Hi,
If they are sharing a cage, then yes, you may want to go ahead and separate them. Many owners don’t understand their bird’s natural instincts and inadvertently create a confusing situation. Basically you have caused a love triangle. Adult cockatiels choose a mate that they bond with, and once this happens, they don’t have physical interaction with flock mates for the most part. Other flock members are considered rivals. Both of your bird are bonded with you, but they also like each other. However, now they are old enough to breed and are probably hormonal right now. The male wants to breed and he gets jealous of the female’s attention to you. And it sounds like she isn’t ready to breed, so he is getting frustrated with her refusal to mate with him. The problem is he will get more aggressive with her and could end up hurting her badly if these attacks continue. You have to decide whether you want to have them both as pets, or let them remain together and stop handling them. The dynamics have changed now that they are sexually mature so it’s not going to keep working out for them to remain together if you want them to remain tame pets. I personally would keep them in separate cages, side by side, so they can have some interaction while being pets with you. If you choose to let them be breeders, you have to cut off contact with them and let them have their privacy. Even giving attention to one of them by just talking can trigger aggression from one or the other. There is no guarantee they will breed successfully, so you could end up with two wild cockatiels and no pet.
Thank you for asking Lafeber,
Brenda