The screamers are generally regarded as primitive members of the group with which they are now associated; but in many respects they are quite peculiar. Not the least interesting of their habits is the great predilection they observe for soaring in the air at immense altitudes, uttering the while the curious cry to which they owe their name. Several birds often do this at once. Yet stranger is the fact that they not seldom gather together in vast flocks to sing in concert. Mr. Hudson, for instance, states that the species known as the Crested Screamer on one occasion surprised him by "an awful and overpowering burst of 'melody,'" which saluted him from half a million of voices at an out-of-the-way spot in the pampas one evening at nine o'clock; and, again, once at noon he heard flock after flock take up their song round the entire circuit of a certain lake, each flock waiting its turn to sing, and only stopping when the duty had been performed.
Like the gannet, these birds are richly supplied with air-cells between the body and the skin, and between many of the muscles; so highly are these cells developed, that it is said a crackling sound is emitted when pressure is applied to the skin.
Photo by J. W. McLellan] [Highbury.
POCHARD.
This is one of the diving-ducks.
The wings of these birds are armed each with a pair of powerful and sharp spurs, recalling those of certain of the Plover Tribe (page [421]), though in the latter only one spur is present on each wing.
The division of the remainder of this group into Ducks, Geese, and Swans is generally recognised, but no hard-and-fast line can yet be drawn between the several sections. We must regard them as representing adaptations to peculiar modes of life, which appear to be most marked in the duck-like forms. These may be divided into Fresh-water Ducks, Salt-water Ducks, Spiny-tailed Ducks, and Mergansers.
Of the Fresh-water Ducks, the most familiar is the Wild-duck, or Mallard. This is a resident British bird, and also the parent of the domesticated stock, which frequently closely resembles the wild form. In this species, as with the majority of the fresh-water ducks, the males wear a distinctive livery; but the males for a few weeks during the summer assume more or less completely the livery of the female, a process aptly described as going into "eclipse." The assumption of the female dress at this season is necessary, since it harmonises completely with the surrounding foliage, and so effectually conceals the bird at a time when it is peculiarly helpless; for, as with all birds, the quills or flight-feathers are cast off by the process known as moulting once a year, but instead of being replaced in pairs, and the flight remaining unaffected, they are shed all at once, so that escape from enemies must be sought by concealment.
