Migrations are regular movements from one place to another and back again - frequently to exactly the same location. Many animals migrate regularly, making long journeys over unfamiliar territory during the normal course of their lives, while other animals do not migrate at all. Most migrations are in search of food, for mates and breeding grounds, or in response to changes in habitat and climate triggered by the seasons. Some take place over vast distances and have clearly identifiable patterns, while others are much more difficult to understand. Some migrations happen daily, such as those made by sand tiger sharks that rise up from the depths at nighttime to feed, then vanish below during the day. Some movements may simply be nomadic, wandering without pattern.

One of the most famous examples of migration is the journey of the Pacific Salmon which is born in streams on the northwest coast of the United States. Once the salmon is old enough, it swims out to the ocean where it lives its adult life until it is ready to reproduce. Then, it swims vast distances up stream to its original birth place to breed. Another example is the migration of Canada geese. Imagine Canada geese migrating south from Canada through the United States. You can almost see them traveling down the coastline as winter sets in, temperatures drop off and crops begin to die. The geese move southward until they have reached a point where food is abundant and the temperatures are comfortable again.