FILE - In this Dec. 9, 2011, file photo a Monarch butterfly sits on a tree trunk at the Sierra Chincua Sanctuary in the mountains of Mexico's Michoacan state. The amount of Monarch butterflies wintering in Mexico dropped 59 percent in 2013, falling to the lowest level since comparable record-keeping began 20 years ago, scientists reported Wednesday, March 13, 2013. (AP Photo/ Marco Ugarte, file)

Associated Press
FILE - In this Dec. 9, 2011, file photo a Monarch butterfly sits on a tree trunk at the Sierra Chincua Sanctuary in the mountains of Mexico's Michoacan state. The amount of Monarch butterflies wintering in Mexico dropped 59 percent in 2013, falling to the lowest level since comparable record-keeping began 20 years ago, scientists reported Wednesday, March 13, 2013. (AP Photo/ Marco Ugarte, file)
FILE - In this Dec. 9, 2011, file photo a Monarch butterfly sits on a tree trunk at the Sierra Chincua Sanctuary in the mountains of Mexico's Michoacan state. The amount of Monarch butterflies wintering in Mexico dropped 59 percent in 2013, falling to the lowest level since comparable record-keeping began 20 years ago, scientists reported Wednesday, March 13, 2013. (AP Photo/ Marco Ugarte, file)
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