A film of hundreds of millions of monarchs in their remote overwintering sanctuaries and along their migratory routes from Canada and across the U.S. to Mexico.A film of hundreds of millions of monarchs in their remote overwintering sanctuaries and along their migratory routes from Canada and across the U.S. to Mexico.A film of hundreds of millions of monarchs in their remote overwintering sanctuaries and along their migratory routes from Canada and across the U.S. to Mexico.