Limited information is available about where and when western monarchs breed following their departure from California overwintering sites each spring. To address this data gap, the Xerces Society launched an online survey to gather information about milkweed locations in the western U.S. that may serve as important monarch breeding sites. The survey initially targeted state and federal resource agency staff, natural resource consultants, native plant scientists, and citizen scientists in California, Oregon, Washington, and Nevada, but has now expanded to include many western states. To aid survey participants in recognizing milkweeds, basic milkweed identification guides were created for each of these states (available for download from Xerces’ milkweed survey webpage).
Xerces has now compiled and mapped over 12,000 milkweed records from this online survey and from the published literature, unpublished reports, online herbaria, and knowledgeable researchers and citizen scientists. The dataset will be analyzed to determine which areas of the west have the largest numbers of milkweed records and monarch breeding observations. Xerces will identify land owners and managers with large numbers of milkweed records and reach out to these groups to determine if they currently manage for monarchs and milkweed breeding habitat. Those identified will be encouraged to consider the needs of monarch butterflies in their management plans and will be provided with the monarch breeding habitat assessment tool that was recently developed by the University of Minnesota Monarch Lab.