The number of monarchs overwintering in Mexico has increased dramatically from the record lows of the past 3 years, although still 30% below historic levels. The clustering butterflies cover 4.01 hectares of forest compared to a peak of 18 hectares in 1996 and an average of 6 hectares. This year's population contains 200 million monarchs compared to a long-term average of 300 million and a peak of 1 billion. Favorable breeding conditions in summer 2015 are credited for the increase.
Monarch numbers are down and people are wondering why. This article examines the factors that caused the decline during the past year and the downward trend over the past decade. Also, see how you can help.