Mexican Overwintering Monarchs Graph
This graph shows the area of forest occupied by colonies of hibernating monarchs in Mexico from 1994-2014 (Graph courtesy of the Monarch Joint Venture). In late January 2014, the World Wildlife Fund in Mexico reported that the size of the 2013–2014 overwintering population is the smallest since monitoring began in 1994, occupying an estimated area of just 0.67 hectares (1.65 acres) (Rendón-Salinas & Tavera-Alonso 2014). Over the last 20 years, the average forested area occupied by monarchs at the Mexican overwintering sites ha been 6.39 hectares (15.79 acres). Researchers estimate that between 10–50 million monarchs exist per hectare. Thus, the size of this year’s population represents only 10% of the 20-year average. Furthermore, this winter’s population is approximately half the size of the previous year’s (2012–2013), which at the time was the smallest population on record.