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New Year’s Count of Western Monarchs Tracks Population Decline During Overwintering Season

By Isis Howard on 2. March 2022
Isis Howard

Western Monarch population experiences seasonal winter decline, but remains higher than previous years.

The Western Monarch New Year’s Count serves as a follow-up to the annual Thanksgiving Count to help scientists better understand how the western monarch population changes throughout the overwintering season.

This winter, Xerces scientists and volunteers recorded a 38% decline through the observation period, within the range of a 36-49% seasonal decline observed over the previous six winters. The overall western monarch population remains higher than in previous years.

Although it is difficult to distinguish the exact reasons for winter declines, we suspect it’s likely due to a combination of factors: mortality from winter storms, predation, other causes of mortality, and butterflies leaving the overwintering sites.

Now in its sixth year, the New Year’s Count provides additional information on the status of the migratory monarch population in the West. While the Thanksgiving Count remains the height of the annual monitoring efforts, the New Year’s Count, which runs for two weeks surrounding the New Year’s holiday, continues to gain momentum among volunteers.

Despite a general uptick in the western monarch population this year, monitoring efforts reveal that the migratory population of western monarchs has undergone a dramatic decline estimated more than 95% in the western U.S. since the 1980s.
 

Volunteers set record number of observations

This year, volunteers surveyed 209 overwintering sites for the New Year’s Count, the most sites monitored since its inception in 2016. Fourteen of these sites were not surveyed for the Thanksgiving Count due to barriers such as site access and weather, leaving 195 sites to be compared across the season in the graph below.
 

Monarch abundance at the 195 overwintering sites in California monitored for both the Thanksgiving and New Year’s Counts during the 2021 – 2022 overwintering season.
 

Between December 25, 2021 and January 9, 2022, volunteers conducted surveys for the New Year’s Count that tallied a total of 151,168 monarchs at 209 overwintering sites. Following the Thanksgiving Count, which tallied nearly 250,000 monarch butterflies, the data from the New Year’s count revealed an average decline of 38% among the sites surveyed during both counts. This year’s decline is very similar to last season, when a decline of approximately 37% was observed. New Year’s Count data is available online at www.westernmonarchcount.org/data.

Of the 209 overwintering sites that were monitored by volunteers, numbers declined at 118 sites, numbers increased at 30 sites, 5 remained unchanged, and 42 sites hosted zero butterflies during both counts. Ellwood East saw the greatest increase, from approximately 4,000 butterflies during the Thanksgiving Count to nearly 11,000 during the New Year’s Count.
 

New Year’s Count provides clues for conservation

Data from the New Year’s Count informs the conservation and management efforts of overwintering sites and gives us an idea of how many butterflies remain in the West to begin the spring breeding population. The Thanksgiving and New Year’s Counts help to prioritize overwintering habitat that would benefit most from active management and other protection measures. Monitoring twice during the overwintering season also helps scientists identify how monarch butterflies are using overwintering sites: some sites host monarchs all winter long, while others serve as autumnal (transitional) sites. Additionally, an extra count period during the overwintering season allows for more opportunity to capture information on habitat health, potential threats, and migration trends.
 

Take action now to recover western monarchs

Despite the recent uptick in the western monarch population, these butterflies are still facing significant threats and require extraordinary levels of conservation to recover. Monarchs are not out of the woods yet, and you can play a meaningful role in helping monarchs on their journey northward and inland this spring.

Here are five ways you can take action to support western monarch butterflies:

  1. Advocate for the protection and restoration of California overwintering sites.
  2. Plant native milkweed and nectar plants to restore breeding and migratory habitat.
  3. Reduce your reliance on pesticides through eliminating their use, buying bee-safe nursery plants, supporting farms that use fewer pesticides, and advocating for changes in your community.
  4. Participate in community science efforts like the Western Monarch Milkweed Mapper to answer key research questions about how to best aid western monarch recovery.
  5. Write to your legislators to get support for pollinator bills and stronger regulations for pesticides, like the Monarch Act of 2021.
     

Report monarchs this spring and summer

The Western Monarch Milkweed Mapper is a community science project where you can report monarch and milkweed sightings year-round to help scientists better understand where monarchs (adults, eggs, larvae, and pupae) and their host plants occur in the landscape. Volunteers can submit their observations to the website or post to iNaturalist and tag the Western Monarch Milkweed Mapper project. (Note that the Western Monarch Milkweed Mapper is not intended to capture overwintering monarch observations, and overwintering/clustering monarch observations should be sent to the Western Monarch Count project.)

For those who live in California, the Western Monarch Mystery Challenge is an extra push to collect monarch observations in the spring as they leave their overwintering grounds. Solving this mystery is central to conserving and restoring the phenomenon of monarch migration in the West. To participate in the Western Monarch Mystery Challenge, report your monarch sightings from February 14th - April 22nd to the Western Monarch Milkweed Mapper website or iNaturalist project, or email [email protected]. All data eventually ends up in the Western Monarch Milkweed Mapper.
 

ACKNOWLEDGEMENTS

A huge thank you to the more than 100 dedicated volunteers who collected data at overwintering sites. And, thank you to our western monarch conservation funders, who make this work possible: Bureau of Land Management, California Department of Fish and Wildlife, California State Parks Foundation, California Wildlife Conservation Board, Chantecaille, Google.org, Forest Service International Programs, The Marion R. Weber Family Fund, National Fish and Wildlife Foundation, Natural Resources Conservation Service, San Diego Zoo Wildlife Alliance, The Taggart Saxon Schubert Fund, US Fish and Wildlife Service, and Xerces Society members.
 

Further Reading

Authors
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As an endangered species conservation biologist, Isis works in California to protect and support the western population of monarch butterflies. She manages several community science projects, including the annual Western Monarch Thanksgiving Count and the Western Monarch Milkweed Mapper, and provides support to land managers and the public on maintaining and restoring western monarch breeding habitat.

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