Western Monarch Overwintering Science Initiative

Although the geographic footprint of the western monarch overwintering habitat is small compared to the butterfly's breeding range, the conservation of these sites is vital to ensure that the migration continues. Western monarch overwintering numbers have declined more than 90% since the 1980s. Protecting and restoring overwintering habitat is a crucial part of the species’ recovery, but significant knowledge gaps remain and have hindered our ability to manage habitat effectively.

The Western Monarch Overwintering Science Initiative (M.O.S.I.) is a new, evolving and highly collaborative group of people invested in advancing our collective understanding to aid conservation. In particular, we are interested in exploring what overwintering monarchs need to thrive, where and when the butterflies move, how we can better support overwintering through forest management, and how to more meaningfully engage the diversity of Californians in community science efforts and applied research projects.

The group draws together land managers, university researchers,  Western Monarch Count  partners and volunteers, governmental and non-governmental groups, and others. We seek to leverage different perspectives, strengths, and resources towards the common goal of a robust and resilient western monarch overwintering population.

Funding for the initiative's two current projects is provided by the  US Forest Service International Programs  and the US Department of Defense (DoD)  Legacy Resource Management Program .

Support for related work on an overwintering site boundaries project is provided by the  US Fish and Wildlife Service .

Building off the  Western Monarch Overwintering Science Meeting  in San Luis Obispo, CA in May 2023, a group of scientists, conservationists, and land managers are working together to refine our understanding of monarch overwintering and apply it to management of the coastal groves the butterflies rely on each fall and winter.

Participants in the initiative include, but are not limited to, California State Parks, California Department of Fish and Wildlife, the US Fish and Wildlife Service, US Forest Service International Programs, US Department of Defense: Vandenberg Space Force Base and Legacy Resource Management Program, Althouse and Meade, Creekside Science, Groundswell Coastal Ecology, California Association of Resource Conservation Districts, California Polytechnic State University, James Madison University, University of California-Davis, Washington State University Vancouver and the US Geological Survey. We welcome others to join us!

From October until March (with the highest numbers congregating in November through February), western monarchs overwinter in forested groves along the Pacific coast from Mendocino County south to Baja California. Over 400 overwintering sites have been documented. These groves occur in many landscape types and can vary greatly from site to site, ranging from just a few individuals to 40,000 clustering in one area. Meanwhile, eastern monarchs and a subset of western monarchs aggregate in a mountainous region of central Mexico.

At Pacific coast overwintering sites, over 60 overwintering sites have been lost to development over the last several decades and every year, more overwintering sites are cut down and damaged. Disease and drought have stressed the trees in many overwintering sites and managers must balance competing needs, including wildfire risk and the unpopularity of non-native eucalyptus tree species, which are prevalent in many of the groves monarchs use. Active management of the groves is critical to recovery of the western monarch, but much remains unknown about monarch overwintering needs and the best forest management to improve habitat quality.

Learn more about western monarch overwintering through the Xerces Society's Western Monarch Count  website  including exploring an  interactive map  of overwintering sites and their counts.

The first phase of this project in 2023 is led by Kyle Nessen, a graduate student at California Polytechnic State University, and a working group consisting of  Althouse and Meade , California State Parks, US Geological Survey, Vandenberg Space Force Base, and the Xerces Society. In future years, we aim to expand this project to include multiple, aligned studies and data collection tools (hence, its also referred to as the "super study").

Key questions this study aims to address:

• How does forest structure affect wind attenuation at overwintering sites?
• How do monarchs respond to disturbances like strong wind events due to storms?
• Do monarchs respond to vibration events due to military operations?
• How can knowledge of cluster locations and wind attenuation be applied to management of overwintering sites?

Winter 2023-24 is the pilot year and consists of two study sites:

1)  Pismo State Beach monarch grove : intensive monarch cluster monitoring will be paired with the installation of a dozen wind and temperature sensor arrays located in the forest canopy.

2) Vandenberg Space Force Base: modified infrared cameras and wind sensors will be installed to track monarch cluster location and movement over the season. A drone-based LiDAR sensor will be used to build a model of forest structure at the pilot sites.

