The hatching period is about the same for the larger birds, such
as the goose and the great bustard; for the middle-sized birds it
extends over about twenty days, as in the case of the kite and the
hawk. The kite in general lays two eggs, but occasionally rears
three young ones. The so-called aegolius at times rears four. It is
not true that, as some aver, the raven lays only two eggs; it lays a
larger number. It broods for about twenty days and then extrudes its
young. Other birds perform the same operation; at all events mother
birds that lay several eggs often extrude one of their young.

Birds of the eagle species are not alike in the treatment of their
young. The white-tailed eagle is cross, the black eagle is
affectionate in the feeding of the young; though, by the way, all
birds of prey, when their brood is rather forward in being able to
fly, beat and extrude them from the nest. The majority of birds
other than birds of prey, as has been said, also act in this manner,
and after feeding their young take no further care of them; but the
crow is an exception. This bird for a considerable time takes charge
of her young; for, even when her young can fly, she flies alongside of
them and supplies them with food.