Some hens will sit tight after laying the first egg. In a large clutch this can cause a vast age difference between the oldest and youngest chicks. The incubation period for most Parrotlets is 18 to 19 days with the Mexican taking 21 to 22 days. The hen will spend all of her time in the nestbox coming out only to defecate. The male will feed her either in the nest box or at the entrance hole. Sometimes a male will even help incubate the eggs, although it is uncommon. If several eggs have been laid before the hen begins incubating, it is possible for several chicks to be hatched on the same day.