A monarch butterfly rests on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. Angangueo is a town and municipality located in far eastern Michoacán state in central Mexico noted for its history of mining and its location in the Monarch Butterfly Biosphere Reserve. The Monarch Butterfly Biosphere Reserve is a World Heritage Site containing most of the over-wintering sites of 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 and State of Mexico, 100 km (62 miles), northwest of Mexico City. Millions of butterflies arrive in the reserve annually. Butterflies only inhabit a fraction of the 56,000 hectares of the reserve from October–March. The biosphere’s mission is to protect the butterfly species and its habitat. Most of the over-wintering monarchs from eastern North America are found here. Western researchers discovered these areas in 1975. Presidential decrees in the 1980s and 2000 designated these still privately held areas as a federal reserve. The Reserve was declared a Biosphere Reserve in 1980 and a World Heritage Site in 2008. The reserve remains predominantly rural. Reserve administrators continue to be concerned with deleterious effects of illegal logging and tourism. Conservation efforts sometimes conflict with the interests of local farmers, community-based landowners, private land owners and indigenous people. (Photo by Carlos Jasso/Reuters)





Monarch butterflies rest on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





A monarch butterfly rests on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies fly near a tree at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies rest on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies rest on a tree at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





A monarch butterfly rests on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies fly at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies rest on the ground at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





A monarch butterfly rests on a tree at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)





Monarch butterflies rest on a tree at the Sierra Chincua butterfly sanctuary on a mountain in Angangeo, Michoacan November 24, 2016. (Photo by Carlos Jasso/Reuters)