Definition and Concept of Migration of Animals and Birds

Studying Biology Topics provides a deeper understanding of life and its processes.

What is Migration? And Why do some birds and animals migrate?

The process in which a bird (or other animal) moves from one place to another in one season and returns again in a different season is called migration. Migration of birds (or other animals) is an adaptation to escape the harsh and cold conditions of their normal habitat in winter so as to survive. This point will become more clear from the following discussion. The birds must remain warm to survive. When the winter sets in cold regions of the earth, the climate becomes extremely cold. The birds which normally live in these regions migrate (fly off) to far flung warmer places to escape the extremely cold winter climate and survive (see Figure). And when the winter season is over, these birds fly back to their original habitats in the cold regions.

The birds which migrate from very cold regions to warmer regions in winter and go back after the winter is over, are called migratory birds. India is one of the destinations of many of the migratory birds coming from the very cold regions of the earth. One of the most common migratory bird which comes to India every year for a few months is the Siberian crane (see Figure).

The normal habitat of Siberian crane is Siberia (which is a very cold place). When winter sets in Siberia, and it gets extremely cold, the Siberian crane flies thousands of kilometres and comes to warmer places in India such as Bharatpur in Rajasthan, Sultanpur in Haryana, some wet lands of North-East, and some other parts of India. The Siberian cranes stay in the warmer places in India for a few months. The Siberian cranes fly back to Siberia when the winter ends there and climate becomes favourable. Thus, the adaptation of “migration” in Siberian crane is to escape the extremely cold winter conditions in Siberia and survive by moving to warmer regions.

Some migratory birds travel as much as 15,000 kilometres to escape the extremely cold climatic conditions at home to reach warmer places where there is plenty of food. The migratory birds usually fly high up in the sky where the wind flow is helpful and low temperature aids in dispersing the heat generated by the constant working of their flight muscles in flapping the wings. An important question now arises : How do migratory birds travel to the same place year after year ? An exact answer to this question is still not available. Some of the probable reasons for how the migratory birds travel to the same place year after year are as follows :

1. It seems that the migratory birds have a built-in sense of direction which tells them in which direction to fly to reach the same place.
2. Some migratory birds probably use land-marks to guide them to reach the same place.
3. Many migratory birds may be guided by the position of the sun during the day and by the position of stars at night to reach the same place.
4. There is also some evidence that the migratory birds may be using the magnetic field of earth to find the direction so as to reach the same place.

It is not only the birds which migrate. Even mammals, many types of fish, and insects (such as butterflies) are known to migrate seasonally in search of favourable climatic conditions and food. For example, reindeer is a mammal which migrates. Reindeers live in herds in the cold, northern regions of North America where they feed on grass and shrubs in the summer. During winter, when the snowfall occurs, all the grass and shrubs get buried in snow and reindeers do not get any food. Due to this, reindeers migrate to the warmer regions in the south where they get sufficient food. They return to the original habitat in the north after a few months when the snow starts melting.