Monarch Butterfly Biosphere Reserve

The Monarch Butterfly Biosphere Reserve (Reserva de la Biosfera Mariposa Monarca) protects key overwintering sites for the eastern population of the monarch butterfly. The reserve is located in the Trans-Mexican Volcanic Belt pine-oak forests ecoregion on the border of Michoacán State in Mexico.

The millions of monarch butterflies that return to this World Heritage site every year bend tree branches by their weight, fill the sky when they take flight and make a sound like light rain with the beating of their wings.

The 56,259 ha (139,000 acres) Monarch Butterfly Biosphere Reserve lies within rugged forested mountains about 100 km (62 miles) northwest of Mexico City. Butterflies only inhabit a fraction of the reserve from October to March. The biosphere's mission is to protect the butterfly species and its habitat.

Every autumn, millions of butterflies from vast areas of North America return to the site and cluster on small forest reserve areas, coloring its trees orange and bending their branches under their collective weight.

The butterflies travel south into Mexico, from Texas and then follow the Sierra Madre Oriental range to the preserve. The overwintering concentration of the monarch butterfly is the most dramatic manifestation of insect migration.

The Biosphere Reserve protects eight of these colonies and an estimated 70% of the monarch butterfly's eastern population's total overwintering population.

In spring, these butterflies make their return migration across North America, sometimes ending up in Eastern Canada. Over the time it takes them to make this journey, four generations of monarch butterflies are born and die.

The Mariposa Monarca Biosphere Reserve is located in a region where natural heritage conservation is challenging because of its unique physical, geomorphological, climatic, hydrological and biogeographic features. However, even more so because it is here that every year millions of Monarch butterflies (Danaus plexippus) complete their migratory cycle, migrating from Canada and the United States.

Oak forests mainly cover the mountains in the region up to 2,900 m (9,500 ft), Pine and Oak and Pine forests between 1,500 and 3,000 m (4,900 and 9,800 ft), and Sacred Fir Abies religiosa, at an altitude of between 2,400 (7,874 ft) and 3,600 m (11,800 ft) above sea level. Less represented are the Cedar and Juniper forests and the grasslands.

It is an important catchment area for rainfall, feeding numerous water bodies in Michoacán and Mexico states. It is also the habitat of various endemic species from the country's center, and particular mention may be made of Pinus martinezii, Ambystoma ordi-narium and Regulus calendula.

As it is a transition zone between the Nearctic and Neotropical regions, attached to the Southern Sierras Province of the Mesoamerican Mountain Region, it hosts enormous biodiversity due to the convergence of flora and fauna from both biogeographical regions. Partial studies have reported 198 species of vertebrates, 493 species of vascular plants, and some 100 species of fungi.

The wildlife in the area ranges from the sub-tropical to the sub-arctic, including some species that are endemic only to this area.

These include white-tailed deer (Odocoileus virginianus), coyotes (Canis latrans), long-tailed weasels (Mustela frenata), grey foxes (Urocyon cinereoargenteus), rabbits (Sylvilagus spp.), crows (Corvus corax), turkey vultures (Cathartes aura), horned owls (Bubo virginianus)(A), as well as various types of hummingbirds, reptiles and amphibians.