They have widely spaced shortened legs (shortened thigh and Tarsus), so on land they go waddle! They are characterized by a rigid and tight to the body plumage. Water birds usually have well-developed coccygeal gland, but, judging by the latest data, its function is not directly related to impermeability of plumage.
The body floating, the birds are usually elongated, diving and water absorption. The proportion of floating, and especially diving birds, significant of the approaching cormorants and grebes to one. In diving birds, the legs are usually far backward, the pelvis is narrow, the wing bones are flattened, and the absolute and relative wing sizes are insignificant.
We can say that well diving birds like are on the way to the loss of the ability to fly; not reluctant to resort to the flight of hard flying birds, among narrow are completely flightless