Birds migrate from an area that has decreasing or low resources to an area that has abundant or high resources. The two main resources that make birds migrate are nesting locations and food supply. During spring, the birds that nest in the Northern Hemisphere regions migrate northward so that they can take advantage of the abundance of nesting locations, thriving insect populations, and budding plants. As winter nears, the availability of insects and other food resources tend to drop thus resulting in the migration of the birds to the south. Even though avoiding the cold is a motivating reason for birds to migrate, the majority of species can withstand the freezing temperatures, provided there are sufficient supply of food.
What Provokes the Migration of Birds?
Various mechanisms initiate the migratory behavior of birds. However, they vary from one species to another and are not always fully understood. The migration of birds can be triggered by a sequence of changes from genetic predisposition, changes in the supply of food, lower temperatures to changes in day length. For many years now, the people who have kept birds in cages have realized that species of migratory birds tend to go through a period of restlessness every fall and spring. The birds keep repeatedly fluttering to one side of the cage which is a behavior known as ‘zunguruhe’, a name given by German scientist meaning migratory restlessness. The migratory patterns of birds are not all the same because different bird species or parts of the population within a particular species may decide to follow different migratory patterns.
Types of Migrations
Migration is defined as the periodic movement of large populations of animal, and one way of looking at migration is to consider the distance the animal populations travel. Birds that are permanent residents do not have to migrate since they can find sufficient food supplies throughout the year. Short-distance migratory birds move short distances such as from higher elevations to lower elevations of a mountainous region. Medium-distance migratory birds cover distances that go as far as one state to several other states. Long-distance migratory birds move from breeding grounds found in the US and Canada to wintering grounds found in South and Central America. Even though the journey being arduous there, are about 350 species of long-distance migratory birds from North America.
How Do Birds Navigate?
During their annual movements, migratory birds can cover thousands of miles, but they often travel the same route every year with little to no deviation each time. Birds migrating for the first time make the journey on their own, and interestingly, these first-time migrators manage to find their winter homes without even having seen them before and are also able to return the following spring to where they were born. The ability of migratory birds to successfully navigate is not fully understood, but birds tend to combine various types of senses when they are navigating. Birds are also able to get information on direction from the stars, the sun, and through sensing the magnetic field of the earth.
Factors Affecting Migration
In recent years, the long-distance migration of birds has been facing some threats such as the establishment of skyscrapers and communication towers. A large number of birds get attracted to the tall buildings and lights thus resulting in the death of millions by collisions every year. Other factors include unpredictable weather changes and increased exposure to predators.