PS 2-15 - Blockbuster year for monarchs; Community science in Los Angeles County, California, captures record overwintering numbers of Danaus plexippus

Background/Question/Methods

Western monarch butterfly populations have plummeted in the last two decades, primarily due to habitat loss, pesticides in agriculture, and invasive plants that transmit disease to larvae. These issues make monitoring their migratory numbers even more urgent. Xerces Society has been conducting the Western Monarch Count at overwintering sites since 1997. Los Angeles County is near the southern extent of the largest roosts of western monarchs and has not had a volunteer coordinator to monitor the historic roosting sites for years. My work as volunteer coordinator began in Summer 2021, leveraging my social and environmental networks to collect and train volunteers throughout the entire county. We worked in collaboration with community scientists to estimate how many monarchs are overwintering in Los Angeles County, with a focus on finding new and unknown roosting sites. We surveyed 27 sites with 16 volunteers on private and public sites. Monarch roosts were typically monitored at sunrise with proper weather conditions utilizing binoculars. iNaturalist was monitored throughout Los Angeles during the count periods to locate individuals with overwintering behavior. As part of this effort, we also focused on outreach to community scientists and the broader public via various media.

Results/Conclusions

19 of the 27 sites were successfully monitored on private and public lands, some needing advanced coordination ahead of time with land managers. 14 sites were found to have overwintering monarchs, and 11 of those sites were included in the official Xerces Society Overwintering Western Monarch Count. Of the 14 sites where monarchs were found, approximately 7,299 individuals were counted. Two new sites were identified by monitoring iNaturalist in Los Angeles County, including one of our largest roosts. We were able to report these findings and answer questions via two television news organizations, one public radio program, two newspapers, three internet articles, one conference, and multiple non-profit organizations and individuals to increase awareness of western monarch conservation. Overwintering western monarch numbers in Los Angeles County were the highest in two decades. Across the state, overwintering monarch numbers increased from 2000 to over 250,000. Communicating and involving the community in monitoring and scientific efforts is important for continuing this momentum. Monarch numbers across North America are still significantly lower from historic counts, indicating the need for continued conservation efforts.