Traveling in a southwesterly direction , the monarchs fly east of the Great Lakes and south-southwest in areas west of the Great Lakes. Those that reach the gulf of Mexico follow the coastline in a continuous stream. They continue in a southwest direction eventually reaching the overwintering site in the Transvolcanic Plateau of Mexico. As many as 300 million spend the winter there. During the migration, monarchs encounter many dangers.
Many butterflies are the casualties of storms and are eaten by birds.
Hundreds are crushed by cars crossing the highways, and still many more can be seen limply trying to keep aflight, ready to collapse at any moment. Even after the monarchs arrive at their winter retreats, the danger of storms is still a major factor on the survival. The danger is greater, particularly in Mexico, where temperatures, strong winds, and snow kill thousands. The exact migratory path is still being plotted today. Scientists are tagging the butterflies, and recording their locations during the months of the fall migration.