Both the eastern and western migrations have experienced significant decline in a matter of decades. In the 1990s, nearly 700 million monarchs made the epic flight each fall from the northern plains of the U.S. and Canada to sites in the oyamel fir forests north of Mexico City. Now, researchers and citizen scientists estimate that there has been a decline of more than 80% in the east. In the west, the news is more dire. Monarchs have experienced a decline of 99.4% in coastal California, from an estimated 4.5 million in the 1980s to 28,429 as of January 2019.
The monarch has been petitioned for listing as a threatened species under the Endangered Species Act. The U.S. Fish and Wildlife Service will make a decision by December 15, 2020.
- Loss of milkweed (breeding) habitat
- Pesticide use
- Climate change
- Logging and development