I understand that the male hummingbird will allow only his off-spring and members of his harem to feed from a feeder that he has claimed. Unless you have a lot of hummers, or a lot of feeders, this "guard bird" usually manages to scare off most others. I have tried to place feeders around the yard where he can't see them all from the same perch as this gives some others a chance to feed. We love watching them.