Cluster monitoring: In addition to these efforts, the Xerces Society's  Western Monarch Count  project will also pilot cluster tracking by staff, volunteers and partners using an upgraded ArcGIS Survey123 form and custom Field Maps forms. Increasing spatial resolution of monarch cluster locations over the season and between years will be valuable information to apply to management and research questions. The functionality and accuracy of these cluster-tracking platforms will be assessed and refined in 2024.

Beyond the pilot year, US Geological Survey and the working group plan to expand the study to include more State Park and other overwintering sites, with an emphasis on understanding groves' current wildfire risk and fuel reduction practices as well as identifying drivers of monarch cluster occurrence.

This project is led by the  Xerces Society  and  Point Blue Conservation Science  . Other working group members include the California Department of Fish and Wildlife,  Dr. Leone Brown  of James Madison University, Vandenberg Space Force Base,  Althouse and Meade  and  Dr. Cheryl Schultz  of Washington State University Vancouver.

The  Motus Wildlife Tracking System  (Motus) has been expanding for the past decade, primarily to track migratory birds in the Americas. However, newer radiotags have recently become smaller and lighter, allowing the possibility of using the Motus network and tagging technology to migratory insects like monarchs. Studies on eastern monarchs and a small study by Idaho Department of Fish and Game began in the past few years, but many questions remain about the tags' impact on insect movement and the application to answer applied questions about movement during migration and overwintering.

Key questions this project aims to address:

• How can the Motus network benefit migratory insect studies?
• How do different radiotags impact monarch movement and survival?
• How can radiotags, telemetry, and Motus be used to answer key questions about western monarch migratory and overwintering movement? How can movement ecology studies using this technology inform habitat management actions at overwintering sites?

Western Monarch Movement Ecology Working Group and early tag testing

In 2023, a working group was formed to discuss opportunities, build knowledge from those with avian Motus experience, and plan a research study and possible Motus tower installation along the Central Coast. The group is also building on a pilot study led by the California Department of Fish and Wildlife in winter 2022-23 to test radiotags on monarchs at Montaña de Oro State Park in San Luis Obispo County, California. The 2023 working group's efforts are summarized in a report authored by Point Blue available  here . Continued working group meetings are planned through 2024-2025 and open to groups and individuals also interested in advancing this area of research. Reach out to monarchs@xerces.org if you would like to join or learn more.

At a field day in January 2024, partners convened to test lighter solar-powered CTT  BluMorpho  tags with handheld receivers at Vandenberg Space Force Base in Santa Barbara County, California.

Winter 2024-25 study at Vandenberg Space Force Base

In late fall and winter 2024-25, Xerces and Point Blue are working with Vandenberg Space Force Base staff and and Environment for the Americas interns to study if and when monarchs move among numerous overwintering sites at Vandenberg Space Fore Base. Up to 60 monarchs will be tagged with CTT's BluMorpho ultralight 0.06g solar-powered wildlife tracking tags and tracked using temporary stations, nodes, and handheld antennas throughout the overwintering season.

The working group will also coordinate with associated tag testing taking place concurrently in 2024 by Dr. Leone Brown and master's student Helen St. John as well as their technicians which aims to quantify flight impacts of tags of various sizes and the toxicity and longevity of various adhesives. Dr. Brown's work is also funded by US Forest Service International Programs and DoD.

Xerces has also joined and is supporting the  Cape May Point Science Center's Project Monarch  which allows anyone who downloads and runs the Project Monarch app (available for free in your app store for Android and Apple devices) to act as a mini-receiver--putting the power to real-time track tagged monarchs right in your pocket! Besides Xerces' work, BluMorpho tagging efforts are underway by Southwest Monarch Study in Arizona, Ashley National Forest in Utah, Wings Across Georgia, Cape May Point Science Center in New Jersey and in Pennsylvania: Allegheny Plateau Audubon Society and the North American Land Trust.

Note: handling and tagging monarchs in California requires permission from the California Department of Fish and Wildlife. Learn more on the CDFW FAQs pdf posted in a sidebar  here .