Many people have heard the proverb "If it walks like a duck, quacks like a duck, looks like a duck, it must be a duck." Do you know what really makes a duck a duck, though?
This diverse group of waterfowl is characterized by 5 physical features and can be broken into two groups: dabblers (that go "bottoms' up" on the surface and reach as far down as possible to forage) and divers (that completely submerge themselves and swim underwater on the hunt for food).
1) Feet: Duck feet are wide and strongly webbed. This allows for efficient swimming and often, agile diving. Many have strong durable claws that provide for gripping ability on differing land surfaces.
2) Bill: Their bills are broad and slightly flattened so it can function as a food scoop. Many have a nail at the bill tip that is used in rooting for food. Slight serrations around the edge of the bills aid in straining water for insects and other foods.
3) Body shape: Duck bodies are compact and this makes for streamlined swimming and efficient body heat preservation when in water. Location of their legs varies slightly depending on if they are dabbling or diving ducks. Dabblers have legs placed farther forward under their bodies, making walking on land easier. Divers' legs are farther back on the body which helps propel them underwater (with the tradeoff that walking on land is harder!).
4) Plumage structure: Their feathers are so well designed that the outer contour feathers keep the down interior feathers dry even when under water! Regular preening (removes parasites and dirt, spreads a waterproofing oil throughout feathers) is an essential part of maintaining a duck's beautiful and functional plumage.
5) Plumage color: It is common for males of a bird species to have elaborate and brilliant breeding plumage, but ducks take this to the extreme. Just check out the wood duck! Females are typically more subdued and/or mottled for camouflage reasons.