Partnering to conserve the monarch butterfly migration

Protecting and Monitoring California Overwintering Sites

Most western monarchs migrate to specific overwintering locations along the Pacific coastline of California. To better understand the status of western monarchs and the condition of their California overwintering sites, the Xerces Society created databases with detailed information on dozens of sites. Based on commonly recognized overwintering site characteristics, they developed a protocol to help quantify attributes that are critical to monarch overwintering survival. This tool will enable assessment of threats to monarch overwintering sites, document changes over time, and inform overwintering site restoration and management strategies.

To put their newly developed protocol and databases to the test, Xerces identified priority overwintering areas to visit and assess. They monitored 71 overwintering sites during the 2012/2013 overwintering season to estimate monarch abundance and assess the habitat. Xerces and Monarch Alert staff surveyed an additional 16 monarch overwintering sites on private lands during the 2013 Western Monarch Thanksgiving Count. Many of the privately owned sites that were monitored in 2013 gave ongoing permission for volunteers to return for an annual monarch count and habitat assessment. At each site, scientists are evaluating the condition of the overwintering habitat using the monarch habitat assessment protocol, conducting counts to estimate monarch abundance, collecting location and land ownership information, and determining potential threats to each site. Monitoring sites were selected based on past cluster size, time since last visit, occurrence on public and private lands, and presence of native tree species.

To aid land managers in monarch conservation, Xerces has developed land management guidelines for California overwintering groves. They are also targeting outreach efforts to citizen scientists, U.S. Forest Service biologists, and others to encourage conservation of monarch breeding and overwintering sites.

A new resource center for western monarch overwintering counts has been launched by the Xerces Society. This site provides information on how to participate in citizen efforts to count western overwintering monarchs and will soon provide an online portal to enter data collected by volunteers. 

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