King of the butterflies

Every year, a spectacular natural phenomena takes place in the forested mountains west of Mexico City. Between mid-January and late March, colonies of monarch butterflies migrate here from colder northern climates to find warmth and begin their breeding season. These huge flying colonies can contain as many as 20 million monarchs, which make use of air currents to travel as far as 100 nautical miles per day.
© Sylvain Cordier/Minden Pictures