If the pairs agree, they must be left entirely to themselves, without endeavouring to use art to help nature, as many do. It is usual to take away the first egg and substitute an ivory one, which is repeated with the others to the last, preserving them in the mean time in a box filled with fine dry sand; they are afterwards restored all together to the nest to be hatched[55]. The females lay three or four times a year, from April till September; there are some even so prolific that moulting does not stop them. The eggs, of a sea-green colour, are at one end more or less spotted or marked with maroon or violet. The period of incubation is thirteen days. If, owing to the weakness of the male or female, it is suspected that some of the eggs are barren, they should on the eighth day be examined by holding them lightly between the fingers in the sunshine or before a candle; the good ones will be already filled with blood-vessels, while the bad will continue clear, or even be already addled: these must be thrown away. It is rare for the male to sit in his turn during some hours of the day, the female seldom allowing it, for as soon as she has eaten she flies back to the nest. If the male gives up his place readily, so much the better; if not, she drives him away by force and by pecking him. She appears to know his want of skill in this employment. The near discharge of a gun, a door slammed with violence, and other similar noises, will often kill the young in the shell; but their death happens generally through the fault of a bad sitter. As soon as the young are hatched, a small jar is placed beside the usual feeding trough, which contains a quarter of a hard egg minced very fine, white and yellow together, with a bit of white bread steeped in water, and afterwards well pressed; another jar should contain rape seed which has been boiled, and then washed in fresh water, to remove all its acrimony. Some persons, instead of white bread, use biscuit, but this is unnecessary; what, on the contrary, is very essential, is to take care that this food does not turn sour, for it would then infallibly destroy the young nurslings. This food I find by experience to be the best. Now is the time when the male assumes his important duties of nursing-father. These he fulfils indeed almost alone, in order to give his mate time to rest before a new sitting. When it is necessary to bring up the young by hand, a bit of white bread, or some biscuit, should be pounded very fine, and this powder should be mixed with well-bruised rape-seed. This composition serves, with a little yolk of egg and water, to make a paste, which is given to the young birds on a quill cut like a spoon; each nursling requires for a meal four beakfuls, well piled upon the quill, and these meals must not be fewer than ten or twelve a day.