5. The little owl feeds during the night, and is rarely visible by day. It lives in rocks and caverns, for its food is of two kinds; and in disposition it is diligent and ingenious. There is a small bird called certhius, which is bold in disposition, and lives on trees and eats the thrips (timber worm). In disposition it is diligent in search of food, and its voice is brilliant. The disposition and hue of the acanthis is bad, but it has a shrill voice. CHAPTER XVII. 1. Among the herons, as it was before observed, the black heron copulates with difficulty, but it is an ingenious bird. It carries its food about, and is skilful in procuring it. It works during the day. Its colour, however, is bad, and its stomach always fluid. Of the other two (for there are three kinds of them), the white heron is beautifully coloured and copulates without pain, and builds its nest and attends its young carefully in trees. It inhabits marshes and lakes, plains and meadows. The bittern, which is called ocnus (the idle), is said in fables to have been originally a slave. Its name indicates its very idle disposition. 2. The herons live in this manner. The bird called poyx is peculiar, for it is its disposition to eat the eyes of other creatures, and is therefore the enemy of the harpa, which lives upon the same food. CHAPTER XVIII. 1. There are two kinds of cottyphus. The one is black, and is found everywhere; the other is white. In size they are alike, and their voice is very similar. The white one is found in Cyllene, in Arcadia, and nowhere else. The læus is similar to the black cottyphus, but is rather smaller. It makes its house upon rocks and tiles. It has not a dark beak, like the blackbird. 2. Of thrushes there are three forms. The one is called misselthrush, for it lives upon nothing but miseltoe and resin. It is as large as the citta; the other is called fieldfare. The voice of this bird is shrill; its size is that of the blackbird. There is another kind, which some persons call illas, which is smaller than the others and less variegated. 3. There is a certain bird living on rocks, which is called blue thrush. This bird generally inhabits Scyrus. It lives upon the wing. It is less than the blackbird, but larger than the finch. Its feet are black, and it climbs up upon rocks. It is entirely blue. It has a smooth, long beak, but its legs are short, and resemble those of the woodpecker. CHAPTER XIX.