkweed seed.

Find out where to see monarchs overwintering in California.

Learn more about the Western Monarch Thanksgiving Count.

Milkweeds and Monarchs in the Western U.S. – This guide outlines how land managers can join existing efforts to help western monarchs by identifying and reporting milkweed stands and monarch breeding occurrences on their lands.



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Program Features
Program Highlights
  • • The Xerces Society has awarded two $3,750 Joan M. DeWind awards for research into lepidoptera conservation
  • Butterfly-a-thon pledges raise $30 per species that Bob Pyle observes for butterfly conservation work
Additional Information
monarch butterflies (Danaus plexippus) by Carly Voight, The Xerces Society