Why can migratory birds fly thousands of kilometers without eating?

This is due to the special energy storage mechanism in their bodies and the way they choose their movement method like a marathon runner.

Some birds, including the Arctic tern, can migrate more than 30,000km per year.

 Arctic terns are monogamous birds and after the breeding season they head south to Antarctica. (Photo: Shutterstock).

Botanists have nicknamed these birds 'The Champions of Migration.' Arctic terns weigh just over 100 grams on average and migrate from pole to pole every year.

Swallows live in pairs, breed in the summer in the Northern Hemisphere and when winter comes to the Arctic, they will migrate south to the Antarctic in flocks.

To put it simply, these birds literally follow the sunlight, aiming to avoid the cold of the Antarctic winter, these migrations include a non-stop flight of more than 8,000 km across the Indian Ocean.

Where do birds get energy for their journey?

Most animals primarily break down different types of carbohydrates and glucose to provide their energy.

However, studies reveal that birds will convert fats and lipids into fatty acids as their energy source.

Before migration, birds will switch to a diet of hyperphagia and high-fat foods. In fact, magpies have been known to double their body weight before each migration.

But eating a lot alone cannot explain their rapid fattening. These birds also do a great job of absorbing nutrients from their food.

The fat they store makes up 50 - 60% of their body mass. The fat is stored in fat cells, located just under their skin.

Avian fat cells can store up to 95% of their volume as fatty acids. They can also store fat in extramuscular tissues and in the liver (similar to glycogen storage).

In addition, birds can also store fatty acids in the liver , which are then converted into triglycerides. These triglycerides are transported out of the liver in the form of VLDL (very low density lipoprotein) which consists of cholesterol (10%), triglycerides (70%), protein (10%), and other fats (10%).

 Albatross birds glide and fly above the surface of water to save energy. (Photo: Shutterstock).

They acidify fats to provide energy for the wing muscles that help birds fly, which are then converted back into fatty acids. The enzyme lipase, produced by the endothelial cells of the flight muscles, mediates this reaction.

How do birds use this energy?

Long-distance migratory birds are like marathon runners, choosing endurance over speed. In fact, this helps birds minimize energy use wherever possible.

Many birds take off by rapidly flapping their wings, which is the most energy-consuming part of their migration. Takeoff is an anaerobic activity and birds use stored glycogen (a type of carbohydrate) to initiate flight.

However, during long flights, birds do not flap their wings much .