Citizen scientists’ data used to study western monarch population

U.S. Fish and Wildlife Service biologist Jeff Phillips observes roosting monarchs at Ellwood Mesa in Santa Barbara County, Calif., recently.  Using the data collected at the Thanksgiving Count, scientists from the Service are researching ways to protect and enhance habitat for monarch butterflies in the western U.S.  Credit: Ashley Soratt/USFWS

By Byrhonda Lyons
November 4, 2016

It happens every year in the weeks surrounding Thanksgiving. Hundreds of citizen scientists rise early and head to the California coast. With their binoculars and clipboards in tow, they examine trees, looking for large clusters of monarch butterflies for the Western Monarch Thanksgiving Count.

A cluster of roosting monarch butterflies at Ellwood Mesa
Preserve, Santa Barbara County, Calif. Credit: Eric

“This is the single effort we have to track the status of monarchs and understand the size of the western monarch population,” said Xerces society biologist Sarina Jepsen. Jepsen directs endangered species and aquatic programs for the  Xerces Society for Invertebrate Conservation—which has managed the Thanksgiving Count since the late 1990s.

Using the data collected at the Thanksgiving Count, scientists from the U.S. Fish and Wildlife Service are researching ways to protect and enhance habitat for monarch butterflies in the western U.S.

Monarchs are large, migratory, orange and black butterflies. The monarch life cycle is like other butterflies. They start off as eggs, transition to caterpillars, then chrysalises and at the last stage—adult butterflies.

Every year, over the course of a few generations, monarchs journey across North America to wintering sites, primarily in Mexico and California. Although there is little genetic difference between eastern and western monarch butterflies, eastern monarchs overwinter in central Mexico; western monarchs live west of the Rocky Mountains and travel both to the California coast and central Mexico to spend the winter.

Overwintering western monarchs can be found in eucalyptus, Monterey cypress, Monterey pine and other trees. Historically, there were more than 400 overwintering sites on the California coast; scientists currently know of about 221 active sites. Since the first Thanksgiving Count in 1997, the western monarch population has declined from 1.2 million to 292,674—74 percent.

A monarch perches on a wildflower during it spring migration.  Credit: Joanna Gilkeson/USFWS

In 2014, monarchs were petitioned for protection under the Endangered Species Act (ESA). To better assess monarch populations, USFWS and its partners are trying to learn more about western monarch habitat and breeding areas. Once scientists understand western monarchs’ patterns, they can determine the best approach to protect them.

“In the western U.S., we are focused on gathering missing information,” said Samantha Marcum, USFWS regional coordinator for the monarch butterfly and coastal program.

Unlike Eastern monarchs, scientists are still putting together the puzzle to figure out why the western monarch population is declining.

A monarch caterpillar feeds on a wild milkweed plant. The mid-western monarch caterpillar shown here is part of the fourth generation in their migration cycle that migrates to and from  Mexico. Peak migration times for both western and mid-western monarchs are late August to early October. Credit: Courtney Celley/USFWS

“We have hypotheses about what is causing western monarchs to decline, but more research is needed to fully answer this question,” Jepsen said.

This is where citizen scientists help out. With technology, citizen scientists are collecting monarch data all over the California coast. USFWS provided funding to help Xerces analyze data that field data and to develop the “State of the Monarch Butterfly Overwintering Sites in California” (PDF, 4.7 MB) report that prioritized the top 50 overwintering sites.

“We know western monarchs have lost overwintering sites; and we know tree removal is a threat,” Marcum said. “Therefore, Xerces and USFWS are working with landowners at priority overwintering sites to conduct site assessments and to develop long-term management plans until we can do something more comprehensive."

Charis van der Heide, of the Xerces Society, peers through a spotting scope at a tree full of roosting monarch butterflies  overwintering in Santa Barbara County, Calif. Credit: Ashley Spratt/USFWS

"We are finishing up our first management plans that lay out proactive things that can be done to protect monarchs and their habitats and working to get as much research and conservation done as quickly as possible,” she said.

In addition to the Thanksgiving Count, when citizens see breeding monarchs and locate milkweed, they can now record that information on the Xerces website or on the newly launched Monarch SOS. All of these tools are helping USFWS and Xerces collect more data about western monarchs and to identify important breeding locations and migratory pathways.

Although scientists are working to gather more information about western monarchs, they are doing things right now to improve monarch habitat. In addition to creating management plans, USFWS and partners are:

   • Planting pollinator gardens,
   • Investing in schoolyard habitat,
   • Hosting education, outreach events,
   • Conducting milkweed surveys,
   • Planting locally sourced, native milkweed in known historical areas, and
   • Planting nectar plants, which are good for monarchs and other pollinators.

Close-up of a monarch butterfly tagged at Minnesota Valley National Wildlife Refuge. Credit: Katie Steiger-Meister/USFWS.

If you want to get involved, here are some ways you can help western monarchs: 1. Plant milkweeds native to your region in known historic locations, 2. Cultivate native nectar plants 3. Avoid Pesticides 4. Participate in citizen science

Find a monarch overwintering site near you at

The Service will determine if monarch butterflies warrant ESA protection in 2019.


Byrhonda Lyons is a public affairs specialist and social media coordinator for the Pacific Southwest Region, based in Sacramento, Calif.