If there's no parents around taking care of it another thing you can do is call a wildlife rehab center. If you don't know yet; it's illegal to take care of it; only licensed Wildlife Rehabilitators are certified to if the situation is really bad to the point of the baby being an orphan. I would suggest also finding a way to keep the cat away. If you have a dog maybe the dog can chase it away. Cats don't like vinegar, maybe you can set up a way to spray the cat if it tries to come near the nest. It won't take much for the cat. It'll get to the point where it will run off just by the sound of the thing about to spray it.

Parents will hear it no matter where it is, if anywhere near the nest, and care for it. They will stay away if they see you near so watch from afar with binoculars.

Hi guys early this morning a cat attacked a black bird in its nets didn't see the bird all day until now he was on the floor all I did was out him back in his nest. Is there anything else I can do?