Had a friend who raised parrots; she finally got her Blue and Gold Macaws to lay eggs. This was a major accomplishment (took five years) and three eggs were laid.
She kept them under the parents and two hatched. Four days later when the third hadn't, she removed it, figuring it was infertile. She was going to toss it but was also busy cooking dinner so she laid the egg on the counter next to the warm range.
Came into the kitchen after dinner carrying the dishes and saw the egg rocking and starting to hatch.
Gail