Animals need to move because of climate changes, food availability or mating seasons. Movements that occur seasonally or annually are called migrations. Many types of animals migrate, such as birds, fish and mammals.
Animal migration is found throughout the entire animal kingdom. Insects, such as butterflies and locusts, migrate. Crustaceans, such as the red crab, also migrate. Many mammals migrate, such as the zebra and the wildebeest. Nearly 2,000 species of birds migrate. Usually animals migrate to capitalize on an abundance of food that is found seasonally, such as Serengeti mammals, which undergo a yearly circular migration that follows the availability of foods for grazing and water.
Some animals migrate without eating, such as the southern white whale, which lives off its blubber for a year while it migrates from the Antarctic to warmer seas and back. The Antarctic waters provide its food, but the warmer waters allow it to breed.
The monarch butterfly is an insect that completes its migration over several generations because its lifespan is not long enough to complete the journey individually. It migrates each year from North America to Mexico, stopping to lay eggs and die, which allows the next generation to complete the journey.
The salmon is an unusual example of migratory fish because it migrates from freshwater to saltwater as it matures. It returns to freshwater streams to lay eggs after several years of adapting to salty ocean waters, completing its life cycle.