3. Many birds at particular seasons change both their colour and their voice, as the blackbird, which becomes russet instead of black, and assumes another voice, for it sings in the summer time, but in winter it chatters and screams violently. The thrush also alters its colour, for in winter it is grey, and in summer is variegated on the neck; but its voice does not alter. The nightingale sings unceasingly for fifteen days and nights, when the mountains become thick with leaves. As the summer advances it utters another voice, not quick and varied, but simple; its colour also is altered, and in Italy it is called by another name at this season of the year. It only shews itself for a short time, for it lies concealed. 3. The erithacus, and the bird called phœnicurus, are changed one into the other. The erithacus is a winter bird, the phœnicurus a summer bird; they differ in nothing but the colour. The sycalis and melancoryphus are the same, for these also are interchanged. The sycalis is found in the autumn, and the melancoryphus immediately after the end of the autumn. They also differ from each other in nothing but their colour and voice, and to prove that it is the same bird, each kind has been seen immediately after the change took place; and when the change was not quite complete, there was nothing characteristic of either form. Nor is it absurd to suppose that these birds change their voices or their colours, for the dove utters no sound in the winter, unless it may be on a fine day in a severe winter, when it will utter its sound to the astonishment of those that know its habits; and as soon as spring commences, it begins to utter its voice: and, on the whole, birds make the greatest number and variety of voices at the season of coition. 4. The cuckoo also changes its colour, and its voice is not distinct, when it is about to leave us. It goes away about the time when the dog-star rises, it having been with us from the commencement of spring to that time. The œnanthe, as it is called, disappears when Sirius rises, and comes again when it sets, for sometimes it retreats before the cold, and sometimes before the heat. The hoopoe also changes its colour and its forms, as Æschylus writes. "He had variegated this hoopoe, the witness of its own evils, and has displayed the bold bird that dwells in the rock in all armour. In the early spring it shakes the feathers of the white hawk; for it has two forms, that of the young bird and of itself, from one origin. And when the young corn of the harvest begins to grow, it is clothed in spotted feathers; and it always hates this place of Pallene, and inhabits deserted forests and mountains."