There is much debate among taxonomists on exactly how to arrange the over one hundred species into families and sub-families. All ducks are swimming birds with relatively short legs and webbed front toes. They typically have bills that are blunt and spatulate in shape, covered with a thin soft skin and with a hard 'nail' at the tip. Their plumage is very dense and waterproof with a thick undercoat of insulating down.
Ducks have a large uropygial or preen gland near the base of their tails.
They use oil from this gland to continuously waterproof their feathers as they preen. In most species the males are larger and more colorful than the females. Photo by Jessie Cohen, NZP The whistling ducks or tree ducks are mostly tropical in distribution and tend to be highly gregarious. They have long necks and long legs located close to their center of gravity, making them among the most graceful of waterfowl on the land. The sexes are very similar in plumage and unlike most other ducks, pairs may bond for life.