Monarch butterflies spend the winter in the remote mountains of Mexico before emerging and flying north to Canada and the northern United States. Scientists believe monarchs have made this journey for thousands of years, though their numbers have declined. Anderson Cooper reported on this remarkable and mysterious migration last year. He spoke with photographer Court Whelan, who has been photographing monarchs for more than 20 years. Whelan gives 60 Minutes an update on this year’s colony in Mex