This happens with some male cockatiels in captivity. Often the reason isn’t clear. Sometimes the male keeps the hen from going into the box. In this case, it sounds like he may want to mate again rather than care for his eggs and his mate. If these birds are under 2 years old, then they are too young to be set up for breeding. They are capable of course, but they still have some physical and mental development to go through. A young male is often more interested in the mating than settling down to care for eggs and chicks. If these birds are 2 or older, then possibly this male will not be a good breeder. Both the male and female share incubation duties. One sits during the day and the other sits at night. It is too much for the female to do by herself. She is either going to only sit on the eggs during the day or night, or her health is going to suffer from her not eating enough and sitting on the eggs all of the time. Was the male taking his shift sitting on the eggs before he started this other behavior? If not, then this is another sign that he may not be cut out to be a breeder. When a male gets like this, you can rotate the parents, leaving one bird in the cage during the day and the other at night. But if he isn’t sitting on the eggs at all, then this clutch may not work out. If this is a first clutch, it is normal for them to fail because both parents are still learning. All you can do is keep the female safe and hope he settles down. If he won’t take his shift and sit on the eggs, then you can let the female try, but again, it’s not the best idea for her to do this alone and you have to monitor her to make sure she is eating. The pair needs to be rested whether or not these eggs hatch. Once the eggs fail to hatch, or once the chicks leave the box, you should take it down and rest the pair for about 6 months. You should only allow two clutches per year. Cockatiels will breed year round in captivity because they do not receive the environmental signals that end breeding season. So you have to step in and make the pair rest between each clutch. In the wild they only have one clutch per year.
Thank you for asking Lafeber,