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Western Monarch Mystery Challenge Documents Spring Migration

Mar 18, 2022


  • Community Science
  • Population Trends

Article contributed by Emily Erickson; photo credit Teresa Bertossi 

The Western Monarch Mystery Challenge is a community science initiative out of the Conservation Biology Lab at Washington State University, led by Cheryl Schultz, Christopher Jason, Emily Erickson, Hannah Machiorlete, and Lilianne de la Esperiella. This project is working to monitor western monarch butterfly populations during the spring months following their overwintering period. Now in its third year, the Challenge is funded by the Monarch Joint Venture as part of its Partner Grant Program.

The Xerces Society for Invertebrate Conservation reports that the migratory population of western monarchs has declined by over 95% since the 1980s. The 2020 Thanksgiving count of adults was the lowest recorded to date, with just under 2,000 individuals recorded at overwintering sites (Xerces 2021). These declines have been attributed to several interacting factors, including loss of overwintering and breeding habitats, exposure to pesticides in agricultural landscapes, and a changing climate (Crone et al. 2019, Espeset et al. 2016, Pelton et al. 2019). 

Early spring is a critical time of year for monarchs (Pelton et al. 2019), as it is when the population numbers are lowest and adults are physiologically stressed. Overwintering is a taxing stage of the monarch life cycle, and throughout their six- to eight-month lifespan, winter adults face a number of threats to their survival such as adverse weather events and predation, resulting in a significantly reduced number of surviving adults come spring. Indeed, the Xerces Society recorded a decline of 38% at overwintering sites between Thanksgiving 2021 and New Year's Day 2022, a number that is consistent with records from the past six winters (Xerces 2022). 

These remaining individuals will be the first adults to reproduce in early spring and start the inland migration. Supporting these early-season monarchs is therefore crucial for enhancing subsequent generations, and protecting and managing spring breeding habitat should be considered a conservation priority. Despite the importance of protecting monarchs during this limiting stage of their migration, researchers know very little about where the butterflies go during the early spring months. Practically, this poses a significant limitation to developing effective and sustainable conservation initiatives.

The Western Monarch Mystery Challenge aims to address these knowledge gaps by leveraging community science to collect wide-scale data on adult monarch distribution and population dynamics throughout the West from Valentine's Day (February 14th) to Earth Day (April 22nd). Participation in the challenge is simple, and involves photographing any adult monarchs that are seen on the West Coast north of Santa Barbara and uploading those photos to either iNaturalist, the Western Monarch Milkweed Mapper, or emailing them directly to We are entering the fourth week of the challenge and have already received some very exciting submissions from participants, a selection of which are highlighted below:

  • We kicked off the first week of the challenge with an observation of an older adult spotted in Fresno, CA on iNaturalist. It is rare to get reports of monarchs in the Central Valley this early in the season. This region was historically an important monarch breeding habitat that has since been impacted by agricultural intensification and resulting habitat loss (Pelton et al. 2019). 
  • In week 2 of the challenge, the Luckenbill family reported four monarch adults at the Berkeley Marina in Berkeley, CA. This project is accessible to all ages and is a great way to get families and children involved in a science project! 
  • Week 3 brought us more sightings out of the Central Valley - one in Tulare, CA and another in Fresno, CA. We are delighted to be learning more about monarchs in these regions that are historically lacking in data. 
  • In week 4, we received a sighting of a monarch in San Luis Obispo ovipositing on Narrowleaf Milkweed (A. fasicularis). Planting native milkweed is one of the best ways for home gardeners to support declining monarchs! We also got more observations from the Central Valley and eastern foothill regions, illustrating how monarchs are starting to spread through the western landscape as the season progresses.

This year, there were just under 250,000 monarchs recorded at overwintering sites along the California coast (Xerces 2021). While these numbers are incredibly promising, particularly in comparison to previous years' counts, this is still a very small fraction (less than 5%) of the numbers estimated at overwintering sites in the 1980s (Schultz et al. 2017). Therefore, there is still a significant need for effective short-term conservation actions that will support this threatened population. These actions cannot be accomplished until we know more about where monarchs are spending the spring months, and for that we need participation from our community. So, next time you are out in your garden or on a walk through your neighborhood and you see a monarch passing through, take a picture (it can be blurry!) and submit it in the Challenge!

We thank Monarch Joint Venture for funding our work for a third season!

The Monarch Joint Venture is a national partnership of federal and state agencies, non-governmental organizations, businesses and academic programs working together to conserve the monarch butterfly migration. The content in this article does not necessarily reflect the positions of MJV or all Monarch Joint Venture partners.


Crone EE, Pelton EM, Brown LM, Thomas CC, Schultz CB. 2019. Why are monarch butterflies declining in the West? Understanding the importance of multiple correlated drivers. Ecological Applications 29.

Espeset AE, Harrison JG, Shapiro AM, et al. 2016. Understanding a migratory species in a changing world: climatic effects and demographic declines in the western monarch revealed by four decades of intensive monitoring. Oecologia 181: 819–830.

Howard I. 2022. New Year’s count of western monarchs tracks population decline during overwintering season.

Howard I, Pelton E. 2022. Western monarch Thanksgiving count tallies nearly 250,000 butterflies.

Pelton EM, Schultz CB, Jepsen SJ, Black SH, Crone EE. 2019. Western monarch population plummets: Status, probable causes, and recommended conservation actions. Frontiers in Ecology and Evolution 7.

Schroeder H, Majewska A, Altizer S. 2020. Monarch butterflies reared under autumn‐like conditions have more efficient flight and lower post‐flight metabolism. Ecological Entomology 45: 562–572.

Schultz CB, Brown LM, Pelton E, Crone EE. 2017. Citizen science monitoring demonstrates dramatic declines of monarch butterflies in western North America. Biological Conservation 214:343-346