How do you tell if a bird is going to lay an egg?

Usually the cockatiel is very protective over her eggs. I suggest that if she is being a good mother and sitting on them properly, to let her hatch the eggs. this is so that the babys will bond with their real mother and if you cage them together when their older they will not squabble. I suggest you research on how to care for the mother though since she needs a different set of nutrients while egg laying.