Have you ever looked up in the sky to see a “V" soaring above your head? No, not a flying alphabet — a flock of birds in formation!

Why do birds seem to prefer the letter V? Spread your wings and let's join the flock to find out the answer.

While not all birds migrate, more than half do. These birds are called “migratory birds." The reasons birds migrate vary but typically involve availability of food or weather.

In the northern hemisphere, many birds migrate south during the winter months when the weather becomes too cold for them to survive in their northern habitats. Once spring arrives, the birds return to their homes.

Equally as varied as the reasons for migrating are the ways in which different migratory birds make their journey. Some birds migrate alone, others travel in pairs and many move in large flocks.

Song birds often migrate in swarms, while larger birds, such as geese, migrate in formation. Many times this migration takes the form of the letter V.

The reason birds prefer to fly in a V shape has puzzled researchers for many years. There are two general theories to explain the V-shaped phenomenon.

The most accepted theory is that the formation of a flock influences aerodynamics, making it easier for the birds to fly. As the birds flap their wings, the air flowing off their wing tips gives birds in the back of the V an extra lift. This reduces the amount of energy the birds need to fly.

Over the course of the migration, birds take turns leading the front of the V, the most difficult position. When a bird has tired of leading, it falls to the rear of the V, where there is the least wind resistance.

Rotating through various positions in the V maximizes the use of each bird's energy, allowing flocks to fly for long periods of time without having to stop.

The second theory suggests flying in a V offers each bird an unimpaired line of sight as the flock flies through the air. This makes it easier for the birds to keep track of each member of the flock. Groups of fighter pilots often arrange their planes in V formation for the same reason.

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