There is no universally accepted reason or definition for migration, but it is widely believed that animals move from one place to another to find more comfortable weather, to seek more food and to reproduce. Many animals travel far distances in groups in order to survive and thrive.
Animal migration is often connected with the burgeoning or lack of food supply. One of the most researched animal migrations is the seasonal migrations of birds. About 650 species can be found in North America, and they have been observed to migrate north in the middle of spring to take advantage of abundant food resources and plenty of nesting locations. In the fall, the same bird species usually travel south as the food supply diminishes. Even marine animals, such as turtles, dolphins and manatees, travel great distances to find temperate waters and search for food.
Aside from seeking warmer climates and eating, many animals migrate in order to reproduce. Scientists believe that the animals are following their inherited instincts when they travel to reproduce. Every year in the early spring, emperor penguins travel on foot over miles of frozen ground to reach a designated breeding ground, which is in the same area where they breed every year. The Pacific trout makes the migration of a lifetime by travelling thousands of miles to mature in the open ocean, then going back to the rivers in which they were born in order to spawn.