The butterflies are losing ground in Mexico • Monarch butterflies that come to Mexico every November to hibernate are so numerous that there is no way of telling. Millions, • tens of millions or hundreds of millions. • The only way we have to measure the population is to calculate the area occupied by forests. • This season the area has declined by 59%: 1.9
hectares compared to 2.89 in 20112012 hibernation cycle, which is the lowest level in 20 years, since no data. They travel more than 4,000 miles south and go through three countries: Canada, from whence, United States, which accounts for most of the journey, and Mexico.