In the case of birds, there is mutual enmity between the poecilis, the crested lark, the woodpecker, and the chloreus, for they devour one another's eggs; so also between the crow and the owl; for, owing to the fact that the owl is dim sighted by day, the crow at midday preys upon the owl's eggs, and the owl at night upon the crow's, the one getting the better during the day, the other at night.