Why do Animals Migrate?
MIgration is the movement of a group of animals, birds or insects to a new location. The primary reasons animals migrate are to avoid unfavorable weather conditions, to breed, and to find food. Animals living in a region that has severely cold winters may migrate to a location with a milder climate during the winter months and return in the spring. Some animals may have specific breeding grounds that they return to when they are ready to bear young, such as when salmon return to the stream where they were born to breed. Sea turtles return to the same beaches year after year to lay eggs. When food or water is in short supply, animals may need to travel long distances in search of nourishment. Animals may also migrate if the population becomes too large for the habitat to sustain it, causing a group to split off and leave in search of a new place to live.
Different Types of Migration
There are several different types of migration, which vary by distance, direction and timing.
- Seasonal migration- migrating when the seasons change is the most common type of migration, and many of the other types of migration are also seasonal.
- Altitudinal migration- migrating to higher elevations in warmer weather, and back down to lower elevations when winter sets in and the temperature drops.
- Latitudinal migration- migrating from north to south and back again, such as geese flying south in the fall and north in the spring.
- Nomadic migration- migrating in search of food, such as grazing animals.
- Removal migration- when a population migrates and does not return. This can happen if the habitat is destroyed and can no longer provide food, water or shelter, or if the population gets too large and becomes crowded, causing a group to leave and settle elsewhere.
- Reproductive migration- migrating to a different location to bear young. This usually occurs to keep the young safe from predators, or when a different type of habitat is needed in which to give birth. For example, frogs may spend most of their time on land, but they need to lay their eggs in water, whereas sea turtles spend their lives in the open ocean but need to lay their eggs in the sand.
- Partial migration- when only part of the population migrates and the rest of the population remains behind.
- Complete migration- when the entire population leaves.
- Irruptive migration- an unpredictable pattern when some members of the population migrate at various times and distances.
Some examples of species that migrate include Monarch butterflies, Arctic terns, salmon, swallows, sandhill cranes, canada geese, gray whales, and wildebeests.
How do Migrating Animals Find their Way?
Migrating animals navigate by using a variety of different sources of information, as well as by instinct, or genetically inherited knowledge. Some animals use the position of the moon, sun and stars to find their way. Others navigate by sensing the Earth's magnetic field. Geographical landmarks such as mountains and rivers, or currents in the case of migrating fish or sea animals, can serve as cues. Many animals use their sense of smell to guide them. Some species release chemicals called pheromones that other members of their group can later follow. Animals that migrate long distances likely use more than one method in combination in order to find their way.
Credit: Joe Mabel
"Migration." New Hampshire Public Television Nature Works
"Migration Basics." US Department of Interior, National Park Service