There are pigeons inside them, which if you leave them 200 km away, they will return to their owner's house before evening.
A very interesting matter is- if you put a magnet on the pigeon's leg, it will not be able to return. Because it will lost direction. Generally pigeon use world geomagnetic direction. But the magnet you have put on, it will create obstacles to find out the geomagnetic direction.
By the way, nice video. I like birdds very much.