As a child, Rebeca Quionez-Pin wondered where monarch butterflies stop for a meal and a night's rest on their long migrations across North America.

Now she and other scientists are attaching tiny tracking devices to hundreds of butterflies to find those critical stopover locations before they disappear.

Swarms of dazzling orange-and-black monarchs use environmental cues to travel some 3,000 miles (4,800 kilometers) from as far as southern Canada to spend the winter in forests of oyamel fir trees in central Mexico, a protected biosphere reserve that's also a World Heritage site.