MIGRATION: HOW DO ANIMALS KNOW WHEN AND WHERE TO GO?
Migration is the mass movement of animals from one region to another. Generally, migration is induced by three reasons:
- The necessity to find food
- Find favourable conditions for breeding
- Preservation of species
Again, migration is of two types:
- Gametic: Migration brought about by the need of a different environment for breeding
- Trophic or Alimental: Migration induced by the search for food
Migration can be individual or collective, seasonal or irregular, and temporary or permanent. The more important migrations that have been known for a long time are those of birds and fish and are mostly connected with seasonal and breeding cycles.
HOW DO THEY KNOW IT’S TIME?
Animals are capable of easily sensing the changing seasons. They note shorter day length in fall at many latitudes and immediately become aware of the dwindling food supply. Sometimes, migration is also triggered when too many animals congregate in the same area for food or for breeding.
HOW DO THEY KNOW THE ROUTE?
Well, there are several possible answers. Many animal and bird species genetically inherit the knowledge of the route to migrate from their parents. Some species, especially birds, use the sun and stars to orient themselves as they fly. A wide range of species depend on the Earth’s magnetic field to navigate themselves as they migrate.
For example, sea turtle hatchlings emerge on moonlit beaches and head for the sea where they join the regular migration route. They use geomagnetic field for their orientation. In birds, a recently identified molecule in the brain may be the chemical connection for detecting geomagnetic energy for navigation.
Birds generally migrate in groups which are very large. However, some birds, such as cuckoos and other birds of prey, travel alone or in groups that are very small.
The wildebeest of the Serengeti National Park migrate from the grass plains to the northwest, where they cross the Grumeti River and travel into Kenya’s Masai Mara. From there, they cross another crocodile-infested river to reach the Mara grasslands by late autumn. They return to their breeding grounds in spring, thus completing the circle that they travel.