Monarch Conservation Program

Status of the Western Monarch Butterfly Population

• There are two primary monarch populations in the U.S. and, unfortunately, both are in decline. The CCRCD’s program focuses on the western monarch population, which is found west of the Rockies. Although we’ll continue to refer to the western monarch population, please note that there is interbreeding between the two populations, and they are not genetically distinct.
• There is still much we do not know about monarch migrations. Here is a map showing the confirmed and unconfirmed migration paths. Read more about monarch migrations here.
• Most western monarchs gather on trees at overwintering sites along 620 miles of the Pacific coast from California’s Mendocino County to Baja California, Mexico. They start to gather at these sites in September and continue to overwinter through February. Check out this map to see where California’s monarch overwintering sites are located.
• The Xerces Society for Invertebrate Conservation reports that the western monarch population overwintering in California has dwindled from approximately 4.5 million in the 1980s to approximately 29,000 in 2019—that’s a decline of over 99%! Xerces also states that “the projected threshold for quasi-extinction of western monarchs is 30,000 individuals.”
• The western monarch butterfly population decrease is primarily due to climate change, pesticides, disease, and habitat loss.
• According to the Xerces Society, the 5 key steps to recovering the western monarch population in the short term are:

• ~ Protect and manage California overwintering sites
• ~ Restore breeding and migratory habitat in California
• ~ Protect monarchs and their habitat from pesticides
• ~ Protect, manage, and restore summer breeding and fall migration monarch habitat outside of California
• ~ Answer key research questions about how to best aid western monarch recovery
• ~ The Xerces Society’s Western Monarch Conservation web page is one of the best places to find updates on the status of the western monarch butterfly population and conservation efforts
• As you can see in the map of California below (left), the entirety of Contra Costa County (circled in red) is within the Priority #1 Action Zone for recovering western monarchs.