Hi,
Hopefully you only have one pair of birds per cage for breeding. You can’t have more than one breeding pair per cage, and you can’t have extra birds in a cage if you have a breeding pair. It’s OK to foster an egg to another pair if they will accept it, but when an egg isn’t formed right, it probably isn’t good. It also indicates a possible issue with the female. Budgies need to be at least 2 years old for breeding. You need to feed a nutritionally balanced diet such as pellets – not a loose seed mix. You should also include leafy greens, veggies, fruit and an egg food. This can be a dry commercial egg food or cook an egg with the shell washed, crushed and cooked with the egg and offer some of this daily. The pair should also have a cuttlebone. Poor nutrition or being too young are the main causes for deformed eggs. You also need to rest your birds – over breeding causes issues with the eggs. The nest box should be removed after every clutch, whether the eggs hatch or not. The pair should be rested for 6 months before returning the nest box.
Thank you for asking Lafeber,
Brenda