Hi Denise,
You didn’t mention the species, but since you say they hiss, I’m going to guess they are cockatiels, or cockatoos. Either way, the cause is because you put them together. Birds don’t have other birds as friends. They bond as mates and when other birds get too close, they are considered a threat or rival. When you have a pet bird, you are the bird’s companion. The bird looks to you for the attention he would get from a mate. When you let birds share a cage, they will almost always end up forming a bond and often no longer remain tame to people. Even same sex birds will form a strong bond and behave like a male and female pair. Your birds have bonded and have no desire to be tame anymore. They provide each other with companionship. They have established the cage as their territory and the dive bombing is their way of protecting their territory. There isn’t much you can do because they are exhibiting perfectly natural behavior. If their wings are kept trimmed, they are not as likely to try to dive bomb you and it will take away some of their confidence. You can try separating them, but cockatiels form a pretty close bond, so if the birds can still see or hear each other, they will most likely only end up stressed and depressed. If you can find another home for the older bird, then the young one might become tame again once the other bird is in a new home. But if the older bird was not tame, he needs another bird as a companion.
Thank you for asking Lafeber,
Brenda
