The Xerces Society’s Western Monarch Thanksgiving Count provides a long-running record of the number of monarchs overwintering in California—including the steep decline of recent decades.
Volunteers and biologists who take part in the Thanksgiving Count have been invaluable in monitoring the monarch population each fall for over twenty years. Last year, another count was added with the launch of the New Year’s Count—an opportunity to monitor the populations during a later period of the winter. Monarchs are mobile and they move around through the season. Combining the data from the New Year’s and Thanksgiving counts allows us to better understand site and rangewide population changes. Monarch numbers at the 115 sites monitored during both of this season’s counts decreased by an average of 49% between Thanksgiving and the New Year. This is similar to the change revealed by the previous New Year’s Count, which saw a 43% drop at 44 sites.