A monarch butterfly rests on a visitor's hand at the Monarch Grove Sanctuary in Pacific Grove, California December 30, 2014. Monarch butterflies may warrant U.S. Endangered Species Act protection because of farm-related habitat loss blamed for sharp declines in cross-country migrations of the orange-and-black insects, the U.S. Fish and Wildlife Service said. (Photo by Michael Fiala/Reuters)

Monarch butterflies cling to a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

A monarch butterfly rests on a visitor's hand at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

A tagged monarch butterfly perches on a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

A monarch butterfly clings to a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

Monarch butterflies cling to a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

A monarch butterfly rests on a rope at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)

A monarch butterfly clings to a plant at the Monarch Grove Sanctuary in Pacific Grove, California, December 30, 2014. (Photo by Michael Fiala/Reuters)