According to a census taken by World Wildlife Fund - Mexico, the number of monarch butterflies wintering in Mexico has fallen to the lowest on record.
Every autumn, tens of millions of monarch butterflies migrate from as far away as eastern Canada to the states of Mexico and Michoacan. Here, they hibernate in the mountainous terrain, coating the oyamel fir trees in brilliant orange blankets. When air temperatures warm in the spring, they begin their long journey back to their northern breeding grounds.
The recent drop in the number of monarch butterflies over-wintering in Mexico is being blamed mainly on drought plus abnormally high and low temperatures in parts of North America where the monarchs reproduce. Also, the insects' Mexican habitat continues to be illegally deforested in order to harvest valuable timber and clear land for agriculture.
Although scientists say that the monarch butterflies are not in danger of extinction, they think that their declining numbers may threaten the annual migration to Mexico.
Mexico has four monarch butterfly sanctuaries in Michoacan and the Estado de Mexico. They were designated a UNESCO World Heritage Site in 2008 and now comprise the 56,259 hectare (about 139,00 acres) Monarch Butterfly Biosphere Reserve.
For tourist information on Mexico's monarch butterfly sanctuaries, visit the WWF- Mexico website.