Summary of available data from the monarch overwintering colonies in central Mexico, 1976–1991

First posted February 1, 2021 For additional information, contact: Director, Upper Midwest Environmental Sciences CenterU.S. Geological Survey2630 Fanta Reed RoadLa Crosse, WI 54602 Historical estimates of the area occupied by overwintering Danaus plexippus (monarchs) in central Mexico (between winters 1976 and 1991) were published García-Serrano others (2004) more recently Mawdsley (2020). Our primary objectives to identify specific data that informed those and, importantly, determine degree which reported reflect total size monarch population during period. Understanding how historical relate is necessary ensure inferences about abundance temporal trends are reliable, particularly as U.S. Fish Wildlife Service process determining if species should be listed under Endangered Species Act.