Eerie bird ringings

There's a flock of pigeons (I believe) tended by a man near our Sanur home. We always know when he lets them out and they're up and above swirling around in eerie tinkling sound that rises and falls depending on their proximity - for they have rings around a foot. I hear this sound at times before we lived here and wondered what it was. I thought it was maybe some electrical transformer.  Then one day room cleaner Ketut at our last residence explained it. I can't find anything on the Internet to explain it. Must ask around. To some it's a slightly disturbing sound - like a 1950s sci-fi movie flying saucer sound.