A study by the WWF in December 2010 has found that the area covered by Monarch Butterflies in the Michoacan state of Central Mexico has grown by 109% compared to 2009.
Monarch Butterflies take part in one of the greatest migrations on earth. Every year they head north from Central Mexico and spread across North America as far as Southern Canada. This northerly Migration is done over three generations of butterflies. The fourth-generation then turn around and head back to the valleys of Central Mexico to spend the winter.
During the winter months (December-February) millions of Monarch Butterflies can be seen in a mere handful of valleys within the Monarch Butterfly Biosphere Reserve.
WWF has been monitoring the monarch butterfly populations year on year by measuring the area covered by butterflies in Michoacan state. Whilst 2009 had the lowest area coverage on record they found that the area covered in 2010 has more than doubled from the previous year to cover an area of 4.02 hectares.