https://www.usgs.gov/media/videos/piedra-herrada-monarch-butterfly-sanctuary-mexico
Piedra Herrada Monarch Butterfly Sanctuary, Mexico | U.S. Geological Survey
A group of monarch butterflies (Danaus plexippus) flying among the oyamel fir tree (Abies religiosa) forest at an overwintering site in the Piedra Herrada...
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