A monarch butterfly rests on a visitor's hand at the Monarch Grove Sanctuary in Pacific Grove, California in this December 30, 2014, file photo. Favorable weather conditions at breeding grounds for Monarch butterflies in Mexico are expected to help raise their numbers to more than 100 million this year, about triple of a few years ago, a study released on February 18, 2016 said. (Photo by Michael Fiala/Reuters)
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