The movement of organisms in large numbers from one place to another place is termed as migration. There are many reasons for migration. The term migration is mainly used to define regular and periodic movements of the population away from or back to their place of origin. These migrations are of various types. Some may span for an entire lifetime and it happens to be a single migration of an individual. This is in the case for the Pacific salmon. On another hand, an individual may migrate frequently, like many of the migratory birds and other mammals.
Animals usually travel in groups along well-known routes or may travel in separate gathering for breeding.
Human migration is defined as the relatively permanent movement of people across territorial boundaries. It is also known as immigration and emigration when they cross the international boundaries.
Factors Affecting Migration
Many factors play their role in the initiation of migration. External factors like climate, natural disasters, drought, shelter, food shortage, etc may cause animals to migrate to seek better conditions.
For example – Consider a species of the deer that live in a certain park. They would migrate to warmer places during winter if the park they reside is harsh for them to survive. But, if they are living near a place, where they can graze throughout the year, then there is no need for their migration.
In birds, the migratory instinct is closely linked to the cycle of enlargement of the reproductive system in spring. There are several species of birds that migrate to long ranges, flying to the north in the springtime to breed in the warm conditions and migrate back to their origin.
Bird migration is the natural seasonal movement, often south and north along a flyway, in between the breeding grounds and wintering grounds. Migratory birds fly several kilometers in search of the best environmental specifications and habitats for food, breeding and raising their young ones. Migration is motivated primarily by the unavailability of food and nesting locations. It occurs mainly in the northern hemisphere, where birds travel in search of warmer places such as the Caribbean Sea or the Mediterranean Sea.
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