We are excited to share our first annual review of academic literature published on monarchs and their habitat. For this project, members of the MJV staff and partner community read 67 papers published between June 2019 and August 2020. The resulting research review summary compiles key takeaways from the latest monarch research. At MJV, we aim to use and share the latest scientific information to inform and support collective conservation actions across the United States.
The research in this review contributes to our knowledge of monarchs both within and beyond the Americas, and covers topics of habitat quality and conservation, monarch populations and biology, threats to monarchs, and the role of community science in conservation. We encourage you to read the research review in full, but have summarized several noteworthy findings below:
- ♦ Monarchs tagged on the same day in SE Arizona migrated to both Mexico and California, suggesting a greater degree of interconnectedness between the eastern and western populations than previously documented (Billings, 2020).
- ♦ Climate change poses significant threats to monarch populations. It has the potential to limit the reproductive capacity of breeding monarchs and is currently the major driver of habitat loss in the Mexican overwintering grounds (Crewe et al., 2020, Flores-Martínez et al., 2019).
- ♦ 36 new monarch predators - all invertebrates - were documented in midwestern grasslands (Hermann et al., 2020). The majority of monarch eggs were consumed at night (Myers et al., 2019).
- ♦ Grant et al. (2020) estimate that only 1.4% of monarch eggs survive through the 5th instar stage (through the end of the larval stage before making a chrysalis) in the wild.
- ♦ There is a higher density of milkweed plants in urban areas and midwestern conservation grasslands than previously estimated (Johnston et al., 2019, Lukens et al., 2020), suggesting that these are important habitat opportunities and warrant greater inclusion in conservation planning.
- ♦ Captive rearing may have negative consequences on monarch behavior and migration success. Both commercial monarchs (those purchased from a commercial source) and those collected from the wild (in Illinois) were not able to consistently orient southward when reared indoors, even with access to natural sunlight. This is necessary for successful migration to the Mexican overwintering grounds and the loss of this ability is likely due to a combination of environmental conditions and genetics (Tenger-Trolander and, Kronforst 2020).
In addition to important findings, researchers identified areas that need further study. As we move forward, the conservation community will need continued research to identify the impacts of climate change, pesticide use, and land use change on monarchs and insect populations.
This research review was coordinated by the MJV science team and made possible through the time and expertise of our volunteer reviewers - thank you! If you have questions about this review, please contact MJV’s National Monitoring Coordinator Laura Lukens (llukens@monarchjointventure.org).
Additional Resources:
- ♦ Many of the 67 research papers that were reviewed in this summary can be read in full in “North American Monarch Butterfly Ecology and Conservation”, a free, special issue eBook published in Frontiers in Ecology and Evolution.
- ♦ For additional literature on monarch butterflies, please visit the MonarchNet Research Library.
- ♦ The MJV shares links to monarch research on our website here.
The Monarch Joint Venture is a 501c3 nonprofit organization and 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 all Monarch Joint Venture partners. Header photo by Wendy Caldwell.