Seasonal changes can kill off or reduce an animal's food supply. When animals can't find food in their environment, they will move to where the food is.
Some animals, especially birds and butterflies, travel incredible distances when they migrate.
Top to Bottom and Back
The robin-sized Arctic Tern travels 10,000 miles from pole to pole and back again every year. Each fall the Arctic Tern heads east, flies across the Atlantic Ocean, and then continues south down the coast of Europe and Africa, flying until it reaches the Antarctic Ocean. In the spring, it flies north up the coasts of South and North America until it reaches the Arctic Ocean.
Winter in Mexico
The monarch butterfly is a long distance migrator! It migrates to its breeding grounds in the spring and to its winter home in the fall. In North America, there are two large population groups that follow separate migration paths. Eastern populations of monarch butterflies winter in Texas, Florida, and Mexico. Western populations of monarchs winter along the coast of California. Monarch butterflies migrating from Canada to Mexico travel over 6,000 miles!
Some animals travel relatively short distances to find food or more favorable living or breeding conditions.
Down from the Mountain
The bighorn sheep changes its home range seasonally. In warm months, it grazes on mountain slopes; in colder months, it moves down to valleys where it is easier to find food.
To Move or Not to Move?
Some animals, like the American robin, may migrate or they may stay where they are, depending on where they live and how plentiful food is in the winter.
Migration can be hazardous for animals. They can face many barriers on the way to their destination.
Migration isn't a vacation for animals; it is a critical behavioral adaptation necessary for survival.