Birds winging their way to the south in mostly V-shaped flocks is perhaps the most common sight of large-scale migration that we can experience. This happens annually when the birds move from their breeding (summer) homes to their non-breeding (winter) grounds. But have you ever wondered why they migrate in the winter and how they navigate? Let’s find out!
Some of the major reasons why birds migrate to areas of abundance are linked to diminishing resources at their breeding grounds and also looking for food and nesting locations. It has been found that birds that nest in the Northern Hemisphere tend to migrate northward in the spring to take advantage of the flourishing insect populations, budding plants and an abundance of nesting locations.
As winter approaches and the availability of insects and other food drops, the birds tend to move south again. Escaping the cold has always been a motivating factor for them to move, however, several species, including hummingbirds, can withstand freezing temperatures as long as an adequate supply of food is available.
The term migration typically describes periodic, large-scale movements of populations of animals. One way to look at migration is also to consider the distances travelled. Permanent residents usually do not have the need to migrate. They are able to find adequate supplies of food all over the year. Short-distance migrants typically make relatively small movements, from higher to lower elevations on a mountainside. Medium-distance migrants cover distances that might span a few hundred miles. Long-distance migrants are found to move from breeding ranges in the United States and Canada to wintering grounds in Central and South America. Despite the laborious journeys involved, long-distance migration is a feature of about 350 species of North American birds. The Ranganathittu Wildlife Sanctuary near Mysore is famous for being a nesting and breeding ground for migratory birds from all across the Earth. Some of the exotic bird species that fly to the sanctuary are said to be of Siberian, Australian and North American origins.
Factors or mechanisms behind a bird’s migratory behaviour can vary vastly and are not always completely understood. Migration can be triggered by a combination of changes in day length, lower temperatures, changes in food supplies, and genetic predisposition. For centuries, people who have kept birds inside cages have noticed that the migratory species go through what could be called a period of restlessness each spring and fall, repeatedly fluttering toward one side of their cage. German behavioural scientists even gave this a specific name: zugunruhe, meaning migratory restlessness. Different species of birds and even various segments of the population within the same species may follow different migratory patterns.
What is more important to ask is how do birds know when, where and for how long to travel and maintain their sense of direction as they fly? As per several studies and a widely believed theory, the shortening length of the day acts as a major ecological trigger to prepare for migration with the sun acting as a natural guide to navigating around the Earth. Experiments have found that with the help of their internal clock, birds can compensate for the time of day and latitude and figure out which direction to fly even amid a change in seasons.
Often a few nocturnal birds prefer to travel at night as winds are relatively stable, which saves energy. Also with fewer predators to worry about and also star patterns guiding their navigation, they can travel without too many obstacles towards their destination. Studies and research have also suggested that natural elements such as rivers, mountains and forests and now, roads often serve as significant landmarks to find their way along a migration route. Also, the various smells around them provide olfactory cues to discover and follow migration routes in several instances. A new study suggests that some birds could even have an ‘internal magnetic compass’ that helps them navigate long distances.
Have you seen birds migrating in a flock during winters and wondered why? Tell us in the comments below.
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