I visited this birdhouse two days ago. I feel that, a four years BH, must have swiftlets staying and flying everywhere. But it does not. It is time to change, change the outdoor sound clip, add some ammonia, then keep the floor dry for a few days. Replace the spoilt tweeters, tune-up the indoor sound a little bit. Then spray the bird's nest aroma once a week for a month. That's all.
