Ducks are part of a large number of species in the waterfowl family Anatidae, which also includes swans and geese. The ducks are divided among several subfamilies in the family Anatidae; they do not represent a monophyletic group (the group of all descendants of a single common ancestral species) but a form taxon, since swans and geese are not considered ducks. Ducks are mostly aquatic birds, mostly smaller than the swans and geese, and may be found in both fresh water and sea water.
Ducks are sometimes confused with several types of unrelated water birds with similar forms, such as loons or divers, grebes, gallinules, and coots.
A common joke in the series involve the Kratt Brothers yelling "Duck!" when a bird (other than an actual duck) delivers the Animal Helpers' messages, though in some episodes, an actual duck actually delivers the message.
A duck (specifically a Welsh Harlequin) first appeared in the episode "Dinosaurs". It was seen in the pond that Chris (as a caveman) swung in. Martin said that ducks and geese have bills with sharp edges for grinding up water plants and that there was a dinosaur that had a bill like a duck. Zoboo then stated that it must have been called the "duck-billed dinosaur".