Hi,
Unfortunately these birds should never have been put together when the male is this young. He is too young to have already had chicks, much less to be going on a second clutch! Cockatiels need to be at least 2 years old before you pair them up. The better breeders do not breed their birds until hey are 3 years old. While they may be physically able to breed, they still have some developing and maturing to go through. In the wild they would not be breeding at under a year old. I would separate, them, remove the nest box, and discard any eggs if she pays more. Do not put them back together until he is over 2. When they are together again, you must remove the nest box after each clutch, even if the eggs do not hatch. Rest the pair for at least 6 months between each clutch. It takes a lot out of the hen to form and lay each egg. Incubating eggs and caring for chicks is even more work. If you allow your birds to breed over and over without resting them, they will eventually die from breeding too often. In the wild, breeding season is once a year. In captivity, they do not get the signals to stop breeding, so you are responsible for making them rest. It’s not easy to breed birds responsibly, but you need to make that commitment if you want to breed birds and have them remain healthy.
Thank you for asking Lafeber,
Brenda