Why monarch butterfly numbers are on the rise

A file photo of monarch butterflies on a plant at the Monarch Grove Sanctuary in Pacific Grove, California. Photos: Reuters

Mexican experts said recently (May 23) that 35% more monarch butterflies arrived this year to spend the winter in mountaintop forests, compared to the previous season.

Experts say the rise may reflect the butterflies’ ability to adapt to more extreme bouts of heat or drought by varying the date when they leave Mexico.