Mexico documents big rebound in monarch butterflies

Monarch butterflies have made a big comeback in their wintering grounds in Mexico, after suffering serious declines, experts says.

The area covered by the orange-and-black insects in the mountains west of Mexico City this season was more than three and a half times greater than last winter. The butterflies clump so densely in the pine and fir forests they are counted by the area they cover rather than by individual insects.

The number of monarchs making the 5,500-kilometer migration from the United States and Canada declined steadily in recent years before recovering in 2014. This winter was even better.