The Screamer is a very heavy bird, and rises from the ground laboriously, the wings, as in the case of the Swan, making a loud noise. Nevertheless, it loves soaring, and will rise in an immense spiral until it wholly disappears from sight in the zenith, even in the brightest weather; and considering its great bulk and dark colour, the height it ultimately attains must be very great. On sunny windless days, especially in winter and spring, they often spend hours at a time in these sublime aerial exercises, slowly floating round and round in vast circles, and singing at intervals. How so heavy and comparatively short-winged a bird can sustain itself for such long periods in the thin upper air to which it rises has not yet been explained. The voice is very powerful. When disturbed, or when the nest is approached, both birds utter at intervals a loud alarm-cry, resembling in sound the anger-cry of the Peacock, but twice as loud. At other times its voice is exercised in a kind of singing performance, in which male and female join, and which produces the effect of harmony. The male begins, the female takes up her part, and then with marvellous strength and spirit they pour forth a torrent of strangely-contrasted sounds--some bassoon-like in their depth and volume, some like drumbeats, and others, long, clear, and ringing. It is the loudest animal-sound of the pampas, and its jubilant martial character strongly affects the mind in that silent melancholy wilderness. The Screamers sing all the year round, at all hours, both on the ground and when soaring; when in pairs the two birds invariably sing together, and when in flocks they sing in concert. At night they are heard about nine o'clock in the evening, and again just before dawn. It is not unusual, however, to hear them singing at other hours. The nest is a large fabric placed among the low rushes and water-lilies, and is sometimes seen floating on the water, away from its moorings. The eggs are five, pointed at one end, pure white, and in size like the eggs of the domestic goose. The young are clothed in yellow down like goslings, and follow the parents about from the date of hatching. Fam. XL. ANATIDÆ, or DUCKS. The Anatidæ or Waterfowl are a well-known family of universal distribution over the earth's surface. As shown in an article published in the Zoological Society's 'Proceedings' for 1876[8], upwards of 60 species of this group of birds are found in the Neotropical Region, and of these about 22 occur in the Argentine Republic. Amongst the Argentine species are some of the finest and most ornamental of the whole family, such as the Black-necked Swan, the Ashy-headed Goose, and the Chiloe Wigeon--all well known from their introduction and acclimatization in Europe. [8] "A Revision of the Neotropical Anatidæ," by P. L. Sclater and O. Salvin, P. Z. S. 1876, p. 358.