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Western Monarch Count Reports More Monarchs than 2015, but Numbers Remain Low

Feb 10, 2017


  • Population Trends

This post is based on information found in this Xerces Society for Invertebrate Conservation Press Release. Find further information and data at the Western Monarch Count Resource Center.

The 2016 Western Monarch Thanksgiving Count (WMTC) population survey has reported 298,464 western overwintering monarchs from 253 monitored overwintering sites across the California coast. These results show a small increase of 5,560 butterflies compared to the 2015 count.

Although the number of reported western monarchs increased this year, the difference is likely due to a large increase in WMTC monitoring efforts. It is now the 20th year of the WMTC, and volunteer participation has reached its highest ever with 100 volunteers and a record-breaking 253 sites monitored. More sites monitored and more volunteers counting could lead to documenting more monarchs.

Important sites such as Pismo Beach and Natural Bridges recorded lower populations this year, and all but one of the 15 sites that have been monitored continuously since 1997 had lower counts than in 2015. The data from individual sites are available here.   

Despite relatively low numbers at sites that have been monitored every year of the WMTC, one site on private land in Monterey County hosted over 39,000 butterflies­. This is the largest aggregation on the California coast seen in 10 years. Four new overwintering sites were also documented in Southern California.

Western Monarch Butterfly Population Graph

The Western Migration

Each winter, monarchs from the western U.S. migrate to dozens of tree groves along the Pacific coast from Mendocino County, California to northern Baja, Mexico. There they find the microclimate they need to stay not-too-cold to freeze during the winter, and not-too-warm to burn off their fat reserves before mating.

These overwintering monarchs live months longer than their parents and offspring, and most delay reproduction until temperatures warm in the spring. In the spring and summer their children and grandchildren will repopulate the western United States with monarchs spreading from California to Idaho to Arizona. When fall comes again after additional breeding generations, the great-grandchildren of last year’s monarchs will make their migration westward. You can find out more about the monarch migration here

Getting Involved In Western Monarch Conservation

Every year during the overwintering season, citizen scientists, biologists, and land managers in California travel to the groves to count monarchs with the Western Monarch Thanksgiving Count. The WMTC would not be possible without volunteers and dedicated regional coordinators including Mia Monroe, one of the Count’s founders.

This monitoring effort is essential to our understanding of the western monarch population, and you can be a part of it. More volunteers allow the WMTC to get a more complete picture of the western population, and it is a meaningful way to get involved in monarch citizen science. Find out how you can take part here. Don’t live in the west? There are many other monarch citizen science opportunities across the country.

 “This extraordinary volunteer effort has recorded more monarchs in California this year than last,” said Sarina Jepsen, Xerces Society Endangered Species program director. “However, monarch butterfly populations are far from recovered. We will still need a focused effort to address the many threats that monarchs face—from pesticide use and habitat loss to climate change and disease.”

Conservation efforts are underway to protect and restore the western monarch population. Monarch Joint Venture partners are working on habitat protection and restoration, research and monitoring, and education and outreach in the west. To learn more about these efforts, visit our Western Monarchs Partner Projects page, and find out how you can get involved in monarch conservation today.  


The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of all Monarch Joint Venture partners. Header photo taken by Lisa Hupp/USFWS on Jan 5 2017 in Goleta CA.