Always supervise your cat and bird when they are together. Cats transmit a bacterium in their bites and scratches that is almost always deadly to a bird. In birds, this is called Pasteurella Septicemia, which usually means death within 24 hours if not treated. Even a tiny puncture from a cat's tooth can cause a massive bacterial infection that will quickly kill a bird.
This is not something that you can treat yourself. You must take the bird to the vet. The bird will more than likely receive an injection of ampicillin. Before taking your bird to the vet wash the wound with hydrogen peroxide and apply antibiotic ointment.
Source: Much research, from books, internet, and my own experiences with owning birds.
By one.of.a.kind from AL
How it can be treated
