Why did people use pigeons to send messages in ancient times?

A carrier pigeon can bring the letter home even if you take it to a strange place thousands of miles away. Wrap a few turns of coils around the top of the pigeon's head and neck, and power it with a small battery, and the pigeon's head will generate a uniform additional magnetic field. When the current flows in a clockwise direction, the pigeons released on a cloudy day will fly in all directions. This shows that pigeons rely on geomagnetic navigation. So how do pigeons navigate by geomagnetism?

Some people regard pigeons as semiconductors with a resistance of 1000 ohms. When they flap their wings in the earth's magnetic field, their wings cut the magnetic lines of force, thus generating an induced electromotive force (i.e., induced voltage) between the two wings. Pigeons fly in different directions, and because they cut the magnetic lines of force in different directions, the magnitude of the electromotive force generated can be used to identify the direction. However, experiments have shown that when they are released on sunny days, the additional magnetic field does not affect their flight, which shows that geomagnetism is not their only compass. It turns out that pigeons can detect polarized light. On sunny days, they can choose the direction of flight according to the position of the sun, and their internal biological clock can make corresponding corrections to the movement of the sun. It must be pointed out that when the current flows counterclockwise, they can fly home regardless of whether it is sunny or cloudy.

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